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HomeMy WebLinkAbout03.18.2019 WRAB PacketWATER RESOURCES ADVISORY BOARD MEETING MEETING DATE: Monday March 18, 2019 MEETING TIME: 6:00 p.m. MEETING LOCATION: Municipal Services Center, 5050 Pearl St., Boulder, CO 80301 Agenda Highlights: 1. Call to Order (6:00 p.m.) 2. Approval of Feb. 25 meeting minutes (6:01 p.m.) 3. *Public Comment (6:05 p.m.) 4. Information Item – Energy & Climate Initiatives Update (6:15 p.m.) 5. Information Item – Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update (6:45 p.m.) 6. Information Item – South Boulder Creek Flood Mitigation Update/Stormwater & Flood Management Utility Funding (7:15 p.m.) 7. Matters from the Board (7:45 p.m.) 8. Matters from Staff (7:55 p.m.) 9. Discussion of Future Schedule (8:10 p.m.) 10. Adjourn (8:15 p.m.) * Public Comment Item Agenda item times are approximate Information: • Please contact the WRAB Secretary email group at: WRABSecretary@bouldercolorado.gov • Packets are available on-line at: http://www.bouldercolorado.gov – A to Z, Water Resources Advisory Board (WRAB), Next Water Resources Advisory Board Meeting WRAB Minutes 2/25/2019 Page No. 1 CITY OF BOULDER, COLORADO BOARDS AND COMMISSIONS MEETING MINUTES Name of Board / Commission: Water Resources Advisory Board Date of Meeting: 25 February, 2019 Contact Information for Person Preparing Minutes: Erika Lowe, 303-441-4257 Board Members Present: Lesley Smith, Kate Ryan, Kirk Vincent, Trisha Oeth Board Members Absent: Ted Rose Staff Present: Jeff Arthur, Director of Public Works for Utilities Douglas Sullivan, Principal Engineer Utilities Ward Bauscher, Utilities Maintenance Manager Ken Baird, Financial Manager, Public Works Chris Douville, Wastewater Treatment Manager Tom Settle, Water Treatment Manager Joe Taddeucci, Water Resources Manager Edward Stafford, Development Review Manager Candice Owen, Stormwater Quality Supervisor Pieter Beyer, Engineering Services Manager Amanda Bevis, Project Coordinator Bret Linenfelser, Water Quality & Environmental Services Manager Erika Lowe, Board Secretary Agenda Item 1 – Call to Order [6:03 p.m.] Agenda Item 2 – Approval of the 28 January 2019 Meeting Minutes [6:06 p.m.] Approved Moved by: Ryan Seconded by: Vincent Vote: 4-0 Agenda Item 3 – Public Participation and Comment [6:05 p.m.] Public Comment: Carl Norby: Residents at Frasier Meadows gave their opinion. January 2014 at a WRAB meeting, Council please do your job, if you cannot protect the people, why are you here? Sums up five years of council meetings: ‘why are you here.’ Individual items of staff work done by city looks reasonable. Big picture - staff does a good job. Someone needs to tell Council to get the job done. John Gerstle: Planning Board liaison to WRAB- a few things to bring to attention of WRAB that might be of interest. Planning Board four nights ago considered the annexation of the Knollwood subdivision and municipal district into the City. Primary reason Knollwood wanted to do this was due to the water supply and road conditions. Planning board recommended annexation to the City Council which will be ultimate decision. It might be appropriate for WRAB to consider the implications for Boulder’s water supply and let City Council know if there are any concerns on that front . This is 50-100 houses. Marginal to Boulder’s demand, but Council should hear WRAB’s thoughts. In A pril, Planning board will be considering options for the former hospital at Alpine and Balsam and one of the aspects of concern is the potential flood plain management issues with this area. Several options have been presented to Planning Board for initial consideration. Another aspect WRAB may want to weigh in on sooner rather than later. Agenda Item 4 – Update on Colorado River Issues with Northern Water [6:12 p.m.] Representatives Joe Taddeucci and Northern Water representatives presented this item. Joe summarized a December, Northern-led tour of the Lower Colorado River, which included meetings with some of the larger lower basin water users. Kyle Whitaker, Northern’s Colorado River Programs Manager presented on the hydrology on the Colorado River, including a summary of drought conditions and critical Lake Powell and Lake Mead reservoir levels. Brad Wind, Northern’s general manager provided an update on upper and lower basin drought contingency plans (DCPs). Brad and Sue Ellen Harrison discussed the role WRAB Minutes 2/25/2019 Page No. 2 Northern foresees for itself in coordinating with the state on Colorado’s contribution to the upper basin DCP. Sue Ellen is one of three Boulder County representatives on Northern’s Board of Directors. WRAB Board Discussion Included: • Comment to thank Northern Water and their board for attending, the residents of Boulder really depend on Northern to help people understand the complexity of this issue. • Comment to thank Northern for interacting and providing an update. As Front Range water consumers, we forgot that we are part of a greater community and as such, the decisions we make do have impacts on projects that we don’t think we are a part of. Hope Northern Water can continue to check in more frequently, so Boulder can continue to be a part of that community. • Question regarding Boulder being lucky that not all the City water comes from Northern, but a lot of communities and farmers strictly rely on water from Norther, so is there any reason Boulder should expect to give up more because it has native water. Agenda Item 6 – Information Item – Public Hearing and Consideration of [6:38 p.m.] Motion Recommending the City Council to Adopt Updates to the Public Works Design and Construction Standards Edward Stafford presented this item EXECUTIVE SUMMARY: This memorandum provides information and a summary of proposed updates to the Design and Construction Standards (DCS) to align with the State of Colorado’s water quality requirements and industry best practices. This memorandum includes an attachment of d etailed proposed changes to the DCS. In some cases, the proposed changes impact the Boulder Revised Code (BRC), therefore necessary changes to the BRC are being developed. WRAB’s role includes reviewing capital improvements conducted or proposed by the utilities division and reviewing, monitoring, and proposing changes to utilities’ master plans. The Design and Construction Standards guide implementation of master plans through capital projects. WRAB is being asked to make a recommendation to City Council regarding the proposed updates. WRAB Board Discussion Included: • Question if stakeholder meeting date and time information will be relayed to WRAB • Question on page 190, regarding service connections and if connection sizes between the 2 inches and smaller and 3 inches and larger are covered. If so, perhaps make it ‘catch all’ language. • Comment on chapter 5 being a good idea for additional language about ground water bar riers • Comment on page 205, the domestic services section was confusing. Trying to understand the difference between what is being done in subsection A vs. subsection B, in particular it seemed as though toilets were allowed in one and not the other accessory structure, so clarification would be useful • Question on page 223 regarding the change in the collection main slopes, what was the basis for making this change • Question on page 268 and the reasoning behind the language for avoiding stormwater discharges into irrigation ditches • Comment on agreeing with the language that showed up in a number of places about streets serving mainly for transportation and should convey stormwater efficiently so that traffic is not impeded • Comment on reading through the red line and the changes made sense and the objective was understood • Question on why manholes are recently showing up with plastic rope that is similar to a tag Public Comment: John Gerstle: Speaking as a private citizen. Congratulate staff on this ef fort. Three elements to inquire about: Reference to the use of streets primarily as transportation and not storm drainage, want to ensure that this does not remove the option of the use of streets for stormwater drainage. Congratulate staff on underlining the importance of removing stormwater connection conveyance by the irrigation ditches and laterals in the City. Speaking as a shareholder in silver Lake Ditch, I have dealt with that issue and it is WRAB Minutes 2/25/2019 Page No. 3 great to see this becoming an explicit policy. Confirm the comments made earlier about connections to various types of outbuildings on lots from a Land Use/Planning aspect, that is a positive addition to the regulations. Motion: WRAB is being asked to make a recommendation to City Council regarding the proposed updates. The Water Resources Advisory Board (WRAB) recommends approval of the proposed change and updates to the Design and Construction Standards (DCS) as identified in Attachment A of the February 25, 2019 memo to WRAB Moved by: Oeth Seconded by: Vincent 4:0 Passes as presented. Agenda Item 7 – Matters from the Board [7:36 p.m.] • In terms of Alpine Balsam and Goose Creek, what is WRAB’s role? -Boulder Revised Code indicates that WRAB shall not involve itself in any review under the land use regulations unless specifically requested by Council. WRAB will be providing feedback relating to flood mitigation, master planning and potential capital projects through that area. Similarly, WRAB is not asked to provide a recommendation on specific annexations such as the Knollwood annexation. WRAB has the opportunity to make recommendations on the master plans that are considered when reviewing annexations. • Question about annexation and what the implications are for flood mitigation in those areas • Question whether the drought plan include the 1% increase in population growth and if this annexation counts as population growth Agenda Item 8 – Matters from Staff [7:52 p.m.] • Update on Barker Gravity Line Rehabilitation -Lining the pipe whenever possible to save future excavation costs -500-foot section if straight, 200 if it is curved - Repair the siphons that are worse off first -12-year program (2018-2030) $3-4 million/year • Update on Baseline/Foothills Sewer Project -Bursting is not an option on Bbaseline because the sewer is not sloped enough, there are also utilities conflicts that prevents bursting - Option 1 in Open Space: not shut down traffic, not interfere with utilities; requires OSBT approval of disposal -Option B, in Baseline Road, would shut down traffic for 2 months -Option C, runs along an Xcel powerline, which would need to be relocated -Cost estimate will be provided ($3.6 million) for the Open Space meeting • South Boulder Creek - Council provided direction for Variant 1 500-year project - Council did not support expedited annexation process. - Align the two projects together so one does not cause delays to the other - City has met with CDOT and has drafted letter of intent for CDOT consideration. Agenda Item 9 – Discussion of Future Schedule [8:17 p.m.] • March - Information on rate study implementation (SBC/storm fund) - Steve Catanach rescheduled to speak from January - Information items on Upper Goose Creek, Twomile, Canyon Creek flood mitigation Agenda Item 10 - Adjournment [8: 21 p.m.] Motion to adjourn by: Oeth Seconded by: Ryan Motion Passes 4:0 WRAB Minutes 2/25/2019 Page No. 4 Date, Time, and Location of Next Meeting: The next WRAB meeting will be Monday, March 18, 2019 at 6:00 p.m., at the City's Municipal Services Center, 5050 Pearl St., Boulder, CO 80301 APPROVED BY: ATTESTED BY: Board Chair: _________________________ Board Secretary: ____________________________ Date: _______________________________ Date:______________________________________ An audio recording of the full meeting for which these minutes are a summary is available on the Water Resources Advisory Board web page. https://bouldercolorado.gov/boards-commissions/water-resources-advisory-board-next-meeting-agenda-and-packet CITY OF BOULDER WATER RESOURCES ADVISORY BOARD AGENDA ITEM MEETING DATE: March 18, 2019 AGENDA TITLE: Information Item – Update on the Upper Goose Creek and Twomile Canyon Creek Flood Mitigation Study and Alpine-Balsam Area Plan Coordination PRESENTERS: Jeff Arthur, Director of Public Works for Utilities Douglas Sullivan, Utilities Principal Engineer Katie Knapp, Engineering Project Manager Jean Gatza, Senior Planner EXECUTIVE SUMMARY This memorandum provides background information and an update on the Upper Goose and Twomile Canyon Creek Flood Mitigation Study and associated coordination efforts with the Alpine-Balsam Area Plan. Based on community feedback and technical screening several alternatives were added and others removed from further consideration. Next steps include additional alternatives assessment using the evaluation criteria developed for the Skunk Creek, Bluebell Canyon Creek and King’s Gulch Flood Mitigation Study; field assessments of the existing creek channels; and consultation with potentially impacted property- owners and residents informing recommendations for draft mitigation plans. This memorandum is intended to be informational and does not require WRAB action. BOARD AND COMMISSION FEEDBACK The Upper Goose Creek and Twomile Canyon Creek Flood Mitigation Study was presented to WRAB on March 19, 2018, following a public open house. The study has not been presented to any other boards or commissions, however, because one of the alternatives under consideration is a new detention facility at North Boulder Park, City Council, Planning Board and the Parks and Recreation Advisory Board have been made aware of this planning effort and the potential park impacts. As part of the Alpine-Balsam Area Planning process, policy choices for flood mitigation in North Boulder Park and on the Alpine-Balsam site were shared with the community, Planning Board and City Council in fall 2018. Feedback from the Planning Board and City Council indicated support for flood mitigation detention both at North Boulder Park and on site to decrease flows on site and increase developable space, while preserving trees, current uses, and the character of the park. