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5B - Public Hearing and consideration of a motion to recommend that the South Boulder Creek (SBC) FlCITY OF BOULDER PLANNING BOARD AGENDA ITEM MEETING DATE: Mazch 22, 2007 AGENDA TITLE: Public Hearing and consideration of a motion to recommend that the South Boulder Creek (SBC) Flood Mapping results be submitted to the Federal Emergency l~anagement Agency (FEMA) REQUESTING DEPARTMENT: Ruth McHeyser, Acting Planning Director Robert E. Williams, Director of Public Works for UtiliUes Robert J. Harberg, Utilities Planning and Projec[ Management Coordinator EXECUTIVE SUNIIVIARY: U6lities Division Staff previously updated the Planning Boazd regarding the South Boulder Creek (SBC) flood mapping study on August 24, 2006. At this time, staff requests that the Planning Board consider a motion to recommend that the study results be submitted to the Federal Emergency Management Agency (FEMA). The study is intended to replace the current regulatory mapping based on a 1986 United States Army Corps of Engineers (USACE) study that is cunently adopted by the city, Boulder County and the Federal Emergency Management Agency (FEMA). The South Boulder Creek flood mapping study is intended to "define the flood problem, not solve it. " The key issues in the study are to develop scientifically defensible results based on sound technical analysis and offer adequate community outreach to educate and inform the public in order to achieve cleaz understanding and acceptance of the study outcome. The technical analysis is documented in the following reports: 1. Climatology Report dated February 6, 2007 2. Hydraulics Report dated February 6, 2007 (Attachment A) Each report with appendices is over 800 pages long and therefore the attachments to this memo present the body of the report only without appendices. The complete reports with appendices may be viewed at city libraries or downloaded at: h~•/lwww southbouldercreek com/paeeinpage/proiectbackgrounddocuments cfm The Peer Review Evaluation Panel (PREP) has provided their summary comments regazding the study presented as Attachment B. The city manager has the authority to amend the boundaries of the flood hazazd areas in order to AGENDA ITEM # SB Paee 1 recognize changed conditions produced by flood channe] improvements and mapping coaections, see Boulder Revised Code (BRC) Pazagraph 9-3-2. Planning Board is asked to review the study results and associated land use implications. Planning Board is not responsible for approving the proposed flood mapping changes. Staff will forwazd any Planning Board recommendations regazding the study results to City Council. BACKGROUND: In 1996, it was discovered that neighborhoods in east Bou3der that were previously considered to be outside the floodplain were actually within the "West Valley" of the South Boulder Creek floodplain. These neighborhoods include about 1,000 structures/homes that are located west of SBC and norch of U.S. 36. This was deternuned during the Universiry of Colorado's (Ci~ due diligence investigation into the purchase of the CU-South Campus property. This discovery raised the importance of updating the existing 1986 regulatory flood hazard mapping to ensure an accurate and updated deternunation of the threat of flooding. As a result, the mapping study was initiated to more accurately identify the flood hazards associated with SBC. Original results of the climatology/hydrology portion of the study including projected flood flow rates were submitted to FEMA for review in May 2005. However, these results were never accepted. Comments from federal, state and local review agencies and members of the public, received in July 2005 indicated concerns that the projected flood flow rates seemed to under- predict [he real flood threat when compazed with the current 1986 USACE regulatory hydrology. In addition, the Urban Drainage and Flood Control District (UDFCD) objected to the use of the new non-standard study methodology when compared to the accepted standard practice. UDFCD recommended that additional scientific research and analysis was needed before accepting the new flood flow rates; otherwise, the study should move forward using the current 1986 USACE regulatory hydrology. These comments triggered a reassessment of the climatology/hydrology portion of the study. Additional scienti5c research and analysis has been performed to ensure the best technical results possible. Further study was done on the size and intensity of historical thunderstorms that are the most likely cause of flooding along SBC. Among numerous assessments completed, the most significant involved the development of detailed characteristics for an additional 37 thunderstorms. This was made possible by the mid-2005 introduction of new Geographic Information System (GIS)-based Doppler weather radar analytical techniques for storms observed from 1997-2004. The initial study had used only 13 thunderstorms and required manual analyses. The new storm sample included a total of 50 thunderstorms and better defined their size and character of area thunderstorms. This improved the quality of the study results. The expanded GIS-aided analysis determined that the size and distribution of regional thunderstorms aze lazger than initially determined. As a result, a thunderstorm in the SBC basin will produce greater flooding conditions than a general storm. Table 1 presents [he 100-year flood flow rate in terms of cubic feet per second (cfs) at key locations along SBC based on various study results and in comparison with the current regulatory model. AGENDA ITEM # SB Paee 2 Table 1 South Boulder Creek 100- ear Flood Flow Rates (cfs) ~ow from Original evised evised Current 1986 ocation (2005) Flow (2006) Flow 2006) Flow SACE efore efore fter e~~atory Study outing (1) outing (2) outing (3) fter Routin (4) ldorado 3260 4520. 4340 4800 wy 93 3940 7120 4900 5740 S 36 3930 7690 5850 6200 aseline Rd 3930 8770 6900 6400 onfluence 3910 8910 5430 6600 Foo[notes: 1. This is the flood flow rate based on the study's original rainfalUrunoff model prior to routing through the hydraulic model and was submitted to FEMA in Apri12005. 2. This is the flood flow rate based on the study's revised rainfalUrunoff model prior to routing ttuough the hydraulic model that is proposed for consideration. 3. This is the flood flow rate based on the revised rainfalVrunoff model afrer routing through the hydraulic model that is proposed for consideration. 4. This is the tlood flow rate based on the current 1986 USACE regulatory model after routing. ANALYSIS: There aze three primary components of the study: Climatolozv/Hvdroloxv Analvsis The confidence of this analysis has improved since the original FEMA submittal in May 2005. Based on the analysis of additional thunderstorms the confidence limits of the discharge parameters increased from +29/-48 percent for the origina] data set to +18/-32 percent for the expanded data set. The confidence limits for the hydrology aze acceptable and the estimated dischazge parameters correlate well with the historic records from the Eldorado stream gage. Hydraulic Analvsis and Flood Hazard Mappin¢ Important study results are the proposed regulatory flood hazard maps. These may be compared to the curren[ floodplain delineation based on the 1986 USACE study presented as Figure 14 - Current City of Boulder Regulatory 100-year F7oodplain (Attachment C~. 1. Figure 20 - Proposed Floodplain Delineation (Attachment D) 2. Figure 21- Proposed Conveyance Zone (Attachment E~ 3. Figure 22 - Proposed High Hazard Zone (Attachment F) The proposed flood mapping indicates similar flood hazards along the main stem of SBC and AGENDA ITEM # SB Paee 3 increased flood hazards in the west valley azea. The number of structures affected by the various flood hazard zones is presented in Table 2. This includes all structures including not only primary living units and businesses but also garages, sheds, storage lockers, and other agricultural out buildings. A breakdown based on City and County zoning is presented in Attachment G. Table 2 Number of Structures Affected lood Zone xisting e lato oposed e lato loodplain AE 363 1137 Floodplain AO 96 0 loodplain X 291 1237 onveyance 30 237 ~gh Hazard 24 99 The process used to delineate and define the floodplain is presented as Attachment H- Hydraulic Report - Appendix F- F7oodplain Zone Definitions and Island Determination. FEMA floodplain zones applicable [o South Boulder Creek include: • Zone AE - Defined as areas of special flood hazazd inside the 100-year floodplain where water surface elevations have been determined. A 100-year flood is a flood that has a one-percent chance of being equaled or exceeded in any given year. • Zone X-shaded - Defined as azeas of moderate flood hazard that aze determined to be within the 500-yeaz floodplain where there is a 0.2-percent chance of being equaled or exceeded in any given year; areas in the 100-year floodplain where average depths aze less than one foot; and azeas protected by levees from the 100- year flood. • Zone X-unshaded - Defined as areas of minimal flood hazard deternuned to be outside of the 500-yeaz floodplain. Study results will change the floodplain maps adopted for regulatory and flood insurance purposes. Many areas in the SBC basin, previously outside the 100-year floodplain on the Flood Insurance Rate Map (FII2M), have now been deternuned to be within the floodplain. These areas will be delineated "Zone AE", areas of special flood hazard subject to regulatory restrictions and mandatory flood insurance purchase requirements if the associated structure was purchased with a federally backed mortgage or through a federally regulated lender. This will primarily affects property owners in [he west valley, where flood hazazds were not previously recognized. Regulatory implications include: AGENDA ITEM # 5B Paee 4 • Zone AE - 100-year Floodplain: A floodplain development permit is required for any development or construction in the 100-year floodplain or Zone AE. Where construction is pernutted, it must conform to flood protection standards that require, at a minimum, the lowest floor of any residential building to be at least two feet above the base flood elevation. Non-residential buildings must be elevated to the same flood protection elevation or may be flood-proofed such that below the flood protection elevation, the structure is water tight with walls substantially impermeable to the passage of water. Additional requirements apply to building crawl spaces, attendant utilities, and the need to adequately anchor structures against flotation, collapse or lateral movement. Any storage or processing of hazazdous materials is prohibited below the flood protection elevation. The city of Boulder also prohibits the development of new automobile pazking where flood depths exceed eighteen inches. • Conveyance (F7oodway) Zone: Those portions of the floodplain required for passage (or conveyance) of the 100-yeaz flood, based on an encroachment of the floodplain from the edges of inundation to a point where the 100-year flood profile (or water surface elevations) will be raised by no more than six-inches (for the city of Boulder, one foot for Boulder County). This definition considers a reasonable expectation of blockage at bridges and other obstructions by flood debris. In the conveyance zone or floodway, any development, encroachment, obstruction or use that would result in any increase in the base flood elevation is prohibited. Boulder County additionally prohibits the development of structures for human occupancy in the floodway. • High Hazard Zone: Those portions of the 100-yeaz floodplain where an unacceptably high hazazd to human safety exists. This is defined as those areas where the product number of velocity (measured in feet per second) times flow depth (measured in feet) equals or exceeds four, or where flow depths equa] or exceed four feet. The high hazard zone applies only to lands annexed to city of Boulder. In the high hazazd zone, the construction, expansion or enlazgement of any structure intended for human occupancy or establishment of a new pazking lot, is prohibited. Additionally, any change in use of an existing structure intended for human occupancy from non-residential to residential is prohibited. An expanded discussion of flood insurance and regulatory implications is presented in Attachment I- Hydraulics Report - Appendix I- Flood Insurance and Regulatory Implications. Risk Assessment Inundation maps have been developed to depict that actual depth of flood waters under various flood flow scenarios. This information will be used to support subsequent flood mitigation planning. Important inundation maps aze presented in Attachment A as follows: 1. Figure 15 - 100-year Design Thunderstorm Inundation Map - page 33 2. Figure 16 - 1986 USACE Dynamic Storrn Inundation Map - page 35 3. Figure 17 - 1986 USACE Steady State Storm Inundation Map - page 36 4. Figure 18 - 1976 Big Thompson Storm Inundation Map - page 38 5. Figure 19 - 1997 Ft. Collins Storm Inundation Map - page 39 AGENDA I1'EM # SB Pa¢e 5 OTHER I5SUES: CU-South Campus Berm An issue that continues [o raise eoncerns in the flood mapping study is the CU-South Campus berm [hat redirects flood waters around the former Flatirons gravel mine. This berm, although a man-made structure, is a significant existing physical feature and will dramatically affect the flow of flood waters and their associated hazards. For this reason, the proposed regulatory mapping has been modeled with the berm in place. This is consistent with the overall modeling approach that considers and includes all topographic features including other man-made structures such as roadway berms, excavated channels/ponds and elevated roadway intersections. The study team recently completed modeling simulations using the study's revised (2006) hydrology without the CU-South Campus berm, as if the berm were removed or was washed away by the flood waters. The results of these modeling simulations aze presented as Figures 12a and 12b - Sensitivity Results Related to University of Colorado South Campus Berm with New Hydtology on page 28 of Attachment A. The University previously submitted informadon to FEMA for certi£cation of the berm for flood protection and it is likely FEMA will eventually certify the berm. All study results will be submitted to FEMA, including those results from simulations without the berm. Downstream Storm Center The primary purpose of the South Boulder Creek F7ood Study is to characterize extreme rainfall events (thunderstorms) that are most likely to cause flooding along the main stem of the creek. Therefore, the most stressing condition for peak flows along the main stem of the creek has been reported and used in the study based on the positioning of thunderstorms somewhat upstream of the urbanized areas of the city. Concems related to the potential for flooding based on positioning of thunderstorms directly over the urbanized azeas of the city were documented in a report titled Hydrologic Impacts of Downstream Storm Centers dated February 2005. As would be suspected, the positioning of thunderstorms in this manner predicted much higher flow rates from sub-basins within the urbanized azeas of the city. This has led to concerns regarding localized flood hazards within these sub-basins as presented in Attachment J- City Council Weekly Information Item dated February 22, 2007. These concems are valid but are beyond the scope of the current South Boulder Creek flood mapping study. It is fortuitous however that work on the soon to be released Stormwater Strategic Plan provided a basis for further evalua[ing this issue. As a result, the city was well positioned to evaluate the significance of this issue that is now documented in Attachment K- South Boulder Creek L,ower Urbanized Storm Center - 100 year Flood Impacts dated March 1, 2007. Analysis results indicate shallow surface flow for a majority of the study area with depths equal to or less than 1-foot. There are locations where depths exceed 2-feet. However, these locations aze isolated to localized depressions in the ground surface. In addition, there are locations where a higher hazard exists, but these locations are confined to existing known drainageways and ponds. AGENDA ITEM # SB Pa¢e 6 Other Current Development ¢nd Annexation Issues The flood study results will have an affect on current annexation and development proposals: Hogan-Pancost - Portions of the site are included in Zone AE, none of the property is affected by either conveyance or high hazazd zones. Waterview (Arapahoe and SBC) - Most of the site is included in Zone AE, limited pottions of the site are affected by either conveyance or