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9 - Discussion of the Fourmile Canyon and Wonderland Creek Major Drainageway Planning Phase A Report and staff recommendations concerning flood mitigation alternativesCITYOF BOLTLDER «~ATER RESC)URCES AD~'ISORY BOARD AGEND:~ ITEl~'I l~ZEETING DATE: December 17, 2007 AGEND~ TITLE: Presentation and Discussion of the Fourniile Canyon and Wonderland Creek I1~lajor Drainageway Plarnling Phase A Report and Staff Recommendations Concerning Flood IVlitigation Alternatives PRESENTERS: Eric Lessard, Engineering Project I~Ianager Bob Harberg, Utilities Plamling and Project Management Coordinator New Williams, Director for Public Works Utilities «~ATER RESOURCES ADVISORY B~~RD ACTION REQUESTED: The Phase A Report presented infoi7nation regarding flood rnitigation planning. City staff has coordinated the flood mitigation planning t~~~ith various internal departments and presented the repoi-t to the Greeni~ ays Advisoryr Comrnittee and held an open house for the affected citizens during which comments were solicited. The report and consultant recommended alternatives were presented to t~'R~B on Oct. 15. The comments from various entities have been compiled and staffhas identitied a recommended plan. The purpose of this agenda item is to provide an opportunity for the public to speak to this issue the t~~R~B to consider the staff recornrnendations. Staff is requesting that WRAB provide City Council a recornmendation concerning the adequacy of the report and the recorn~nended alternati~~es. FISCt1L I117PaCT: The flood mitigation plan recommended by staff and endorsed Uy the Urban Drainage and Flood Control District is estirnated to have a total cost of $48,~~25,U68, of ~~vhich $38,901,fl68 ~~~ould l~e at public expense and $9,124,UU0 would l~e l~orne by private property o~~rners. Property~ o~~~ners ~~ould not be required to bear this expense but ~i~ould be encouraged to protect their property from future flood damages. Significant total benetits of over $6f),000,~00 are estimated based on a reduction in total property damage due to future flooding. City of Buulder Fouimile Canyon and Wonder(and Creek Phase A Report December 2O07 EXECUTIVE SUMMARY: The Fourmile Canyon Creek and Wonderland Creek Major Drainageway Planning -Phase A Report -Alternatives Analysis {Phase A Report) focuses on the development, evaluation, and recommendations of alternatives to mitigate future flooding in both the Fourmile Canyon Creek and Wonderland Creek flood hazard areas within the City of Boulder (City) and Boulder County. The work was jointly sponsored by the Urban Drainage and Flood Control District {UDFCD) and the City of Boulder, Colorado. The Phase A Report was prepared by the consultant Love & Associates. The Phase A Report presents information regarding flood mitigation planning and investigates a number of strategies to be evaluated by staff, the public and City review boards. Staff has coordinated the flood mitigation planning with other objectives of the Greenways Program and presented the report to the Greenways Advisory Committee (GAC). An open house for affected citizens was conducted in addition to a presentation of the document to the V4~ater Resources Advisory Board {WRAB) in October. Staff has prepared the recommended alternatives to be presented to WRAB. Upon referral by WRAB, a presentation of this information shall occur to Council and Planning Board early next year. The Phase A mitigation analysis evaluated a number of alternate drainageway planning concepts to mitigate existing flood damages, taking into consideration the impacts of the spill flows from Fourmile Canyon Creek to Wonderland Creek. The study is divided into two phases. The first phase (Phase A) is the initial report that covers the hydrologic, hydraulic, and alternate evaluation aspects of the project. The future, second phase (Phase B), will cover the preliminary design of the selected alternates. A complete copy of the Phase A report is available at: httpa/www.bouldercolorado.~ov/index.php?option=com content&task=view&id=4976&Itemid =2360 BACKGROUND: The study area includes the Fourmile Canyon Creek floodplain from the mouth of the canyon to its confluence with Boulder Creek and the Wonderland Creek floodplain from downstream of Wonderland Lake to its confluence with Goose Creek. Additionally, the Fourmile Canyon Creek spill floodplain, located between Fourmile Canyon Creek and Wonderland Creek, upstream of Broadway approximately to 19th Street, is also included. The initial flood mitigation planning effort began in June of 1999. Both a Phase A and Phase B study were completed for Fourmile Canyon Creek. Following the review and input from the Independent Review Panel (IRP) comprised of floodplain experts in 20174, it was recommended that a combined Phase A Alternate Analysis report should be undertaken for both Fourmile Canyon and Wonderland Creek. Subsequent to the completion of the LOMR, the combined Alternate Analysis began in the Fall of 200&. Since that time, a series of internal progress meetings have taken place to exchange information and discuss ideas and findings of the combined study. The progress meetings were regularly attended by representatives of the City and UDFCD. City of Boulder Founnile Canyon and Wonderland Creek Phase A Report December 2007 2 Recently Staff has presented the consultant recommended mitigation plan to GAC and WRAB. Following the WRAB meeting in October, staff has worked with the consultant and UDFCD to finalize the recommendations. ANALYSIS: The flood analysis for these two creeks indicated significant differences from the original FEMA regulatory studies, resulting in additional properties being located within the t«~o floodplains. Of particular importance, the re-study identified reaches of Fourmile Canyon Creek west of 19th Street, where, once the channel capacity is exceeded, flood flows overtop the south bank of the creek and flow in a southeasterly direction towards Wonderland Creek. These "spill flows" result in a reduction of flows in Fourmile Canyon Creek dov~~nstream of 19th Street but also result in an increase in the flows in Wonderland Creek. During the 100-year flood event, approximately 3,300 cubic feet per second (cfs) is in Fourmile Canyon Creek near the mouth of the Canyon, of this amount approximately 1,600 cfs will overtop the south bank spill and flow toward Wonderland Creek. The remaining 1,700 cfs will remain in the Fourmile Canyon Creek Channel. Likewise, the 100-year discharge in Wonderland Creek significantly increases downstream of the spill inflow. Some of the spill returns to Fourmile Canyon Creek near 19th Street but the majority remains in the Wonderland Creek floodplain. Early in the study, a broad range of alternates were identified. These alternates were screened following an analysis of each stream and detailed discussions held during progress meetings on a reach by reach basis, for each stream. A wide array of options were looked at as potentials for mitigation of the flooding, ranging from a `do-nothing' status quo alternate to construction of a 100-year flood channel for each stream thereby confining the spill fiom Fourmile Canyon Creek. Alternates: The alternates considered for both streams included a High Hazard Containment and Floodproofing of Structures alternate. Original alternates considered in the initial Fourmile Canyon Creek Major Drainageway Master Plan also included both a 50- year and 100-year storm event protection channel alternate. The 100-year storm event protection channel would be designed by an inter-disciplinary team of engineers, geomorphologists and biologists to emulate a natural channel. This alternate would eliminate spills from Fourmile Canyon Creek to Wonderland Creek during the 100-year or smaller flood event. The channel would be designed to UDFCD and City criteria with FEMA and City required freeboard. The 50-year alternate for Fourmile Canyon Creek (only) would contain the 100-year flows but would have no freeboard built into the design. The Urban Drainage and Flood Control District, based on legal opinion from its counsel, has indicated reluctance to participate in any Alternate which includes containment or reduction of the Fourmile Canyon Creek spill unless downstream property owners' concerns are properly addressed. The High Hazard Zone (HHZ) 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 City of Boulder