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 1 PUBLIC FEEDBACK The Upper Goose Creek and Twomile Canyon Creek Flood Mitigation Study has included several opportunities for the public to provide feedback on the flood mitigation study. The following table summarizes the public process to date: Date Meeting Oct. 24, 2013 Post-Flood Open House April 12, 2017 City-wide Flood Open House July 13, 2017 Flood Mitigation Workshop March 19, 2018 Flood Mitigation Open House and WRAB Public Meeting March 18, 2019 Update to WRAB The March 19, 2018, open house was held to present information on several different mitigation alternatives. On that same day, the alternatives were also presented to the Water Resources Advisory Board (WRAB). Comments were received through email and an on-line questionnaire was also developed to capture public feedback. Over 200 emails and over 450 responses to the online questionnaire were received. The questionnaire was organized by sections of the drainageway (or ‘reaches’) to inform respondents of downstream impacts and encourage site specific feedback. The complete results of the questionnaire can be seen at this link: https://data.surveygizmo.com/r/349531_5acb842cd95904.61712895. For Twomile Canyon Creek reaches, favored alternatives included ‘no action’ and alternatives that would direct floodwaters east on Iris Avenue to discharge into Elmer’s Twomile Canyon Creek. For Goose Creek, the questionnaire feedback favored detention at North Boulder Park and 100-year containment within storm drains upstream of 19th Street. Downstream of 19th Street, channel improvement alternatives were generally not preferred. In addition, over 800 individual comments were received through the questionnaire. Many of the comments related to 100-year flood containment both in favor of and against, though most responses expressed concern about private property impacts from 100-year flood containment. Comments from Reach 1, the most upstream area of Twomile Canyon Creek, included suggestions for new alternatives not included on the questionnaire. There were also several comments suggesting that the city perform creek assessments to better understand the condition of the existing creek channels and maintenance needs. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 2 Utilities staff have also met with individuals and small neighborhood groups to share information and receive feedback about the study. A compilation of public comments is included in Attachment A. Property owners and residents in the study area have been notified of public meetings using post cards, emails, social media (Nextdoor) and the project webpage: (https://bouldercolorado.gov/pages/skunk-creek-bluebell-canyon-creek-kings-gulch-upper- goose-and-twomile-flood-mitigation-studies). BACKGROUND This study is for the Upper Goose Creek and Twomile Canyon Creek drainageways. The floodplain map for this area is depicted below: Upper Goose Creek and Twomile Canyon Creek Floodplain Map The floodplain maps for Upper Goose Creek and Twomile Canyon Creek were updated in 2015 and incorporated improvements and changes along the drainageways. For this flood mitigation study, the city retained ICON Engineering, Inc. (ICON) to develop and evaluate several flood mitigation alternatives which included: 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 3 1.Detention Facilities 2.Sediment Capture Facilities 3. Channel and Culvert Improvements 4. Piped Storm System Improvements 5. Roadway Conveyance These alternatives were presented to the public and the WRAB for feedback in March of 2018. Additional background information about the study area, flood history and the initial alternatives under consideration was included in the March 19, 2018 WRAB memo and is available at this link: https://bouldercolorado.gov/links/fetch/39460 ANALYSIS Community feedback on the initial flood mitigation alternatives has helped shape the study process and revisions have been made to the alternatives being evaluated. New alternatives were added to the analysis and an initial screening process was completed to eliminate alternatives that were determined to be unfeasible or would not be acceptable to the community. An Alternative Selection Memorandum (Attachment B) was completed by ICON to summarize the initial public process, development of alternatives and initial alternatives screening. As described in the memo, the following additional alternatives were added to the evaluation: 1.Alternate detention facility sites for Twomile Canyon Creek, including areas west of the city limits. 2. Roadway conveyance for Twomile Canyon Creek, west of Broadway. The flood mitigation alternatives were then reviewed through an initial screening with the following results: 1. Alternatives that would impact Long’s Garden’s have been removed from further consideration. 2. Alternatives that would require the removal of the Alpine Condominiums have been removed from further consideration. 3. 100-year channel alternatives that would require a significant removal of houses were removed from further consideration. 4.Detention facilities for Twomile Canyon Creek, upstream of Broadway were determined to not be feasible and were removed from further consideration. 5.Open channel alternatives that would require removal of existing commercial structures were removed from further consideration. Alpine-Balsam The city-owned Boulder Community Hospital site is along the upper reach of Goose Creek and is currently in an area planning process known as the Alpine-Balsam Area Plan. Utilities staff 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 4 have been coordinating with this project team and Parks and Recreation staff on alternatives to reduce flooding risks in conjunction with redevelopment of this area. One alternative includes altering a portion of the North Boulder Park to accommodate flood detention. Consideration of park detention was informed by the baseline assumptions of respecting existing tree canopy and preserving usability of ball fields with flexibility of an open lawn area. City Council, Planning Board and the Parks and Recreation Advisory Board are aware that a detention facility at North Boulder Park is under consideration and could result in potential impacts and will require additional analysis, design, and community process. Both City Council and the Planning Board expressed support for investigating this option further to decrease flows on site and increase developable space, while preserving trees, current uses, and the character of the park. To further understand the feasibility of this option, a geotechnical investigation is being completed and groundwater monitoring wells were installed collect groundwater data. Additional analysis is currently underway on the detention in the park, conveyance channel locations and design considerations related to daylighting goose creek. If this alternative advances, additional public engagement would be planned to gather community input from park users and the Parks and Recreation Advisory Board to help guide changes to the park. NEXT STEPS The alternatives will undergo additional assessment using the evaluation criteria developed for the Skunk Creek, Bluebell Canyon Creek and King’s Gulch Flood Mitigation Study. This criteria was developed with input from the WRAB on August 20, 2018: •Life Safety (includes protecting vulnerable populations and providing emergency response capability) •Property Damage Mitigation •Water Quality Enhancement •Habitat Protection and Restoration •Operation/Maintenance Costs •Protection of Cultural Resources •Recreation Opportunities •Alternative Transportation Routes •City Construction Costs (including benefit to cost ratio) •Public Opinion/Community Acceptance •Resiliency/Adaptability to Climate Change and Uncertainty •Ability to Implement Quickly City staff will also conduct field assessments of the existing creek channels to obtain a more accurate understanding of the current conditions of these creeks and maintenance needs. Staff members will access the creeks on properties where there are existing flood and drainage 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 5 easements and will be reaching out to property owners for a right-of-entry where needed. The field assessments will include: •Taking notes and photos of the flood channel and any associated structures such as bridges, pipes, fences, etc.; •Gathering survey information; and •Noting any observed hazards such as fallen trees, sediment build-up, trash or severely eroded channel banks. Once draft recommendations are developed, staff will work with potentially impacted property owners to refine the recommendations prior to presenting the draft mitigation plan to WRAB at a future meeting. Following a WRAB recommendation to approve the mitigation plan, it will be presented to City Council for acceptance. Once accepted, the flood mitigation plan will be a long-range planning tool to help guide future flood mitigation projects for Upper Goose Creek and Twomile Canyon Creek. Projects identified within the plan will need to be prioritized against the city’s other flood mitigation needs. ATTACHMENTS Attachment A: Public Comment Summary Attachment B: Alternative Selection Memorandum (ICON) 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 6 Floodplain Management Program Open House Date: 04.12.2017 Meeting Location: Boulder High School Number of Attendees: 29+ (Note: not all attendees signed-in) Staff in Attendance: Katie Knapp, Christin Shepherd, Kurt Bauer, Laurel Olsen-Horen, Joanna Bloom, Annie Noble, Doug Dunn, Edward Stafford, Alysha Geiger, MaryAnn Nason, Candice Owen, Ryan Martin Others in Attendance: Brooke Seymour (Urban Drainage and Flood Control District), Craig Jacobson (ICON Engineering), Brian Ledoux (ICON Engineering) Purpose of Meeting: Community members were provided with city-wide flood planning and mitigation information. This public open house was also the official “kick-off” the flood mitigation planning process and provided the public an opportunity to discuss problem areas and provide ideas for consideration. A website was developed to provide information and updates on the mitigation study: https://bouldercolorado.gov/pages/skunk-creek-bluebell-canyon-creek-kings-gulch-upper-goose-and-twomile-flood-mitigation-studies An interactive map was also developed to allow people to submit comments and suggestions: https://iconengineering.github.io/maps/boulder/flood-mitigation-comments/ Comments Received: None of the written comments received pertained to the Upper Goose or Twomile Canyon Creek areas. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 7 Attachment A Upper Goose and Twomile Canyon Creek Flood Mitigation Workshop Date: 07.20.2017 Meeting Location: North Boulder Recreation Center Number of Attendees: 22 Staff in Attendance: Katie Knapp, Christin Shepherd, Kurt Bauer, Laurel Olsen-Horen, Doug Dunn, Robby Glenn Others in Attendance: Brooke Seymour (Urban Drainage and Flood Control District), Craig Jacobson (ICON Engineering), Brian Ledoux (ICON Engineering) Purpose of Meeting: City staff hosted a flood mitigation workshop with residents within the Upper Goose and Twomile Canyon Creek watersheds. A presentation was given that highlighted the development and flood history for Twomile Canyon and Goose Creek and described several different mitigation strategies that could be considered. Table top discussions were arranged and facilitated by city and UDFCD staff to brainstorm options, evaluate priorities, and capture the residents’ preferred flood mitigation strategies. Comments Received: Exercise 1: Current Drainage Conditions During storm events, what is currently working well? •Helping push the water runoff downhill (south.) •Downstream (28th St.) the mitigation has cleared up & opened up the 2-miledrainage which clears pretty easily. •Most storm drains. •Existing creek has sufficient capacity & more since the flood/storm event. •Creek handles stormwater well. •In 2013, the area where mitigation efforts were made really helped. The city cantake further judicious action to mitigate floods. •Hard to assess sine we have had smaller storm events. o Is North Boulder Park intended as a flood collection area or is this just anoutcome? •Except for 2013, seems to generally work ok. •Not so much in my area. •Ecological processes, low impact development, green infrastructure, wetlands,healthy riparian areas. •No surface water on our property. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 8 Attachment A •Water flowed down 19th into sewers. •Only surface water in lower areas in crawlspace. •Floodwaters followed the 2D mapping (mostly.) •Broadway drainage Iris → Elder.What is not currently working well with storm drainage? •Too much water doesn’t run off fast enough (when ground is soaked.) •Old drainages clogged with trees & brush. •Unimproved streetscapes. •Unanticipated storm/sanitary interconnect. •Culverts under Linden, Kalmia, Juniper, Broadway are undersized. •Broadway & Iris, Linden & @ Mile – underpass with pedestrian path & flood controlwould be brilliant. •Flooding even with light rain at south end of North Boulder Park. •Sump pumps in neighbor houses constantly pump into alleyway. •Not drainage with 17” of rain in 3 days. o You might encourage people to keep their own storm drains clear of stuff - ifyou only check some of these once a year – for their own benefit. •Iris & Broadway culvert not working well. •Sewer backup issues. •Water backs up at 4th & Linden and comes down the bike path – turning that into ariver. A larger culvert along Two-Mile Creek at Wonderland might help. •2013 water came across Ideal parking into our underground parking – no changefor this! •Culvert at Iris and Broadway is blocked by a lot of big debris – causing a pond withstanding water → mosquito breeding. Also worried about people doing their ownmitigation causing issues for neighbors in the next flood. Needs to be done on acitywide basis. •Impervious pavement, low floor to area ratios especially for commercialdevelopment. Big parking lots, encroachment on streams & wetlands. •Some water flowed down Floral. •Culvert at Iris & Broadway is not cleaned out this standing water during the floodshot up two stories at intersection on west side. Exercise 2: Rank Study Objectives •Vulnerable population (schools, nursing homes, etc.) o Yes to residential uses. Not to public (part time) uses. •Protection of cultural resources. o Open space at Linden should be left as is! Kalmia should not be torn up! •Life safety (high hazard) mitigation. o Reduce high hazard by placing culvert from hospital BCH east. o Protecting life and limb is most important along with •Recreation opportunities o Free the floodplains. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 9 Attachment A •Operation and maintenance cost savings o Increase water rates slightly to mitigate damage. o Be effective but spend what is necessary. •Minimize City construction costs. o This huge project is overkill! o Reduce damage potential. •Habitat protection and restoration. o Do not disrupt our lives with a huge project for an unlikely future event! o Wetlands & riparian areas, fluvial geomorphology. Exercise 3: Rate Flood Mitigation Strategies •What is your opinion of each mitigation strategy? o Detention and/or Sediment Capture Facility Slow the damage before it reaches population. o Open Channel and Culvert Improvements I like a combination of these two (plus underground piped stormdrainage system) based on initial cost AND cost of maintenance forclearing both during storm event. o Roadway Conveyance See a danger to an unwilling populace. Already happens. o Detention and/or sediment capture facility; open channel and culvertimprovements; and underground piped storm drainage system convey morewater, expensive. •Comments on mitigation strategies: o We need to contain sediment, so it does not plug storm system. o Take advantage of demolition at hospital when the development happens.Use different solutions to mitigate as much flooding as possible – openculvert where available. Street drainage. Box culvert. o Make as many improvements as financially possible. o Kalmia being rebuilt into a sunken culvert would be unacceptable to Kalmiaresidents & other neighbors. o Combination: Larger culverts under Linden, Kalmia, Juniper, Broadway.Focus flooding on roads/storm drains. Pedestrian underpass underBroadway. o For 2-Mile, all strategies must be employed. Detention at Linden & LakeBriar, open channel improvements to Broadway & Iris, undergrounddrainage to Iris & 16th, roadway conveyance from Iris to Elmers. o I am both confident in the city and consultancy to solve the problem andwilling to do all in my power to support. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 10 Attachment A o Suggest open channel from Foothills Elementary, under Broadway, alongnorth of Iris at county buildings, past ballpark, then go underground on Irisas roadway conveyance, would also include bike/pedestrian. o Should layer these and use as most appropriate. o Would immediately increase detention/sediment capture facilities. o Open channel on Alpine! o Detention ponds have to be really big – how practical? o 2-mile Creek need to be utilized – see below. * o Restoring ecological processes, wetlands, healthy riparian areas goes a longway with multiple benefits at lower costs. o Open conveyance sounds best but land is not available. o Combination makes sense. Open channels could be deeper. o Roadway conveyance makes sense in many locations. o Researched other cities should carry a great deal of influence. o Does it have to be “one size fits all?” or can we use different strategies fordifferent neighborhoods? •What are the biggest challenges you can identify for drainage improvements in your neighborhood? o The biggest challenge is to not overdo it. concentrate on preventingblockages in existing system. Our neighborhood is already besieged byconstruction. A huge “mitigation” project will be very unwelcome. o No improvement necessary on property. o Convincing the community to take the necessary integrated approach. Openchannel → culvert → roadway. For 2-mile, all will be required. o New construction – depth of foundation/basements. Changes in individual property impact community solution. o Sprinkler systems. o I bought all new gutters & extension for downspouts. o Biggest challenge is trying to mitigate the flow down 4th St. along the bikepath between Linden & Kalmia. The roadway conveyance map (the greenlines) would make things worse. It seems like the main diversion should bedown Linden, not 4th St. & Kalmia. o Parking lots west of us will always make us vulnerable. o With the redevelopment of the old hospital, there is a real chance to bringback Goose Creek west of Broadway. This was extremely popular at theredevelopment workshop favoring more natural drainage patterns. o Existing housing. o Access to land to build open channels. o Please pick the one which will have the greatest impact on the currentfloodplain map. Without understand how each strategy might change themap, our opinions are out of context. o Broadway higher than most property east of it. •Flood Mitigation Workshop Feedback: 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 11 Attachment A o I look forward to seeing the proposals. o The individual table conversations worked well to get people warmed up tothe topic, but it seemed most productive when the entire group (one at atime) spoke with a presenter so everyone could hear and respond to eachidea or concern. o One suggestion: opening statement really underscoring opinion and wishesof stakeholders is the goal. A very few people questioned the goal. It’s clearyou care what we think. o Our staff (#2) – Robby Glenn was helpful & clear. o More information on cost estimates & budget for doing reality check/ o Next phase – invite same people, provide 2-3 options (by area) & ask forinput then. o Briefness of many slides. o Assistance to questions. o *I was a little surprised at the format. It’s time for key people to haveopinions, but I was expecting a little more concrete/scientific informationabout the city’s plans and thoughts about the various mitigation options. Itseems to me that certain options are more appropriate than others in certainsituations and I would leave that up to the experts as long as something isdone. o Well done! o There was enough time for people to ask questions and give comments. o With only a small bit of information, you are asking us to rank variousoptions. I fear you will overvalue this input. I think we have to trustexpertise and experience over (potentially) uninformed opinion. I knowpublic input is important – but opinions passed on only surfaceunderstanding of the complexity of issues is dangerous. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 12 Attachment A Upper Goose and Twomile Canyon Creek Flood Mitigation Open House Date: 03.19.2018 Meeting Location: City of Boulder | Municipal Services Center Number of Attendees: 61+ (Note: not all attendees signed-in) Staff in Attendance: Katie Knapp, Christin Shepherd, Robby Glenn, Laurel Olsen-Horen, Joanna Bloom, Ward Baucher, MaryAnn Nason Others in Attendance: Jim Watt (Urban Drainage and Flood Control District), Craig Jacobson (ICON Engineering), Wyatt Reis (ICON Engineering) Purpose of Meeting: City staff hosted a flood mitigation open house prior to the regularly scheduled Water Resources Advisory Board (WRAB) meeting to present information on several different mitigation alternatives. The open house format was laid out in an arc, with different reaches of the mitigation study at different tables. Other information stations included irrigation ditches, and general flood information. Open House attendees were encouraged to provide feedback using an online questionnaire. Comments Received: Comments were received from 477 individuals through an on-line questionnaire. The results of the questionnaire can be seen at this link: https://data.surveygizmo.com/r/349531_5acb842cd95904.61712895 Comments were also received by email summary of emails After the open house, the alternatives were presented to the WRAB and members of the community were provided an opportunity to speak to the WRAB. Water Resources Advisory Board Public Comments: •Troubled by lack of notification to his neighborhood of the earlier meetings. Theoptions presented are missing some solutions he would like to see. It seems likepiping solutions in his neighborhood have gone by the wayside. He would like to seeit as a principle of this process that taking someone’s home or process is a lastresort. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 13 Attachment A •Has lived on Broadway between Hawthorne and Iris for 28 years. Has come to knowand value the Long family as good friends and neighbors. Pleased to see that the ideaof converting the productive agricultural center into a swamp is off the table. If adetention area is needed, look at the possibility of installing a cistern under all orsome of the property north of Iris and east of Broadway. Should be able to constructa cistern and still utilize the surface. Recommends using Broadway as a runoffchannel. It already serves that purpose. Same for Iris. Use it to dissipate the impactof the water into shallow flooding. •Has lived on Iris court for 37 years where the current channel goes into FarmersDitch. The map is in error on this location. It is a couple of hundred yards to the east.Doing nothing is not an option. There was a lot of damage in 2013. Sediment fromthe runoff filled Farmers ditch completely. It was costly to dredge. Piping is a betteroption. •Lives near Mr. Guesman. Shares many of the same ideas on reach number 3. Echoesthe comments that trying to have Farmers Ditch accept this kind of flow is notacceptable. A ditch is to channel water in a controlled flow. Uncontrolled flow is justdiverting the problem to a different area. Such as his neighborhood. •Neighbor of Rick Brew. Echoes Rick Brews sentiment about the proposed channelsgoing through his property. Also very concerned that the decision to turn away frompursuing pipe solutions around Kalmia/ Iris was based on only a small sample size.Echoes sentiments around not taking private properties. It would be nice to solveother utility problems as well. Looking at the 100-year flood plain mapping, theremay be unintended consequences from changing the flows. •Lives on Juniper where it backs up on Twomile behind Foothills school. At somepoint, we need a clarification on where the money comes from for these projects.Encourages improving and maintaining the 25-year channel. Enlarge the culverts allthe way up and work on maintaining a 25-year floodplain. This would probablymitigate many problems. If the city is doing more, still do less than the 100-yearchannel and maintain it. Stop the paving of pervious land in this area. There is toomuch paving in new development in the area, which makes flooding worse. If thewidening of Twomile is adopted, she urges adoption of the Broadway underpass.Plenty of room for a channel. Foothills will lose most of their playground if the openchannel option is adopted. •Appreciative that option D is coming off the list. There are still many options thatcreate a very destructive effect on their property. Understands that it is theresponsibility of staff and the board to consider all options. But their property is not“undeveloped” though it is sometimes perceived that way. It takes many years todevelop the soil and it can’t just be moved around and put back without direconsequences. The soil has been conditioned and developed for more than 100years. Any option, including “do nothing”, is still a risk to their soil and the soilcommunity. If a house is damaged during an event, even when a family iscompensated, they still lose their home. Although they are private property, theirland is very public. There is no similar plot of land in the city that could bepurchased to serve the same functions, Help preserve land and the soil to benefit thecommunity into the future. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 14 Attachment A •Executive Director of Growing Gardens. Leases 11 acres of land from the Longs andserves the community with education about agriculture. Agrees with Catherine LongGates. Pleased that alternative D is off the table. Option B, with a culvert across theproperty, would also have negative impacts to the soil and would be toxic tosustainable agriculture. Her organization is in favor of Option A. •Alpine Condo resident. She and her neighbors did have a big clog at their propertyduring the 2013 flood, and a lot of crawl space was impacted. She therefore has aproperty interest, but she would like to think about the problem more systemicallythan she currently has the information to do. If we could intervene sooner, maybemitigation would be better. Who would the city have to collaborate with on thereaches higher in the watershed, outside City limits? What happens to NorthBoulder park? She is willing to consider intervention there that helps what goes onfurther downstream. Willing to sacrifice if it makes things better for the wholecommunity. •Speaking as someone who has grown up in the Twomile creek drainage andcontinues to live there. Not trying to push one alternative over another but doesthink that we need a much clearer process outlined for how options are chosen oreliminated. Thinks street conveyances are viable but does not see them on the mapof options tonight. Were these eliminated? Please make a very clear process forevaluation of alternatives and their elimination. Because a large portion of thedrainage is in the county, it would be inappropriate for the City to not considerCounty features and issues, such as Pinebrook Reservoir, when planning mitigation. •Lives on Jonquil place. Has paid for a number of flood studies and LOMAs for hisproperty. For the most part, the 100-year flood stayed within the ditch in thestudies. It does not stay within the ditch anymore. He did not receive notification ofthe meeting or the open house. Neighbors let each other know it was happening.There is a 20-foot easement that runs along and maintains Twomile creek ineveryone’s back yards. Years ago, crews would come down the creek every year andclear the channel. That ended in 1992. City staff told them that equipment used toclear the creek had been sold, and that the obligation would be on the propertyowners going forward. Property owners have been doing this for 20 years. If theCity is concerned about safety, why are they no longer maintaining the creek? Urgesthe city to perform maintenance and maybe enlarge the culverts. •Lives on Iris, in the elbow of the creek. Has lived there for 32 years. Has never hadany problems, because right behind his house is a berm. During 2013 floods, nowater came in his yard from that direction. But he did get water from overflowupstream, which came in as sheet wash, flooding his basement and causing $65,000worth of damage. Agrees with Mr. Bundy regarding lack of maintenance of the creek.Culvert at Broadway is always filled with junk at the overflow. Because there is aneasement on both sides of the creek, building a small berm along this could be aninexpensive way to mitigate issues in this area. While much of the conversation isaround the 100-year flood, the 2013 event was more than that. We should preparefor larger floods. Proponent of open channel with berms and regular maintenance.Upstream area outside of City limits should be a major priority. The $170 million tospend over the next 100 years, seems like a trifle amount to spend on the effort. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 15 Attachment A There should be more money available. Foothill Elementary is downhill from my property, but the floodplain map goes around the school. There should be consideration for areas that do flood. •15th street, north of Elder. Is a hydrologist who has lived in the area for about 20years. “Me too” on road conveyance. There is too little consideration of these optionsin the plan as presented. Where we see it on Iris is a great idea, but there are moreopportunities for this. It is inexpensive. City already owns the land. Resists clogging.Allows for dispersed movement of water. Improve safety by preventing clogging of asingle channel. Many options for the flow mean less flooding overall. Look at it againand look at it harder. •17th Street. Open ditch under the power lines would be hugely invasive to herproperty. 100-year plan would be huge cut through property. In favor of usingstreets as conveyance. How about offering flood insurance to the people in theseconveyances? Private insurance does not cover well. Notify all people in these areasspecifically for their feedback as they are the ones most impacted. Why can’t wework with the County on upstream reaches? Take a vote in this room and see howwe feel about these options. •Lives on Juniper. Concerned that notices did not get out to enough people. Thereneeds to be a second opportunity for public input, as this first provided only limitedinformation. There is a lot of interest and much depends on it. There is a lack ofclarity. He cannot get a consistent definition of 100 and 500-year flood plains andplans from city staff at the open house. What is the correlation between a rainfallevent and the floodplain? Is there a discussion about defending our utilities in aflood event through mitigation? Defending properties is one thing, but should we bealso protecting important utilities so we’re not without water, power, etc. duringthese situations. Alternate routes should be looked at in the grey areas. Seems likesomething needs to be looked at there, for implementation now. Concerned thatwidened areas through private properties might become public areas. This is notclear in the plans. Second John Gerstle and Craig Bundy. •Loraine Court further down Twomile. Property has been in the family a long time.Further down the Twomile, (closer to the confluence) there were floodedcrawlspaces. For her, digging a 100-year channel through the property to mitigatethe flooded crawlspace does not jibe. What would the long-term effects of that be?Old trees might be removed. Power line that goes through people’s property alongFloral should be considered in plan. •Edgewood Drive. Supporting all those who talked about maintaining what we haveso that it works most efficiently. When he walks down the goose creek path, thereare concrete culverts with gates that can be closed. Ever since the 2013 floods, thereare always several inches of sediment. If mitigation infrastructure is not maintained,it will not work. There’s no way to get in the culvert to clean them unless they use abig pump truck. Drains just don’t work anymore. Water backs up into own property.After an event, there needs to be easy access to clean it out. This should beconsidered during construction. Inexpensive, easy access maintenance. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 16 Attachment A Upper Goose Creek Informal Neighborhood Meeting Date: 03.23.2018 Location: 2242 Edgewood Number of Attendees: 8 City staff present: Katie Knapp, Christin Shepherd, and Laurel Olsen-Horen Meeting Purpose: Residents along Edgewood Drive reached out to city staff to invite us into their neighborhood to observe the current state of Goose Creek south of Edgewood Drive and discuss different flood mitigation alternatives under consideration. Staff also walked the creek area with the Edgewood residents who described the different wildlife and activities they see along the creek. Summary of Comments: Current uses of Goose Creek include, but are not limited to: •Wildlife sanctuary for bears, foxes, coyotes, deer, beaver, racoon, water fowl, heron,owls and other birds of prey, etc.; •Outdoor education for the nearby Unity Church School; and, •Wooded and grassy oasis in the heart of an otherwise urbanized neighborhoodThe attendees also shared with staff some of their concerns should the area be impacted by any flood mitigation project. These included: •Loss of wildlife habitat. •“engineered channel” – residents are not in favor of a concrete channel and preferthe natural look of the current waterway. •Loss of privacy if any of the existing trees (larger ones) were removed. •Residents are not in favor of any public access trail or road. •Should any of the large trees need to be removed, residents do not want femalecottonwoods replanted. •Residents are not in favor of any new diversions of storm water into the channelfrom other problem areas. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 17 Attachment A City staff discussed additional observations and concerns about the existing creek channel with the neighbors: •The south bank of the channel is very steep and eroded in some areas. The erosionof the embankment could be contributing to the sediment found in the creekdownstream. •Existing fences along the north bank of the creek may be in jeopardy from continuederosion. •There is a lot of woody debris piled along the north side of the creek which couldcause a potential hazard to the flows in the creek. •Access for creek maintenance is difficult or non-existent. •The existing piped storm drain system does not function as it should because theoutfall pipes that drain to the creek are filled with sediment and buried in somelocations. •There were several dead racoons in the creek. •There are people camping near the creek. •A bicycle bump track is being constructed along the north bank of the channel,although nobody was seen working on it during our site visit. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 18 Attachment A Twomile Canyon Creek Informal Neighborhood Meeting Date: 04.03.2018 Location: 6th & Kalmia Number of Attendees: 12+/- City staff present: Katie Knapp, Christin Shepherd, and Laurel Olsen-Horen Meeting Purpose: Residents within the Kalmia/Juniper neighborhood area organized a walking meeting with city staff to discuss the flood mitigation study and the different mitigation alternatives under consideration. Attendees participated in a neighborhood walk that began at 6th and Kalmia and included several sections of Twomile Canyon Creek between Linden and Broadway. Summary of Comments: Meeting participants shared with staff concerns with some of the flood mitigation alternatives under consideration and the current state of the creek. These included: •Widening the existing creek channel would require significant impacts to privateproperty. •The existing creek channel is not being properly maintained. •Undersized culverts need to be replaced. •Some property owners do not want to grant easements to the city for floodmitigation. Upper Goose Creek Ideal Market and Community Plaza Meeting Date: 02.05.2019 Location: Brenton Building City staff present: Katie Knapp, Jean Gatza, and Laurel Olsen-Horen 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 19 Attachment A Ideal and Community Plaza representatives present: David Carter, Henry Beer, and Steve Leblang* (*Steve has been Planning’s primary contact for this group) Meeting Purpose: City staff met with three of the nine property owners of the Ideal Market and Community Plaza buildings to update them on the city’s process for the area plan with a focus on land use and flood mitigation. Summary of Comments: The plaza representatives would like to ensure uncertainty in the development of a future area plan is finessed as much as possible. They also shared their observations of perception with regards to the flood mitigation detention option in North Boulder Park is misunderstood by many in the community. It is believed the detention is thought to have a result of a constant lake rather than a temporary storage facility of stormwater during weather events where the park would not be in use anyway. Additional comments included: •They have contracted with Danica Powell to help understand redevelopment issues •The area east of Broadway would not favor an open channel •Future land use opportunities for the buildings could possibly include residentialand/or senior living facilities •BC2 Zone – be mindful of the unintended consequences of this zoning (i.e. businesstenant turnover) •Recommended staff provide the community with renderings of the park to helpreduce the misunderstanding of the city’s intended purpose of stormwaterdetention •Suggested the city look into the landscape architect works of Jim Burnett (Houston,TX) with regards to creating a more “amenity” feeling of the park to the surroundingneighborhood (i.e. Klyde Warren Park [Dallas, TX], Playa Vista Park [L.A., CA], andSouthern Gateway Deck Park [Dallas, TX] •Interest in creating a parking district – plaza is in dire need for employee parking 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 20 Attachment A TO:City of Boulder Public Works, Katie Knapp, P.E., CFM FROM:ICON Engineering, Brian LeDoux, PE, CFM DATE:February 22nd, 2019 RE: Upper Goose Creek and Twomile Canyon Creek – Flood Mitigation Plan – Alternative Selection Memorandum Background and Purpose ICON Engineering Inc. (ICON) has been placed under contract by the City of Boulder to develop, select, analyze, and recommend flood mitigation alternatives for Upper Goose Creek and Twomile Canyon Creek. This effort follows the previously completed Letter of Map Revision (LOMR) for Upper Goose Creek and Twomile Canyon Creek (Case No. 16-08-0026P) that became effective on August 18, 2016. The LOMR provided updated hydrologic and hydraulic analysis for flooding from Upper Goose Creek and Twomile Canyon Creek. This memorandum summarizes the initial public process and alternative development that was completed in 2017 and 2018 and describes an additional screening process for the previously developed alternatives as part of this alternative selection effort. The remaining alternatives as recommended by this memorandum, will ultimately undergo further evaluation including a scoring process, benefit/cost analysis, and additional public coordination. Following these efforts, a recommended approach to flood mitigation will be developed. The recommended approach will then undergo conceptual design and inclusion into the final Upper Goose Creek and Twomile Canyon Creek Flood Mitigation Plan. Public Process A city wide flood planning and mitigation open house was held on April 12 th, 2017. This open house served as the official “kick-off” for the Upper Goose Creek and Twomile Canyon Creek Flood Mitigation Plan project. This open house prov ided the public with an opportunity to discuss flooding problem areas and to provide input on flood mitigation approaches. On July 20th, 2017, a public workshop was held at the North Boulder Recreation Center. This public workshop covered a spectrum of potential mitigation strategies to gain initial input on the preferred flood mitigation strategies and to rank the flood mitigation priorities. Of the attendees, 22 people provided written input on both table top maps 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 21 Attachment B and in a written questionnaire. The data from the public input was compiled by the City of Boulder and used to help refine flood mitigation alternatives along Upper Goose Creek and Twomile Canyon Creek. The public attendees ranked the flood and greenways objectives as follows: The public attendees also provided opinions on different mitigation strategies. The ratings for each mitigation strategies are illustrated by the graphs below. 