high hazazd zones. Gapter Road neighborhood - Most of this azea was already included in Zone AE and conveyance zone based on existing regulatory mapping and this remains unchang8d. Portions of this area would be included in the high hazard zone if annexed to the city. Interiin Regulation of Development It is anticipated that 9-12 months will be required for FEMA to complete their review of the study results. During the FEMA review period, City staff will consider the study results in the regulation of all annexation and development proposals. This approach is consistent with the BRC Pazagraph 9-3-2(d)(13): "The city manager shall administer [he requirements of this Section and shall Obtain, review, and reasonably utilize any base flood elevation and floodway data available from federal, state, and other sources, including data developed pursuant to Chapter 9-12, "Subdivisions," B.R.C. 1981, as criteria for requiring that all new development meet the requirements of this Section." It is proposed that property owners be notified of the city's intent to regulate according to the study results at least one month in advance. PUBLIC REVIEW PROCESS TO DATE: Numerous public meetings and hearings have been held since the study's beginning in 2004. The most recent public meeting was hosted on Wednesday, Nov. 15 at 7 p.m. at the Spice of Life Catering Center, 5706 Arapahoe Ave. The intent of the meeting was to provide information about the study results, flood hazazds, and to offer the community an opportunity to learn more about the associated property impacts. Detailed flood hazazd mapping and a tabulation of the affect of the proposed regulatory flood mapping on individual structures was presented. Approximately 125 people attended. Numerous questions were asked and aze summarized as Attachment L- QuesUOns and Answers. A Peer Review Evalua[ion Panel (PREP) comprised of three Boulder area residents with scientific knowledge in water resources was established to review and evaluate the technical aspects of the SBC flood study. The PREP members aze Lynn Johnson with CU-Denver, Doug Laiho with Hydrosphere and Gordon McCurry wi[h CDM. The PREP also advised the study team about how to effectively present the study results to the public in order to ensure the greatest level of understanding for a non-technical audience. The Peer Review Evaluation Panel (PREP) has provided their summary comments regazding the study presented as Attachment C. AGENDA ITEM # 5B Paee 7 The Water Resources Advisory Boazd (WRAB) has hosted to public hearing regarding the study on December 18, 2006 and Pebruary 26, 2007. The February 26 meeting summary is presented as Attachment M- Summary of February 26, 2007 Water Resources Advisory Board Meeting At [his mee[ing the WRAB unanimously recommended that Ihe study be submi[ted to FEMA based on the followiag motion: "Motion: 77xe Water Resources Advisory Board (WRAB) recommends the South Boulder Creek Flood Mapping study be submitted to FEMA, but before final submittal, staff wouid continue fo address technical issues io a degree practical, and develop policies and recommend those to city council to ensure only ponions of propenies located in the future regulated floodplain be subjected to the rules. Staff should develop a policy and recommend to council how to handle the development or annexation of propenies that are not currently, but woudd be subject to regulation under the newest floodplain. " WRAB's motion is consistent with the city's regulatory approach under Chapter 9-3 of the BRC. A special post card mailing to over 5,000 addresses potentially affected by the flood mapping study was delivered to the United States Postal Service on February 9, 2007. The post cazd contained information about the public review process including an announcement of the February 26, 2007 WRAB public hearing. In addition, staff has responded to many specific questions from the public over the past several months. Website and Resource Atlas: The study has developed a large amount of information available to the public under the Resource Atlas link of the http://www.southbouldercreek.com/ Website. NEXT STEPS: F7ood Mapping Submittal to FEMA: The City's par[icipation in the National Flood Insurance Program (NFIP) requires that new information concerning flood hazards be submitted to FEMA within 6 months after the information has been developed. City staff will respond to any recommendations provided by the Planning Board. It is likely that modifications to the reports and flood hazard mapping will be made based on additional ground survey information presented by property owners. The City Council will be asked to review and concur that the results should be submitted to FEMA. The City Council public hearing and discussion has not yet been scheduled but is anticipated to occur in Apri12007. Based on recommendations from the WRAB, Planning Boazd and City Council, it is anticipated that the study results will be submitted to FEMA for approval in May 2007. It is likely that the FEMA review period will take 9-12 months. FEMA will also solicit public comment as part of their review process. Provided FEMA accepts the study results, the Colorado Water Conservation Board will be also be asked to adopt the study results and associated flood hazard mapping. AGENDA ITEM # SB Paee S Risk Assessment and Flood Mitigation Planning: The risk assessment will be completed during 2007 in order to support subsequent flood mitigation planning. F1ood mitigation planning will begin as soon as practical after the flood study results have been accepted by FEMA, Boulder County, the city of Boulder and other agencies. Currently, $1OQ000 has been appropriated in the city's Capital Improvement Program (CIP) to begin the flood mitigation planning in 2007, but this funding may be needed to complete the flood mapping study itself. Additional funding has been allocated in the city's CIP in 2008 ($150,000) and 2009 ($300,000) to complete flood mitigation planning. Also, $3,000,000 has been allocated in 2010 to help fund selected flood mitigation improvements, whatever these might be. The city is also pursuing Federal funding for the cost of flood mitigation and its planning. It is anticipated that the focus of these efforts would be to mitigated the impacts of flooding in the west valley, where flood impacts were previously undefined and substantial urban development has occuired. STAFF RECOMMENDATION: Staff recommends that the study results and flood hazazd mapping be submitted to FEMA. Approved By: Ruth McHeyser, Acting Planning Director Planning Department ATTACfIMENTS Attachment A- Hydraulic Modeling Report without Appendices Attachment B- PREP Summary Comments dated February 22, 2007 Attachment C- Current Regulatory Floodplain Delineation Attachment D- Proposed F7oodplain Delineation Attachment E- Proposed Conveyance Zone Attachment F- Proposed High Hazard Zone Attachment G - Zoning Breakdwon Attachment H- Hydraulics Report - Appendix F- Floodplain Zone DeSnitions and Island Determination Attachment I- Hydraulics Report - Appendix I- Flood Insurance and Regulatory Implications Attachment J- City Council Weekly Information Item dated February 22, 2007 Attachment K- South Boulder Creek Lower Urbanized Storm Center - 100 year Flood Impacts dated March 1, 2007 Attachment L- Questions and Answers Attachment M- Summary of February 26, 2007 Water Resources Advisory Board Meeting AGENDA I1'EM # 5B Paee 9 ATTACHMENT A Hydraulic Modeling Report without Appendices This report can be found online at: www.boulderwater.net, click on the Water Resources Advisory Board tab on the left bar> click on the 2/26/07 agenda AGENDA ITEM # SB Paee A'I ATTACHMENT B 22 February 2007 PREP Summary Statement on the South Boulder Creek Flood Mapping Project Climatology, Hydrology and Hydraulics Reports dated February 6, 2007. The Peer Review Evaluation Panel (PREP) has provided a technical review of the Climatology, Hydrology and Hydraulics Reports dated February 6, 2007 and aze of the opinion that the South Boulder Creek Floodplain Mapping Study meets, and in notable ways exceeds, the accepted standards of engineering practice for floodplain mapping and delineation. The effort is commendable in taking advantage of modem data from weather radars and advanced state-of-the-art computer modeling of rainfall, flood runoff and two- dimensional floodplain hydraulics. The customized Design Storm for the 100-year return interval and related rainfall scenarios are considered to be reasonably representative of the flood producing climatology for the Boulder azea. The hydrologic modeling defines a range of possible flood scenarios which could occur and the 2-D hydrodynamic modeling provides a high level of detail in defining risks of flooding in east Boulder from South Boulder Creek. We believe that the reports, supporting data and computer models provide a scientific information base for deliberations on South Boulder Creek flood plain management by the City of Boulder and by potentially impacted residents. This opinion is provided at a point in the study where the climatology, hydrology and hydraulics work is essentially complete subject to some work to refine details of flood risks and to respond to regulatory agency policies. The PREP does have some ongoing concerns with these reports that are provided in an itemized list of detailed comments being provided to the City. 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'. ,,~ ~, .~~. ~ . . . . f . - F ' . r . :.I j f ` ; ~ - ;~~ ~~~ f'~ ~ . .~'' ~~ ~~ " ~ i _ t," , f~. - q ~' . ~~ ~'"~ ~~ ~ . + - ~~ ~ . .,~ ' .. ~ ; ~ ~ , ~ • • ~ ~ ~~:~ . . ~ .., ~ r , ,~4 ~~,.; ,.~ ;::.,~,~,, ~ ~ y~ ~~ 0 ~/~ f ; 2 500 5,000 7,500 10,000 + Legend Floodplain Delineation ~ AE Floodplain ~ ~ ~T ! Feet ~ AC} Floodplain HDR En~~~inQ. Inc. '~ 0 X Zone (500yr Flaodplain) _ ~ ~ , b ~ J-- ATTACHMENT D ~~ ~, f P r ~ Restud Flaod lain Y p ATTACHMENT E Pro osed Canve a nce Zane p Y Y ` ~~ ~ R ~ S_`, ~._.. ' ~~ , ~_ _ ` ~~ ~~ ; ~~ `.y ,~,y ~ ~~ ` -}'^' . r~ / ~L`~'""~~~ ~~r ~_i . ' . ` 1 . . ' ~ ' ' --t~- _ I J :~^ ~ 'r;k"'~ ~, ~ .: ~'' ( ' ~ 1 ~ _ ~ ~~: ~ ~ ~ ~~t' ~ ~ 0 ;' ~ , ~ ~ ' L : '~ I '~' ~ ~~ ,5~. _ =2. t ~ n ~ ~ ZT~ ~, ~_. r„ ~ ~. .~ ~ ~ ~- ~ J i~ " ' ' '' ,l~ ~j~ ' ~ ~ J ~ ~~ '~ ' 7 { ..- ~ . 7. ~ Y ~ ~ . i " i . ~ V~ ~~ ' ,- ~ . ,,r .~ ~ ~ I- ~~( ~ ` ~.a ;F~ i~.f~ j ~ ~ ~~ ~ I . 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Y f .+~rc . ~.. . f f` S,J~:, n-y~ ~- ~q~'~ ~ l~ ~Fi .,~.-j , ,.., , ..r+s ~. l ,~/'~.~y ~~ ..~f•~ • . ~y'~ f~~, - . ~ r~ ~,. - y i 2 l :a;' . r-~,: - . i ~ r , ~a : .~q-r ~ ~!~,_,~ ~t'~ ,K„,' ~ - ..-.~.. ;!- ~': -;• -~~~"~. . -~,~:~"`.. ,~~ •.~.~--~'/ .'~'~` . y" ,~ .~ ~-.,~ - 3 ^ '~:3 ... ,':'~~: ~ : ~~ ~ ~,,,,r_r --~~` -...s..- ~~d , . ~•~._ f.~1•~1~ `,. ~ ~~y~~ y~ ~ ~~-~~~~~. -, ~ . ~~_ + ~ . ~, , , J •~N ~! ;~ y. ~ ` ~ ,~ ~,-:~ ,:~• =_ ' _, ~ :~'c~,J 4 .'~~ ~ k~ ~~' + ~.: 1 ~'~ _ ~ ,- . ~ . . - ~! - `s `,~'.~e ~.: ~. . ~+~~~ , ~ ' , 7~ ~ 4'; ~ ~ , ;' ~i t ~ M~ ~ } , - A ~: ~ , ~ ~ ~~.t' •~ . y . . •~.V•-`~ {,~. ~'. , r.~t„ r •~f - . . f._~:~ ,4'~'~ ~''~_ ,x' _~~~I.: ~ , ~ ~,. 1-AIIVP.~/~lI1C@ ZAII@ " 0 ThF Cit~r' and FEMP,both rely onthe conveyance xone (dFfined as the 1loodw~y b+~ FEPAA)1o help deflne tlood haz,rds. 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' ~' ~;~, :- ~r~ Leaend ~ Restudy Hicyh Hazar'ci Zur~ „, ~, 0 2,500 5,000 7.500 10. ~~ -~' ~J, .•r.v r .,, ,, Date: November 2006 , ~~ ~~ ~~~` . ~ ..~„ ~. ~,-.., ~. :~genda Item ~ _~ ~ . . ~'age # F -I ATTACHMENT G Property Affected by AE and X Floodplain Delineation AE Cily Zoning Zone Zone Acres Struetures RM-1 Residential-Medium 1 21.38 37 RR-1 ResidenGal-Rural1 27.20 38 RE Residentlal-Esqte 54.64 160 RH-5 Residenlial-Hi h 5 33.52 18 RM-2 Residential-Medium 2 31.95 50 RL-1 Residential-LOw 1 46.77 34 RH-4 Residential-Hi h 4 7.54 3 P Public 19429 11 E Enclave 24.96 32 IM Industrial-Manutacturin 5.86 3 RL-2 Residential-Low 2 74.45 169 BG2 Business-Communi 2 2.08 1 BG1 Business-Communi 1 27.97 23 IS-2 IndusVial-Service 2 3.65 0 BT-1 Business-Transilionall 3.21 3 IG Industrial-General 114.46 70 Total 674 652 X City Zoning Zone Zone Acres Structures RM-1 Residential-Medium 1 4.23 10 RR-1 Residential-Rurall 0.87 8 RE Residentia~-EsNate 23.71 99 RH-5 Residen6al-Hi h 5 13.67 19 IM Industrial-Manufadurin 28.35 31 RM-2 ResidenGal-Medium 2 16.96 74 RL-1 ResidenUal-Low 1 39.16 156 RH-4 Residenlial-Hi h 4 1.47 6 P Public 29.99 14 E Enclave 2.59 6 RL-2 ResidenGal-Low 2 95.72 479 BC-2 Business-Communi 2 0.28 0 BC-1 Business-Communi 1 5.68 17 IS2 Industrial-Service 2 1.30 0 BT-1 Business-Transitionall 8.03 14 IG Industrial-Generel 112.91 68 Total 385 1,001 AE County Zoning Zone Zone Acres Structures A ricultural 491.11 48 F Fwes 0.52 0 C Commercial 3.59 10 LI Li ht Industrial 20.82 24 MH Manu(adured Home 6.17 80 GI Generallndusirial 59.55 9 XBO Boulder 4.68 4 RR Rural Residential 646.80 257 ED Economic Develo ment 34.56 1 ER Estate Residential 16.42 24 T Transitional 0.95. 1 SR Suburban Residential 25.81 25 B Business 1.64 2 Total 1,313 485 X County Zoning Zone Zone Acres Structures A A ricuttural 61.98 5 F Fores 0.32 0 C Commercial 0.00 0 LI Li ht Industrial 1.56 3 MH Manufactured Home 423 37 GI Generallndustrial 11.14 1 XBO Boulder 2.05 2 RR Rurel Residential 103.56 124 ED Ecorromic Develo ment 5.83 0 ER Estate Residential 10.82 27 C Commercial 0.73 1 SR Suburban Residential 26.39 26 B Business 1.72 10 Total 230 236 Grand Total 1,987 7,'137 615 7,237 ~~~ s~ ~# o-~ ~ PropeRy AHected by Conveyance and High Hazard Zones Conveyance Ciry Zoning 2one Zone Acres SWetures A A ricultural 0.00 0 BC-1 Business-Commun' 1 0.00 0 BT-1 Business-TransRionai t 1.04 1 E EnGave 0.35 1 IG Industrial-General 60.43 41 IM Industrial-ManufacWrin 2.42 0 IS-2 Industrial-Service 2 7.42 0 P Public '173.64 7 RE Residential-ESlate 0.00 0 RH-0 Residential-Hi h 4 1.98 0 RH-5 Residential-Hi h 5 0.15 0 RR-1 Residential-Rurall 3.68 1 RL-2 ResideMial-Low 2 2.36 0 RM-1 Residen6al-Medium 1 6.69 1 RM-2 Residential-Medium 2 0.00 0 RR-1 Residential-Rurel1 0.00 0 Tolal 247 52 High Hazard Ciry Zoning Zone Zone Acres Struetures A A rialtural 0.07 0 BC-7 Business-COmmun' 1 3.00 4 BT-1 Business-Trensitbnall 0.79 2 E Endave 4.98 0 IG Indusirial-General 1920 1 IM Industrial-Manufacturi 3.19 0 IS2 InduslrialService 2 0.96 0 P Pubtic 36.57 1 RE Residential-Estate 4.60 7 RHd Residendal-Hi h 4 0.51 0 RH-5 Residential•H' h 5 6.70 2 RL-1 ResidenUal-Low 1 2.54 2 RL-2 Residendal-Low 2 623 4 RM-1 Residential-Medium 1 2.89 0 RM-2 Residential-Medium 2 4.31 6 RR-t Residential-Rural7 2.60 1 Total 80 30 Conveyance County 2oning 2one Zone Aeres Structures A A ricultural 449.78 38 B Business 1.59 2 C Commerciai 0.14 0 ED Economic Develo ment 32.51 1 ER EsWle Residential 9.79 10 F Fores 0.33 0 GI Generallndusirial 56.37 8 LI Li ht Industrial 9.93 53 MH Manufaclured Home 1.26 0 RR Rural Residentia~ 5M15.67 112 SR Suburban Resitlential 2.56 0 XBO Boulder 1.59 1 Total 1,172 185 High Hazard County Zoning Zone Zone Acres Structuras A A riwlturel 179.79 18 B Business 1.31 0 C Commercial 0.00 0 ED EwnomicDevelo ment 1927 0 ER Es~ate Residential 11.03 13 F Fores 0.45 0 GI General industrial 34.71 0 LI L' ht Induslrial O.H6 0 MH Manufaclured Home 0.12 0 RR Rural Residential 154.06 38 SR Suburban Residential 2.54 0 XBO Boulder 1.06 0 Total 405 69 GrandTOWi 1,359 237 485 99 pgendalt~nt~-P~# G'2 ATTACHMENT H APPENDIX F Floodplain Zone Definitions and Island Determination HDR ENGINEERING, INC. ~_ r_~ n C2 D9nu ~~( FEMA Floodplain Zoning One of the outcomes of the South Boulder Creek Flood Mapping Study will be the revision and update to the current Flood Insurance Rate Map (FIRM) adopted by the Federal Emergency Management Agency (FEMA). The FIRM is the primary basis for local floodplain regulation and determining flood insurance premiums and mandatory purchase requirements in communities that participate in the National Flood Insurance Program (NFIP). Both Boulder County and the City of Boulder aze members of the NFIP and have been active in the program since the late 1970s. FEMA floodplain zones applicable to South Boulder Creek include: 1. Zone AE - Defined as areas of special flood hazard inside the 100-year floodplain where water surface elevations have been determined. A 100-year flood even is a flood that has a one-percent chance of being equaled or exceeded in any given yeaz. 2. Zone X-shaded - Defined as areas of moderate flood hazard that are determined to be within the 500-year floodplain where there is a 0.2-percent chance of being equaled or exceeded in any given yeaz; areas in the 100-year floodplain where average depths are less than one foot; and areas protected by levees from the 100- year flood. 