Jackass Gulch MDP FHAD | Calibre Engineering

Jackass Gulch MDP & FHAD

Project Sponsers

Jackass Gulch was last studied in 1990/1991 alongside Lower Dad Clark Gulch with a FHAD and Outfall Systems Plan (Centennial Engineering, 1990; 1991). The 1990/1991 studies identified significant flood risk at the highly traveled intersection at Santa Fe Dr and Mineral Ave (5+ foot flood depths in the 100-year storm) and proposed several Capital Improvement Projects (CIPs) throughout the watershed. In addition to the 1990/1991 study, the following individual studies have been completed in this area:

Phase II Drainage Report for Riverpark Subdivision (Harris Kocher Smith, 2019)
Final Drainage Report for Stonecreek Assisted Living & Memory Care (HKS, 2018)
Final Drainage Report, RNDC Site (Kimley Horn, 2016)
Final Drainage Report and Stormwater Management Plan, Southbridge Shopping Center (Wyatt & Assoc, 2007)
Addendum to Phase III Drainage Report for Peakview Office Park (MMC Engineering, 2001)
Addendum to Phase III Drainage Report for Peakview Office Park (MMC Engineering, 2001)
Final Drainage Report, Centennial Covenant Church (Robinson Dalton, 2001)
Phase III Drainage Study for A Part of Lot 1, Southbridge Filing No 3 (Murray Consulting Engineers, 1998)
Phase III Drainage Study for A Part of Lot 2, Southbridge Filing No 3 (MMC Engineering, 1998)
Phase III Drainage Report, Mineral Avenue Station, RTD Light Rail Transit System (RTD, 1998)
Drainage Report, Southwest Corridor Light Rail Transit and Freight Rail Relocation (RTD, 1997)
Phase III Drainage Report (Robinson Dalton Consulting, 1996)
Phase III Drainage Study for Littleton Apartments at Mineral Avenue (Parsons & Assoc, 1994)
Phase III Drainage Study, Southbridge Filing No 9A (Carroll & Lange, 1994)
Phase III Drainage Study, Southbridge Filing No 9B (Carroll & Lange, 1994)
Phase III Drainage Study for Southpark Subdivision Filing No 11 (Carroll & Lange, 1992)
Phase III Drainage Report for the Southbridge Business Park (Fowler & Assoc, 1992)
Phase III Drainage Report for Allstate at Southpark Subdivision (Colorado Land Consultants, 1989)
Final Drainage Report for South Broadway Car Care Center (Merrick & Co, 1987)
Final Drainage Report for Southpark Shopping Plaza (Merrick & Co, 1987)
Drainage Report for Jackass Hill Road (KKBNA, 1985)
Southbridge Filing No 5, Drainage Study and Erosion and Sediment Control Plan (KKBNA, 1985)
Final Drainage Report for Martin Marietta Littleton Systems Center (Merrick & Co, 1983)
Southbridge I and II Office Buildings Drainage Study (KKBNA,1981)
Drainage Study for Southpark Subdivision (Tir-Consultants, 1981)
Viewpoint at Southpark Final Storm Drainage Report (Merrick & Co, 1981)
Surface Drainage Report for Mineral Avenue/Atchison Topeka, Santa Fe, and Denver and Rio Grande Railroads Grade Separation Project (Centennial Engineering, 1981)
Southbridge Filing No 4 Final Drainage Study (Gingery, 1981)
Southbridge Filing 1, Final Drainage Study (Gingery, 1979)

In recent years, Jackass Gulch has experienced significant headcutting, specifically behind residential neighborhoods that abut the Gulch. In addition, planning for development near the intersection of Santa Fe and Mineral has been underway and will be impacted by the stormwater runoff within Jackass Gulch. Finally, the last FHAD was completed in 1990, and there is no FEMA mapped floodplain at Jackass Gulch. As a results of these conditions, the City of Littleton and Mile High Flood District (MHFD, The District) contracted with Calibre Engineering to perform an update of the Master Drainage Plan (MDP) and to either delineate the local floodplain or establish a FEMA Floodplain with an updated Flood Hazard Area Delineation (FHAD).

GOals

Update modeling from 1991 study
Verify 1991 study
List expected risks and challenge areas
Verify and define flood levels at Mineral and Santa Fe intersection
Investigate areas of significant headcutting and erosion at upper reaches
Investigate options for regional ponds/detention
Map floodplain (either local or FEMA) with updated FHAD
Investigate/address trash accumulation during large storms

Critical issues

Old models of the Jackass Gulch watershed show 5+ foot flood depths at Mineral and Santa Fe during the 100-year storm. However, this level of flooding has never been witnessed.
The 1990 FHAD was completed before the redevelopment of the RTD Park N Ride and Aspen Grove shopping center, which may have significantly changed the flood levels in varying storm events.
There is very significant headcutting present at the downstream end of Jackass Gulch, abutting existing neighborhoods. The cause of the headcutting must be identified and mitigated, and Capital Improvement Projects should be identified.
Development is underway southwest of Jackass Gulch (immediately southwest of Santa Fe and Mineral). This development will be impacted by storm runoff from Jackass Gulch and may impact the adjacent Platte River. The development plan suggests channelizing flows and incorporating beaver ponds with wetlands. with wetlands.
High Line Canal may become available for stormwater conveyance, which could impact the conveyance, functionality, and needs of Jackass Gulch.
There is no water quality in this basin.
Significant channel stabilization will be required within this watershed.

Scope of Work

Define the watershed and subwatershed boundaries
Runoff hydrographs for subwatershed (CUHP) and hydrologic points (SWMM) (2-, 5-, 10-, 25-, 50-, 100-, and 500-year storms)
Hydrological inputs for hydraulic models
Confirm impacts of regional facilities, irrigation, splitflows, etc.
Perform hydraulic modeling and calculations, including site facilities for existing and future (CUHP, SWMM, HECRAS)
Analyze effects/impacts of existing detention including water quality detention facilities
Integrate structures, surveyed data, surface data and elevations, LOMR, DFIRM, and other resources
Calibrate floodplain mapping resulting from future flows
Schematic map of changes
Compare hydrology with existing CWCB/FHAD/FEMA data
Identify and evaluate peak flows (existing and future conditions)
Quantify impacts of future development on percent imperviousness
Prepare mapping of 100-year floodplain
Create floodway and 500-year model, apping, and tabular encroachment table
Identify areas of concern
Identify wetlands, riparian zones
Prepare cost calculations for existing and future infrastructure with FEMA Benefit Cost Analysis Tool
ROW determination and cost estimate for land acquisition
Develop alternative sketch plans
Develop alternatives, determine best alternatives
Determine impact of alternatives on water quality in watershed
Summary of Operation and Maintenance
Detailed cost estimate for best alternatives
Feasibility analysis for alternatives
Provide survey recommendations for future design
Hydraulic and hydrologic studies for selected plan
Updated detailed cost estimate for selected alternative
Conceptual design for selected alternative
Public presentation/community meeting
Provide and maintain project website
Integrate community input received at public meeting
Project management & QA/QC review
Agency coordination
Utility coordination

Project Schedule