Founnile Canyon and Wonderland Creek Phase A Report December 2007 3 where flow depths equal or exceed four feet. These portions of the 10~-year floodplain pose an unacceptably high hazard to human safety. In the high hazard zone, the construction, expansion or enlargement of any structure intended for human occupancy or establishment of a new parking lot is prohibited. The High Hazard Containment alternate would remove structures identified in either stream from the City's High Hazard Flood Zone through direct purchase of the property, the enlargement of road crossing structures, channel excavation, and/or floodproofing or a combination thereof. This alternate does not eliminate the out of channel bank floodplain; however, it reduces flood levels to those structures in the High Hazard Zone for increased safety when evacuating occupied buildings and allows for emergency access to residential structures. Floodproofing is a combination of adjustments and/or additions of physical features installed in, on or around individual structures designed to eliminate or reduce the potential for flood damage to the structure. Floodproofing consists of the techniques and approaches for preventing or minimizing flood damages to a structure and its contents in flood hazard areas. Floodproofing techniques range from: the construction of levees and flood walls around a structure, to installing water-tight doors and windows, physically raising the structures elevation using fill or pilings, measures designed to reduce water seepage and/or resist lateral pressure from flood water in the structure, etc. Floodproofing measures may be applied to new structures as well as retrofitting existing structures which may allow for development within the floodplain in low hazard areas. The purpose of floodproofing is to minimize flood damages by either keeping floodwaters away from damageable property or making the property less susceptible to damages when floodwaters reach the structure. Floodproofing does not eliminate all flood damages but can, if done correctly, significantly reduce damages from flooding. The City may offer guidance and disseminate information regarding various floodproofing techniques; however, it would be the responsibility of the individual property owner to implement this alternate for their own individual properties. Intangible Benefits (Greenways Objectives) There are numerous intangible benefits that would arise from the implementation of flood mitigation improvements. Many of these intangible benefits are related to other Greenways Program objectives. The intangible benefits that may be realized through flood mitigation include the following: Improved traffic movement during floods Improved emergency response Improved recreation and alternative transportation Improved public health and safety including life safety due to flash flooding Improved enviromnent, water quality and riparian habitat Lower flood insurance for private property owners Increased property values Creation of urban open land Creation of cultural, educational, and scientific resources City of Boulder Founnile Canyon and Wonderland Creek Phase A Report December 2007 4 Intangible benefits have not been quantified from a monetary perspective and included in the benefit/cost analysis. As a result, the benefit/cost ratios are lo~~er than what would be realized if dollar values were placed upon the intangible benefits. Bigger floods can and will occur. This statement holds true whether you are talking about a 10- year, 100-year or 504-year flood event. The Fourmile Canyon Creek and Wonderland Creek drainageways have not had a significant flood in the recent documented past. The public a~~~areness of the significance of the flood situation is low since many of the residents in the floodplain have not seen the results of a disaster, or had to clean up after a flood in their neighborhood or experienced the injury to or loss of a family member or friend in a flood event. CONSULTANT RECOMMENDED ALTERNATE: Love & Associates, Inc. recommended a combination alternate for both Fourmile Canyon Creek and Wonderland Creek. For each creek, the recommended alternate consisted of a combination of the 100-Year Channel, High Hazard Containment, Floodproofing and Maintaining Status Quo. The recommended alternates were developed utilizing areach-by reach approach. UDFCD SELECTED PLAN: The UDFCD has developed a draft selected plan. The selected plan endorses the Love & Associates recommendations and provides additional direction to be considered. INTERNAL STAFF INPUT: Utilities Planning and Project Management staff have responded to solicited input received from other internal city departments and work groups. This information was presented at the previous WRAB meeting. OPEN HOUSE & PUBLIC INPUT: Utilities Planning and Project Management staff have solicited input and received a number of comments from the public during the open house conducted on September 27. This information was presented at the previous WRAB meeting. In addition to comments generated during the WRAB meeting, a number of concerns have been conveyed through phone conversations and meetings with affected citizens. UTILITIES STAFF RECOMMENDATIONS: Utilities Planning and Project Management staff have considered the input from the above sources and formulated their recommended mitigation plan. A meeting with the consultant and representatives from the UDFCD was held to obtain the District's approval. The staff recommended plan is consistent with the consultant recommended plan with the following exceptions: On Reach & of Wonderland Creek, 3 structures were determined to be in the HHZ at Poplar Avenue, east of 19~' Street, and recommended for purchase. Additional evaluation has indicated there is a more cost effective and desirable way to mitigate the high hazard zone. This alternative, identified as No. 2 in Section C of Attachment B, eliminates the need to purchase the City of Boulder Founnile Canyon and Wonderland Creek Phase A Report December 2007 5 properties and helps mitigate flooding near the school. This alternate has a cost of $933,500 versus the anticipated cost of $1,593,200 for the property acquisition. Staff is recommending this new alternate instead of the original alternate identified (No. 1 in Section C of Attachment B). On Reach 6a of Fourmile Canyon Creek west of Broadway, a concern was raised that the HHZ would make re-development very limited in this area. Staff asked the consultant to develop an additional alternate in order to contain the HHZ and floodway, allowing for land use improvements in this reach. In the new design, the channel would be excavated to contain the overbank flooding and the Yarmouth and Rosewood road crossings would be improved. The cost for this option would be $2,350,000. Due to the high cost, staff is recommending that this alternate be implemented if and when property owners in the area wish to redevelop (See Section B of Attachment B). During the public review, a question was raised whether flood detention storage was feasible for upstream Fourmile Canyon Creek in order to mitigate the spill to Wonderland Creek. The consultant determined that a 259 acre-foot reservoir would be required in addition to significant channel work. The cost was estimated at $36,000,000. Because of the significant environmental impacts this approach is not recommended (See Section A of Attachment B). A question that has come up numerous times is why the Fourmile Canyon Creek flood flows are not contained in the channel, thereby lessening the impact to Wonderland Creek. This is primarily because the spill from Fourmile is due to the existing topography and has historically occurred. Changing historical flow patterns has enormous implications and is traditionally avoided. If containment was initiated, a great deal of mitigation work would haj~e to be completed on Fourmile since the existing facilities and flood protection is sized for the historical flow rates. All of these costly projects would have to be completed before any diversion could occur. Additionally, there are a number of legal issues associated with changing flood patterns of this magnitude and UDFCD has indicated that they would not support this concept. Their opinion is contained within Attachment A. For these reasons, this approach is not recommended. Even with the great deal of drainage improvements suggested with this study, there