Flood Mapping, River Restoration, and Dam Failure Investigation

St. Vrain Creek Flood Damage Restoration

Boulder County Parks & Open Space, Boulder County, Colorado

Significant flooding and damage occurred along a four‑mile stretch of St. Vrain Creek between the Town of Lyons and the Town of Hygiene in Boulder County in September 2013. Very heavy rains in the mountains west of Lyons created a 500-year flood event with flows of greater than 12,000 cfs in the creek.

EA was retained by Boulder County Parks and Open Space to provide design for repair of one embankment dam, two augmentation reservoirs, and seven embankment breaches along the creek. The overall project goal was to provide a design that met the requirements of the NRCS Emergency Watershed Protection Program and FEMA funding constraints. The design was prepared to mitigate the impacts of the 2013 flooding along the creek and to reduce the impact of future flooding on life and property, while restoring reservoir capacity and riparian and wildlife habitat throughout the reach.

Preliminary and final designs were prepared for the reservoirs including repair of an existing slurry wall, the 30 foot tall embankment, and replacement low level outlet works. The embankment breach repairs were designed to resist flood flows and reduce underseepage and internal erosion during flood flows. Embankments were founded on the undisturbed native soils below sediment and disturbed materials.

 

 

Reservoir Outlet and Toe Drain Remediation

Henrylyn Irrigation District, Weld County, Colorado

Horse Creek Reservoir had aged outlet works. EA was retained by Henrylyn Irrigation District (HID) to provide design for the rehabilitation of the outlet works. The project scope of work included removal of the existing head gates; removal of the existing maintenance building; extending the existing conduit with a 48-inch diameter steel pipe; and construction of a new concrete intake structure.

 

Flood Channel Erosion Protection Design

Raton Water Works, Las Animas, Colorado

EA provided the design, bidding and construction management for the rehabilitation of the concrete ogee spillway for this dam, located in Las Animas County, Colorado. EA saved the owner approximately $137K in negotiations with the contractor, value engineering, and effective construction management. This cost savings allowed the owner to increase the scope for additional improvements and stay within their budget. Deliverables included design, construction plans and specifications. Final as-built drawings were prepared for the concrete overlay of the spillway floor and a portion of the spillway wall; drains under the spillway floor and behind the spillway wall; valve vault lid with hatch doors; and woody vegetation removal. EA also developed plans to add a toe seepage collection swale for the ongoing monitoring of seepage.

Dam Breach Inundation Mapping

Various Clients, Western United States

EA staff has performed dam breach inundation mapping for earthen embankment dams with heights of over 150 feet and reservoirs impounding from 16 acre-ft to 26,000 acre-ft. Our staff has performed analyses with distances of over 40 miles through municipalities and along highways and bridges. Our ability to work with existing topographic surveys and mapping help control costs for our clients. EA staff works closely with emergency management professionals to ensure that modeling results can be incorporated into emergency planning to aid in preventing the potential loss of life.

 

Diversion Dam Rehabilitation

Union Ditch Company, Weld County, Colorado

Diversion Dam RehabilitationThe Union Ditch Diversion Dam, constructed in the early 1900s, was no longer functional for checking the river and controlling diversions to the Union Ditch. The diversion dam is approximately ten feet in height and 200 feet in length and provides for diversion of up to 175 cfs. EA provided geotechnical investigations and design; conducted hydrologic and hydraulic analysis; and provided structural design for the replacement diversion dam. EA also provided construction drawings, specifications, and contract documents for the project and provided the contract administration and resident inspection and quality control testing during construction. The new diversion dam structure includes a 40 foot Obermeyer gate with automatic controls, and the diversion structure into the ditch contains two 10 foot Obermeyer gates that are also remotely controlled.

 

Reservoir Feasibility Study

Mundt Dam and Reservoir, Weld County, Colorado

Mundt Farms wanted to construct a private reservoir for recreational purposes. EA performed the geotechnical investigation, provided the dam design, technical specifications and drawings, and construction oversight. EA developed several alternative design concepts for the size, shape, and alignment of Mundt Dam. Since this was a private reservoir, aesthetics and fish habitat were an important part of the alternatives analysis process. Once an alternative was selected, EA finalized the design and provided construction oversight until the completion of the dam.