3. Zone X-unshaded - Defined as areas of minimal flood hazazd determined to be outside of the 500-year floodplain. HDR ENGINEERING, INC. Agenda Item #~_ Page #~Z 20NE 2QNE X 16 21 Figure F-1: Flood lnsurance Rate Map ((F1RM) Flood zone delineation on the F1RM reflects Zone AE, the 100-year floodplain, in dark grey shading. Inside the Zone AE boundaries, base flood elevations (BFEs) are defined by a wavy line across the floodplain at various sections, with a water surface elevation notated. Thesc BFEs are dctcrmined by the detailed flood mapping study and are used to apply floodplain regulations and determine flood insurance premiums. Zone X-shaded is the 500-ycar floodplain, delineated in light grey shading. The 100-year floodplain, Zone AE, will always fall inside the Zone X-shaded boundaries. However, where thc outer flood limits of thc 100-year and 500-ycar floodplain are similar, there may be no Zonc X-shadcd delincation. Zone X-unshaded are areas that are determined to be outside the 500-year floodplain. They are delineated without shading. The South Bouldcr Creek Flood Mapping Study employed the use of MIKE FLOOD, a one-dimensional and two-dimensional linked hydraulic model. Model results for the - HDR ENGINEERING, INC. a~~'~_5~--- ~~~ ±~3 floodplain provide a detailed grid of four-meter by four-meter pixel cells. All grid cells where flood water depths are determined to be more than 0.01 feet are highlighted and reflect an inundation map showing the extent of 100-year flooding. Using the grid cell inundation map, a regulatory floodplain map was produced by conducting a detailed visual review of the MIKE FLOOD results. These results were ovcrlaid in ARC-G1S on the city's 2003 six-inch pixel aerial photography and one-foot topographic contours. This topography was used to create the digital elevation model (DEM) for the two-dimensional analysis. This quality assurance review offered a "physical rcality chcck" to rcfinc thc rcgulatory floodplain map. The FEMA flood zones outlined above were applicd to the grid cell inundation map to define a regulatory floodplain map to update and replace the current FIRM for South B~ulder Creek. In general, the grid cell inundation map for the 100-year design storm designates Zone AE, with some exceptions. The hydraulic model determines a 100-year water surface elevation for each grid cell that is then used to create the BFEs, which are illustrated on the regulatory floodplain map. IIDR ENGINEERING, INC. ~g~ia rre~r, ~ _ ~ ~ _ ~~~~ ~ f ~_y Exceptions to the Zonc AE designation includcd disconnected flow paths such as offline or separatcd irrigation ditch spills, areas designated Zone X-shaded, and areas around certain structures that covered grid cells that were not wet or; where only a portion of the grid cells were wct. Conversely, minor dry islands within the 100-year grid cell inundation map, whcre grid cells showed no wetting and were insignificant with respect to flooding, were included in the Zone AE designation. Areas in the 100-year grid cell inundation map that did not define primary flow paths and where flood depths were determined to be very shallow (less than 0.25 feet), were designatcd Zone X-shaded as provided for under the Zone X-shaded definition. Zone X- shaded also includes all areas in the 500-year grid cell inundation map and in the Flatirons Industrial Park areas protected by the levee system that are not in the 100-year grid cell inundation map (Flatirons Industrial Park areas within the ] 00-year grid cell inundation map are designated Zone AE). All remaining areas in the South Boulder Creek basin outside the 100-year and 500-year grid cell inundation maps are designatcd Zone X-unshaded, identifying areas outside of the detcrmined 500-ycar floodplain. * , , .~ 4 ~ ~°, ; ,~~- ~, ~. ~~ ~ ~ ~: ~ .~,~ ` ~ , ~ ~. - • . ~~ ~~, ~ ~ .~, - ~ - ~ . ~ `' ~~'{: ~ ~ '" i `k'' ; , ,-- • - . . . ~c' i iw = ~" , f " . _ . ; = ~.. ' ~ ~~ ~ . ~~;ff - ~' ~ ,'. ti .&' y~ ~. ~,: -~ j . i. - ~ +: ' ~ f€: - -- ' ~ E . ~ :.y.i~ ~~ ~ . _~ .~~ ~ . b ` f ` ; ~ ~~ ~ -- . 1 ,,. ~ . ~ '~~ ~ . "i,~_ . ~~ ~ 9 .1'+ _ `4 ~:. ~ ~ ~~ ~ r . ~,4 . ~~ F .~ .~~L ~ ° . : a : , ~_ ,.~ .~ . ~~ ~~ _ . , , ` ; _~ ~- ~ Figure F-3: 100-year Regulatory Floodplain Overlay (Zone AE) on 2003 Aerial HDR ENGWEERING, INC. ~~=--~a -~~~-~-s AGENDA ITEM # SB Paee t"I'~ ATTACHMENTI APPENDIX I Flood Insurance and Regulatory Implications HDR ENGINEERING, INC. Age~al~m# S15 Page#S~ I Flood Insurance and Regulatory Implications Results of the South Boulder Creek Flood Mapping Study will change the floodplain maps adopted for regulatory purposes and flood insurance requirements. Many azeas in the South Boulder Creek basin, previously identified to be outside the 100-year floodplain on the Flood Insurance Rate Map (FIRM), have now been determined subject to 100-year flooding. These azeas will be delineated within "Zone AE", areas of special flood hazard subject to regulatory restrictions and mandatory flood insurance purchase requirements. Flood Iusurance The city of Boulder and Boulder County participate in the National Flood Insurance Program (NFIP). Anyone in a community that participates in the NFIP is eligible to purchase flood insurance. Flood insurance policies are available for structures and their contents, struchues only, or contents only, as applied to: (1) dwellings (homes for one- to four-unit buildings and individual residential condominium. units); (2) general properties (apartments and businesses); and (3) condominium building associatio~s (condominiums). Flood insurance covers property losses caused by flooding. Standazd homeowner's insurance policies do not cover flood losses. Flood insurance may be pwchased from a licensed private insurance company or independent property and casualty insurance agent. In most cases, this may be a person's normal homeowners insurance agent. Flood policies will take efFect 30 days after ihe date of purchase. Flood insurance premiums are based on a number of conditions and physical factors. In order to ensure accurate calculation of each policy premium it is important to verify that the selected insurance agent is familiar with the NFIP. All FEMA-based flood insurance sold by private insurance companies is federally subsidized, so premium costs should be the same regardless of the company Selling the policy. Information on locating an insurance agent or identifying companies that participate in the NFIP may be obtained by HDR ENGINEERING, IIdC. Agenda Item # ~l~_ Page #~_Z contacting an NFIP representative at (888) 379-9531 or by visiting the NFTP Website at F1oodSmart.Gov. The Federal Emergency Management Agency (FEMA) defines flood zones for insurance purposes according to varying levels of risk. These flood zones are identified on a community's FIRM. FEMA flood zones applicable to South Boulder Creek include: Low to Moderate Risk Areas • Zones X-unshaded: Areas of low flood risk determined to be outside the 500- year floodplain with less than a 0.2-percent chance of flooding each year. ^ Zone X-shaded: Areas of moderate flood risk that aze determined to be within the 500-year floodplain, where there is a 0.2-percent chance of being equaled or exceeded in any given yeaz, azeas in the 100-yeaz floodplain where average depths are less than one foot, and areas protected from the 100-year flood by levees. Properties located in Zone X areas aze eligible for the Preferred Risk Policy (PRP), which is a lower-cost option for buildings and contents in low to moderate risk areas. For a home with no basement, a homeowner may purchase a minimum $20,000 building and $8,000 contents coverage for $112 a yeaz; $137 a year if a basement is present. Eligibility requirements are determined based on the current FIRM flood zone in place on the effective date of the policy. NFIP grandfathering rules do not apply. If there is a previous history of flood losses, the building may not be eligible for a PRP. There aze certain exclusions under the PRP. Contents located entirely in a basement aze not eligible for contents-only coverage. Nearly 25 percent of flood insurance claims come from areas located in Zone X. Hieh Risk Areas • Zone AE: Areas of special flood hazard (high risk) inside the 100-yeaz floodplain where water surface elevations have been determined. A 100-year HDR ENGINBERING, INC. Agendaltem#~_Page# Z-3 flood event is a flood that has a one-percent chance of being equaled or excecdcd in any givcn year Structures located in high-risk flood areas have a significant chance of suffering flood damage. In Zone AE areas, there is a 26-percent chance of experiencing a 100-year flood over the life of a 30-year mortgage. This is compared with a 9 percent chance of loss from fire. That makes a Zone AE property thrce times morc (ikely to suffer damage from flood than from fire. Because of this, flood insurance is required as a condition of receiving federally-backed financial assistance. The purchase of flood insurance is mandatory for all property located in Zone AE areas where the structure was purchased with a federally backed mortgage. This applies to all mortgages that are issued by a Federally-regulated lender. The purchase of flood insurance is not regulated or required by Boulder County or the City of Boulder. Flood insurance coverage under each policy typc is available as follows Policy Type Maximum Amount of Covera~e Building Contenfs Dwellin $250,000 $100,000 Non-residential $500,000 $500,000 ~ Condon~inimn Associ~tion $250,000 times number of $100,000 per building buildin<~ uniis Estimated premium costs of the maximum level of flood insurance for residential properties located in Zone AE are as follows: Structure T e Buildin Onl Contents Onl Bnildin and Contents Pre-FIRM Residential/No $1,285 $798 $2,053 Basement Post-FIRM Residential $499 $226 $695 Plus ] -Foot Freeboard Once the South Boulder Creek Flood Mapping Study regulatory floodplain map results are accepted by FEMA for adoption into the FIRM, the mandatory flood insurance HDR ENGINEERING, INC. ~a~enda I~em #~~_ ~~ ~ S -'~ requirement will take affect for Zone AE properties, as discussed above. Premiums will be based upon Pre- or Post-FIRM (whether the building was constructed before or after July 17, 1978) conditions, elevation of the first floor of the building, whether a basement is present, type of policy, and any specific building factors. An Elevation Certificate is required for Post-FIRM structures to assess a premium and may benefit cer[ain Pre-FIRM structures. FIRM adoption is expected to occur approximately 12 months after the flood mapping is submitted to FEMA for review and approval. In addition to the public process activities associated with the South Boulder Creek Flood mapping Study, FEMA conducts a public process to allow community review and comment. The public may appeal flood zoning designations proposed under the flood mapping study subject to the submittal of technical data that supports any findings to revise the proposed floodplain zoning. An option for properties that are re-designated from Zone X to Zone AE as a result of FEMA adoption of the flood mapping study, as part of the updated FIRM, is taking advantage of "NFIP Map and Zone Grandfather Rules." The grandfather rules recognize policyholders who have "remained loyal customers of the NFIP by maintaining continuous flood coverage" and/or "built in compliance with the FIRM that was in effect at the time of construction." For Pre-FIRM construction, a policyholder is eligible to maintain the prior flood zone and base flood elevation as long as continuous coverage is maintained and the policy was purchased prior to the effective date of a FIRM change. The flood policy can also be assigned to a new owner at the option of the policyholder. If a policy for a Pre-FIRM building is not obtained prior to the effective date of the FIRM change, the applicant is eligible to receive the Pre-FIRM (subsidized) rates based on the new flood zone rather than actuarial elevation based rates. For Post-FIRM construction, a policyholder is eligible to maintain the prior flood zone and base flood elevation as long as continuous coverage is maintained and the policy was purchased prior to the effective date of the FIRM change. The flood policy can also be assigned to a new owner at the option of the policyholder. If the building was HDR ENGINEERING, INC F~A~~II#'~-~~ ~-5 constructed in compliance with a specific FIRM, the owner is always eligible to obtain a policy using the flood zone and base flood elevation from the FIRM that was in effect at the time of construction. Proof of compliant construction and a copy of the FIRM that was in effect at the time of construction must be submitted to the insurance company as part of obtaining a policy. Continuous flood insurance coverage is not required to remain eligible For this rating. For Preferred Risk Properties (those in Zone X), buildings are required to be located in Zone X on the FIRM that was in effect on the date of policy application and on the date of each subsequent renewal. A building that becomes ineligible for a PRP due to a map change designating the property to be in Zone AE can be rewritten on a standard policy using the former Zone X rating. Regulatory Implications As a condition of participating in the NFIP, local communities must adopt floodplain regulations to manage and restrict construction inside areas of special flood hazard (Zone AE). At a minimum, this includes flood zone designations adopted in the FIRM. FEMA encourages communities to adopt more restrictive standazds suitable to local conditions and flood risks, so there may be flood zone designations and local rules that exceed the FEMA minimum standards. Regulatory flood zones that affect properties located in the South Boulder Creek floodplain include: ~ Zone AE: Areas of special flood hazard (high risk) inside the 100-year floodplain, where water surface elevations have been determined. A 100-year flood is a flood that has a one-percent chance of being equaled or exceeded in any given year. Again, this is the FEMA minimum flood zone designation standard. It may not incorporate all areas subject to 100-year flooding (such as Zone X-shaded areas that reflect 100-yeaz flooding of depths less than one foot). However, it does designate all areas subject to mandatory flood insurance purchase requirements. HDR ENGINEERING, INC. ~ndaltem#~Pa9et Z_~ • 100-year Floodplain: Areas subject to a flood that has a one-percent chance of being equaled or exceeded in any given yeaz. Some communities chose to regulate all areas of the 100-year floodplain, recognizing that in many cases flooding of shallow flood depths (that may be considered Zone X under FEMA standazds) can still cause significant damage to basements and structures built close to grade. The city of Boulder is a communiry that may designate areas in the 100-yeaz floodplain that are not in FEMA's Zone AE, as a regulatory floodplain zone. A floodplain development permit is required for any development or construction in the 100-yeaz floodplain or Zone AE. Where construction is pernutted, it must conform to flood protection standazds that require, at a minimum, the lowest floor of any residential building to be at least two feet above the base flood elevation. Non-residential buildings must be elevated to the same flood protection elevation or may be flood-proofed such that below the flood protection elevation, the shucture is water tight with walls substantially impermeable to the passage of water. Additional requirements apply to building crawl spaces, attendant utilities, and the need to adequately anchor struchues against flotation, collapse or lateral movement. Any storage or processing of hazardous materials is prohibited below the flood protection elevation. The city of Boulder also prohibits the development of new automobile parking where flood depths exceed eighteen inches. • Conveyance (Floodway) Zone: Those portions of the floodplain required for passage (or conveyance) of the 100-year flood, based on an encroachment of the floodplain from the edges of inundation to a point where the 100-year flood profile (or water surface elevations) will be raised by no more than six-inches (for the city of Boulder, one foot for Boulder County). This defmition considers a reasonable expectation of blockage at bridges and other obstructions by flood bom debris. HDR ENGINEERING, INC. ~a flem s~_Q._ Pags 6~ In the conveyance zone or floodway, any development, encroachment, obstruction or use that would result in any increase in the base flood elevation is prohibited. Boulder County additionally prohibits the development of structures for human occupancy in the floodway. ~ High Hazard Zone: Those portions of the 100-year floodplain where an unacceptably high hazazd to human safety exists. This is defined