will still be areas that experience shallow flooding. Theses situations are of concern to the City and will be addressed as budgeting allows. It should be mentioned that local flooding is only made worse by overwhelmed larger drainage facilities. In order to assure the most efficient operation of local drainage systems, the creeks that intercept this drainage need to have the capacity to handle these points of runoff inflow. Citizens are encouraged to come forward with drainage concerns in order for the City to prioritize and attempt to mitigate local flooding problems. An additional comment was received indicating that some property owners would be willing to accept some risk and tolerate mild flooding along Fourmile Canyon Creek. This was raised due to concerns of impact to the existing riparian corridor. These impacts include preservation of wildlife and vegetation. These comments will be included in the next phase of preliminary design. City of Boulder Founnile Canyon and Wonderland Creek Phase A Report December 2007 6 Another aspect of the recommended flood mitigation plan is the impact to flood insurance costs borne by private property owners. As a result of some of the recommended mitigation alternatives, there are a significant number of policy holders that will no longer be required to hold flood insurance with their mortgages. It is estimated that a total premium savings of $352,404 per year would be realized by property owners if the outlined mitigation recommendations were implemented (See Section F of Attachment B). Finally, a comment was received regarding completing the plan but questioning why implementation of mitigation projects has to occur before a flood event. Staff feels that risk to life safety and property compels the City to pursue mitigation projects prior to an actual storm event. A memo from the consultant detailing the above issues is included in Attachment B. It contains detailed information including cost estimates, figures and tables that describe the analysis and results. NEXT STEPS: A public hearing with the Planning Board is currently scheduled for January 24, 2047. A public hearing ~~-~ith City Council is anticipated in February 2448. Phase B -Preliminary Design will be initiated and should be completed in 2448. The preliminary design will be reviewed as part of the city's Community and Environmental Assessment Process (CEAP). Money has been budgeted in the 2448-2413 Capital Improvement Program (CIP) budget to begin to fund selected flood mitigation work. It is likely complete implementation of the selected flood mitigation plan will take several decades to complete. STAFF REQUEST: Staff requests a recommendation to City Council from the WRAB on the flood mitigation plan and the staff recommended alternates. For additional information, please contact Eric Lessard at 343-441-4232 or lessarde(a~l~ouldercolorado. og_v ATTACHMENTS: A UDFCD Legal Opinion B Consultant Memo City of Boulder Founnile Canyon and Wonderland Creek Phase A Report December 2007 7 ~.PPENDIX G , i~GAL OPINION This page intentionally left blank. Edward J. Al1DOr (1960), that downstream owners had to accept additional runoff from an upstream developer. AttOriley At LaW As the engineering technology has become more precise in drainage matters, it is possible to 1666 South University Boulevard, Suite B determine from the actual development and from land use decisions that will determine future development Denver, Colorado 80210 what the additional (more than natural) runoff will be because landowners make their land impermeable. 303 777-5501 Fax: 303 698-0919 elQisor®ix.netcom.com The Colorado Legislature in 1973 recognized this and adopted Sec. 30-28-113(4)(b) which requires developers in unincorporated areas to detain greater than historical flows. As a matter of drainage practice, cities as well as counties and the Urban Drainage District work to identify with precision "who is doing January 19,1998 what" to whom so that the cost of drainage solutions to problems created by future development can be placed on those who would change the use of land from permeable to impermeable. Runoff from existing development is also computed and the need, if any, to solve existing drainage problems can be determined and costs of solutions estimated. Mr. Ben Urbonas, P.E. Drainage matters historically were resolved between or among property owners. However, as Chief, Master Planning Program urbanization (multiple property owners) has taken place, governments have become involved for several Urban Drainage And Flood Control District reasons. In some cases, the government itself helped create additional runoff by making improvements. ]n 2480 West 26th Avenue, Suite 156 B other cases, govemment approved land use changes without regard to the problems of additional runoff. In Denver, Colorado 80211 still other situations, government got involved because constituents (owners) wanted govemment help in the difficult and expensive field of determining (identifying) where the additional runoff was coming from and BY HAND DELIVERY the paying of costs of solutions. For whatever the reason, whenever government gets involved, it can be expected to be treated like a private party. 2 Farnham, Water and Water Rights, pp. 975 and 977, adopted Re: Legal opinion in regard to alternative and planned drainage facilities in by the Colorado Supreme Courtin Cit~of Boulder v. Boulder and White Rock Ditch Co., 73 Colo. 426, 216 general as contained in alternatives development and evaluation P. 553 (1923). A municipality can be held to its negligence. It can also determine whether to become reports involved at all, if it did not create the problem. Dear Ben: An update of these legal principles has yielded the conclusion that the law of drainage as set forth You have asked me to provide you with a legal opinion that you may use to initially evaluate in above has not really changed to any substantially degree over the years. Both the Hankins and Ambrosio general all alternatives development and evaluation reports for compliance with the law of the State of cases continue to be cited by the Colorado courts when dealing with the law of drainage. In the case of Colorado applicable to drainage. What follows is such an opinion which will need to be supplemented by a Metro Docheff v. City of Broomfield, 623 P. 2d 69 (Colo. App.1980) the Colorado Court of Appeals held short legal opinion in regard to each report to either indicate that no further comment is necessary or that Although we recognize the right of the owner of higher land to a drainage easement over the lower land of others, ...the discharge of water will be enjoined as a continuing trespass if the drain sends the certain other factors, other than those noted herein, will need to be considered before proceeding to the water down `in a manner or quantity to do more harm than formerly. In the case of Hoff v. Ehrlich, 511 P. selection and construction of drainage improvements contained in that specific report. 2d 523 Colo. A 1973 the Colorado Court of A eals was faced with the uestion of the ro rie of a ( PP• ) PP q P P In order to properly evaluate these reports you first must take note of the following comments in servient owner blocking drainage from a dominant estate in order to protect the servient owner's land. The regard to the law of drainage in Colorado: Court held that: The owner of the dominant estate has a legal and natural easement or servitude in the lower or servient estate for the drainage of surface water flowing in its natural course and manner . When an interruption in the natural flow or passage of surface waters is caused by the servient owner to the I. GENERAL LEGAL DRAINAGE PRINCIPLES detriment or injury of the estate of the dominant owner, the court should issue a mandatory injunction for the opening of the easement which has been blocked [the servient owner] may not act to the extent that Natural drainage conditions may be altered by an upper (dominant) owner provided the water is not damage is caused thereby to the dominant landowner in order for the owner of the servient estate to be sent down in a manner or quantity to do more harm than formerly to the lower (servient) owner, Hankins v, afforded a remedy, it must be evident that the water was sent down in a manner or quantity causing more Borlan 163 Colo. 575, 431 P.2d 1007 (1967). Colorado follows the "rule of reasonableness" as