0 2 4 6 8 10 12 14 16 18 High Priority Mid priority Low Priority 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 22 Attachment B No Action: Detention and/or sediment control facilities: Open channel and culvert improvements: 0 2 4 6 8 10 12 14 Strongly Dislike Dislike Neutral Like Strongly Like 0 2 4 6 8 10 12 14 Strongly Dislike Dislike Neutral Like Strongly Like 0 2 4 6 8 10 12 14 Strongly Dislike Dislike Neutral Like Strongly Like 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 23 Attachment B Storm drain system: Roadway Conveyance: Feedback Incorporation Following the July 20th, 2017 public workshop, the mitigation strategies were refined based on the public feedback and city staff input. This refinement generally focused on an open channel mitigation strategy where applicable, which was also the public’s highest ranked strategy. Less popular than open channels - detention, storm drains, and roadway conveyance were all three generally favored on the same level by the public. For areas that would be more challenging to incorporate an open channel, storm drains and detention pond solutions were also incorporated into project alternatives. These two options were also generally supported by the public responses for the watershed. Roadway conveyance was not included west of Broadway due to the existence of an open channel west of Broadway, and the concern that roadway conveyance could potentially bring additional flood risk to areas that currently have low 0 2 4 6 8 10 12 14 Strongly Dislike Dislike Neutral Like Strongly Like 0 2 4 6 8 10 12 14 Strongly Dislike Dislike Neutral Like Strongly Like 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 24 Attachment B risk. The alternatives developed following the July 20th, 2017 public workshop are included in Appendix A. These alternatives were then presented at a public open house and to the Water Resources Advisory Board (WRAB) meeting on March 19th, 2018. Following this meeting, revisions to the alternatives were completed based on further public and WRAB input, which included the following dominant comments: Many comments were made with respect to the potential use of the Long’s Garden area as a potential detention site or for an open channel. Comments related to the historic use of the site and the incompatibility of garden soils with stormwater applications. Many comments were made regarding the potential removal of the Alpine Condominiums for mitigation. Comments related to the importance of this housing stock and the ramifications if current residents were to be displaced. Comments also included a desire to look at moving the detention from the Long’s Garden area upstream and into Boulder County and/or to the Boulder County complex at the north east corner of Broadway and Iris Avenue. Comments also included a desire to utilize roadway conveyance west o f Broadway as a way to reduce or eliminate the need to enlarge the existing Twomile Canyon Creek Channel. Unlike the initial workshop, public opinion was no longer in favor of an enlarged 100-Year open channel west of Broadway, rather maintenance of the existing channel was preferred. The feedback from the March 19th, 2018 public open house was gathered through an online survey. A total of 477 individual responses were logged by the survey, with 191 individuals completing the full survey. The survey asked responders to rank the flood and greenways objectives. The results of this ranking were very similar to the same ranking exercise completed at the July 20th, 2017 workshop (see graph on page 2). It should be noted that the life safety objective was inadvertently not included in the questionnaire. The survey also asked for opinions on the presented alternatives. The corresponding survey results are included as pie-charts on the applicable sheets located in Appendix A.Additional comment summary tables are included in Appendix A. The feedback from the online survey was taken into consideration and utilized in the initial screening process as discussed below. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 25 Attachment B Full results from this survey can be found on the project website at: https://bouldercolorado.gov/pages/skunk-creek-bluebell-canyon-creek-kings-gulch- upper-goose-and-twomile-flood-mitigation-studies Initial Alternative Screening Flood mitigation alternatives at the following areas have been adjusted based on initial screening that reviewed feasibility, public support, level of mitigation, and the greenways objectives. Long’s Garden Property along Twomile Canyon Creek Due to a lack of public support, all alternatives that would have the potential to impact the Long’s Garden area have been removed from consideration. Additional storm drain alternatives have now been developed east of Broadway in order to include a drainage route south of Iris Avenue. Alpine Condominiums Property along Upper Goose Creek Due to a lack of public support, all alternatives that would require removal of the condominium structures have been removed from consideration. Current alternatives consider an underground storm drain across the property. However, should the Alpine Condominium area undergo a significant redevelopment in the future, the option to daylight flood mitigation measures should be considered if other mitigation is not yet complete. 100-Year Open Channel Due to a lack of public support and the excessive cost, several reaches of 100- year channel conveyance have been removed where acquisition and removal of a large number of privately held residential structures would be required. Detention in Boulder County Detention alternatives within Boulder County and at the Boulder County complex near Iris and Broadway were reviewed and presented to Boulder County staff during a meeting on June 25th, 2018. As discussed, new flood water detention upstream of the City of Boulder limits would require approximately five new dam/detention facilities in order to provide storage for the 100-year event down to the capacity of the downstream drainageway. Due to steep topography in this area, all five dams would be expected to range in size from 3 to 19.3 acre-feet, with all five likely to fall under state jurisdictional high hazard status. In addition, 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 26 Attachment B impacts to private property, transportation and roadways, and viewscapes would be considerable. To date, a formal response from Boulder County regarding their assessment and thoughts behind these alternatives has not been received. However, based on land use impacts and high costs, new detention upstream of the City of Boulder limits was chosen to not be pursued further. The flood storage that exists within the Pine Brook Reservoir was revi ewed as a detention alternative. However, the discharge rates out of the service and emergency spillways at the elevations within the flood storage pool are relatively high resulting in a lack of peak flood discharge attenuation. Based on this lack of mitigation impact, detention within Pine Brook Reservoir was chosen to not be pursued further. The area along Twomile Canyon Creek just upstream of Linden Avenue and Spring Valley Drive is owned by the City of Boulder. The site does not provide for significant storage volume for a detention facility, but the location is ideal for a sediment capture facility. The sediment capture facility would function similar to the current sediment capture facility in this location, but would be expanded including a second embankment upstream of Spring Valley Drive. Detention in Boulder County Complex (NE corner of Iris & Broadway) The original detention concept for the Boulder County Complex at the north east corner of Iris Avenue and Broadway included detention options for both the ballfields on the east side of the property and where the current Boulder County offices are located. The project team discussed the likelihood of any redevelopment of the county offices and potential for vacating that portion of the parcel. This was found to be unlikely due to property values and therefore, detention on the County's building site itself was removed from consideration. Should the portion of the parcel that includes the County offices be redeveloped in the future, the option to include detention could be reconsidered if other mitigation measures are not yet complete. The ballfields on the east side of the property have been retained as an alternative for detention consideration. The detention alternative will reduce the footprint available for ballfields, but the area could still function as fields. The City is currently leading efforts to discuss this use and impacts with the management for Iris Field and local little league. Community Plaza and Ideal Market Commercial Area The City of Boulder met with representatives of the Community Plaza and Ideal Market commercial area to discuss major redevelopment efforts of the commercial area. Extent and timing of any redevelopment of the area is 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 27 Attachment B unknown at this time. Furthermore, the alternative of an open channel, while being a potential focus point of a redevelopment, would also likely reduce the developable footprint of the area. For this reason, the open channel alternatives between Broadway and 13th Street along Upper Goose Creek have been removed from consideration. Should the Community Plaza and Ideal Market commercial area redevelop in the future, the option to daylight flood mitigation could be reconsidered if other mitigation measures are not yet complete. Roadway Conveyance on Twomile Canyon Creek west of Broadway While a roadway conveyance mitigation approach west of Broadway had originally not been moved forward based on public input from the July 20 th, 2017 public workshop (open channel favored over roadway conveyance), this alternative has now been incorporated into the alternatives for further evaluation. This inclusion is based on comments received in the 2018 questionnaire which requested that roadway conveyance be investigated further in place of major changes to the existing Twomile Canyon Creek channel. Alternatives for Further Evaluation Following the public process, feedback incorporation, and initial screening, the alternatives for additional analysis for the Upper Goose Creek and Twomile Canyon Creek Flood Mitigation Plan are summarized in Table 1 (Twomile Canyon Creek) Table 2 (Upper Goose Creek), and Figures 1 through 11 below. 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 28 Attachment B Attachments: Table 1: Twomile Canyon Creek Alternatives Summary Table 2: Upper Goose Creek Alternatives Summary Figure 1: Reach Overview Figure 2: Twomile Canyon Creek Reach 1 Figure 3: Twomile Canyon Creek Reach 2 Figure 4: Twomile Canyon Creek Reach 3 Figure 5: Twomile Canyon Creek Reach 4 Figure 6: Upper Goose Creek Reach 1 Figure 7: Upper Goose Creek Reach 2 Figure 8: Upper Goose Creek Reach 3 Figure 9: Upper Goose Creek Reach 4 Figure 10: Upper Goose Creek Reach 5 Figure 11: Upper Goose Creek Reach 6 Appendices: Appendix A: WRAB Figures (from March 19th, 2018 meeting) Appendix B: Detention Alternatives Figure 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 29 Attachment B Upper Goose Creek and Twomile Canyon Creek – Flood Mitigation Plan – Alternative Selection Memorandum Table 1: Twomile Canyon Creek Alternatives for Further Evaluation Summary Reach Reach Description Alt Mitigation Measure Project Benefits (pro)Project Issues (con) Twomile-01 City Limits to Linden Avenue A 100-Year channel improvements; new Spring Valley Drive and Linden Avenue culverts • Reduces spill flow out of Twomile Canyon Creek • Reduces overtopping of roadways • May require removal of mature trees • Does not address sediment capture • Channel work requires drainage easements Twomile-01 City Limits to Linden Avenue B <100-Year channel improvements; new Spring Valley Drive and Linden Avenue culverts • Reduces spill flow out of Twomile Canyon Creek • Reduces overtopping of roadways • May require removal of mature trees • Does not address sediment capture • Channel work requires drainage easements • Does not contain 100-year event Twomile-01 City Limits to Linden Avenue C Enlarge existing sediment capture facility • Reduces sedimentation impact downstream • Existing City ownership of sediment capture facility footprint • Can be constructed independent of other improvements • Change in natural sediment transport • May require removal of mature trees • Embankment may impact viewscape • Impacts Open Space Mountain Parks land • No significant reduction in flood risk Twomile-02 Linden Avenue to Broadway A <100-Year channel improvements; new Kalmia Avenue, Juniper Avenue, and Broadway culverts; channel to Broadway and Iris • Reduces spill flow out of Twomile Canyon Creek • Reduces overtopping of roadways • Follows existing channel alignment • Opportunity for underpass at Broadway • Requires some structure acquisition • Requires extensive drainage easements • Requires Iris or 13th Street alternatives Twomile-02 Linden Avenue to Broadway B <100-Year channel improvements; new Kalmia Avenue, Juniper Avenue, and Broadway/Hawthorn Avenue culverts; channel to Broadway and Hawthorn • Reduces spill flow out of Twomile Canyon Creek • Reduces overtopping of roadways • More efficient connection to downstream channel • Opportunity for underpass at Broadway • Not as feasible for Broadway underpass • Requires some structure acquisition • Requires extensive drainage easements • Requires downstream improvements Twomile-02 Linden Avenue to Broadway C Roadway conveyance along Linden, Kalmia and/or Juniper to Broadway • Captures spill flow out of Twomile Canyon Creek • Utilizes existing roadway corridors • Conveys flood risk into areas without previous risk • Possible utility conflicts • Increases surface flow within Broadway • Life safety and emergency access concerns with street flooding Twomile-03 Broadway to 19th Street A 100-Year channel improvements; new 13th Street, 14th Street culverts, culvert from 16th Street through Farmer's Ditch; Iris Avenue Roadway Improvements for surface flow • Conveys flood flows to Elmer's Twomile • Less property acquisition than southern alignments • Major impact to Iris Avenue Twomile-03 Broadway to 19th Street B <100-Year channel improvements; new 13th Street, 14th Street culverts, culvert from 16th Street through Farmer's Ditch; Iris Avenue Roadway Improvements for surface flow • Conveys flood flows to Elmer's Twomile • Less property acquisition than southern alignments • Major impact to Iris Avenue • Does not contain 100-year event Twomile-03 Broadway to 19th Street C 100-Year storm drain outfall system • Utilizes existing City Right-of-Way • Provides for local drainage along 13th Street • Requires downstream improvements • Does not impact Iris Avenue • Susceptible to clogging Twomile-03 Broadway to 19th Street D <100-Year storm drain outfall system • Utilizes existing City Right-of-Way • Provides for local drainage along 