as those areas where the product number of velocity (measured in feet per second) times flow depth (measured in feet) equals or exceeds four, or where flow depths equal or exceed four feet. The high hazard zone applies only to lands annexed to city of Boulder. In the high hazard zone, the construction, expansion or enlargement of any structure intended for human occupancy or establishment of a new pazking lot, is prohibited. Additionally, any change in use of an existing structure intended for human occupancy from non-residential to residential is prohibited. ^ 500-year Floodplain: Areas of the floodplain subject to the 500-yeaz flood that have a 0.2 percent chance of being equaled or exceeded in any given yeaz. Some communities choose to regulate areas within the 500-year floodplain based on the understanding that floods larger than the 100-yeaz event can and will occur. In some instances, regulation of the 500-yeaz floodplain is applied to critical facilities to ensure such facilities aze not damaged and remain operational during and after a flood event. The city of Boulder is considering the regulation of critical facilities within the 500-year floodplain. Beyond the restrictions associated with development in the 100-yeaz floodplain, property owners and members of the public may be concerned with any potential impacts to property values and existing uses. The sale of properties located in the 100-yeaz floodplain is not restricted or regulated by floodplain regulations. There is no assurance that a floodplain designation will not affect the market value of a property. However, HDR ENGINEERING, INC. Agenda Mem a-~(~_ Page ~~- S there is no evidence in the local assessor's records to indicate that market values for developed floodplain properties are reduced. Properties located in the 100-year floodplain that aze damaged may be repaired subject to the restrictions adopted under City of Boulder and Boulder County floodplain regulations. In all cases, repair requires the issuance of a floodplain development permit and building permit. In addition, developed properties are subject to "substantial improvemenY' limitations. If the cost to repair the damage exceeds 50 percent of the mazket value of the structure, the entire structure must be made to conform to current floodplain regulations. Further details about floodplain regulations and their implications on propeRies located in the South Boulder Creek Flood Mapping Study floodplain may be obtained by contacting the city of Boulder or Boulder County (based on the location of the affected property). HDR ENGINEERING, INC. Ag~daNem#~S(~PegeB Z-`~ ATTACHMENT J WEEKLY INFORMATION PACKET MEMORANDUM To: Mayor Ruzzin and Members of Council From: Frank Bruno, City Manager Stephanie Grainger, Deputy City Manager Robert E. Williams, Director of Public Work for Utilities Robert J. Hazberg, Utilities Planning and Project Management Coordinator Date: February 22, 2007 RE: Information Item - Update on South Boulder Creek flood mapping study EXECUTIVE SUMMARY At the Water Resources Advisory Board (WRAB) meeting on Monday, Feb. 26, city staff is recommending that the South Boulder Creek (SBC) flood mapping study results, including hydrology, climatology and flood maps, be submitted to the Federal Emergency Management Agency (FEMA). The study is intended to replace the current regulatory mapping based on a 1986 United States Army Corps of Engineers (ilSACE) study that is presently adopted by the city, Boulder County and FEMA. See Attachment A for the Feb. 26 WRAB memo. At the Feb. 20 City Council meeting, Jeff McWhirter presented information in his comments regarding the Lower Basin Storm Center Report, dated Feb. 24, 2005. The primary purpose of the South Boulder Creek Flood Study is to chazacterize extreme rainfall events (thunderstorms) that aze most likely to cause flooding along the main stem of the creek. Therefore, the most stressing condition for pealc flows along the main stem of the creek has been reported and used in the study based on the positioning of thunderstorms somewhat upstream of the urbanized areas of the city. Mr. McWhirter's issues will be presented and discussed at the WRAB meeting. Based on concerns related to the potential for flooding based on positioning of thunderstorms directly over the urbanized ueas of the city, the Lower Basin Storm Center Report was developed and released in February 2005. As would be suspected, the positioning of thunderstorms in this manner predicted much higher flow rates from sub-basins within the urbanized areas of the city. This has led to concems regarding localized flood hazazds within these sub-basins. These concerns aze valid but aze beyond the scope of the cunent South Boulder Creek flood mapping study. City staff plans to further investigate the significance of the localized flood hazards and provide further information regarding this subject. NEXT STEPS: City staff will respond to any recommendations provided by the WRAB at the Feb. 26 meeting. It is likely that modifications to the reports and flood hazard mapping will be made based on comments from the public, WRAB and the Peer Review Evaluation Panel. The city's Planning Boazd and City Council will also be asked to review and concur that the results should be submitted to FEMA. The Planning Board public hearing and discussion is currently scheduled Agendalt~n#~-~~9e~ ~ -I for March I5. The City Council public hearing and discussion has not yet been scheduled, but is anticipated to occw in April. Based on recommendations from the WRAB, Planning Boazd and City Council, it is anticipated that the study results will be submitted to FEMA for approval in May 2007. It is likely that the FEMA review period may take nine to 12 months. FEMA will also solicit public comment as part of their review process. Provided FEMA accepts the study results, the Colorado Water Conservation Board will be also be asked to adopt the study results and associated flood hazazd mapping. For additional information, contact Ned Williams at williamsnC~bouldercolorado.¢ov or (303) 441-3209. ATTACHMENT Attachment A- Water Resources Advisory Board memo, Feb. 26, 2007 Agenda ltem # S 4~ _Page # 'S -2- CITYOFBOULDER WATER RESOURCES ADVISORY BOARD AGENDAITEM MEETING DATE: February 26, 2007 AGENDA TITLE: Final recommendation on South Boulder Creek (SBC) Flood Ma in Stud , includin h drolo , climatolo and flood ma s PRESENTERS: Robert E. Williams, Director of Public Works for Utilities Robert J. Harberg, Utilities Planning and Project Management Coordinator BOARD ACTION REQUESTED: Consideration of a motion to recommend that the South Boulder Creek Flood Mapping Study results be submitted to the Federal Emergency Management Agency (FEMA) EXECUTIVE SUMMARY: City staff previously updated the Water Resources Advisory Boazd (WRAB) regazding the South Boulder Creek (SBC) Flood Mapping Study on December 18, 2006. A copy of the meeting agenda item and meeting summary aze provided as Attachment A and B respectively. Staff requests that the WRAB consider a motion to recommend that the study results be submitted to the Federal Emergency Management Agency (FEMA). The study is intended to replace the current regulatory mapping based on a 1986 United States Army Corps of Engineers (USACE) study that is currently adopted by the city, Boulder County and the Federal Emergency Management Agency (FEMA). The South Boulder Creek flood mapping study is intended to "define the flood problem, not solve it. " The key issues in the study aze to develop scientifically defensible results based on sound technical analysis and offer adequate community outreach to educate and inform the public in order to achieve clear understanding and acceptance of the study outcome. Since the December 18 meeting, work has been completed to better document the analysis such that the proposed flood mapping may be considered for floodplain regulatory and flood insurance rating purposes. This has included the consolidation of previous information into the following summary reports: 1. Climatology Report dated February 6, 2007 (Attachment C) 2. Hydraulics Report dated February 6, 2007 (Attachment D) Agenda Item # ~ 6 ~age # S -3 Each report with appendices is over 800 pages long and therefore the attachments to this memo present the body of the report only without appendices. The complete reports with appendices may be viewed at city libraries or downloaded at: http://www.southbouldercreek.com/pa~page/proiectbackerounddocuments. cfin The study team has attempted to respond to comments from the public and the Peer Review Evaluation Panel (PREP). Responses to previous PREP comments aze presented as Attachments E and F. In addition, staff secured the continued participation of the PREP in reviewing and commenting on the adequacy of the latest reports. Comments from the PREP regazding these reports are anticipated prior to the meeting on February 26. One azea of analysis that has not been completed is the definition of the conveyance or floodway zone. It is anticipated this work will be completed prior to the meeting on February 26. BACKGROUND: Original results of the climatology/hydrology portion of the study including projected flood flow rates were submitted to FEMA for review in May 2005. However, these results were never accepted. Comments from federal, state and local review agencies and members of the public received in July 2005 indicated concerns that the projected flood flow rates seemed to under-predict the real flood threat when compared with the current 1986 U5ACE regulatory hydrology. In addition, the Urban Drainage and Flood Control District (UDFCD) objected to the use of the new non-standard study methodology when compared to the accepted standazd practice. UDFCD recommended that additional scientific reseazch and analysis was needed before accepting the new flood flow rates; otherwise, the study should move forward using the current 1986 USACE regulatory hydrology. These comments triggered a reassessment of the climatology/hydrology portion of the study. Additional scientific research and analysis has been performed to ensure the best technical results possible. Further study was done on the size and intensity of historical thunderstorms that aze the most likely cause of flooding along SBC. Among numerous assessments completed, the most significant involved the development of detailed characteristics for an additiona137 thunderstorms. This was made possible by the mid- 2005 introduction of new Geographic Information System (GIS)-based Doppler weather radar analytical techniques for storms observed from 1997-2004. The initial study had used only 13 thunderstorms and required manual analyses. The new storm sample included a total of 50 thunderstorms and better defined their size and character of azea thunderstorms. This improved the quality of the study results. The expanded GIS-aided analysis determined that the size and distribution of regional thunderstorms are larger than initially determined. As a result, a thunderstorm in the SBC basin will produce greater flooding conditions than a general storm. Table 1 presents the A~endattemd~(,~_Pagei :f-`I 100-year flood flow rate in terms of cubic feet per second (cfs) at key locations along SBC based on various study results and in comparison with the current regulatory model. Table 1 South Boulder Creek 100- ear Flood Flow Rates cfs ocation riginal evised evised low from 2005) Flow 2006) Flow 2006) Flow urrent 1986 efore efore fter SACE outing (1) outing (2) outing (3) egulatory Study fter Routin 4 idorado 260 520 340 800 wy 93 940 7120 900 740 S 36 930 7690 5850 200 aseline Rd 930 8770 6900 400 onfluence 910 8910 5430 600 I. This is the flood tlow rate based on the study's original rainfalUrunoff model prior to rouring Uuough the hydraulic model and was submitted to FEMA in Apri12005. 2. This is the flood flow rate based on the study's revised rainfalUrunoff model prior to routing tluough the hydraulic model that is proposed for consideration. 3. This is the flood flow rate based on the revised rainfall/runoff model after routing through the hydraulic model that is proposed for consideration. 4. This is the flood flow rate based oa the current 1986 USACE regulatory model after routing. Please refer to Attachment A for more background information. Other study results have been updated as presented below. ANALYSIS: There aze three primary components of the study: Climatoloq~/Hvdroloev Analvsis The confide~ce of this analysis has improved since the original FEMA submittal in May 2005. Based on the analysis of additional thunderstorms the confidence limits of the discharge pazameters increased from +29/-48 percent for the original data set to +18/-32 percent for the expanded data set. Hvdraulic Analvsis and Flood Hazard Mappin2 Important study results aze the proposed regulatory flood hazazd maps presented in Attachment C as follows: 1. Figure 20 - Floodplain Delineation - page 40 2. Figure 21 - Conveyance Zone - page 41 (please note this figure is currently unavailable. It is anticipated this work will be completed prior to the meeting on February 26.) Agenda Rem # ~ 4- ~`age # ~ -S Figure 22 High Hazazd Zone - page 43 These may be compared to the current floodplain delineation based on the 1986 USACE study presented as Figure 14 - Current city of Boulder Regulatory 100-year Floodplain - page 32 of Attachment C. The floodplain delineations and defmitions have been modified since November 2006. The process used to delineate and define the floodplain is presented as Attachment H- Hydraulic Report - Appendix F- Floodplain Zone Defmitions and Island Determination. FEMA floodplain zones applicable to South Boulder Creek include: Zone AE - Defined as areas of special flood hazard inside the 100-year floodplain where water surface elevations have been determined. A 100- yeaz flood is a flood that has a one-percent chance of being equaled or exceeded in any given yeaz. Zone X-shaded - Defined as azeas of moderate flood hazazd that are determined to be within the 500-year floodplain where there is a 0.2- percent chance of being equaled or exceeded in any given year; areas in the 100-year floodplain where average depths are less than one foot; and areas protected by levees from the 100- year flood. Zone X-uns6aded - Defined as areas of minimal flood hazazd determined to be outside of the 500-year floodplain. Study results will change the floodplain maps adopted for regulatory purposes and flood insurance requirements. Many azeas in the SBC basin, previously outside the 100-year floodplain on the Flood Insurance Rate Map (FIRM), have now been determined to be within the floodplain. These azeas will be delineated within "Zone AE", areas of special flood hazard subject to regulatory restrictions and mandatory flood insurance purchase requirements if the associated structure was purchased with a federally backed mortgage or fluough a federally regulated lender. Other implications are discussed in Attachment I - Hydraulics Report - Appendix I- Flood Insurance and Regulatory Implications. Risk Assessment Inundation maps have been developed to depict that actual depth of flood waters under various flood flow scenarios_ This information will be used to support subsequent flood mitigation planning. Important inundation maps aze presented in Attachment D as follows: 1. Figure 15 - 100-year Design Thunderstorm Inundation Map - page 33 2. Figure 16 - 1986 USACE Dynamic Storm Inundation Map - page 35 3. Figute 17 - 1986 USACE Steady State Storm Inundation Map - page 36 4. Figure 18 - 1976 Big Thompson Storm Inundation Map - page 38 5. Figure 19 - 1997 Ft. Collins Storm Inundation Map - page 39 An issue that continues to raise concerns in the flood mapping study is the CU-South Campus berm that redirects flood waters around the former Flatirons gravel mine. This A~a~~~ s a p~~ 1-~ berm, although a man-made structure, is a significant existing physical feature and will dramatically affect the flow of flood waters and their associated hazazds. For this reason, the proposed regulatory mapping has been modeled with the berm in place. This is consistent with the overall modeling approach that considers and includes all topographic features including other man-made structures such as roadway berms, excavated channels/ponds and elevated roadway intersections. The study team recently completed modeling simulations using the study's revised (2006) hydrology without the CU-South Campus berm. The results of these modeling simulations are presented as Figures 12a and 12b - Sensitivity Results Related to University of Colorado South Campus Berm with New Hydrology on page 28 of Attachment D. COUNCIL FILTER IMPACTS: Both the current and proposed flood mapping provide similaz information regazding flood hazazd azeas near the main stem of South Boulder Creek. However, the new flood mapping also identifies newly recognized flood hazard areas located west of SBC and north of U.S. 36 (West Valley.) The economic, environmental and social impacts aze discussed within this cotttext. Economic Economic impacts will primarily affect existing business and residential real property owners in the West Valley. The impacts aze primarily due to flood insurance costs that will likely be required by mortgage companies. However, this same flood insurance will also provide protection from catastrophic loses due to potential floods. The flood mapging will require that additional properties will be subject to the city's and county's floodplain regulations. These regulations aze intended to promote sustainable development by requiring that structures be protected from the 100-year flood. There aze no perceived economic impacts on the business community which could impact city revenues. Environmental Environmental impacts are limited since the proposed flood mapping changes primazily affect existing developed areas of the city. There are no perceived significant environmental impacts based on considerations of rtansportation, climate, energy, greenhouse gas emissions, recycling; renewable and non-renewable resources. Social The flood study results provide better information for the community to assess flood hazards. There aze no perceived impacts on the needs of diverse communities, e.g. different ethnicities and cultures, abilities, age, income, family demographics, or under- represented residents. There are no perceived impacts based on intergovernmental relation issues. The affected community has been engaged for input as summarized below. Agenda I~m #~S _ Page N ~ -?