related to harm than it formerly had done. drainage matters and in each drainage situation, the court will look at the relationship of the parties and at If a government permits the development which in turn causes "more harm than formerly", then the who is doing what to whom in order to determine "what is reasonable under the circumstances". Prior to the government, as well as the developers, maybe held liable. (Cases consistently move toward governmental, Hankins case, the Colorado Supreme Court ruled in Ambrosio v. Perl-Mack, 143 Colo. 49, 317 P.2d 803 as well as developers' liability.) See Metro Docheff, supra, which held as follows: "The trial court found Finally, any drainage, "facility" built by a government must be maintained. "If you're not going to that the city had accepted the streets and storm drains for maintenance and control and, therefore, had maintain it, then don't build it!" is the theme of a long line of cases. exclusive control over the water collected in the subdivision. It determined that by approving the subdivision and drainage plan and accepting control, the city interfered with the natural conditions and thereby caused surface water to be collected and discharged upon plaintiff s land `in a greater quantity or in II. GENERAL COMMENTS ON COMMONLY PROPOSED FACILITIES different manner than had previously occurred under natural conditions." AND CONSTRUCTION TECHNIQUES Recently, govermmental entities have raised in their defense of drainage cases the Governmental 1. It is my understanding that the purpose of all reports in regazd to this subject is to examine Immunity Act. Iri two recent cases, that defense has not been successful. In Burnworth v. Adams County, alternatives which will, if implemented, improve upon and/or formalize the drainage that is within the study 826 P. 2d 368 (Colo. App.1991) the Colorado Court of Appeals held that actions "...against public entities area. arising from the maintenance of a sewer, a storm sewer, or a storm drainage system." were not prohibited by the Governmental Immunity Act. In the case of Scott v. City of GreeleX, 931 P. 2d 525 (Colo. App. 1996), 2. In general, consideration must be given to any potential adverse effects of the selected alternative the Colorado Court of Appeals again denied protection under the Governmental Immunity Act to a public on properties within the study azea and downstream of the study area. entity when it argued that the damage complained of was the result of a design flaw rather than from the operation of a facility. The facts were that the City designed and constructed a new storm water line which 3. If any selected facilities would increase or materially change the direction of the flows across was 42" and connected it to a line which was only 15". This caused the water to back up, or surchazge, downstream property in a study azea, the downstream.propertyhas aright to claim damagesand/or through the storm drains and manhole covers, overtopping the curb and flooding adjacent property. In protection from such a material increase or change inflow. Thus, caze should be taken to make sure that addition to the denial of protection to the entity under the Governmental Immunity Act, the Court also increased flows from upstream facilities aze accommodated by sufficiently increasing the size of the rejected the City's defense that the connection to the smaller pipe was only temporary. downstream channels and conduits. If in final design, the selected alternative still has the effect of placing water on the residents and land owners in the azea that they either never had or in a quantity lazger than what Any improvements upstream must be made taking into consideration the outlet capability they have had previously, the same must be revised to eliminate that result or the selected alternative must downstream. (Long line of case law.) See Hankins, supra, which states: "The trial court has found that the not be constructed. water which these defendants have sent into the Borland drain is in greater quantity and more rapid in time - a finding fully justified by the evidence. Under such circumstances it is the court's duty to determine 4. If re-alignment of a channel is the selected alternative, cazefizl consideration should be given to what the dominant owners must do in order to prevent their increased waste water from damaging the the channel's geometry, alignment and ability to carry flood flows so as not to create additional potential servient owner." damages to surrounding landowners. Colorado eng erallX imposes strict liability on owners of dams (regional detention ponds). (Long line 5. If the selected alternative is the collection of overland flows from a specific area and returning of cases.) those flows to a drainage sriucture of some kind, care should be taken not to adversely impact landowners in the area. Interfering with natural drainageways or channels is eng_eral~ looked upon with disfavor by Colorado Courts. However, builders of imgation canals, railroads, and highways in other times were not 6. If a selected alternative involves the redirection of flows from their historic path, prior to its aware or were unconcerned with the problems they might be creating in the future by artificially blocking fmalization in the design process, caution should be taken that this redirection will not cause any increase in natural drainageways. Sometimes the very passage of time (at least eighteen yeazs) provides an argument damage to those adjacent or downstream of the proposed redirection. that the blockage should be allowed to be continued because parties have relied and should be able to continue to rely on this "protection". Generall ,the laws of nature prevail in these situations and artificial 7. If any selected alternative, when it is finalized in the design process, is changed to include a plan structures such as canals, railroads and highways do not rise to the status of permanent dams which require for the diversion of runoff from one watershed to another; extreme caution should be used in implementing spillways and other features under the jurisdiction in the State of Colorado of the State Engineer. that portion of the selected alternative since the participants may be faced with the imposition of strict liability for any damage that occurs from any size storm event if it can be shown that the same would not With the enactment of federal environmental (including water quality) provisions, the uali of the have been suffered if the diversion had not occurred. runoff may also have an effect, as well as on other ecological matters. 8. If the construction of crossing structures over irrigation canals aze part of the selected alternative Natural waters aze subject to the doctrine of prior appropriation in Colorado and what may have for the project, caution must be taken in regard to the capacity of those crossing structures. The structures, become a water right must also be considered with any plan for the "handling" of surface runoff in natural when designed for the design event, should not cause any more water than presently exists to flow into those waterways. canals. The intentional routing, as opposed to inadvertent inflows, of flood flows into an 16. During construction of the selected facilities, care should be taken in constructing those facilities ~i,~n.,~~,m ditch should be eliminated from any plan if at all possible unless a written agreement from the so that downstream property is not adversely affected temporarily by such construction. Usually, with the ci ~~ne~ of the irrigation ditch is obtained permitting the use of the ditch to carry those exception of the construction of detention facilities, the best method to avoid that problem is construction l~~ood flows. The participants have no control over the available capacity of the ditch at the time it would be from the downstream limit of the project in an upstream direction which would then have the effect of necessary to carry flood flows so the ditch cannot realistically be used to control the flows downstream. having the downstream facilities ready to accept any increased flows as a result of the project. 10. If an alternative is being selected that relies upon inadvertent detention and the participants do If you have any questions in regard to my comments and opinions contained in this letter, please feel not intend to formalize such detention by written agreement, it is my opinion that the effect of that non- free to telephone me to discuss the same. formalized inadvertent detention cannot be taken into consideration in the fmal design. 