13th Street • Requires downstream improvements • Does not impact Iris Avenue • Susceptible to clogging Twomile-03 Broadway to 19th Street E Detention facility within the Boulder County Complex at Broadway and Iris (ballfields only) • Reduces downstream discharges • Utilizes publicly owned property • Retain or re-purpose park uses • Impact to existing park uses • May require removal of mature trees • Embankment may impact viewscape Twomile-04 19th Street to Elmer's Twomile Creek A Iris Avenue Roadway Improvements for surface flow • Conveys flood flows to Elmer's Twomile • Major impact to Iris Avenue • Life safety and emergency access concerns with street flooding Twomile-04 19th Street to Upper Goose Creek B <100-Year Iris Avenue Roadway Improvements for surface flow • Conveys flood flows to Elmer's Twomile • Major impact to Iris Avenue • Life safety and emergency access concerns with street flooding • Does not contain 100-year event Twomile-04 19th Street to Upper Goose Creek C 100-Year storm drain outfall system • Utilizes the 19th Street Right-of-Way • Does not require open channel construction • Does not remove Twomile Canyon Creek discharge from Goose Creek between 19th and historical confluence • Susceptible to clogging Twomile-04 19th Street to Upper Goose Creek D <100-Year storm drain outfall system • Utilizes the 19th Street Right-of-Way • Does not require open channel construction • Does not remove Twomile Canyon Creek discharge from Goose Creek between 19th and historical confluence • Susceptible to clogging • Does not contain 100-year event Twomile-04 19th Street to Upper Goose Creek E 100-Year channel improvements; new 21st Street and Edgewood Drive culverts • Provides open channel connectivity to Goose Creek • May reduce groundwater issues in local area • Requires significant land acquisition • May require removal of mature trees • Places channel in backyards Twomile-04 19th Street to Upper Goose Creek F <100-Year channel improvements; new 21st Street and Edgewood Drive culverts • Provides open channel connectivity to Goose Creek • May reduce groundwater issues in local area • Requires significant land acquisition • May require removal of mature trees • Places channel in backyards 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 30 Attachment B Upper Goose Creek and Twomile Canyon Creek – Flood Mitigation Plan – Alternative Selection Memorandum Table 2: Upper Goose Creek Alternatives for Further Evaluation Summary Reach Reach Description Alt Mitigation Measure Project Benefits (pro)Project Issues (con) Goose-01 North Boulder Park to 9th Street A Detention facility within North Boulder Park; new 9th Street culvert •Reduces downstream discharges •Reduces overtopping of 9th Street •Retain or re-purpose park uses •Impact to existing park uses •May require removal of mature trees •Embankment may impact viewscape Goose-01 North Boulder Park to 9th Street B No detention; Roadway collection to deliver flows to Alpine-Balsam site •Provides flooding protection for the Alpine-Balsam site •Does not impact North Boulder Park •Reduces flooding on Balsam Avenue •No reduction in discharges •Concentrates discharges onto the Alpine-Balsam site •May require roadway reconfiguration Goose-02 9th Street to Broadway A 100-Year open channel through Alpine-Balsam site •Provides flooding protection for the Alpine-Balsam site •Reduces flooding on Balsam Street •Aligns with the Alpine-Balsam Master Plan • Provides open channel habitat / green infrastructure •Final configuration of Alpine-Balsam site unknown • Requires more room than storm drain system Goose-02 9th Street to Broadway B <100-Year open channel through Alpine-Balsam site •Provides flooding protection for the Alpine-Balsam site •Reduces flooding on Balsam Street •Aligns with the Alpine-Balsam Master Plan • Provides open channel habitat / green infrastructure •Final configuration of Alpine-Balsam site unknown • Requires more room than storm drain system • Does not contain 100-year event Goose-02 9th Street to Broadway C 100-Year storm drain through Alpine-Balsam site (detained flow) •Provides flooding protection for the Alpine-Balsam site •Reduces flooding on Balsam Street •Aligns with the Alpine-Balsam Master Plan •Final configuration of Alpine-Balsam site unknown • Susceptible to clogging Goose-02 9th Street to Broadway D 100-Year storm drain through Alpine-Balsam site (full flow)•Provides flooding protection for the Alpine-Balsam site •Reduces flooding on Balsam Street •Final configuration of Alpine-Balsam site unknown • Susceptible to clogging Goose-02 9th Street to Broadway E <100-Year storm drain through Alpine-Balsam site (full flow)•Provides flooding protection for the Alpine-Balsam site •Reduces flooding on Balsam Street •Final configuration of Alpine-Balsam site unknown • Susceptible to clogging • Does not contain 100-year event Goose-03 Broadway to 13th Street A 100-Year storm drain system •Utilizes existing Right-of-Way •Does not require property acquisition •Provides local drainage along Broadway and Alpine Avenue •Construction disruption to busy business corridor • Susceptible to clogging Goose-03 Broadway to 13th Street B <100-Year storm drain system •Utilizes existing Right-of-Way •Does not require property acquisition •Provides local drainage along Broadway and Alpine Avenue •Construction disruption to busy business corridor • Susceptible to clogging Goose-04 13th Street to 17th Street A 100-Year open channel •Provides additional open channel habitat •Enhances existing drainage path •Green infrastructure •Requires extensive drainage easement acquisition •Disruptive to residential back-yards Goose-04 13th Street to 17th Street B <100-Year open channel •Provides additional open channel habitat •Enhances existing drainage path •Green infrastructure •Requires extensive drainage easement acquisition •Disruptive to residential back-yards • Does not contain 100-year event Goose-04 13th Street to 17th Street C 100-Year storm drain system •Utilizes existing Right-of-Way •Does not require property acquisition •Provides local drainage along Alpine Avenue •Does not address overland flow in existing flow path • Susceptible to clogging Goose-04 13th Street to 17th Street D <100-Year storm drain system •Utilizes existing Right-of-Way •Does not require property acquisition •Provides local drainage along Alpine Avenue •Does not address overland flow in existing flow path • Susceptible to clogging • Does not contain 100-year event Goose-05 17th Street to 20th Street A 100-Year storm drain system from Alpine/17th through 20th •Utilizes some existing Right-of-Way •Does not require Alpine Condos removal •Provides local drainage adjacent to Alpine Condos •Requires drainage easement acquisition •Disruptive to Alpine Condo property (construction) • Susceptible to clogging Goose-05 17th Street to 20th Street B <100-Year storm drain system from Alpine/17th through 19th •Utilizes some existing Right-of-Way •Does not require Alpine Condos removal •Provides local drainage adjacent to Alpine Condos •Requires drainage easement acquisition •Disruptive to Alpine Condo property (construction) • Susceptible to clogging • Does not contain 100-year event Goose-06 20th Street to 24th Street A 100-Year Open channel •Provides additional open channel habitat •Enhances existing drainage path •Green infrastructure • Requires extensive drainage easement acquisition • Disruptive to residential back-yards • Requires tall retaining walls on south bank Goose-06 20th Street to 24th Street B Open channel (sizing per previous study recommending a "5-Year" improvement; exceeds 5-Year with detained flow and/or Twomile improvements) •Provides additional open channel habitat •Enhances existing drainage path •Green infrastructure • Requires extensive drainage easement acquisition • Disruptive to residential back-yards • Requires tall retaining walls on south bank • Does not contain 100-year event 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 31 Attachment B Twomile Canyon CreekReach 1 Twomile Canyon CreekReach 2 Twomile Canyon CreekReach 3 Twomile Canyon CreekReach 4 Upper Goose CreekReach 1 Upper Goose CreekReach 2 Upper Goose CreekReach 3 Upper Goose CreekReach 4 Upper Goose CreekReach 5 Upper Goose CreekReach 6 Twomile Canyon CreekReach 4 FARMERS DITCHSILVER LAKE DITCH28th St4th St19th StBroadway9th St6th StKalmia Av Alpine Av5th StLinden Av Folsom St7th St3rd StCedar Av11th St17th StNorth St Bluff St10th St13th St23rd St26th StElder Av 18th StGrape Av Iris Av Hawthorn Av 8th StJuniper Av Mapleton Av Floral Dr Edgewood Dr Glenwood Dr Meadow Av 24th St21st St25th StPine St20th StValmont Rd15th StArnett St14th StCloverleaf DrLi n d e n D r Mesa Dr 27th S t Balsam Av22nd StJefferson StCatalpa WyI r i s C t Fremont AvAlpine Dr Sunset Bv Lombardy Dr Balsam Dr Hermosa Dr Vista Dr16th StPanorama Av Forest Av Kingwood Pl Valley View Dr Dellwood Av Iris Walk CtWashington StC h o l l a C t Jordan PlAspen CtLittleleaf LnKirkwood PlMoss Rock Pl Arthur CtEvergreen Av Tyler RdGarland LnRoundtree CtHawthorn Pl Hazelwood CtGlenwood CtJuniper CtNottingham CtCopper StJonathan Pl Jasper Ct Sherwood Cr Del Rosa Ct Keystone Ct Jackpine CtChestnut PlLinden CrArnett St20t h S t 20th StHawthorn Av 15th St15th StGlenwood Dr9th St14th StAlpine Av Dellwood Av 13th StGrape Av17th StKalmia Av 16th StForest Av Cedar Av Iris Av 8th St24th S t Grape Av9th St21st StBalsam Av Juniper Av North St Bluff St Kalmia Av Meadow Av Balsam Av 13th St23rd S t 25th St26th S t Hawthorn Av14th StLinden Av 16th StBOULDER WHITE ROCK DITCH±700 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 1: Reach Overview Legend Reach Limits Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year 500 Year 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 32 Attachment B Twomile Canyon CreekReach 1 Twomile Canyon CreekReach 2 Twomile Canyon CreekReach 3 Twomile Canyon CreekReach 4 Upper Goose CreekReach 1 Upper Goose CreekReach 2 Upper Goose CreekReach 3 Upper Goose CreekReach 4 Upper Goose CreekReach 5 Upper Goose CreekReach 6 Twomile Canyon CreekReach 4 FARMERS DITCHSILVER LAKE DITCH28th St4th St19th StBroadway9th St6th StKalmia Av Alpine Av5th StLinden Av Folsom St7th St3rd StCedar Av11th St17th StNorth St Bluff St10th St13th St23rd St26th StElder Av 18th StGrape Av Iris Av Hawthorn Av 8th StJuniper Av Mapleton Av Floral D r Edgewood Dr Glenwood Dr Meadow Av 24th St21st St25th StPine St20th StValmont Rd15th StArnett St14th StCloverleaf DrLi n d e n D r Mesa Dr 27th S t Balsam Av22nd StJefferson StCatalpa WyI r i s C t Fremont AvAlpine Dr Sunset Bv Lombardy Dr Balsam Dr Hermosa Dr Vista D r 16th StPanorama Av Forest Av Nichol l S t Kingwood Pl Joslyn Pl Kincaid Pl Valley View Dr Dellwood Av Iris Walk CtWashington StC h o l l a C t Aspen CtLittleleaf LnKirkwood PlMoss Rock Pl Arthur CtEvergre e n A v Tyler RdGarland LnRoundtree CtHawthorn Pl Hazelwood CtGlenwood CtJuniper CtNottingham CtCopper StJasper Ct Sherwood Cr 16th Cr Del Rosa Ct Jimson Ct Keystone Ct Fern PlJackpine CtChestnut PlLinden CrArnett St15th StForest Av 9th St20th St15th St17th St16th St14th St14th StGlenwood Dr Dellwood Av Alpine Av Evergreen Av Kalmia Av Cedar Av Kalmia Av 13th StIris Av 8th St21st StGrape Av9th StBalsam Av Juniper Av Meadow Av North St Bluff St 26th S t Hawthorn Av25th St24th S t22nd St13th St23rd S t 20t h S tGrape AvLinden Av Balsam Av 16th StBOULDER WHITE ROCK DITCH±700 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 1: Reach Overview Legend Reach Limits Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year 500 Year 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 33 Attachment B Twomile Canyon CreekReach 1 Twomile Canyon CreekReach 2 Alternative C(sediment capture) Alternative A(100-year channel) Alternative B(<100-year channel) Alternative A and B(culvert crossings) Alternative A and B(culvert crossings) Alternative C(sediment capture)SILVER LAKE DITCHLinden Dr Linden Av Wonderland Hill AvSpring Valley DrWil d P l um C t Lakebriar DrLin d e n P a r k D r Spr i n g V a l l e y D r ±100 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 2: Twomile Canyon Creek - Reach 1 Legend Reach Limits Alternative A/B (culverts) Alternative B (channel) Alternative A (channel) Alternative C (sediment capture) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Twomile Canyon Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 34 Attachment B Alternative A and B(culvert crossings) Twomile Canyon CreekReach 2 Twomile Canyon CreekReach 1 Twomile Canyon CreekReach 3 Alternative A & B(<100-year channel) Alternative A(<100-year channel) Alternative B(<100-year channel) Alternative A & B(culvert crossing) Alternative A & B(culvert crossing) Alternative A(culvert crossing with potential Broadway underpass) Alternative B(culvert crossing with potentialBroadwayunderpass) Alternative C(roadway conveyance) Alternative C(roadway conveyance) Alternative C(roadway conveyance) Alternative C(roadway conveyance) Twomile Canyon CreekReach 2 SILVER LAKE DITCHLinden Av Kalmia Av Iris Av4th StHawthorn Av Juniper Av Broadway13th St14th St9th StAspen CtBuckeye CtKingwood Pl Jonquil PlLinden Dr Linden CrJaponica WyJasmine Cr Hawthorn Av9th StIris Av 9th St±250 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 3: Twomile Canyon Creek - Reach 2 Legend Reach Limits Alternative A/B (culverts) Alternative A (channel) Alternative B (channel) Alternative B (culvert) Alternative C City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Twomile Canyon Creek Flowpath Ditch / Canal City of Boulder City Limits 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 35 Attachment B Twomile Canyon Creek Reach 3 Alternative A(100-year channel) Alternative C(roadway conveyance) Reach 2 Twomile Canyon Creek Reach 3 Twomile Canyon Creek Reach 4 Twomile Canyon Creek Reach 4 Twomile Canyon CreekReach 3 Twomile Canyon Creek Alternative A & B(culvert crossings) Alternative E(detention facility) Alternative A & B(culvert crossings)Alternative B(<100-year channel) Alternative C(100-year storm drain) Alternative D(<100-year storm drain) Alternative C/D (connection for Reach 2Alternative B alignment) Long's Garden AreaNo alternatives