~ OTHERIMPACTS: Fiscat The flood study results have limited budgetary impacts to the city organization. Funding for completing the flood study and submitting the information to FEMA is appropriated in the city's 2007 budget. Sta time Completing the flood study and submitting the information to FEMA is anticipated in the 2007 staff work plan. PUBLIC REVIEW PROCESS TO DATE: In addition to the public process summarized in Attachment A, WRAB hosted a public hearing on the SBC Flood Mapping Study on December 18, 2006. Please refer to Attachment A- Agenda Item and Attachment B- Meeting Summary. The study team has attempted to respond to public comments made at the December 18 meeting in part by routinely updating the flood study website with new information. In addition, a special post card mailing to over 5,000 addresses potentially affected by the flood mapping study was delivered to the United States Postal Service on February 9, 2007. The post card contained information about the public review process including an announcement of the February 26, 2007 WRAB public hearing. City staff has responded to approximately 20 questions from the public since the December 18, 2006 meeting. The vast majority of these questions were about the impacts of the proposed flood mapping on specific properties. NEXT STEPS: City staff will respond to any recommendations provided by the WRAB at the February 26 meeting. It is likely that modifications to the reports and flood hazazd mapping will be made based on comments from the public, WRAB and PREP. The city's Planning Board and City Council will also be asked to revieyv and concur that the results should be submitted to FEMA. The Planning Boazd public hearing and discussion is currently schedule for March 15, 2007. The City Council public hearing and discussion has not yet been scheduled but is anticipated to occur in Apri12007. Based on recommendations from the WRAB, Planning Boazd and City Council, it is anticipated that the study results will be submitted to FEMA for approval in May 2007. It is likely that the FEMA review period may take 9-12 months. FEMA will also solicit public comment as part of their review process. Provided FEMA accepts the study results, the Colorado Water Conservation Boazd will be also be asked to adopt the study results and associated flood hazard mapping. ~gendaHemt ~6 FageA 5-Y STAFF RECOMMENDATION: Staff recommends that the study results and flood hazard mapping be submitted to FEMA. ATTACHMENTS Attachment A - WRAB December 18, 2006 Meeting Agenda Item Attachment B- WRAB December 18, 2006 WRAB Meeting Summary Attachment C- Climatology/Hydrology Report without Appendices Attachment D - Hydraulic Modeling Report without Appendices Attachment E- Questions and Answers Attachment F- PREP Comments and Study Team Response on Climatology Task Enhancements Memo Attachment G - PREP Comments and Study Team Response on Draft Hydraulics Report Attachment H - Hydraulics Report - Appendix F- Floodplain Zone Definitions and Island Deternunation Attaclunent I- Hydraulics Report - Appendix I- Flood Insurance and Regulatory Implications Agenda kem k_.~{~ P~ #~~. ATTACHMENT K ~~/() I ONE COMPANY i y/L ~ MHhy SOIYtJOA3'~ Technical Memorandum To: Bob Harberg, City of Boulder From: RichTfrorntan,JerryKenny-HDR Project: BoulderStortnwaterStrategicPlan CC: File Dale: February 22, 2007 Job No: 34640 RE: South Boulder Creek Lower Urbanized Storm Center - 100 year Flood Impacts Introduction The purpose of this analysis was to develop an order-of-magnitude understanding of the potential flood impacts within the urbanized subbasins tributary to South Boulder Creek during a 100-year design storm event centered over the southeast portion of the city. This analysis is a follow-up to the observations noted in the Hydrologic impacts of Downstream Storm Centers memorandum (HDR, February 24, 2005) which identified the potential for flood hazards resulting from local, urban subbasin runoff during an extreme storm event. is and Results The analysis consisted of an evaluation of the basin hydrologic and hydraulic response to a 100-year rain event using the XPSWMM model developed for the Boulder Stormwater Strategic Plan (SSP). The XPSWMM model developed for the SSP was developed for the analysis of the city's collector system and as a result includes a more detailed assessment of subbasin boundaries and local/collector conveyance elements. As such, there are minor differences in the subbasin boundaries delineated for the South Boulder Creek (SBC) analysis and the SSP analysis. The South Boulder Creek Lower Urbanized Storm Center - 100 year Flood Impacts analysis approach and results are summarized in the following sections. Hydrology The rainfall depth and temporal distribution associated with a thunderstorm cell centered over the South Boulder Creek C2 subbasin was entered into the XPSWMM model. Runoff hydrographs were generated for the applicable subcatchmenis and ihen routed through the collector storm drain and open channel systems. The resulting 100-year runoff peak simulated in XPSWWM was approximately 1200 cfs. This runoff peak is slightly lower than the 1650 cfs predicted with the MikeFlood model used in the SBC analysis. The slightly lower peak from XPSWMM is attributed to runoff being routed through the collector storm drain and open channel system thus attenuating the hydrograph peak. Agenda I~m k ~[~ Page #~ Flood Risk Assessment The XPSWMM model was developed for the collector system and used to evaluate the basin response for relatively minor rainfall events (up to a 5-year design storm). As a result, it does not provide an adequate, standalone tool to assess potential flood risk and flood hazard damage. However, the XPSWMM model can be used in conjunction with the XP-2D module to assess the combination of piped conveyance and surface flow conveyance. The XP-2D model was developed to route surface flow that exceeds the capacity of the existing storm drain system. In addition, where flow depths are greater than the open channel top of bank, overland flow is also routed via the 2D model. Therefore, the potential flood risk was assessed at this orderof-magnitude level using the XPSWMM/XP-2D model. A simplified dataset was used for the XP-2D model development. Data for the XP-2D model consisted of a digital elevation model (DEM) and an average surface roughness. Data such as ineffective flow areas (e.g. bui{dings) were not used due to the large urban area ihe analysis covers. In addition, multiple roughness factors accounting for different land use types and land cover characteristics were not used, again, as a result of the large urban area the analysis covers. The 2D analysis was limited to the C2 subbasin boundary. The City's (DEM) was sampled at 10-foot grid intervals and used as the DEM within the XP-2D model. The grid cell size within the XP-2D model was limited to 65-feet due to the large analysis area and model license requiremenis. As this analysis is intended to provide a general estimate of flood risk, the relatively large cell size was deemed appropriate. An average surface roughness of 0.030 was assigned based on the area consisting mainly of pavement, lawns, open space, and buildings. Analysis results indicate shallow surface flow for a majority of the study area with depths equal to or less than 1-foot as shown on Figure 1. There are locations where depths exceed 2-feet. However, these locations are isolated in areas where the DEM identifies localized depressions in the ground surface. These high inundation depths may be attributed to the accuracy of the DEM or 2D grid size. Flood hazard risk can be expressed by the product of overland flow velocity and depth. Typical definition of low hazard areas is if the velocity-depth product is less than 4. Flood hazard maps were produced with the XP-2D (Figure 2) and generally indicate low flood hazard risk across a majority of the study area with risk values of less than 1. However, there are localized areas where the risk value approaches 4. Specifically, there is a depressed area modeled in the DEM southwest of the intersection of Foothills and US 34 and another location approximately 800- feet southwest on the Viele Channel. Given the assumptions used to develop this model, it is anticipated that a 100-year thunderstorm event centered over the lower subbasins of South Boulder Creek would produce surface flooding on average less than 1.5-foot in depth. This 100-year inundation depth within a collector system meets the City's level of service defined within the Design and Construction Standards. kgenda ~em # ~ Page i K~Z Depth , 4.00 3.56 i 3.11 - I ~ 2.67 j j 1 2 22 ~ i 1.78 --~_ ~ _, ~ - L33 0.89 .~~r- ".y - _ 0.44 0.00 _ - _ \ - ~ --- -- --- - - j ~, Figure 1- Approxi»~ate Iriuridation Depths, 100-year Design Storm Hazard , ~ 4.OD , 3.56 3.11 '~ ~ -- - ~ 2.67 ' 1.78 --~ -- - -- - .. , 222 I .' 1.33 'f ~` 0.89 ~1 ,' ..`, _ \ ~ . 0.44 `r_'~ ~r; ~ ~ € < 0.00 ~ - -- - _. -- ~ ! , ~ ~ ~~ ~ 4 ~ I ~ ~ ~` ` wy • Figure 2- Approximate Flood Hazard, 100-year Design Storm ~1~~1de~ Item i~ _ ~ ~ -;,yb ~ K -3 / ~ awe.ncw.~u..~ ~ SWriYGr! ~~ ^-~ _ v ~ .' i ~ ` i v~ Ps / ~~ i'~ ~ .r.. .. . ec~ -~_,J ,11 ~ ` ' ~\ ~ I ~~~~ . \ _~ `• ) / _/ ~ - N ~ a !~al ~eaend Modeled neMrork _ 8ear Canyon Creek ~ Elmers Twomile Creek Kings Gulch South Boulder Creek /~/ Pipes - Bluebell Canyon Creek ~ Fourmile Canyon Creek Lower Boulder Creek ~ Twomile Canyon Creek CanaU D'Rch - pry Creek ~` Goose Creek Middie Boulder Creek - Vele Channel /~/ Mapr drainageway _ Dry Creek No. 2 I' Gregory Canyon Creek Skunk Creek _ Wonderland Creek ~ SBC SubBasin Figure 3- South Boulder Crevk and Starmmater Shntegic P7an Subbnsins i ( \ I f ~ ~ ~;ed ~ 7 ~ ! i ~ ~ n / \ 1 J Eo.n, ew -_~ ~ ~~~~a ~~ ~ S 6 _ ~~f~; ~ K -y - ATTACHMENT L Questions and Answers General 1. How was the scope of the South Boulder Creek Flood Mapping Studv determined? The flood mapping study scope was developed in response to the South Boulder Creek Major Drainage Planning, Phase A Report, developed by Taggart Engineering Associates, Inc. in 2001. The Phase A Report proposed flood mitigation alternatives to eliminate the potential for flooding identified in the west valley. However, community uncertainty and concerns about the Phase A study effort, the accuracy of an associated hydrologic analysis, and the proposed level of flood mitigation required in the plan resulted in local rejection of the report and public demands for a detailed flood risk assessrnent. Recommendations about defining the hazuds and problems created by South Boulder Creek flooding and the level of technical analysis and evaluation needed to develop community acceptance of the results were presented to City Council by the Independent Review Panel (IRP) and the Citizen Advisory Group (CAG) in August 2001. The IRP included local floodplain grofessionals, Dr. Gilbert White, Mary Fran Meyers, Dr. Rich Madole, Brian Hyde and Dr. Jonathan Friedman, convened at the request of City Council to assess and recommend improvements in the City's approach to floodplain management and mitigation. The CAG was convened as part of the Phase A community process to provide input and recommendations for floodplain management and mitigation planning from the citizen's perspective. City Council accepted the IRP and CAG recommendations and a formal Hydrology Advisory Panel (HAP) made up of nine professionals with extensive background in multiple disciplines dealing with flood hydrology studies was convened in December 2001 to outline and determine a detailed scope of work to complete an updated flood study for South Boulder Creek. The HAP was committed to develop a state of the art scope of work that would produce results with a high level of confidence. Critical study elements outlined by the HAP included an online resource atlas, updated climatology, multiple-approach hydrology analysis, two-dimensional hydraulic modeling, multiple storm frequency risk assessment and extensive public involvement process. The recommended scope of work determined by the HAP was reviewed and accepted by the IRP and representatives of the city of Boulder, Boulder County, University of Colorado and the Urban Drainage and Flood Control District in late 2002. It was advertised as part of the original request for proposals (RFP) posted for response by Feb. 28, 2003. HDR Engineering, Inc. was selected to conduct the South Boulder Creek Flood Mapping Study in August 2003. The final scope of work connected with the HDR study contract is available online at: AgendaltemA~B.._~~ ~-I h~tt :l/www.southbouldercreek.comJmedia/SBC%20SCOPE°/a200F%20WORK.PDF 2. The South Boulder Creek floodplain has been studied several times in the past. Why is another study needed? The study is intended to replace the current regulatory mapping based on a 1986 United States Army Corps of Engineers (USACE) study that is currently adopted by the City, Boulder County and the Federal Emergency Management Agency (FEMA). This study is in need of updaring because it does not identify the flood risk in the West Valley or South Boulder Creek. The previous study developed by Taggart Engineering Associates, Tnc. proposed alternatives to eliminate flooding in the West Valley without first restudying the floodplain and defining the flood problem. The City Council, Boazd of County Commissioners and the public at lazge rejected this approach and indicated that new floodplain mapping was needed before flood mitigation planning could occur. The new flood mapping study is intended to first define the flood problem and answer questions about where and to what extent flood risks exist. Once community understanding is achieved, a public planning process can then move forward in developing flood management and mitigation oprions. 