11. If a selected alternative includes the formalization of inadvertent detention it will be necessary for at least one of the participants to formalize that detention by entering into a written agreement with the Very truly yours, owner of the facility causing the detention. The agreement must prohibit the owner from operating or modifying the facility in a way that would have the effect of lessening the inadvertent detention of the facility necessary to implement the selected alternative. Further, the owner must either agree tomaintainthe - / ' facility so that the same does not lose its current inadvertent detention or agree to permit at least one of the ~W ' th facilit participants to mamtam a y. 12. If the owner of the facility will nat agree to maintain the inadvertent detention facility, at least ~ Edward J. Krisor one of the participants should confirm in writing to all of the participants that the participant is committed to maintaining the inadvertent detention facility in a manner that assures the necessary inadvertent detention to implement the alternative. This should be done prior to the implementation of any of the alternatives involving inadvertent detention. The level of maintenance must at least permit the facility to function as relied upon in flooding events and not fail structurally during the design and larger events. 13. Any formalized detention facilities that are utilized in the fmal design of a project will need to be the subject of a written agreement between the owner and at least one participant that the facility will be maintained in a manner that assures the necessary flood storage to implement the design and that adequate maintenance will be performed by either the owner or the participant so that the facility will function as designed in flooding events and that it will not fail structurally during the design and larger events. The participating entities must agree amongst themselves, in writing, that any one of the participants may enforce the terms of the agreement with the owner of the facility if the responsible participant does not. This agreement must include the maintenance of no more than a certain level of water in the facility at any one time and that any one of the participants may, at their sole cost and expense, maintain the facility so that its effectiveness in the selected alternative will be continued in perpetuity. 14. The embankments of all detention facilities should be designed so that they will not fail during a design event. 15. If a potential wetland is involved in a design alternative, it will be necessary that a Section 404 Permit from the United States Army Corps of Engineers be applied for and obtained, if necessary. Such a Permit should be obtained before any construction is done on the recommended alternative. Edward J. Krisor March 20, 2002 . Attorney At Law Page Two 4949 South Syracuse Street, Suite 400 Deuver, Colorado 80237-2747 720.489.0555 Fax: 303.713.9413 approach and the fact that this approach would be selected by one governmental entity and ekrisor@ix.netcom.com adversely impact another governmental entity's residents. 4. The concept of increasing the flood damages for downstream homeowners for benefit of upstream landowners is legally impermissible without some solution for the March 20, 2002 downstream homeowners which is accepted by 100% of the downstream homeowners. Any solution that is not accepted by 100% of the downstream homeowners will, in all likelihood, expose the governmental entities that would implement the solution to legal liability which may include exemplary damages. Clearly, those participating in the Fourmile Report know that the Mr. Ben Urbonas, P.E. alternatives that they are considering will increase damage to homeowners downstream. Urban Drainage and Flood Control District Therefore, since the record will be clear that all decision makers involved knew that they were 2480 W. 26th Ave., Suite 156B selecting an alternative that exposed, at least the governmental entity, to liability for violating the Denver, CO 80211-5304 legal principle of not causing more harm than formerly as a result of drainage improvements, proving liability of those governmental entities will be quit easy. BY FACSIMILE TRANSMISSION - 303.455.7880 S. The solutions suggested for dealing with the increased damage to downstream Re; Fourmile Canyon Creek homeowners include either the purchase of a liability waiver or the purchase of flood insurance Major Drainageway Planning on an ongoing basis. The pursuit of either of these alternatives first must recognize that without 100% participation in one of these two alternatives must be obtained prior to the proposed Dear Mr. Urbonas: construction of the selected structural alternatives is begun in the upper reaches. In response to your letter to me of January 28th in regard to the above-referenced 6. The alternative of purchasing a liability waiver in addition to being difficult to Technical Memorandum Alternative Analysis, I have reviewed the Analysis and have the complete due to the anticipated resistance of the homeowners will cause additional problems in following opinions in regard to the report and specifically in regard to the liability waiver and regard to notification of subsequent purchasers of these homes ofthe increased possibility of flood insurance alternatives. flood damage to their home as well as possibly effecting the value of their homes. Normally, such notification would be accomplished by placing some notification of record. However, there 1. Reference should be made to my general opinion letter in regard to my comments is no sure way of notifying subsequent homeowners of the increased possibility of flood damage that apply to all drainage reports and those legal factors to be considered in selecting an since most purchasers, when purchasing a home, do not review the title commitment which is alternative for implementation. where the recorded notice would be noted. This failure to notify subsequent purchasers is important since, in the case of the alternative being considered, the current homeowner is being 2. I have no specific comments in regard to the structural improvements discussed compensated for the possibility of future increased damage to the home. This compensation thus and considered in the Fourmile Report covering the upstream reaches of the creek and the requires an increased duty to put subsequent purchasers on notice of the possibility of increased Technical Memorandum covering the downstream reaches, except that none of construction of flood damages. the improvements in upper reaches should be begin until the issue of the increased potential damage to the downstream homeowners is resolved an completely implemented. In addition, if the alternative of a liability waiver is pursued, consideration must be given to what specifically will the homeowners be waiving. First and foremost, consideration must be 3. The larger issue in regard to the alternatives discussed and considered in the given to the engineering accuracy of what the homeowner is being asked to waive with an Fourmile Report is the concept that downstream landowners' damages are going to be increased additional allowance for possible inaccuracy in the engineering calculations. As to how to for the benefit of upstream landowners, if some of the upstream alternatives being considered are describe the waiver, consideration should be given to what makes most sense to the homeowner selected. Such an alternative will be difficult to implement due to the public reaction to that Mr. Ben Urbonas, P.E. Mr. Ben Urbonas, P.E. March 20, 2002 Page Three in this alternative are the annual maintenance cast of the flood proofing and the fact that there is and is therefore easily understood by the affected homeowners. Also, consideration should be no real difference between the cost of the flood proofing alternative for current conditions versus given to what will be the easiest measure to use to determine if the increased damage a upstream 100-year containment conditions. homeowner suffers is within the scope of the waiver. I assume two measurers that might be considered is a certain event frequency or a certain rise in flood elevation. In order to assure proper