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HomeMy WebLinkAboutagenda.council.worksession.20140902 CITY COUNCIL WORK SESSION September 02, 2014 4:00 PM, City Council Chambers MEETING AGENDA I. Council Goals Update II. Storm Water Plan Update City Council Top Ten Goals 2014-15 DRAFT 1. Create a list of concepts by May 1st 2015 that can be used as “test projects” to illustrate what a Initiate and complete a “walkable city plan” in the downtown area might look like by May 1st, 2015. (public spaces and rights-of-way) that prioritizes pedestrian access and safety; and emphasizes the overall enjoyment and well-being for residents and guests alike. (Scott Miller, Chris Bendon, Randy Ready, Jeff Woods, Mitzi Rapkin, Richard Pryor, Barry Crook, and Karen Harrington) 2. In conjunction with Pitkin County and the APCHA Board of Directors, complete a review of the Housing Guidelines as they pertain to the following areas: a. Asset/Income Limits – what counts as income, what is discounted as “not really disposable income” b. Ability to qualify for more bedrooms than you can currently – so you can “grow in place” as your family grows c. AirBNB – short-term rentals as an option for deed-restricted owners/renters d. Product mix – what are we building and for whom? (Barry Crook, Don Taylor, Jim True) 3. Re-do of the Malls: (Randy Ready, Jeff Woods, Chris Bendon, Mitzi Rapkin, Dave Hornbacher, Scott Miller) a. Design – use of the malls, how much outdoor dining, utilities, brick pavers, drainage, features, furniture, lighting, water ditches, etc. b. Public Outreach c. Construction and timing Proposed for Postponement P1 I. 4. Develop policies and procedures by March 1st that would reduce the duration and intensity of construction impacts in residential areas and the downtown. (Scott Miller, Chris Bendon, CJ Oliver) 5. Implement Propose creative additions to the economic fabric of the community by May 1st, including (a) new or enhanced uses on the North Mill property and a redefinition of the SCI zone; and (b) the development of a framework for an “uphill economy”. (Chris Bendon, Barry Crook, Karen Harrington, Don Taylor) 6. Create a financial plan for Wheeler RETT revenues, determine the available funding level for a Community Investment Fund, and decide on a methodology for a community discussion and decision about repurposing and extending the Wheeler RETT. (Randy Ready, Steve Barwick, Jim True, Don Taylor) 7. Complete a review of HHS funding that identifies the purpose of the city’s involvement in funding of HHS services, how we will participate in that funding effort, and the amount and source of the city contribution. (Steve Barwick, Barry Crook, Karen Harrington, Don Taylor) 8. Achieve direction from city council on a solution for the loss of downtown Police and municipal office spaces. (Scott Miller, Randy Ready, Barry Crook, Don Taylor, Alissa Farrell, Richard Pryor, Mitzi Rapkin, Ashley Perl) 9. By July 1, 2015 identify carbon reduction opportunities in transportation and lay out a pathway that in fuses appropriate and forward thinking technologies into the Aspen community. (Ashley Perl, Randy Ready, Steve Barwick, Dave Hornbacher) 10. Engage the community in the creation of a resiliency plan that identifies Aspen's climate related vulnerabilities and establishes a plan for reducing those risks and monitoring progress. The resiliency plan will focus on energy, water, recreation, ecosystems, health, and infrastructure. (Ashley Perl, CJ Oliver, Dave Hornbacher, Karen Harrington) P2 I. Page 1 of 3 MEMORANDUM TO: Mayor and City Council FROM: April Long, P.E. – Stormwater Manager THRU: Trish Aragon, P.E. – City Engineer Scott Miller – Capital Asset Director DATE OF MEMO: August 28, 2014 MEETING DATE: September 2, 2014 RE: Update of Master Plan Models and Detention Analysis REQUEST OF COUNCIL: Staff requests that Council provide direction on detention requirements for private development, the capital improvements plan for the stormwater program and the development of water quality treatment goals for the City. BACKGROUND: In May of this year, Council approved a contract with Wright Water Engineers for $31,000 to update the models used in the existing Surface Drainage Master Plan (Master Plan) that was developed in 2001 and to analyze the extent of detention required on private developments given the available capacity and goals for our existing stormwater system. The 2001 Master Plan was developed to identify major surface drainage systems in the City that convey runoff from the mountain and urbanized portions of the City via storm drains, pipes, and streets to the Roaring Fork River. It also analyzed the stormwater system to determine its condition and the portions of the system that would be overwhelmed during certain storm events. For