3. Why should the ~ublic exnect this studv to be any different than the nrevious studies? There aze several ways in which this technical study is different than previous studies: This study separates the technical floodplain mapping analysis from the public discussion about how the community can mitigate flooding. Achieving community understanding first about the flood problem and its risks provides the basis for a public planning process to develop flood management and mitigation options. This study combines some of the best technical expertise in floodplain analysis with a public involvement plan that will include the public as a partner from the very outset of the project. This study will take advantage of a more technologically advanced approach that allows for a much finer level of analysis than previous technology allowed. This is perhaps the most comprehensive and thorough floodplain mapping study ever done in this region. The City is confident that the multi-dimensional scope of this study will produce sufficient detail and understanding of the South Boulder Creek flood hazards, and will clearly define the flood problem the community faces in this azea. 4. Bv the time the studv is approved will another technoloeical advance vield new and different results? Agenda Item # ~_ P~ ~ ~'~Z The study team used the most scienrifically defensible data and analytical approach available at this time. Technology is continuing to improve, but there is a great need for new flood hazard mapping that appropriately recognizes the flood risks in the South Boulder Creek azea. 5. Will this study explore altematives for flood management and mitieation? No. This study is intended to define the flood problem not solve it. This study is a technical analysis to determine the likelihood of flooding, the conditions that are likely to cause flooding, and the azeas that are most likely to be impacted by flooding. It is crirical to understand the flood problem before the community can begin to discuss how to mitigate the flood risk. The flood mapping study will produce a new regulatory flood map to replace the outdated 1986 regulatory map. The new regulatory flood map will be used to regulate floodplain development and define the flood zones on FEMA's Flood Insurance Rate Map used to determine flood insurance premiums. The risk assessment component of the flood mapping study will be completed in 2007 and will be used to support subsequent flood management and mitigation planning. A community planning process with direct public involvement to develop floodplain management and mitigation alternatives will begin as soon as practical after the flood study results have been accepted by FEMA, Boulder County, the Ciry of Boulder and other agencies. Currently, $100,000 has been appropriated in the City's Capital Improvement Program (CIP) to begin the flood management and mitigation planning process in 2007. However, this funding may be needed to complete the flood mapping study itself. Additional funding has been allocated in the City's CIP in 2008 ($150,000) and 2009 ($300,000) to complete flood mitigafion planning. In addition, $3,000,000 has been allocated in 2010 to help fund selected flood mitigation improvements, whatever these might be. The City is also pursuing Federal funding for flood mitigation planning and construction. 6. How much money has been snent on the flood study to date? Approximately $1,250,000 has been spent on the flood mapping study to date. 7. Will this studv look at water qualitv in South Boulder Creek? Water quality investigation and analysis is not in the scope of the flood mapping study. City staff is looking into available water quality information that may be included in the online Resource Atlas. South Bouider Creek is currently identified as having one of the highest water quality rarings in the state. Agendaltemt_~_P~~ ~'-3 Public Involvement Process 8. Where can I find the most comprehensive information conceming the South Boulder Creek Flood Map.pin~ Study? Comprehensive information is available on the South Boulder Creek Website - go to: www.southbouldercreek.com 9. Are there hiQher resolurion flood~lain ma~s availabie than presented on the Web site? The flood hazazd maps posted on the Sauth Boulder Creek Website aze in Adobe Acrobat pdf format to allow convenient Intemet access with limited download requirements. These maps allow a viewer to pan azound the image and to zoom in to areas of particular interest. However, the resolution is of lower quality than may be offered in a GIS format. The City is also hosting an ArcIMS Web site for the South Boulder Creek flood maping study (httv://Qisweb.ci.boulder.co.us/website(pds/sbc flood/viewer.hhn). This Web site allows the viewer to select various mapping study results and zoom in to areas of particular interest at an even higher resolution. 10. What aze the next steps with this shxdy? When will FEMA approve or disapprove the new flood mans? The flood mapping study results will undergo review by City staff and the Peer Review Evaluation Panel (PREP) before submittal to the Water Resources Advisory Board (WRAB) on December 18, 2006 and January 22, 2007. The WRAB will be asked to review and provide a recommendarion for submitting the study to FEMA for approval. For more informarion about the WRAB go to: htto://www.bouldercolorado,eov/index.nhn?option=com content&task=view&id=108 &Itemid=1192 The City's Planning Boazd will also be asked to review and provide a recommendation for submitting the study to FEMA for approval. Planning Boazd review is anticipated to occur in February 2007. Boulder County will also be asked to review the study for submittal to FEMA. For more information about the Planning Board go to: http:/iwww.bouldercolorado.gov/index.pl~p?oation=com content&task=view&id=141 &Itemid=469 City staff anticipates that the flood mapping study will be submitted to FEMA for review and approval in Mazch 2007. The FEMA review period is expected to take 6-9 months. FEMA adoption of the new floodplain mapping is expected by the end of 2007. Hgenda I~m ~ ~.b Page # ~_ How mav the public remain involved with and provide input into the flood mapping studv? Public involvement is a critical part of the flood mapping study. There have been and will be open public meetings during the development of the study. The most recent public meeting was held on November 15, 2006. For more information about this public meeting go to: h~t ://southbouldercreek.com/paQeinpaQe/publicinvolvement.cfin#publicmeetin¢s There was a long period of time in 2006 during which the Web site was not updated. The Web site has recently been updated to include We latest technical study results and public process elements. For more information go to: httn://southbouldercreek.com/naeeinnaee/home.cfin The public is encouraged to attend the upcoming WRAB meerings on December 18, 2006 and January 22, 2007 to hear about the study results and provide input. The public may also contact the study team or the City staff with your comments and questions. The City's Project Manager, Bob Harberg, may be contacted directly at: E-mail: hazberebCa~bouldercolorado.gov Telephone: 303-441-3124 11. What is the Peer Review Evaluation Panei? The Peer Review Evaluation Panel (PREP) is comprised of three Boulder azea residents with scientific knowledge in water resources and floodplain management. The PREP was established to review and evaluate the technical aspects of the SBC Study on behalf of the public interest and to offer an independent assessment to ensure the study meets generally accepted standards of engineering pracrice for flood hazard mapping. The PREP also advised the study team about how effectively the study results are presented to the public in order to ensure the greatest level of understanding for a non- technical audience. To access the PREP wmments regarding the flood study results, go to: http://southbouldercreek.com/oa~einpage/nublicinvolvement nrenbios.cfrn Climatoloev/Hvdroloev Analvsis 12. Where can I find the most comnrehensive information concernine the results of the revised climatology/hydrology analysis? Agenda Item # ~f~_ Pa~e ~ ~-~ The Interim Climatology/Hydrology Summary Report is available on the South Boulder Website - go to: www.southbouldercreek.com 13. The current hvdroloev results increased the original 2005 hvdrologXresults bv as much as a factor of two. Whv were these changes made? Comments received from FEMA, the US Army Corps of Engineers, the Urban Drainage and Flood Control District, the Colorado Water Conservation Boud and members of the public following submittal of the original hydrology to FEMA in 2005 indicated a concem that the hydrology underestimated the flood hazazd. The comments recommended additional reseazch and analysis to expand and refine the scientific data used to produce the results. The study team was able to collect additional storm records and utilize a new computer- based analytical tool to expand the climatology analysis from 13 to 50 storms. The expanded data offered a better understanding of the size and shape of regional storms. The results determined that local storms cover more azea, produce more rainfall and result in greater peak flows and volumes than previously indicated. 14. How does the new hvdrologXcompaze to the currently adopted 1986 steady-state hvdrologx? The table below presents 100-year peak flow rates at various locations for the new hydrology as originally determined in 2005 and subsequently revised in 2006, and for the currently adopted 1986 steady-state hydrology. Flood flow rates are presented in terms of cubic feet per second (cfs). South Boulder Creek 100-vear Flood Flow Rates (cfs) ocation riginal evised evised low from 2005) Flow 200~ Flow 2006) urrent 1986 efore efore low After SACE Agenda Nem # ~b Page # L ~ _-_ outing (1) outing (2) outing (3) egulatory Study fter Routin 4 ldorado 260 520 340 800 wy 93 940 120 900 5740 S 36 930 690 850 200 aseline d 930 8770 900 400 onfluenc 910 8910 5430 600 1. This is [he flood flow rate based on the study's original rainfaWrunollmodel prior to routing through the hydraulic model and was submit[ed to FEMA in April 2005. 2. This is the flood flow rate based on the study's revised rainfalUrunoff model prior to routing Uvough the hy&aulic model tha[ is proposed for considerafion. 3. This is ttte flood flow rate based on the revised rninfaWrunoff model after routing through the hydraulic model that is proposed for consideration. + 4. This is the flood flow rate based on [he current 1986 USACE regulatory model after routing. 15. How do the chan¢es in the flood mappina study's findings relate to data eeneration (real data vs. simulatedl. and how is the level of confidence determined? Changes in the study zesults apply only to the design storms. The design storms are by definition, generated data, but the data generation was based on the analysis of real data from 50 thunderstorms and seven general storms. This represents the most complete data set available for anlaysis that is applicable to South Boulder Creek. The study team is in the process of developing quantitative confidence limits on the design storm discharges. 16. How were the increased design storm values determined and what drives increased storm values~ The South Boulder Creek design storms developed in the 2005 climatology results were reviewed by FEMA, the US Army Corps Of Engineers, the Urban Drainage and Flood Control Dish-ict (UDFCD), the Colorado Water Conservation Boazd and the Peer Review Evaluation Panel (PREP). Review comments recommended increasing the storm sample from the original 13 storms used to create the design storm. HDR hydro-meteorologists used surface rainfall observations available from the National Weather Service, Colorado Climate Center, National Climate Data Center and the UDFCD to identify thunderstorms that produced a 100-yr rainfall in and along the Colorado Front Range foothills from Fort Collins to azeas just north of Palmer Divide. Once idenrified, the Storm Total Precipitation product (STP) for National Weather Service WSR-88D Doppler radars located at Watkins, Colorado and Cheyenne, Ngenda Item #.~b _ Page # L-'~ Wyoming were used to define the spatial storm rainfall pattern This pattem was then "ground-truthed" with surface rainfall observarions to develop a comprehensive storm rainfall pattern. The STP product (released in mid-2005) offers computer generated storm analysis that was not previously available and made it economically possible to increase the storm sample from 13 manually analyzed storms to 50 storms. The resulting 100-yr design storm (based on a thunderstorm event) was spatially larger (~15 percent) than the original thunderstorm and was observed to be quasi-stationary during heavy rainfall production periods. The increased design storm volumes were caused by two factors: 1. The increased size of the final desigi thunderstorm as described above, and 2. Application of a stationary design storm aligned along the basin below Gross Reservoir. The original design storm was moving across the watershed in a ~ manner consistent with historical South Boulder Creek storms. 17. Have extreme "dooms-day" storm situations been considered in the flood maoping studv? (i.e. If Gross Reservoir is at canacity durine snrinQ runoff season and the 100/500-veaz storm hits simultaneouslvJ . The flood mapping study was designed to develop a scientifically based, purely technical analysis that would define the most accurate and physically real results possible in order to truly "define the flood probiem." This required analyzing the most probable conditions expected rather than the worst case conditions. To understand and consider the impacts of more extreme or "worst case" flooding, the study has included simulations of the 500-yeaz storm, 100-yeu and 500-year storms with and without the CU-South Campus berm and the transposition of rivo extremely lazge historical events; the 1976 Big Thompson storm and 1997 Ft. Collins storm. Both exh-eme storms were significantly larger than the 500-year storm. 18. Does the flood mappine study include releases from Gross Reservoir and imgation ditch diversions? Yes. The flood mapping study includes releases from Gross Reservoir based on annually observed condirions and expectarions. Diversion of flood waters from the stream into irrigation ditches was based on the capacity of each ditch and its location to intercept and convey flows as determined in the hydraulic model. 19. Has the flood mappin~ studv considered all the variables: season, eround saturarion, temnerahue and snow pack? Rgenda kem t S b Pags ~ Lg -- The study team attempted to incorporate as many variables as possible into the analysis. Changes in seasonal rainfall and temperature were explored. Irrigation practices and rainfall preceding design storms were considered. The model represents basin conditions that aze probable at the rime of the storm - late spring to eazly summer for the general storm and mid to late summer for the thunderstorm. 20. Has the revised hydroloev been re-submitted to FEMA for review? No. The study team is working to complete the floodplain delineation mapping for the flood study so that the climatology, hydrology and hydraulic analyses can be submitted together for a comprehensive FEMA review. The updated results have not yet been forwazded to any review agencies for comment. Please refer to the answer to question 8 for more information about the timetable for submitting the revised hydrology to FEMA. 21. How aze water table levels and seasonal chan eg s in eroundwater addressed in the hydrologv analvsis? The flood mapping study is designed to determine surface flows in the South Boulder Creek floodplain and does not provide a detailed analysis of goundwater condirions. However, understanding general groundwater condirions and the level of anticipated ground sahuation is important in determining flood water infiltration affecting flood runof£ The study reflects groundwater and soils conditions through the model calibrarion efforts. The model does not explicitly compute groundwater depths or changes in groundwater tevels during a flood. Such level of resolution is not necessary to compute surface runoff during a flood. 22. Is the flood model calibrated to the Eldorado Springs gage data? If not, wiil FEMA quesrion the studv's results? The hydrology model was calibrated using extensive rainfall data for three storm events (September 1938, May 1969, 1998 thunderstorm). The calibration was then validated through a"blind" analysis of a fourth storm event (1999 thunderstorm). Model calibration was not based directly on the Eldorado Springs gage because this is the only gage record for the South Boulder Creek basin and it is located well above the valley where flooding is critical. However, the calibration analyses using the fow storms produced results consistent with flow rates and storm volumes recorded at the Eldorado Springs gage for these events. The hydraulic model was calibrated nsing historical informarion and visual records from the 1969 flood. The base model was refitted with topographic conditions representing those that existed in 1969, and the extent of flooding was compared to photographic evidence and recounts from area residents. H~en~a Item #._.5,.~_ ~ac~ # L_ `1 The overall calibration effort produced successful results that were consistent with the benclunazk storm events and the Eldorado gage rewrd. This is compelling evidence that the model appropriately represents the watershed and the design storms for this azea. Further adjustment of the calibrated model to directly match the Eldorado gage values would adversely affect the validity of this comparison and weaken the credibility of the results. 