functioning of the flood proofing, it appears that annual maintenance would need to be carried on for these fifteen structures. Although the cost is For the reasons noted above, if one of the two alternatives of purchase of a flood waiver relatively small, the obligation on an ongoing basis is onerous. I would be concerned that over or flood insurance is going to be pursued, I would rate the purchase of a flood waiver as my the years that the maintenance would not be completed, a homeowner would be damaged as a second choice. result of a rainfall event and assume that the lack of maintenance was the sole cause of damage. In addition, the question of whether it is appropriate for public funds to be used to protect private 7. In regard to the purchase of flood insurance, this certainly would assure long term property from existing potential damage would need to be considered and answered before protection of the homeowners that would be affected downstream. However, the difficulty proceeding with this alternative. would be of assuring homeowners that sufficient funds exist today to adequately provide for the cost of the insurance for the foreseeable future. This, in my opinion, would require that the 10. Another possible alternative that is not addressed in the Alternative Analysis is participating governmental entities would deposit in a trust account, prior to the start of that of pursuing eminent domain actions against each homeowner for the purpose of condemning construction, sufficient moneys to assure that the homeowners' flood insurance needs would be the right to elevate the level of drainage flows on each of their properties. This course of action paid into the foreseeable future. The length of that payment should be the subject of a debate could be very expensive from the standpoint of costs to pursue those actions as well as the based upon a criteria that should include when, if ever, additional improvements would be potential exposure to substantial awards for the right to increase the level of drainage flows. It constructed to the drainage system to alleviate the increased flooding caused by the alternatives would be most likely that some homeowners would take the position that by reason of these being considered. increased drainage flows there was a complete taking of their property. An outcome such as that would be cost prohibitive. 8. I do think that the concept suggested of a governmental entity reimbursing homeowners for their paid flood insurance is a good concept since it does provide assurance However, the eminent domain actions could all be filed and pursued to conclusion funds will be available in the future to cover a homeowners' flood insurance expenses. without actually taking immediate possession. This approach would permit the condemning However, it too has some practical problems in its implementation. First, the notification of agency the opportunity to review the outcomes of the proceedings before electing to pursue that subsequent purchasers again would be problem. However, this could be alleviated by notifying approach by taking possession of the properties. The difficulty with this course of action would each resident of the homes involved each year by mail that they needed to check that their flood be the cost that would be incurred with the possibility that, at some time in the future, all of the insurance was in force and that the bill will be reimbursed by the governmental entity upon proof funds expended would be for naught because of the ultimate cost of each taking. of its payment. This procedure would assure that at least each homeowner would receive notice each year of the governmental entity's obligation to reimburse those flood insurance expenses. For these reasons, I would not recommend that this option be pursued. An additional problem would be assurance to each homeowner that sufficient moneys In conclusion, since the suggested structural alternatives will increase damage will be available on an continuous and on going basis to reimburse them for their flood insurance downstream to homeowners, among others, the governmental decision makers should carefully expenses. My concern focuses around an adequate deposit so that no additional funds will be consider proceeding along this course even if those involved would successfully negotiate either required from the participating entities in the future. This process would assure that no future liability waivers or flood insurance payments to the homeowners involved. governing board would be requested to appropriate additional funds which, according to law, they would not be bound to do in these circumstances. If it is decided to go forward and use either one or both of the liability waivers or flood insurance payments to homeowners, 100% of the effected homeowners must voluntarily 9. Another alternative discussed in the Alternative Analysis was flood proofing the participate in the alternative selected and a program must be implemented to notify subsequent fifteen structures affected by the proposed improvements. The two difficulties that are inherent Mr. Ben Urbonas, P.E. Mr. Ben Urbonas, P.E. March 20, 2002 March 20, 2002 Page Five Page Four purchasers of those homes, in advance of their purchase, of the increased flood potential if a liability waiver alternative is selected and to notify and adequately fund a flood insurance program if that alternative is selected, Of course, if you have any questions in regard to the contents of this letter, please feel free to telephone to discuss the same. Very holy yours, Edward J. Krisor & Associafes,inc. r e s o u r c e con s u l t o n t s MEMORANDUM TO: Bob Harberg, P.E. -Utilities Division Eric Lessard, P.E. -Utilities Division FROM: David Love, P.E. -Love & Associates, Inc. REF: 0217GX - SUB-ALTERNATE ANALYSIS SUMMARY FOLLOWING PUBLICATION OF PHASE A REPORT FOR FOURNIILE CANYON AND WONDERLAND CREEKS MAJOR DRAINAGEWAY PLAN REPORT DATE: December 5, 2047 The Fourmile Canyon and Wonderland Creek Floodplain Restudy (Letter of Map Revision - LOMR) was adopted by FEMA in March 2007. Love & Associates then prepared the Phase A Drainaaeway Nfaster Plan Report - Alternate Anal for the Urban Drainage and Flood Control District (UDFCD) and the City of Boulder which was published in May 2007. Following publication of the Fourmfle Canyon Creek and Wonderland Creek 11~fator Drafna~eway ~~laster Plan, Phase A Report, the initial Public Open House (9-27-07j and the first presentation to the Water Resource Advisory Board (10-15-07), City staff received several comments and questions regarding the `recommended plan' in the Phase A report. In response to many of these questions and/or comments raised, City staff requested Love & Associates, Inc. to re-visit and/or reanalyze alternate options at specific locations along Fourmile and/or Wonderland Creeks. The following Memorandum is a summary of additional alternates and their associated estimated costs at the various locations requested to for reconsideration. ADDITIONAL FOURMILE CANYON AND ~TONDERLAND CREEK ALTERNATES REQUESTED TO BE CONSIDERED BY CITY STAFF: A. Unger Fourmile Containment Reservoir One alternate briefly considered in the original Fourmile Canyon Creek Major Drainageway Master Plan - Phase A Alternate Analysis published in June 2000 considered a large reservoir constructed on Upper Fourmile to decrease the spill from Fourmile Canyon Creek to Wonderland Creek. 