East Side Detention Facility

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The East Side Detention Facility (ESDF) dam is a high-hazard dam in northern Colorado. As the on-call engineering consultant for the Boxelder Stormwater Authority, Ayres was retained to analyze the Gray Lakes Reservoir area as a possible location for the ESDF as part of the Boxelder Basin Regional Stormwater Master Plan. This major regional flood control facility was needed to mitigate flooding in the lower half of the Boxelder Basin.

Ayres performed a siting study, preliminary design, final design, and construction observation and administration.

Ayres’ siting study looked at approximately nine possible locations for flood storage. The selected site is called Gray Lakes because the three existing irrigation reservoirs located there are known as the Gray Lakes. The flood control facility ultimately includes nearly 1,800 acre-feet of flood storage behind a 30-foot-tall dry dam. The facility reduces the 100-year inflow design flow from 6,700 cubic feet per second (cfs) to 2,400 cfs downstream of the dam.

The following services were performed for the dam analysis and design:

  • Hydraulics and hydrologic evaluation

  • Updated hydrologic model to analyze hydrologic impacts of dam on Boxelder Creek and surrounding communities.

  • Calculated probable maximum flood (PMF) and performed hydraulic analysis to determine inflow design flood (IDF).

  • Performed incremental damage assessment to reduce spillway size.

  • Prepared hydrology report and design report for State Engineers Office.

  • Prepared dam failure inundation maps.

  • Determined hazard classification for ESDF.

  • Created SRH 2D model of dam and outlet works to ensure dam operated as designed.

  • Prepared and submitted Conditional Letter of Map Revision (CLOMR) to Federal Emergency Management Agency (FEMA) to represent the reduction in floodplain boundaries downstream of the site.

  • Performed groundwater analysis to ensure nearby reservoirs would not be dewatered.

Dam design

  • Completed utility and adjacent roadway coordination.

  • Completed emergency and primary spillway design and outlet structure design and analysis.

  • Prepared emergency action plan and instrumentation plan.

Environmental evaluations

Ayres teamed with Alpine Eco to provide environmental services, evaluations, and permitting, including threatened and endangered and cultural resource surveys, aquatic monitoring, and coordination of approvals through State Engineers Office and through 404 permit from U.S. Army Corps of Engineers because of wetland impacts.

Geotechnical evaluations

Ayres teamed with Lithos Engineering to provide the required geotechnical analysis, evaluations, and permitting, including geotechnical investigation, slope stability analysis, embankment analysis, and foundations analysis.


Ayres developed construction documents for the dam and provided construction observation and administration during construction.

Project Information

Client's Name

Boxelder Basin Regional Stormwater Authority


Larimer County, CO

Primary Service

River Engineering + Water Resources


Local Government