23. Where do the Eldorado Snrines eage volumes come from? Eldorado gage volumes were developed using recorded flow rate data. For each year of gage record, the study used the day with highest peak flow and calculated a 24-hour volume for that day. The average daily flow rate for these days was then used to calculate corresponding flow volumes used to determine peak flows in the flood frequency anlaysis. The flood frequency analysis used a standard statistics package developed by the U.S. Army Corps of Engineers (Flood Frequency Analysis package) that applies the log Pearson Type III distribution together with a station skew. This analysis determines benchmark volumes corresponding to flows with specific retum periods (i.e. 10-,25-, 50-, 100-, and 500-yeazs). 24. How flexible aze the simulations/models? Can they incomorate different calibrarions and inputs? The MIKE FLOOD model used for South Boulder Creek integrates hydrology and hydraulics simulation modules into one program. This modeling tool represents the state-of-the art in hydrologicll~ydraulic modeling. MIKE FLOOD offers significant flexibility in representing various watershed and floodplain condirions. This flexibility along with the 1D/2D capabilities was the basis for selecting this program. The South Boulder Creek model will allow the City to evaluate and simulate the affects of various conditions including the impacts of blockage, physical land features, and various storm conditions. This offers a powerful tool in evaluating future opportunities for floodplain mitigation and land use acrivities. 25. Have the impacts of global warmin¢ been included in the flood mappin¢ study? The study included the addition and analysis of regional rainfall records for the last 30 years to update the 1972 NOAA Rainfall Atlas. This additional data did not change rainfall rates in the South Boulder Creek basin and did not reflect any trends that could help define the expected impacts of global warming. Given this, specific affects or adjushnent factors to account for global warming could not be included in the study with any scientific confidence. ,qgenda Item ~ 5 6 Page # L- I fl The study team is sensitive to and concerned with the affects of global wanning and climate change. A recent dra8 American Meteorological Society Statement on Climate Change, now under review by the AMS Council, has been posted to the AMS web site: httu://www.ametsoc.org/policv/draftstatements/index.html. This draft statement provides a very good summary of current science consensus on climate change. In general it supports the likelihood of more frequent, lazger and more intense thunderstorms in the Western United States. 26. Whv is South Boulder Creek being allowed to go almost drv in the winter? It appeazs to have eotten worse over the last 30 years and is harmin~Z the fish. The focus of this study is the examination of high flow events, so low periods were not studied. The study team will look into available information that may respond to this question and post it on the Web site. 27. I~neazs that the consultants used the wrone data in developing the orig_uial climatology_and hvdrology in 2005 that has now been changed. Whv should the public pay to correct their errors? The consultants have not requested payment for any work done to correct enors. The revision to the climatology and hydrology was the result of adding storm data to increase the sample from 13 to 50 storms as recommended in review comments received from FEMA and others in 2005. The City has only been billed for additional work necessary to incorporate this new data into the analysis. Hvdraulic Analvsis and Flood Hazard ManainQ 28. Where can I fmd com~rehensive information concemine the results of the hvdraulic anal~is to date? The Draft Floodplain Hydraulic Modeling Report is available on the South Boulder Website - go to: www.southbouldercreek.com 29. The denth of flow in Drv Creek Ditch is not shown nro~erlv. The ditch is deener than renorted on the flood~lain information nresented. The modeling of ditches and culverts is based on information assembled during the course of the study. The study uses high resolution one-foot contour topographic mapping developed in 2003, record drawings from previous studies, and fieid survey information to assemble the best possible data set. As with any model of such complexity and lazge area of coverage, errors or misinterpretations are possible. The study team will explore such areas of concern as the study continues and detailed Rgendal~m~_~'~Page# L"II quality reviews aze completed. Members of the public aze invited to identify any other areas of concern and report these to the team via the project Web site. 30. How is at risk floodplain status determined in relation to outbuildings, sheds, senric and leech fields? The identification of properties within the various flood zones was based primarily on habitable structures that aze impacted. Efforts were made to screen out sheds and other non-habitable struchves Any questions related to specific structures should be reported to the study team via the project Web site. 31. Can the hi~,h hazard zone be chaneed as part of the flood maauing study to address structures in danaer and can we call to discuss structures in quesrion? The high hazud zone is defined by the physical properties of flood depth and velocity, and is detecmined without regard to individual structures at~'ected. Changes to the high hazard zone proposed as part of the flood mapping study or requested by members of the public must be supported by technical data. Questions related to specific structures and the impact of the high hazazd zone may be submitted to the study team via the project Web site. 32. How aze the floodplain zones (AE, AO and Xl reflected on the mavs defined? The flood zones aze defined as follows: • Zone AE: Areas where 100-year flows are hydraulically connected to the South Boulder Creek mainstem or other conveyance paths with a hydraulic gradient will be designated as Zone AE. All azeas of flooding in excess of 3', regardless of hydraulic connectivity or gradient will be designated as Zone AE. BFEs will be reported for all the areas designated within Zone AE. NOTE: Given the +/- 0.5-foot accuracy of the one-foot contour interval mapping, the AE boundary will be determined where the computed depth is equal to or greater than one foot (when rounded to the nearest one foot). Zone AO: Areas where 100-year flows have a computed depth (when rounded to the nearest one foot) equal to or geater than one foot that do not meet ihe criteria established for Zone AE will be designated as Zone AO. This will generally include ponded and shallow flow areas between 1' and 3' deep. • Zone X-shaded: Areas where 100-year flows do not meet the criteria established for Zone AE or Zone AO, or areas inundated by the 500-year flood. • Zone X-unshaded: Areas outside of the 500-yeaz flood. ilg~dal~m# Sg P~ge~ t%I'L _ 33. Will the flood mapping studv imvact flood insurance rec~uirements? Yes. The flood mapping study will replace the currently adopted Flood Insurance Rate Map (FIRM) used to set flood insurance premiums and idenrify mandatory flood insurance requirements. Areas identified in Zone A(i.e. AE and AO) aze considered areas of special flood hazazd (in the 100-year floodplain) and mandatory flood insurance requirements apply in this zone. Mandatory flood insurance is not required in X zones. However, flood insurance is available in all flood zones and flood insurance premium rates aze adjusted accordingly. 34. What can propertv owners do to reduce the flood insurance impacts if their propertv is determined by the flood mappine study to be in the Zone A floodnlain? Some proveriv owners have heazd about a type of "g~ndfatherine" for flood inswance. A discussion about flood insurance was presented early in the study. In summary, property owners who currently have and continue to maintain a flood insurance policy will have the option of retaining their existing insurance rate status when the new maps aze adopted. This has been referred to as FEMA's flood map "grandfather" rules. Property owners without flood insurance at the time of map adoprion would face the mandatory flood insurance purchase requirement based on the new floodplain designations. For more information on the grandfather rules, go to http://www.fema.gov/ndf/nfi~/hillsboroueh/grndfthr sht.~df. 35. Could I build a berm to protect mv house or pronerty, and would it reduce or , eliminate flood insurance requirements? Flood protection measures can help mitigate the impacts of flooding and reduce potential losses. Such measures could be as elaborate as constructing a berm around or flood proofing an at-risk struclure, or as simple as relocating valuable records and possessions above the flood grotection elevation. Conshucrion of flood protecrion improvements may not adversely impact neighboring properties and must comply with building standards and engineering pracrices. They aiso require a permit from the City or County to enswe compliance with floodplain ordinances. FEMA will not recognize flood protection or flood proofing measures for flood insurance purposes. While such measures may reduce the flood damage risk exposure, they will not eliminate the mandatory flood insurance requirement or reduce flood insurance premiums. Risk Assessment 36. What is the~uruoses and status of the risk assessment component of the shtdv? Rgendakem#_S!~__Pac~# L ~3.~ The purpose of the risk assessment is to identify and quantify life safety, property damage and environmental risks associated with South Boulder Creek flooding. To assess the risk to life safety, important information includes inundation mapping and basin response time. Property damage assessments involve depth of flooding and the corresponding value of associated losses. Environmental risks consider erosion and sediment transport, the loss of vegetation and changes in the creek path. The risk assessment will help to inform and educate those affected by flooding and support subsequent flood management and mitigation planning. The study has produced information identifying the flood hazard zones affecting individuai properties (see Floodplain to Structure Address Table) that is available on the South Boulder Creek Web site. The risk assessment will be completed in 2007 to support the subsequent flood mitigation planning. CU South Berm 37. What is the leeal status of the CU-South Camnus berm? Construction of a berm on the CU-South campus property was originally approved by the Boulder County Ptanning Commission on February 20, 1980 under Special Permit #AR- 79-4. The permit approved conshvction of an embanlunent and channel in the South Boulder Creek floodplain to provide flood protection for sand and gravel mining. The berm was approved as a"land feahue" in the floodplain and was not proposed as an official flood protection levee to remove property from the 100-yeaz floodplain. Removing the land use floodplain zoning with a flood protecrion levee would have required review and approval by the Boazd of County Commissioners. The uea landward of the berm remained in the 100-year floodplain as delineated on the 1979 Flood Insurance Rate Map (FIRM) for Boulder County. The CU-South Campus azea landwazd of the berm was removed from the 100-yeaz floodplain following the completion of the 1987 Greenhome & O'Mara Flood Hazard Area Delineadon (FHAD) for South Boulder Creek as adopted by Boulder County and FEMA. Floodplain analysis discussed in the FHAD identified the berm as a natural land feature and determined that the area landwazd of the berm would be an ineffective flow zone during flooding. This area was officially removed from the 100-year floodplain on the 1990 Boulder County FIRM. The berm was significantly enlarged, increased in height and strengthened following the university's purchase of the CU-South Campus property in 1996. Authorization to implement these modifications to the berm was approved by the Colorado Mined Land Reclamation Boazd (MLRB) in 1997as part of a"Technical Revision" to the approved 1989 Deepe Pit Mine Reclamation Plan. The MLRB may approve a technical revision to an approved reclamation plan under an effective mining permit without the consent and approval of extemal agencies such as k~nda4Pem!? S(~ p~~# L-1`/ _ Boulder County, the US Army Corps of Engineers and the city of Boulder. The MLRB approved the Deepe Pit technical revision following the City's and County's airing of opposition at the approval hearing. Several members of the public have opined that the berm is not a legal land feature despite the series of govemmental approvals that produced its current physical condirion. However, there has been no legal determination that the berm is in violation of any local ordinances or state statutes. 38. Has the CU-South Camnus berm been cer[ified as a flood protection levee under FEMA standards? No. Leonard Rice Consulring Water Engineers, Inc. (represenring the Flatiron property seller in coordination with CU's acquisition) submitted technical documentarion to FEMA on August 26, 1999 requesting "FEMA's review of a previously recognized levee" on the FIRM. Documents certified by professional engineers included a general report on the levee, a site plan and "as-constructed" surveys, a geotechnical engineering report, an erosion protection report and a CU operation and maintenance manual. Subsequent documentation submitted included an analysis of seepage along the berm to ensure the levee met shuchual stability requirements. FEMA determined that the upper reach of the CU-South Campus berm satisfied all requirements of Section 65.10 of the National Flood Insurance Progam (NF1P) regularions as indicated in FEMA's July 15, 2000 letter to Leonard Rice Consulting Water Engineers, Inc. This means that the structural integrity and maintenance and operations plans for the upper reach of the berm satisfy national standards for the construction of flood protection levees. However, FEMA also deternuned that the lower reach of the berm did not meet the requirements of Section 65.10, and required additional data before the FIRM could indicate that the upstream reach of the levee provides protection from the 100-year flood. Additional data requested included the submittal of existing conditions topography and hydrologic and hydraulic analyses indicating the impacts of a levee failure on the lower reach. FEMA indicated that the levee certification could not be further processed until the requested analyses were submitted. To date no existing conditions hydrologic and hydraulic analyses have been submitted to FEMA. As a result, the 1999 levee certification submittal was suspended and a complete new submittal will be required to process future levee certificarion. The South Boulder Creek Flood Mapping Study is the only hydroiogic and hydraulic analysis being developed at this time. Levee certification of the CU-South Campus berm can not be processed without complerion of the flood mapping study to address hydrologic and hydraulic issues. ~~nda liem #._~._.. ~~ ~ `'1-S . 39. What aze the South Boulder Creek floodglain imuacts with and without the CU-South Campus berm, and why hasn't the studv completed detailed 100-yeaz and 500-veaz hvdraulic simulations without the berm? This Uerm, although a man-made shucture, is a significant existing physical feature and will dramatically affect the flow of flood waters and their associated hazuds. For this reason, the proposed regulatory mapping has been modeled with the berm in place. This is consistent with the overall modeling approach that considers and includes all topographic features including other man-made structures such as roadway berms, excavated channels/ponds and elevated roadway intersections. The scope of the study included modeling for both the "with" and "withouY' CU-South Campus berm conditions under both 100-yeaz and 500-year flood flow rates. The rational for this effort is to assess the risks associated with a possible failure of the berm. This modeling effort to date is based on the study's original (2005) 100-year flow rate, the results of which are presented in Figures 10 on page 17 of the Draft Floodplain Hydraulic Modeling Report. The study team is proceeding with modeling of the 100- year and 500-yeaz flood flow rates using the study's revised (2006) hydrology without the CU-South Campus berm in order to complete the risk assessment. It is anticipated this work will be completed prior the January 22, 2007 WRAB meeting. Based on the fact that it is unlikely the CU-South Campus berm will be removed prior to the completion of the flood mapping study, the study team pians to base the proposed regulatory flood hazard mapping on modeling with the berm in place. In order to address public concems and offet greater understanding of the berm and its impact on flooding, hydraulic analyses of the 100-yeaz and 500-yeaz storm events using the study's revised hydrology without the berm will be performed and available prior the January 22, 2007 WRAB meeting. 