800 Jefferson Avenue, Suite B Louisville, Colorado 800271873 Phone: 303~73~796 Fax: 303739796 1 The June 2000 report states an off-channel detention pond would require approximately 30 surface acres of City Open Space acreage and would include a 10 feet high embankment and approximately 1.3 million cubic yards of excavation in order to decrease the outflow of Fourmile Canyon Creek to 1,000 cfs which would be conveyed completely in the Fourmile channel. An on-channel reservoir would be required to be even larger. This alternate was rejected due to the enormity of project cost and the impact to City Open Space lands. At the request of several individual property owners, City staff requested Love again revisit this alternate and estimate the costs for constructing this reservoir in 2007 dollars. Using the hydrology previously developed by Love & Associates and estimating the reservoir volume based on the flow tributary to the design point just upstream of Broadway, Love & Associates developed a hydrograph at this location. The assumptions used were design of a 1,000 cfs channel which would convey flood discharges through the proposed reservoir site. The channel would side channel spill to storage located both north and south of Fourmile Canyon Creek. The reservoir was then sized for the cumulative volume in excess of what will be contained and conveyed in the channel. Assuming a reservoir depth of 10 feet for safety, approximately 30 acres of land would be required to contain this volume. Due to the steep terY•ain, a series of stepped reservoirs would be needed and 1.3 million cubic yards of excavation would be necessary to achieve the required volume. Both City of Boulder Parks and City Open Space property would be required for this reservoir. The 1,000 cfs discharged downstream of this resen~oir would be contained in the existing Fourmile channel and there would be no spill discharge from Fourmile Canyon Creek to Wonder Creek downstream during a 100-year event. Table 1 outlines the estimated costs associated with this detention pond alternate. In light of the cost estimate of $36 million and significant Open Space and Park lands required for this alternate this Alternate continues to be cost prohibitive and was not considered a viable option. Table 1 U stream 34-acre Reservoir -Estimated Costs Descri tion Quantit Unit Unit Cost Item Total Channel Excavation {190 sfx 36001f} 684000 CY $ 15 $ 10,260,000 Pond Excavation 1300000 CY $ 10 $ 13,000,000 Pond Embankment 300000 CY $ 7 $ 2,100,000 Remove & Replace Topsoil (30 acres x 6") 24200 CY $ 8 $ 193,600 Grade Control Structures 33 EA $ 18,750 $ 618,750 Seeding/Mulching 30 AC $ 3,750 $ 112,500 Land Acquisition 30 AC $ 127,000 $ 3,810,000 Spillways/Outlet Works 1 LS $ 2,500,000 $ 2,500,000 Wetland Mitigation {20 ft x 3600 ft) 1.65 AC $ 127,000 $ 209,917 Contingency/Mobilization 25°/a - $ 7,251,167 $ 1,812,792 En ineerin /Administration 15% - $ 9,063,959 $ 1,359,594 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 303-673-9795 Fax: 303-673-9796 2 I ESTIMATED COSTS $ 36,000,000 I DETENTION POND PARAMETERS: Pond Volume required with 1000 cfs channel 259 AC-FT 417,853 CY Pond Depth (assumed) 10 FT Area re uired assumin 100% land efficienc ~ 25.9 AC Assumed 30 Acres Excavation Re uired due to stee terrain 1,300,000 CY B. Flow colledio~i and redistribution upstream of Broadway Following the Public Open House held on September 27, 2007 owners of commercial property just upstream of Broadway (on the north bank of Fourmile Canyon Creek) approached City staff regarding modification of an alternate previously explored in the June 2000 Fourmile Phase A Report whereby flows along Fourmile Canyon Creek were proposed to be collected upstream of their commercial property and redistributed on the downstream side of Broadway. The original alternate was not considered in the combined Fourmile-Wonderland Creek Master Plan because of the decision by the City and the UDFCD to not contain the spill flows above Broadway. However, City Staff requested Love & Associates to reconsider an alternate at this location that might allow for minimization or elimination of the conveyance (floodway) and/or High Hazard Zone fiom this property north of the creek as the City anticipates future redevelopment of properties along Broadway as indicated in the North Boulder Subcotnr~nunity Plan. In keeping with UDFCD policy; however, the spill from Fourmile south of the creek must remain unchanged regardless of which alternate is selected. Containing a portion of the spill results in adverse impacts to properties downstream on Fourmile Canyon Creek. Love analyzed an additional alternate along Reach 6a of Fourmile Canyon Creek sizing an area of conveyance to carry the average right overbank 100-year flow (approximately 1300 cfs). Love's analysis extends from the west (upstream) side of Broadway to just west of the low flow trail crossing at the west side of Jack Lacy's property. The 100-year channel has been widened through this stretch as shown on Figure 1 to convey the right overbank flow. The spill from Fourmile Canyon Creek to Wonderland Creek is not changed by this alternate. The cost for these channel and road improvements is estimated at $2,350,000. This cost includes the channel improvements as well as roadway improvements for Yarmouth and Rosewood. This alternate would result in a modified floodway and High Hazard Zone (HHZ). However, some properties would still remain in the floodplain and flood insurance would still be required/recommended. 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 303-673-9795 Fax: 303-673-9796 3 Figure 1 Flow Collection & Redistribution Upstream of Broadway ~ 4 hR~ i ~ 0 ROQICI~ ~ ~`s ~'F .~".ac.. ~ 'I t . ~ ~ 3 ~ I ~ p j( ` r~ 4n 1 + oo ¦or ou~swiRaNr a ~sn~mar~~ulaan ~~s ~ D~ ~ ~9 I~R~' IYIYIYII ~ T ~ ~ ~ ~ ~~r •IFII~ r M~ 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 3D3.673~795 Fax: 3D3.673.9796 4 A progress meeting was held at Love & Associates offices on November 15, 2007 ~~ith City and UDFCD staff. City staff will present this alternate as a possible scenario the developer may undertake in the future to improve his site for future development. The City may or may not participate financially in implementing such an alternate. Figure 1 illustrates the components of this alternate included in the estimated costs of this alternate. Table 2 estimates costs associated with the collection/redistribution scenario. Table 2 Collection/Redistribution U stream of Broadwa -Estimated Costs Description Quantity LJnit Unit Cost Item Total Channel Excavation {240 sfx 14001f) 12450 CY $ 13 $ 161,850 Interceptor Channels {150 sfx 2001fl 1111 CY $ 13 $ 14,443 Grade Control Structures 15 EA $ 25,500 $ 382,500 Rick Wall -North Bank {8.5 ft x 1000 ft) 8500 FSF $ 32 $ 272,000 Utility Relocations (w, ss, gas, elec) 1 LS $ 19,100 $ 19,100 Remove & Replace Silver Lake Ditch Crossing 1 LS $ 31,750 $ 31,750 Remove & Replace Pedestrian Trail Crossing 1 LS $ 31,750 $ 31,750 Remove & Replace Pedestrian Trail 600 LF $ 51 $ 30,600 Revegetation {80 ft x 1400 ft + 50 ft x 200 ft} 2.8 AC $ 3,800 $ 10,640 Landscaping {80 ft x 1400 ft + 50 ft x 200 ft) 2.8 AC $ 12,700 $ 35,560 Wetland Miti ation 30 ft x 1400 ft 0.96 AC $ 127,000 $ 122,452 Contin enc /Mobilization 25% - $ 950,795 $ 237,699 En ineerin /Administration 15% - $ 1,188,493 $ 178,274 SUB-TOTAL $ 1,528,618 Roadwa Im rovements* Yarmouth Avenue 1 LS $ 254,000 $ 254,000 11th Street 1 LS $ 222,250 $ 222,250 Rosewood Avenue 1 LS $ 127,000 $ 127,000 Utilit ~ Installations* Yarmouth Avenue 1 LS $ 107,950 $ 107,950 11th Street 1 LS $ 109,250 $ 109,250 Contingency/Mobilization/Engineering/Admin* 0% - SUB-TOTAL $ 820,450 COMBINED COST ESTIMATE $ 2,349,068 * Roadway/utility costs for this alternate were developed by City staff and contingencies have already been added to their costs and brought forward to 2007 costs. 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 303-673-9795 Fax: 303-673-9796 5 C. Improved Channel near Centennial Middle School as an alternate to purchasing three properties. Love & Associates' recommended alternate for Reach 6 on Wonderland Creek includes the City's future acquisition of three residential properties near Centennial Middle School adjacent to Wonderland Creek. In preparation for the September 27, 2007 Public Meeting, Love & Associates was requested to reexamine additional alternates for removing these three properties currently in the HHZ. Our analysis was based on the following assumption: Under the previous (Greenhorne & O'mara) regulatory flood study which indicated no spill fiom Fourmile to Wonderland Creek, the properties recommended for acquisition on Poplar and Emerald were not in the HHZ. With the current knowledge that these properties are in the HHZ with the new spill hydrology, Love developed an alternate for City and UDFCD consideration based on providing 100-year conveyance for only that portion of the discharge in excess of the previous 100-year discharge. Two options were analyzed for conveying the additional 100-year flow in Wonderland Creek resulting from the decision not to contain the spill flows from Fourmile Canyon Creek at Broadway. The previous regulatory study had a 140-year flow of 990 cfs at Centennial Middle School. The current adopted floodplain study has a 100-year flow of 2,285 cfs at 19th Street (just upstream of the school). Therefore, the additional alternates analyzed at this location required conveying the additional 100-year discharge of 1295 cfs in a channel or box culvert. The following are possible alternatives to acquiring HHZ properties on Poplar and Etnerald along Wonderland Creek: 1. Install a large pipe or box culvert under Centennial Middle School's playing field/track to convey the additional 1295 cfs. Two 12'W x 6'H reinforced box culverts (RCB) would be required to convey only the additional 100-year flow (1295 cfs). 