Agenda Date: 08/20/2024
Subject:
Title
Resolution 94-2024: Approving an Intergovernmental Agreement with Mile High Flood District, regarding funding of Major Drainageway Planning and Flood Hazard Area Delineation for Slaughterhouse Gulch
Body
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From: |
James L. Becklenberg, City Manager |
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Prepared by: |
Brent Soderlin, Public Works Director |
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Sarah White, Water Resources Manager |
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Presentations: |
N/A |
PURPOSE:
Approval of an Intergovernmental Agreement with Mile High Flood District for funding of Major Drainageway Plan and Flood Hazard Area Delineation for Slaughterhouse Gulch.
LONG-TERM OUTCOME(S) SERVED:
Safe Community; High-Quality Governance; Sustainable Community with Natural Beauty
DISCUSSION:
Watershed planning is an important way to help protect people and property against flooding, erosion, and stormwater quality problems. These plans contain a strategy and work plan to identify flood risk management projects, guide new land development projects and identify high risk areas.
The Slaughterhouse Gulch drainageway was originally studied in 1974, and subsequently updated in 1982, 1983, 1992 and 1993.
Mile High Flood District (MHFD) along with project sponsors, Southeast Metro Stormwater Authority (SEMSWA) and the City of Littleton, are proposing updates to the Major Drainageway Plan (MDP) and Floodplain Hazard Area Delineation (FHAD). The studies will evaluate the hydrology and floodplain limits of Slaughterhouse Gulch in consideration of new rainfall data and development that has occurred in the basin since the previous study in 1993. The MDP will provide a conceptual design of recommended improvements in the watershed, including estimated costs. The MDP will be used as a guide for implementing drainage improvements. The FHAD study will identify flood risk information and boundaries. The FHAD will then be used to update the FEMA floodplain maps as a physical map revision, updating the regulatory boundaries of the floodplain.
BACKGROUND:
Slaughterhouse Gulch drains approximately 2.2 square miles in Littleton and Centennial from its origin near University Boulevard and Arapahoe Road to its outfall at the South Platte River near the north end of downtown Littleton. The Slaughterhouse Gulch drainage basin is mostly comprised of residential and commercial developments. The previous studies reflected a higher single family residential composition than what exists today and anticipated future use and higher density development.
Slaughterhouse Gulch is piped through most of the city until it becomes an open channel on the west side of South Windermere Street. Powers Park is an inline regional detention facility, meaning the main channel runs through the detention basin. The majority of the storm infrastructure throughout the basin is undersized which can lead to localized street flooding.
Prior Actions or Discussions
This master plan and floodplain update has not previously been discussed by city council.
FISCAL IMPACTS:
The total project costs is estimated to be $400,000. The City’s share of the cost of the project, as set forth in the Agreement, is 25% of cost for the master plan preparation, and 0% for the floodplain study costs.
The cost for the studies is shared with SEMSWA and Mile High Flood District as follows:
City of Littleton: $50,000 (MDP 25%)
Southeast Metro Stormwater Authority: $50,000 (MDP 25%)
Mile High Flood District: $100,000 (MDP 50%)
Mile High Flood District: $200,000 (FHAD 100%)
The city’s share of the project will be from the Storm Drainage Enterprise Fund.
STAFF RECOMMENDATION:
Staff recommends approval of the resolution.
ALTERNATIVES:
If not approved, future design of improvements will be based upon the 1993 study which may have inaccurate hydrology that would lead to either over-designing infrastructure (greater cost), or under-designing infrastructure (increasing risk to public). Not updating floodplain maps as the watershed develops and rainfall data updates lead to under and over enforced floodplain regulations.
Not entering into a partnership agreement with MHFD and SEMSWA would require the city to fully finance the studies at $400,000 instead of the $50,000 proposed.
PROPOSED MOTION:
Proposed Motion
I move to approve Resolution 94-2024 approving an Intergovernmental Agreement with Mile High Flood District, regarding funding of Major Drainageway Planning and Flood Hazard Area Delineation for Slaughterhouse Gulch.