proposed Boulder CountyComplex FARMERS DITCHIris Av 19th StBroadwayHawthorn Av15th StIri s C t 13th St14th St16th St11th St17th StGrape Av Garland LnHawthorn Pl Juniper Av Vista Dr Joslyn Pl 16th Cr Del Rosa Ct Jimson Ct Joslyn CtGlenwood DrHawthorne HlGrape Av16th StGrape Av Hawthorn Av Vista D r ±200 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 4: Twomile Canyon Creek - Reach 3 Legend Reach Limits Alternative A/B (culverts) Alternative A (channel) Alternative B (channel) Alternative C (storm drain) Alternative D (storm drain) Alternative E (detention) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Twomile Canyon Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 36 Attachment B UpperGoose Creek Upper Goose Creek Twomile Canyon CreekReach 4 Reach 3TwomileCanyon CreekReach 4TwomileCanyon Creek Reach 3 Twomile Canyon Creek Alternative E(detention facility) Alternative A & B(roadway conveyance) Alternative C(100-year storm drain) Alternative D(<100-year storm drain) Elmer's TwomileCreek Alternative C & D(storm drain) Alternative E & F(culvert crossing) Alternative E & F(channel) Alternative C & D(storm drain - this part not used with Alternative E/F) Storm drain connection for Alternatives E & F Reach 3 Twomile Canyon Creek Twomile Canyon CreekReach 4 BOULDER WHITE ROCK DITCHFARMERS DITCHIris Av 19th St28th St30th StFolsom St17th St23rd St18th StGrape Av 29th StValmont Rd Floral Dr Edgewood Dr Glenwood Dr 24th St21st St25th St20th StElder Av15th StArnett StCedar Av16th StBalsam Av22nd StBluff StFremont AvHermosa Dr Balsam Dr Vista Dr Panorama Av Forest Av Hawthorn Av Nicholl StDellwood Av Iris Walk CtLittleleaf LnEvergreen A v Garland Ln Thornbird Pl Glenwood CtIris CtLorrain e C t Shady Hollow WShady Hollow EEagle Wy Arnett Pl Forest Av Glenwood DrArnett St25th StIris Av Glenwood Dr Balsam Av 20t h S t 15th StGrape Av 22nd St±400 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 5: Twomile Canyon Creek - Reach 4 Legend Reach Limits Alternative B (roadway) Alternative A (roadway) Alternative D (storm drain) Alternative C (storm drain) Alternative E/F (culvert) Alternative F (channel) Alternative E (channel) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Twomile Canyon Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 37 Attachment B Upper Goose CreekReach 1 Upper Goose CreekReach 2 Alternative A(detention) Alternative B(storm drain / roadway collection) Alternative A(connection tostorm drain system) North Boulder Park FARMERS DITCHAlpine Av9th St7th StBalsam Av11th St10th St8th StCedar Av Cedar Av ±100 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 6: Upper Goose Creek - Reach 1 Legend Reach Limits Alternative A (detention) Alternative B (storm drain) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Upper Goose Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 38 Attachment B Upper Goose CreekReach 1 Upper Goose CreekReach 2 Alternative A(100-year channel) Upper Goose CreekReach 2 Upper Goose CreekReach 3Alternative B(<100-year channel) Alternative C(100-year storm drain)Alternative D(<100-year storm drain) Alpine-Balsamredevelopment areaFARMERS DITCHAlpine Av 9th StBalsam Av Broadway11th St10th St±100 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 7: Upper Goose Creek - Reach 2 endLeg Reach Limits Alternative A (channel) Alternative B (channel) Alternative C (storm drain) Alternative D (storm drain) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Upper Goose Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 39 Attachment B Upper Goose CreekReach 2 Upper Goose CreekReach 3 Alternative A(100-year storm drain) Upper Goose CreekReach 3 Upper Goose CreekReach 4 Alternative B(<100-year storm drain) Ideal MarketCommercial Area Community PlazaCommercial Area North St Alpine Av Balsam Av 13th StBroadway14th St11th St±100 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 8: Upper Goose Creek - Reach 3 Legend Reach Limits Alternative A (storm drain) Alternative B (storm drain) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Upper Goose Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 40 Attachment B UpperGoose CreekReach 2 Upper Goose CreekReach 3 Alternative B(<100-year storm drain) Upper Goose CreekReach 4 Upper Goose CreekReach 4 Upper Goose CreekReach 5 Alternative A(100-year storm drain) Alternative C(100-year storm drain)Alternative D(<100-year storm drain) Alpine Av North St Balsam Av 13th St14th St15th St17th StSunset Bv Broadway16th St18th St±150 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 9: Upper Goose Creek - Reach 4 Legend Reach Limits Alternative A (channel) Alternative B (channel) Alternative C (storm drain) Alternative D (storm drain) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Upper Goose Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 41 Attachment B UpperGoose Creek Reach 6 Upper Goose CreekReach 4 Upper Goose CreekReach 5 Alternative A(100-year storm drain) Upper Goose CreekReach 5 Upper Goose CreekReach 6 Alternative B(<100-year storm drain) Alpine Condominiums Cedar Av 15th St17th St19th StBalsam Av Alpine Av Mesa Dr North St Edgewood Dr20t h S t16th St18th StAlpine Dr Balsam Dr Bluff St Tyler Rd 2 1 s t S t Sunset Bv Alpine Av 20 t h S t 1 9 t h S t ±150 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 10: Upper Goose Creek - Reach 5 Legend Reach Limits Alternative A (storm drain) Alternative B (storm drain) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Upper Goose Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 42 Attachment B Upper Goose CreekReach 5 Upper Goose CreekReach 6 Alternative A(100-year channel) Alpine Condominiums Alternative A(<100-year channel) Edgewood Dr Alpine Av Balsam Av20th StAlpine Dr21st StBalsam Dr Panorama AvNicholl St23rd StTyler Rd Bluff St Lorraine Ct 22nd St25th St24th St2 3 r d S t ±150 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure 11: Upper Goose Creek - Reach 6 Legend Reach Limits Alternative A (channel) Alternative B (channel) Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Upper Goose Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 43 Attachment B Appendix A: WRAB Figures (from March 19th, 2018 meeting) 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 44 Attachment B !(!( !( !( !(!( Linden Av Balsam Av Neher Ln Valmont Rd Twomile Canyon & Upper Goose Creek Legend !(Flow Direction Decision 100-yr Channel <100-yr Channel Culvert Detention Roadway Sediment Basin Storm Main City 100-Year Floodplain City Limits 0 0.50.25 Miles± Reach 1 Reach 2 Reach 3 Reach 4 Reach 1 Reach 2 Reach 3 Reach 4 Reach 5 Reach 6 Proposed Alternatives 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 45 Attachment B Twomile Canyon Creek Reach 1: Wild Plum Ct to Linden Av Information about the Alternatives Alt Description Cost Benefits Issues A 100-year open channel improvements; new culverts at Spring Valley Dr. and Linden Av $2.5M Eliminates 100-year spill flows Eliminates overtopping of roadways during 100-year storm May require mature tree removal Does not address sediment capture Extensive property impacts Requires downstream improvements a <100-year open channel (smaller version of Alt A) $1.6M Similar to Alt A Reduced cost and property impacts Similar to Alt A Does not contain 100-year flood B Enlarge existing sediment capture facility $1.0M Reduces sedimentation impact downstream Existing City ownership of facility footprint Can be constructed independent of other improvements Change in natural sediment transport May require mature tree removal Embankment may impact viewscape Impacts Open Space Mountain Parks land No significant reduction in flood risk The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Existing Sediment Capture Facility Example Culvert Improvement Existing Culverts at Spring Valley Rd. Sediment and Debris from 2013 Flood A a B No Action 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 46 Attachment B Twomile Canyon Creek Reach 2: Linden Av to Broadway Information about the Alternatives Alt Description Cost Benefits Issues A 100-year open channel improvements; new culverts at Kalmia Av, Juniper Av, and Broadway; channel to Broadway and Iris $27M Reduces spill flows Reduces overtopping of roadways Follows existing channel alignment Opportunity for underpass at Broadway Requires structure acquisition Extensive property impacts Requires Iris or 13th St alternatives Requires downstream improvements a <100-year open channel (smaller version of Alt A) $10M Similar to Alt A Reduced cost and property impacts Similar to Alt A Does not contain 100-year flood B 100-year open channel improvements; new culverts at Kalmia Av, Juniper Av, Broadway; channel to Broadway and Hawthorn $32M Reduces spill flow Reduces overtopping of roadways More efficient connection to downstream channel Opportunity for underpass at Broadway Not as feasible for Broadway underpass Requires structure acquisition Extensive property impacts Requires downstream improvements b <100-year open channel (smaller version of Alt B) $14M Similar to Alt B Reduced cost and property impacts Similar to Alt B Does not contain 100-year flood The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Example Underpass Existing Culvert at Broadway A a B b No Action 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 47 Attachment B Twomile Canyon Creek Reach 3: Broadway to 19th St Information about the Alternatives Alt Description Cost Benefits Issues A 100-year open channel improvements; new culverts at 13th, 14th and from 16th St through Farmer's Ditch; Iris Av Roadway Improvements for surface flow $8.4M Conveys flood flows to Elmer's Twomile Creek Less property impacts and acquisition than southern alignments Major impact to Iris Av Requires downstream improvements a <100-year open channel (smaller version of Alt A) $5.7M Similar to Alt A Reduced cost and property impacts Similar to Alt A Does not contain 100-year flood B 100-year open channel improvements; new culverts at Farmer's Ditch, 17th, 18th and 19th St $9.5M Utilizes southern alignments Significant property impacts Requires downstream improvements b <100-year open channel (smaller version of Alt B) $3.3M Similar to Alt B Reduced cost and property impacts Similar to Alt B Does not contain 100-year flood C 100-year open channel improvements; new culvert south on 13th St, Farmer's Ditch, 17th, 18th and 19th St $9.0M Utilizes southern alignments Provides for local drainage along 13th St Significant property impacts Requires downstream improvements c <100-year open channel (smaller version of Alt C) $4.9M Similar to Alt C Reduced cost and property impacts Similar to Alt C Does not contain 100-year flood D 100-year detention facility; new culvert south on 13th St; outfall to existing storm drain system $44M Reduces downstream discharges Reduces sedimentation impact downstream Ability to retain existing use of gardens or re-purpose area Can be constructed independent from other improvements Significant property impacts May require removal of mature trees Embankment may impact viewscape d <100-year detention facility (smaller version of Alt D) $35M Similar to Alt D Reduced cost and property impacts Similar to Alt D Does not detain the full 100-year flood The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Example Culvert Example Detention Facility No Action A a B b C c D d 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 48 Attachment B Twomile Canyon Creek Reach 4: 19th St to 24 th St Information about the Alternatives Alt Description Cost Benefits Issues A Iris Av roadway improvements for surface flow $3.1M Conveys flood flows to Elmer's Twomile Less property acquisition than southern alignments Major impact to Iris Av Life safety and emergency access concerns with street flooding a <100-year roadway improvements (smaller version of Alt A) $1.6M Similar to Alt A Reduced cost and property impacts Similar to Alt A Does not contain 100-year flood B 100-year open channel improvements; new culverts at 21st St and Edgewood Dr. $2.8M Provides open channel connectivity to Goose Creek May reduce groundwater issues in local area Significant property impacts May require mature tree removal Places channel in backyards b <100-year open channel (smaller version of Alt B) $2.0M Similar to Alt B Reduced cost and property impacts Similar to Alt B Does not contain 100-year flood D Storm drain outfall system (detained flow) $0.5M Utilizes existing storm drain infrastructure Does not require open channel construction Relies on existing infrastructure Susceptible to clogging d <100-year storm system (smaller version of Alt D) $0.3M Similar to Alt D Reduced cost and property impacts Similar to Alt D Does not contain 100-year flood E Storm drain outfall system (full flow) $3.0M Utilizes the 19th St Right-of-Way Does not require open channel construction Does not remove Twomile Canyon Creek discharge from Goose Creek between 19th and historical confluence Susceptible to clogging e <100-year storm system (smaller version of Alt E) $2.0M Similar to Alt E Reduced cost and property impacts Similar to Alt E Does not contain 100-year flood The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Example Roadway Conveyance No Action A a B b D d E e 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 49 Attachment B Upper Goose Creek Reach 1 & 2 Information about the Alternatives Reach 1: North Boulder Park to 9th St Alt Description Cost Benefits Issues A Detention facility within North Boulder Park; new 9th St culvert. $3.0M Reduces downstream flows Reduces overtopping of 9th St Retain or re-purpose park uses Impact to existing park uses May require mature tree removal Embankment may impact viewscape B No detention; Storm drainage collection to deliver flows to Alpine- Balsam site $0.5M Provides flooding protection for the Alpine-Balsam site Does not impact North Boulder Park Reduces flooding on Balsam St No reduction in discharges Concentrates discharges onto the Alpine-Balsam site May require roadway reconfiguration Reach 2: 9th St to Broadway *Reduced costs if detention is implemented at Reach 1 Alt Description Cost Benefits Issues A 100-year open channel $0.5M Provides additional open