2. Construct a channel to convey the additional 1295 cfs. Using a 5' depth, 4:1 side slope, trapezoidal channel and a 7 fps velocity (assumed), the channel would need to be approximately 60' wide with an 18-foot bottom width. The attached drawing shows a red lined layout of this supplemental channel. If this alternate is selected by the City and the UDFCD, a natural type channel configuration would be recommended. Figure 2 illustrates the area of channelization or the reach of box culvert under the school track. Table 3 includes cost estimates for the additional alternates identified for the portion of Wonderland Creek Reach & near Centennial Middle School and the properties recommended for acquisition. 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 303-673-9795 Fax: 303-673-9796 6 Figure 2 Improved Channel near Centennial A'Iiddle School „ + s~ a I i v. e, 1' {,7 ~ ' F' y f s ti ~ ~ l~1AA117ML ~u ~ . ~ ~ ~ oo~w,eas o~ e~mre r o~a~ , o~ ~o~rtx ~n ~nx ~ ~m ore~c~ • ~camaNK. r ~ GIII~OAlARfT ~ - StNNN~WIIGIT qua ~ ~ - ~ • .~i ~gnwi~ J~ ~ C' OI ~GRIN~IWIN rya ' Ndlr74ti IN~AR ~ ~ ~M y • CIM~ GAl4~IT ~ ~ r! ~ , ! ~r ~ ~~w~wix ~ ~ ~ ' u~mucn~ ~.1, ~ ~ ¦ N 11011 N1LIY~ ~ iY0 ~r ~ , p rr Rmvar ~ ~ 4 I I ""~~Q . s~ 1 ~ D 9 ~ t ' ~ 1>,!1 a n°" e"""rn mr°~'~"' ~ d FQURMILE CANYON CREE]S FlOl1RE ,~oune w,.~w~ ~ a e~wr ~ UR9AN DRAIFI~QE ANA FLQ~D I~NiRQL ~lI$TRI~T ANa YYONDERIAND CREEI[ IMPROVED CFIANNEL 2 o ~ m r- - u GIlYOF BOULDER. COLOR11D0 PLAN AT CENTENNIAL MIQDLE 9CH©DL 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 3D3.673~795 Fax: 3D3.673.9796 Table 3 Reach 6 Alternates near Centemual Middle School -Estimated Cost Alternate Cost Total Reach 6 Cost 1) HHZ Containment including Property $ 1,593,200 $ 3,168,300 Ac uisition Published Alternate 2) HHZ Containment including Channelization of Additional Flow (New $ 933,500 $ 2,508,600 Alternate) Original) HHZ Containment including Conveyance of Additional Flow in RCB (New $ 3,406,000 $ 4,981,100 Alternate) Neither the supplemental channel nor the RCBs require acquisition of any residential structures. As discussed with the City and UDFCD at the November 15~' Progress Meeting, Love understands the Project Sponsors (City and UDFCD) prefer (and will likely recommend) the alternate which incorporates the channelization of the additional flow. D. Topaz Culvert Replacement The published Phase A report proposes to remove the crossing at Topaz making it a cul- de-sac. City staff requested Love size and estimate a cost for construction of a 100-year structure at this location. Table 5 includes the estimated costs for this structure using pricing similar to that employed for other structures recommended for replacement along the creek. Figure 3 indicates the location and size of road improvements required at Topaz based upon this alternate. Table 5 To az 100- eai• Culvert -Estimated Cost Item Item No. Description Quantity Unit Total 1 Channel Excavation 1 LS $134,444 2 Remove Existing Culvert, Wingwalls and Pavement 1 LS $5,000 3 Grade Control Structures 1 LS $45,000 2-12-foot-Wide x 6-foot-High Reinforced Concrete Box 4 Culverts (includes RCB Culverts and Road Restoration} 1 LS $168,000 5 Landscaping/Revegetation 1 LS $12,821 6 Wetland Mitigation 1 LS $31,500 7 ROW/Easements 1 LS $36,736 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 303-673-9795 Fax: 303-673-9796 8 8 Contingency/Mobilization 25% - $108 375 9 Engineering/Administration 15% - $65,025 TOTAL $606,901 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 303-673-9795 Fax: 303-673-9796 9 Figure 3 TOPAZ bridge replacement , . ~ ~ f 1.~ a ~ r t - ' ~ aa~,~x~ _ 'fit IIdQ11! #II~LAi! T~4L4~¦11 ~ w{~RI~IIIOL e _ t ~ n- ~ „ r ~ ! t - ~ l r ~ { ~ ~ ~ ~ f 4 ~4~1W~C ArL QLI~ 'V a. q ~ ~ I _r A ~ Y A l - c ~ I' R,~iIWI° ' 1~lbsix~,l~r ~oaanM eaw~e eaoaE+r~x xe rwo~rrR~x ~nas~rar~ wa~ro r~ r~aao~i wrtx usn~ oagh ~aa ~a~s y : auR,u~~ o~~ i oe>r~ ~ omE ~ ew~err ' 1 ~ ~ yrrx~n~rr.ni~?ua J ew~,xhan~ I ~ a` ID_----. iJ ~ 1r ~QI! RATi ~IGINi1rP Q f1~ r r ~i ~ • ? ~ ~ » ~rararmROm~n~r~~ 1~101Dl~1R7MNN~~L000dIYIi~ ' . ~ r y~ ~ * ~ • • ~ ~ 1 I ~ ~ w~a vw, Nor n ~ a neNr ¦ ,.o.w,c~wt ~:s~ ~ URBAN DRAJFlAt3E AND FLOOD I,~]NiFiOL DI$TRI(,T FOURMILE CANYON CREEK TOPAZ CULVERT m ~'@ u CITY OF BOl1LDER, GOLORIMDO AND WONDERLAND CREEL( 9 e'er r~ASTER PuN REPLACEMEM 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 3D3.673~795 Fax: 3D3.673.9796 la E. Insurance Premium Surnmary The City of Boulder requested Love compile a summary of Insurance Premium estimates for properties located in the Fourmile Canyon Creek , Wonderland Creek and the spill area floodplains. In determining the flood insurance premium for these flood prone properties, Love made the following assumptions: • Structure value was taken from City of Boulder most recent Boulder County Assessor's data base. • Premiums were assigned to each property based on general premium tables published on ww~w.floodsmart.;;ov for low and high risk structures which assume a $500 deductible and no-basement. • Structure values were rounded up for premium classification and Building and Contents premium applied to account for contents insurance estimate. • Class 7 Community Rating System insurance premium reduction (15%) was applied. • Zone designation dependent upon finished first floor (FF) depth of water for 100-year and 500-year events was taken from the previously published damage analysis. The NFIP Manual can provide detailed, case-by-case insurance costs including premium calculations for structures with basements. Insurance rates with respect to flood zone were applied and a summary of the cost of insurance per reach based on the properties in the Zone AE and Zone X floodplains is included in Table 6. Note: These are annual insurance premium costs and will be incurred each year. Table 6 Annual Insurance Premium Estimated Costs Fourmile Can on Creek Flood lain Pro erties Reach # of Structures Total Annual Premium Lower FCC 18 $ 8,100 1- 0 $ - 2- 7 $ 3,700 3- 4 $ 4,200 4- 29 $ 40,400 5- 59 $ 66,600 6- 22 $ 34,500 Total FCC 139 $ 157,200 Wonderland Creek Floodplain Properties # of Structures Total Annual Premium 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 303-673-9795 Fax: 303-673-9796 11 1 0 $ - 2 16 $ 20, 800 3 82 $ 77, 800 4 5 $ 8,700 5 70 $ 67,300 6 19 $ 17,600 7 3 $ 2,600 8 1 $ 200 Total WC 196 $ 194,800 Total Annual Insurance Premium 335 $ 351,900 We have verified with Dan Carlson fiom FEMA and Diane Oestman of Flood Insurance Services the maximum coverages for residential/non-residential properties as well as contents coverage. F. Partial containment and threshold fre~ruency and impacts to County properties. Following the October 15, 2007 WRAB meeting, City Staff requested Love respond to questions raised by Elizabeth Black, a property owner whose residence is located in the spill area. The following are the questions asked and Love's response: Q: V4~hat is the maximum flood event the current creek channel can carry before it starts to spill to the south? A: Approximately two (2} cfs begins to spill from the Fourmile Canyon Creek Chamlel at the 10-year flood event. Significant spills (700+ cfs) are occurring at the 50-year event. The 10-year event can be considered the threshold event at which water begins spilling from Fourmile Canyon Creek to Wonderland Creek. Q: What event could the downstream County properties handle before these structures are impacted by floodwaters? A: Downstream county properties begin to see water at their structures between a 20 to 50 year event for the current spill scenario depending upon the location of the structure. Any increased containment will result in these properties getting wet for smaller, more frequent events. The UDFCD has stated that they cannot support any alternates which result in adverse impacts to downstream properties unless mitigation is being proposed. 800 Jefferson Avenue, Suite B Louisville, Colorado 80027-1873 Phone: 303-673-9795 Fax: 303-673-9796 12