example, most of the stormwater system in Garmisch would flood in an event as small as the 2-yr storm, which has a fifty-percent chance of occurring in any given year. From this Master Plan, the City developed a capital projects list to address flooding concerns, and developed regulations for detention and conveyance for developing and redeveloping properties in the basin. The City’s goal is to have a stormwater system that can carry the 10-year storm (ten-percent chance of occurring in any given year) through the piping network without flooding streets or properties. DISCUSSION: With the increasing costs of designing and installing detention and water quality facilities on each private property, and the frustration from our customers over the time needed for engineering department review of these designs, staff felt it was important to evaluate ways to streamline the design and review processes. Therefore, one goal for this project was to determine if the City can and would like to assign a standard detention volume and release rate that could be applicable to every property within a certain P3 II. Page 2 of 3 basin. The other goal of the project was to determine if water quality treatment requirements are lessening the demand on our stormwater system, and therefore, providing more allowable capacity in the system than was calculated in 2001. During the analysis required for the project staff discovered that NOAA – the National Oceanic and Atmospheric Administration – recently released new hydrology (rainfall records) for the Aspen area. Staff requested that WWE review the new data and compare it to our existing data. The previous data available for the Aspen area was based on NOAA Atlas 2 which included a period of record from 1948-1973 (roughly 25 years). The new NOAA Atlas 14 provides data for this area through 2010 – 40 more years of rainfall record that wasn’t previously available to us. This new data shows smaller rainfall events than in the previous Atlas, and describes return storms as smaller events than in the previous Atlas. Design Storm Event URMP/NOAA Atlas 2 Depth (inches) NOAA Atlas 14 Depth (inches) Percent Change 10-yr, 1-hour storm 1.20 0.77 35% 100-yr, 1-hour storm 1.69 1.23 28% Per the Urban Runoff Management Plan, development and redevelopment projects must design detention to meet the historic runoff rates (i.e. sites cannot discharge runoff at rates higher than what was discharged when the area wasn’t a city). WWE analyzed existing runoff rates and historic runoff rates for all of the sub-basins in the Aspen Mountain Drainage Basin. WWE then modeled scenarios of providing detention to the historic rate for every development within a sub-basin to determine the effects this might have on the pipe network downstream of that basin. It was determined that the upland portion of the watershed, which includes practically all of Aspen Mountain, produces much greater flows than those detained here in town. So, providing detention for the relatively small developed area here in the City had fairly insignificant impacts on decreasing the demand on the stormwater system, especially during the 10 year storm. Additionally, changing the timing of the flow with detention does not gain any decreased chance of flooding in the river. WWE also analyzed the effects of implementing water quality treatments (infiltration and green infrastructure) in each basin at different levels of implementation – 25%, 50%, 75%, and 100%. At 100% implementation, the first quarter-inch of runoff from all impervious surfaces in the basin would be infiltrated into the ground. This analysis showed significant effect during small storm events (up to the 10-year event) on decreasing the demands on our system. Infiltration and green infrastructure also have the added benefit of recharging groundwater, therefore delivering more water to the river in the months after the “rainy season,” which is when the river is at its lowest flow levels for the year. RECOMMENDED ACTION: Staff is requesting direction from Council regarding: 1. Adoption of the new NOAA Atlas 14 hydrology (which would guide drainage design) 2. Adoption of decreased detention requirements, especially for those properties that discharge directly into the City’s stormwater system Adoption of this new information will require changes to the URMP that could be approved by Resolution in the September 22 Council Meeting. P4 II. Page 3 of 3 NEXT STEPS: Staff plans to return to Council in work session to present recommendations for a reprioritized capital improvements plans for regional detention projects, pipe upgrades and replacement (including updated estimates in 2014 dollars), and a water quality project implementation plan by basin. CITY MANAGER COMMENTS: ATTACHMENTS: None. P5 II.