channel habitat Green infrastructure Aligns with the Alpine-Balsam Vision Plan Final configuration of Alpine- Balsam site unknown Could require more room than piped system a <100-year open channel (smaller version of Alt A) $0.3M Similar to Alt A Reduced cost and property impacts Similar to Alt A Does not contain 100-year flood B 100-year storm system $0.6M $0.2M* Could require less room than open channel Final configuration of Alpine- Balsam site unknown Susceptible to clogging b <100-year storm system (smaller version of Alt B) $0.4M Similar to Alt B Reduced cost and property impacts Similar to Alt B Does not contain 100-year flood The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Example Detention Facility Example Open Channel Through Alpine-Balsam No Action A B No Action A a B b 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 50 Attachment B Upper Goose Creek Reach 3: Broadway to 13th St Information about the Alternatives Alt Description Cost Benefits Issues A 100-year open channel $1.8M $1.3M* Provides additional open channel habitat Green infrastructure Opportunity for underpasses Extensive property impacts Disruptive to existing businesses a <100-year open channel (smaller version of Alt A) $0.8M Similar to Alt A Reduced cost and property impacts Similar to Alt A Does not contain 100-year flood B 100-year storm drain system $1.2M $1.0M* Utilizes existing Right-of-Way Does not require property acquisition Provides local drainage along Broadway and Alpine Av Construction disruption to busy business corridor Susceptible to clogging b <100-year storm system (smaller version of Alt B) $0.9M $0.8M* Similar to Alt B Reduced cost and property impacts Similar to Alt B Does not contain 100-year flood *Reduced costs if detention is implemented at Reach 1 The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Example Underpass Example Storm Drain Example Storm Drain No Action A a B b 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 51 Attachment B Upper Goose Creek Reach 4: 13th St to 17 th St Information about the Alternatives Alt Description Cost Benefits Issues A 100-year open channel $2.4M Provides additional open channel habitat Enhances existing drainage path Green infrastructure Extensive property impacts Disruptive to residential back- yards a <100-year open channel (smaller version of Alt A) $1.2M Similar to Alt A Reduced cost and property impacts Similar to Alt A Does not contain 100-year flood B 100-year storm drain system $3.1M $2.9M* Utilizes existing Right-of-Way Does not require property acquisition Provides local drainage along Alpine Av Does not address overland flow in existing flow path Susceptible to clogging b <100-year storm drain system (smaller version of Alt B) $2.0M $1.9M* Similar to Alt B Reduced cost and property impacts Similar to Alt B Does not contain 100-year flood *Reduced costs if detention is implemented at Reach 1 The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Example Storm Drain Example Storm Drain Example Channel Improvement Example Channel Improvement No Action A a B b 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 52 Attachment B Upper Goose Creek Reach 5: 17th St to 20 th St Information about the Alternatives Alt Description Cost Benefits Issues A 100-year open channel $26M Provides additional open channel habitat Green infrastructure Removes high hazard structures from floodplain Requires Alpine Condo acquisition Reduces residential units within City a <100-year improvements (smaller version of Alt A) $2.9M Similar to Alt C Reduced cost and property impacts Similar to Alt C Does not contain 100-year flood B 100-year storm drain system $2.2M $2.0M* Utilizes some existing Right-of- Way Does not require Alpine Condos removal Provides local drainage adjacent to Alpine Condos Requires drainage easement acquisition Disruptive to Alpine Condo property (construction) Susceptible to clogging b <100-year improvements (smaller version of Alt B) $1.6M $1.5M* Similar to Alt B Reduced cost and property impacts Similar to Alt B Does not contain 100-year flood The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Example Storm Drain Example Channel Improvement No Action A a B b 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 53 Attachment B Upper Goose Creek Reach 6: 17th St to 24 th St Information about the Alternatives Alt Description Cost Benefits Issues A 100-year open channel $12M Provides additional open channel habitat Enhances existing drainage path Green infrastructure Extensive property impacts Disruptive to residential back- yards Requires tall retaining walls on south bank a <100-year channel (sizing per previous study recommending a "5-year" improvement; exceeds 5- year with detained flow and/or Twomile improvements) $5.7M Similar to Alt A Reduced cost and property impacts Similar to Alt A Does not contain 100-year flow The information depicted on this map is provided as graphical representation only. The City of Boulder provides no warranty, expressed or implied, as to the accuracy and/or completeness of the information contained hereon. Example Channel Improvement Example Channel Improvement No Action A a 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 54 Attachment B Feedback from the March 19th, 2018 public open house: 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Comment Feedback Compiled by Reach 100-Year Containment Impacts to Alpine Condos Impacts to Habitat/OSMP Impacts to Long's Gardens Impacts to Private Property Maintenance Misc.New Alternatives Proposed Reach Specific Feedback 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Comment Feedback Compiled by Reach (w/o reach specific feedback) 100-Year Containment Impacts to Alpine Condos Impacts to Habitat/OSMP Impacts to Long's Gardens Impacts to Private Property Maintenance Misc.New Alternatives Proposed 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 55 Attachment B 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Comment Feedback by Issue Reach 1 Reach 2 Reach 3 Reach 4 Reach 5 Reach 6 Reach 7 Reach 8 Reach 9 Reach 10 Whole Drainageway 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 56 Attachment B Appendix B: Detention Alternatives Figure 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 57 Attachment B Existing ConditionsQ100 = 699 cfsQ10 = 186 cfs Pine Brook Reservoir DetentionFull Volume (31 ac-ft)Q100 at Linden = 646 cfs Existing ConditionsQ100 = 521 cfsQ10 = 212 cfsEE EEEELinden Avenue Sediment CaptureFull Volume (14.2 ac-ft)Q100 in = 699 cfsQ100 out = 626 cfsQ10 in = 186 cfsQ10 out = 85 cfs Linden Avenue Sediment CaptureHalf Volume (7.1 ac-ft)Q100 in = 699 cfsQ100 out = 640 cfsQ10 in = 186 cfsQ10 out = 158 cfs County Complex Field DetentionFull Volume (26.6 ac-ft)Q100 in = 838 cfsQ100 out = 578 cfsQ10 in = 235 cfsQ10 out = 39 cfs County Complex Field DetentionHalf Volume (13.3 ac-ft)Q100 in = 838 cfsQ100 out = 723 cfsQ10 in = 235 cfsQ10 out = 123 cfs North Boulder Park DetentionFull Volume (35.8 ac-ft)Q100 in = 521 cfsQ100 out = 45 cfsQ10 in = 212 cfsQ10 out = 1 cfs North Boulder Park DetentionHalf Volume (17.9 ac-ft)Q100 in = 521 cfsQ100 out = 245 cfsQ10 in = 212 cfsQ10 out = 1 cfs Existing ConditionsQ100 = 838 cfsQ10 = 235 cfs FARMERS DI T C H SILVER LAKE DITCH28th St19th St4th StBroadway9th St6th StKalmia Av Alpine Av5th StLinden Av 7th StFolsom St3rd St11th St17th St26th St10th St23rd StElder Av 18th StGrape Av 13th StIris Av Hawthorn Av 8th StJuniper Av Floral D r Edgewood Dr Bluff St Glenwood Dr Meadow Av 24th St21st St25th St20th St15th StArnett St14th StMapleton Av Valmont RdCloverleaf DrMesa Dr Balsam Av22nd StJefferson StCatalpa WyIris CtFremont AvAlpine Dr North StBalsam Dr16th StPanorama Av Neher Ln Forest Av Nicholl StJoslyn Pl Kincaid Pl Iris Walk CtJordan Pl Littleleaf LnKirkwood PlArthur CtEvergre e n A v Tyler Rd Roundtree CtRepplier StGlenwood CtJuniper CtNottingham CtCopper StMeadow Pl Jonathan Pl Jasper Ct Sherwood Cr 16th Cr Del Rosa Ct Jimson Ct Keystone Ct Fern PlJackpine Ct9th St17th StEvergreen Av 14th StArnett StBalsam Av Juniper Av Kalmia Av Forest Av 23rd StGrape Av Hawthorn Av Iris Av 15th St23rd St22nd St21st St20t h S t Kalmia Av 8th StAlpine Av 5th St25th St22nd St13th St20th St14th StBalsam Av BOULDER WHITE ROCK DITCH±700 Feet Upper Goose Creek and Twomile Canyon Creek - Flood Mitigation PlanAlternative Selection MemorandumFigure B1: Upper Goose Creek and Twomile Canyon Creek - Detention Legend TCC_01_C_detention_volume TCC_03_E_detention_volume UGC_01_A_detention_volume Ditch / Canal City of Boulder City Limits City of Boulder Floodplain 100 Year Flooding Limits 500 Year Flooding Limits Upper Goose Creek Flowpath 03/18/2019 - WRAB Agenda 5 - Twomile Canyon Creek and Upper Goose Creek Flood Mitigation Study Update Page 58 Attachment B CITY OF BOULDER WATER RESOURCES ADVISORY BOARD AGENDA ITEM MEETING DATE: March 18, 2019 AGENDA TITLE: Information Item – South Boulder Creek Mitigation Project Update and Stormwater & Flood Management Utility CIP and Rates PRESENTERS: Jeff Arthur, Director of Public Works for Utilities Douglas Sullivan, Utilities Principal Engineer Ken Baird, Senior Financial Manager, Public Works EXECUTIVE SUMMARY This memo is intended to provide WRAB an update on the South Boulder Creek Flood Mitigation project. Since the development of the 2019-2024 Flood/Stormwater Capital Improvement Program (CIP), additional planning, engineering, and discussion has taken place with WRAB, City Council and other stakeholders related to this project. This memo serves to highlight changes in the estimated project cost and schedule, and to provide an overview regarding recent City Council updates. BACKGROUND AND ANALYSIS Based on the 2019-2024 CIP, the average total budget (Operating and Capital) for the Stormwater and Flood fund is around $15 million/year. The Utility funding is split between $6 million for operating expenses and $9 million for capital projects. Of the $9 million, roughly half ($4.5M) is used for cash-funded capital projects, and the other half pays the debt service on bonds. Most of the large drainageway projects, including South Boulder Creek, receive funding through issuing revenue bonds that are paid back over 20 years. In round numbers, each $1 million in bonded project cost will require around $100,000 annually in debt service. In the Stormwater and Flood Management fund, each one percent of rate increase result in nearly $125,000. So, for each additional $1.25 million in bonded project cost, an additional 1% rate increase would be needed. In the most recently adopted CIP, $30.7 million was estimated for the South Boulder Creek project construction phase in 2020, to be funded by bonds. This amount was based on cost estimates developed during the SBC concept development phase. With this cost, along with other CIP, debt service, and operating expenses, the financial outlook for the Stormwater/Flood Fund anticipates annual rate increases of 5% in 2020 and each of the subsequent years of the fund financial. On February 5, 2019, City Council provided direction to Utilities staff to proceed with the preliminary design associated with the Variant 1, 500-yr project option. The project cost for this option is estimated at $36 million. This estimate represents what is considered a Class IV level (conceptual) estimate with a projected accuracy of +50% and -30%. Therefore, the estimated project cost can reasonably be expected to fall within a $25 to $54 million range. These costs do 03/18/2019 - WRAB Agenda 6 - South Boulder Creek Flood Mitigation Update/Stormwater & Flood Management Utility Funding Page 1 not include OSBT recommended purchase of OS-O land or associated requested site improvements. At the March 5, 2019 City Council meeting, Utilities staff provided a South Boulder Creek project “briefing”. This briefing including an acknowledgement of the City Council direction provided at the February 5, 2019 meeting as well as an overview of the upcoming project phases, associated schedule and estimated cost range. The project schedule included all future project phases and identified several critical milestones that must occur with the project stakeholders (CU & CDOT) to maintain the projected schedule. The revised project schedule estimates the project’s construction phase will occur in 2022. The schedule included the following key project components: 1.CU South Annexation Process 2.Preliminary Design Phase 3.CDOT Negotiations 4.Environmental and Flood Related Permitting 5.Final Design Phase 6.Advertisement & Bidding 7.Construction Phase, and 8.Estimated Letter of Map Revision (LOMR) timing Based on this revised information, Utilities staff will be recommending the following updates to the 2020 Stormwater & Flood Management Utility CIP. •Move the current SBC project construction phase funding from 2020 to 2022 •Increase the SBC project construction phase funding from $30.7 million to $40 million •Identify final design phase funding of $2 million in 2020 To get a better idea of potential rate impacts of these changes, the 6-year Stormwater & Flood Management Utility Fund financial has been updated. The change from the 2019 adopted fund financial includes (unaudited) 2018 actual revenues and expenditures, anticipated capital and encumbrance carryovers into 2019, and South Boulder Creek project updates to reflect schedule and cost estimate revisions. Due primarily to moving the debt payments out two years in the fund financial, these changes do not require adjustments to the current rate increase plan of 5% per year. Through the 2020 budget process, this amount may be further refined, and other key projects will be updated which may result in further discussion on future rate increases. Utilities staff will be providing information on other Stormwater & Flood Management Utility project needs during the budget process. NEXT STEPS Utilities staff will provide future updates to the WRAB on South Boulder Creek project related milestones including preliminary design, CU South Annexation, and CDOT negotiations. 03/18/2019 - WRAB Agenda 6 - South Boulder Creek Flood Mitigation Update/Stormwater & Flood Management Utility Funding Page 2