40. How many shuctures are at risk wit6 and without the CU-South Camvus berm? Current study results based on existing conditions with the berm in place indicate that 741 structures will be impacted by 100-year flooding and 1,621 structures will be impacted by 500-yeaz flooding. The number of structures impacted by flooding without the berm has not yet been determined. However, since flooding will be greater in the W est V alley without the berm and remains very similar along the main creek corridor, the number of structures impacted by flooding is expected to increase. 41. How is fuhue development for the South Boulder Creek floodplain, the West Vallev and CU impacted with and without the CU-South Cam»us berm? Under either condition, with or without the CU-South Campus berm, development in the West Valley will become more restrictive in areas impacted by flooding. Because flooding in the West Valley is expected to be greater without the berm in place, A~enda Item €! _~_ _ f'zg° # ~~O- development restrictions will also be greater. Development restrictions along the main creek comdor in the eastem valley aze expected to be similu under both condirions since flooding appears to remain very similaz under either the "with" or "withouY' berm conditions. Development on the CU-South Campus property would likely be more impacted without the berm in place since flooding across the site would be more widespread under existing topographic conditions on the lowered former gravel mining floor. 42. What aze the benefits and disadvantaees oF certifyine the CU-South Camnus berm as a FEMA compliant flood protection levee? The benefits of certifying the CU-South Campus berm as a FEMA compliant flood protection levee include: • Officially recognizing the signi6cant physical land feature that currently exists. • Confirming that the existing berm meets technical standards to ensure struchual integritq and continued long-term maintenance. • Ensuring that the flood protection it provides to prevent additional West Valley flooding remains in place into the fixture. • Confirming the use and acceptance of the existing conditions topography in the flood mapping study. The disadvantages of certifying the CU-South Campus berm as a FEMA compliant flood protecrion levee include: • Officially recognizing the berm as an approved flood protection land feature may not prevent new development from occurring in the levee shadow. • Reducing oprions to remove the levee and replace it with other flood mitigarion measures. 43. Has the studv evaluated the CU-South Camvus berm and its uotenrial for failure? The flood mapping study has not included a structural analysis of potential failure for the CU-South Campus berm. The flood mapping study will include a hydraulic analysis without the berm (by removing the feature from the existing conditions topography) and simulate the results for the 100-year and 500-year storms. This approach will identify the maximum volume of flood water that would be expected to flow to the West Valley since there would be no berm to restrict or divert the flow. 44. Could the CU-South Campus berm and proneriv be transformed into a flood detention structure to mitigate South Boulder Creek flooding? The evaluation of altemative mitigarion measures is beyond the scope of this study. No evaluations have been performed that address the viability of berm transformation. 45. Will FEMA require hydraulic simulations with and without the CU-South campus berm as oart of the floodplain studv? ~yendai4emR~4 ~~9e# L"I~". FEMA has required the submittal of existing conditions topography and hydrologic and hydraulic analyses indicating the impacts of a levee failure on the lower reach of the CU- South Campus berm in order to process the certification of the upper levee reach (that has been determined to meet FEMA standards and be struchually stable). There has been no FEMA requirement to analyze the floodplain without the upper reach of the berm in place. The flood mapping study will satisfy the FEMA required hydraulic analyses based on the existing conditions topography with the upper reach of the berm in place. The lower reach of the berm is hydraulically disconnected from flood waters (meaning that the lower berm reach is not confining or diverting flood flows) and has no impact on the West Valley flow split at US 36. The flood mapping study will exceed the FEMA levee certification review requuement by completing additional analyses of flooding without the upper reach of the berm in place. 46. Who would be responsible for seeking and obtaining certification of the CU-South Campus berm as a FEMA comnliant flood protection levee? The owner of the CU-South Campus berm, the University of Colorado, is responsible for obtaining certification to recognize the existing physical feature as a FEMA compliant flood protection levee, and is then responsible for all operations and maintenance needs for the levee. 47. There is a perception that the CU-South Campus berm is protecting universitv propertv for fuhue development by diverting flood flows into residenrial areas. Has political influence plaved a role in developing the studv's findin~s? No. The study team has endeavored to develop the flood mapping study in a scienrifically defensible and purely technical manuer. The flood mapping study is designed and intended to define the flood problem as accurately as is scientifically possible, and has no component proposing a predetermined outcome. ~~ndal4e~~~6__Pa~9 L I`~ _. ATTACHMENT M CITY OF BOULDER, COLORADO BOARDS AND COMMISSIONS MEETING SUMMARY FORM NAME OF BOARD/COMMISSION: Water Resources Adviso Board DATE OF MEETING: February 26, 2007 NAMElfELEPHONE OF PERSON PREPARING SUMMARYc Jennifer Gra , 303-441-4073 ' NAMES OF MEMBERS, COUNCIL, STAFF, AND INVITED GUESTS PRESENT: BOARD MEMBERS - Ken Wilson, Jim Knopf, Robin Byers, Bart Miller, Kelly DiNatale STAFF - Ned Williams, Bob Hazberg, Douglas Sullivan, Bret Linenfelser, Ridge Dorsey, Megan Monroe, Jennifer Gra - Secret WHAT TYPE OF MEETING OLD ONE REGULAR SPECIAL UASI-NDICIAL Agenda Item 1- Call to Order The meeting was called to order at 6:03 p.m. Agenda Item 2- Meeting Minutes -January 22, 2007 Motion: Motiou to accept the meeting minutes with corrections by K°oaf Seconded: Bvers Vote: 5-0 in favor, Passed • Agenda Item 3- Public participation and comment. T6ere was none. Public Partici ation was closed. Agenda Item 4- Final recommendation on Mercury limits in the Industrial Pretreatment Program, including proposed rules to require the installaGon of amalgam separators in some dental o(tices. Dorsey, Monrce and Linenfelser presented on the background and changes of the project since their last visit to the boazd and asked for a final recommendation on the project. WRAB questions and comment: • Byers: Have some offices lost the Best Management Practices certification? : Yes, but not necessarily because of Mercury requirements. There is more to the certificarion than just mercury. • Byers: How do you get tlte numbers you are presenting tonight? Dorsey: The measurements are d'uectly from the reports at the analytical laboratories. • Byers: Aas there been a significant decrease in dental offices? Dorsey: No. • DiNatale: Did you run a blank during the Boulder dental sampiing? Dorsey: We do noimally run blanks and feel cotnfortable that the statistics aze accurate. • Byers: Have you looked into vet clinics? : We have thought of it, but our program doesn't cunently have the funding for that outreach. • Byers: What is the foundation for the statement from the city concerning the costs for this program not being passed onto dental customers? Williams: Based on our conversations with dental o~ces, they aze not able to pass on the wst because of insurance program regulauons. • Byers: I do not think this is a good draft of the regulation. It is too long, the machines aze not good enough to be mandatory, the line of responsibility is not in place, and the norice of non- compliance needs to be more specific about what the den[ist is deficient in. • Byers: Does EPA have [o approve this after City Councii? Dorsey: There is a 30-day comment period and they are involved. • Dorsey: The city attomey's office prepared the regulation and future legal questions will need to be directed at them. • Wilson: How many dentists commented on this? Dorsey: We have three written comments and spoke to some on the phone. Motion: Wilson moves t6at Water Resources Advisory Board (WRAB) recommends this rule and furthermore asks the City Manager to apprise City Council on the program. Seconded: Knopf Discussion: Byers: ] cannot support the motion based on the penalties and the language on who is responsible for the mle. Ngenda Item #_5~ Page t_~Yj_ I___ Vote: 41, motion passed Agenda Item 5- Update on tLe Stormwater Strategic Plan Harberg, Sullivan presented on the upda[ed Stomiwater Shategic Plan and asked for WRAB feedback. The presentation was shortened in order to accommodate to a public hearing following this agenda item. WRAB members were asked ro send detailed question, comments, concems and addirional information through email channels. This will appeaz on a future WRAB agenda for further discussion. WRAB questions and comment: • KnopL• A sense of how we are going to fund this would be important to include. • Byers: Will Gunbacrel be included in this? SulGvan: We aze not even planning this for another 20 years. I will get more infocmation for you for the April meeting. Agenda Item 6- Final recommendation on Sonth Boulder Creek Flood Study, including hydrology, climatology and tlood maps. Harberg along with consultants and peer evaluation panel represen[atives presented on [he South Boulder Creek Flood Smdy and asked for a recommendation from WRAB. WRAB questions: • Wilson: Why are there about two and a half times properties in the AE zone? Harberg: It is using our new hydrology modeling techaiques. • DiNatale: We have a lot more properties in a regulated floodplain. At what point at time would the properties be responsible for these designarions? Harberg: We are projecting a yeaz out from now after the approval of FEMA. DiNatale: They would be regulated before a flood mitigation study? Harberg: Yes. • Byers: What percentages aze in the AE zone from the city and the county? Harberg: Ciry: 652 structures, County: 458 shuctures. This is detailed in an attachment. Public Questious: • Alan D. Katc,103 Genesse Court: How does this account for future developmenu? Harberg: The study does not take into account future developments. Future developmenu would follow floodplain regulations. • Tom Christoffel, 2285 Rillsdale Circle: How are multifamily structures land it two different zones? Harberg: They are drafts and I am happy to look at each property personally at a later date. WRAB is not approving those lists; the regulatory agencies will do [ha[ later. • Gifford Millard,1051 Gifford: What if a structure on my property, but not my primary residence is listed? Do I have to get flood insurance? Aarberg: Your primary residence may not need flood insurance if it is not in the actual floodplain. • Spence, 665 Emporim: Should there be some mechanism in place to change the iunoff pattems that will change the studies you have done to date. Harberg: We have not considered this. Right now we aze just asking FEMA to review our current data and analysis and mitigarion studies wIll come at a later time. • Ben Binder, 720 S. 21" Street: Conceming the CU South Berm area, what is the ciry's policies conceming floodplains? Have they changed? The city opposed long-earthen levies before. Wilson: We do not have jurisdiction for this prope~ty. • Carl Williamson: Why didn't FEMA like this plan in the past? What has changed so we aze confident FEMA will approve it now? Harberg: The results we have today have been more thoroughly reviewed. Public Comment: • Ann Christoffel, 2285 Hillsdale Circle: Because this does impact people's lives, I do not think the boud should approve this while there ue so many pieces still floating around. I don't think this is ready for a federal agency. • John Weiner,135 Manhattan Drive: Concerning the Hogan annexation, I got the impression that ciry staff was not directly going to address this large issue if the time did not suit. I think it is ~gendal~m~~l~Page# ~~Z unsettling to here this since there aze so many people affected by it. Additionally, I am not sure that you realize how much it affecu people if you make a sm~ll mistake and put a residence on flood zone list. • Jeff McCehirter, 5435 Illini Way: Citizens have been involved, but there has been good that has come out of it. The amount of work that comes out is staggering and I would hope that ciry could take a breather and slow the process down a bit. l am not sure the ciry is looking at all of the aspects of this; an example being of the difference the flood would make if shifted by hvo miles. There are a lot of flaws in the smdy. • Alan D. Katz,103 Genesse Court: If the board has been able to read of the documents received by this meering, then do as you wish. If not, please do not move forwud now. WRAB Discussion: • DiNatale: If WRAB does recommend these reports to go to feedback, what can the public do to stay invoived? Harberg: We will continue to work with residents on their specific properties in question. There will be a public hearing with Planning Board in March and with City Council in April. • Miller: Is there a cleaz process for resolving issues property owners have regarding how to non- residence shvctures in the floodplain? Harberg: I am sure we can but I have not specified a cleaz process. • Miller: When will you look into mitigation? Harberg: There will be future mitigation planning when it comes time. • Knopf: The insurance impacts seem to rely on mitigation. When aze people beginning to be responsible? How can get out of the floodplain map. Harberg: In May of 2008. There will be a map realignment process. • Byers: Note to keep the real estate professionals in the loop. • Harberg: We will continue to modify the reports based on feedback from the public, the peer review and WRAB. • Byers (to the peer reps.): Is there anything in this that is a big deal-breaker? Doug L.: It has evolved and we aze very close to the end product. No deal-breakers. Motion: T6e Water Resources Advisory Board (WRAB) recommends the South Boulder Creek F7ood Mapping study be submitted to FEMA, but before final submittal, staff would continue to address technical issues to a degree practical, and develop policies and recommend those to city council to ensure only portions of properties located in t6e future regulated 17oodplain be subjected to the rules. §tafi should develop a policy and recommend to council how to handle the development or annexaNon of properties that are not wrrently, but would be subject to regulation under the newest floodplain, Seconded: Knopf • Wilson: Prep has given us good feedback. I think we have stepped back, but now is not the appropriate time. While other boazds look more politically, we aze looking at the technicalities. I think we should move this along. • Miller: In keeping options open for fuhtre mitigation, would FEMA in any way hinder our options? Knopf: There will already have to be more work done in regards to the berm. Harberg: Conect, right now it is not a certified flood levy. • Knopf: We may need to add something abou[ WRAB being uneasy abou[ the berm. Byers: There has been a court case and therefore might be handled in a whole different realm. Vote: 5-0, motion passed Agenda Item 7- Matters From Staff - • Williams presented a revised WRAB calendaz. • Williams resented the ublic comments concemin the water bud et methodolo . rlgenda item ~~~_ Page N V~'1-3 . • Byers asked for updates on the South Platte Wells trial. The Vial is in its [hird week and it expected that the city of Boulder side will begin next week. The case is expected to be completed in March. Matters from Board - • The Mazch meeting will be Ken's last meeting. Miller will be organize a social gathering to celebrate Ken's departure. Agenda Item 8- Discussion of schedule for future mee[ings. Agenda Item 9- Adjournment Motion: MoHon to adjourn by Miller Seconded by Byers Vote: 5-0 in favor, passed. Meeting adjourned at 9:57 PM Date, Time, and Location of Nezt Meeting: T'he next meeting wilt be Monday, March 19 - 7 p.m., regulaz meeting, Municipal Services Center, 5050 East Pearl Street unless othenvise decided b staff and the boazd. These aze surnmary minutes. Audio tapes are available tluough Centra] Recoids for full record. Minutes approved by: Date: Agendakem~~~_p~~ ~-~{