Agenda Date: 06/07/2016
Subject:
Title
A resolution authorizing an agreement regarding funding of a conceptual plan to repurpose a portion of the High Line Canal for stormwater collection, treatment and conveyance of treated stormwater to vegetation adjacent to the canal.
Body
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Presented By: |
Mark Relph, Public Works and Utilities Director |
POLICY QUESTION:
Does city council support an intergovernmental agreement to fund a conceptual plan to repurpose a portion of the High Line Canal for possible stormwater improvements?
BACKGROUND:
The High Line Canal is an irrigation and water supply canal meandering through Littleton from about C-470 to South Grant Street. It is owned and operated by Denver Water, who diverts water from the South Platte River and delivers it to customers in the metro area. Denver Water is considering a change to its operations that may include discontinuing the canal for irrigation and water supply; in part, due to excessive water losses caused by evaporation and seepage. The canal was the historic water source to fill Ketring Lake.
The Urban Drainage and Flood Control District (UDFCD), along with many local governments, completed the High Line Canal Feasibility Study for Stormwater Runoff Reduction and Treatment in August, 2014. The study determined it may be possible to collect stormwater runoff within portions of the canal. This water may be passively treated and utilized to support the diverse vegetation, wildlife and other uses along its banks.
It is proposed to enter into an intergovernmental agreement with UDFCD to prepare a conceptual plan to utilize the canal for stormwater collection and treatment. This plan would be focused on providing treated stormwater to vegetation adjacent to the canal, but it also may identify additional opportunities in the general area.
UDFCD would manage the project with Littleton assistance.
STAFF ANALYSIS:
The High Line Canal is not efficient for water conveyance; however, the water losses to seepage support the many cottonwood trees and other plant species along its banks. If the river water is cut off and the canal dries up, the trees and related vegetation, along with the wildlife that uses it, may suffer and decline.
There are several locations in Littleton where stormwater runoff either flows under or into the canal. The 2014 feasibility study determined it may be viable to collect some of this stormwater within the canal and improve its quality through means such as extended detention, bioretention, infiltration and similar forms of passive treatment. This treated stormwater may then support and sustain the current environmental and recreational uses of the canal. Treated stormwater for the vegetation adjacent to the canal would be the primary goal, but it might also be considered as a supplemental source of water to convey to Ketring Lake and surrounding area.
The plan will consider hydrology, storm inflow locations, drainage or flooding problems, right-of-way, wetlands, legal issues, in particular water rights, and other factors. The end result of this effort would be a report listing specific improvements that could be constructed, along with phasing and costs. Implementation of the plan would eventually require Denver Water approval.
Implementation of the plan has the potential of reducing the city’s larger stormwater infrastructure needs. This may be especially true since the canal lies in some of the higher elevations of Littleton’s drainage basins, thereby reducing the size of downstream infrastructure. This plan would create a methodology to measure the success of both a reduction of water quantity into Littleton’s system and an improvement in the water quality of the stormwater. Using these measures along with the cost to build the plan, could aid the city in future decisions regarding the cost effectiveness of this approach.
FISCAL IMPACTS:
The city’s contribution would come from the Storm Drainage Fund. UDFCD has agreed to contribute funding for this project in 2016. There are no funds at this time for construction. If the plan is ultimately supported by council, it is anticipated there might be a multi-year project(s), requiring additional contributions from both the city and UDFCD for future construction. The 2014 feasibility study indicated final design and construction costs, in general, could be about $4 million dollars.
UDFCD and the city contribution amounts and percentages to fund the plan are proposed as follows:
|
|
Percentage Share |
Contribution |
|
UDFCD |
28.571% |
$20,000 |
|
City of Littleton |
71.429% |
$50,000 |
|
TOTAL |
100.00% |
$70,000 |
STAFF RECOMMENDATION:
Staff recommends the city council approve the intergovernmental agreement with the UDFCD for the High Line Canal Plan.
PROPOSED MOTION:
Proposed Motion
I move to approve the resolution authorizing an agreement regarding funding of a conceptual plan to repurpose a portion of the High Line Canal for stormwater collection, treatment and conveyance of treated stormwater to vegetation adjacent to the canal.