Hydraulic Analysis & Design for County Road 29 Repairs

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Ayres performed hydraulic analysis and developed hydraulic design recommendations for the repair of County Road 29 along both sides of the Big Thompson River between the County Road 29 Bridge and the dam downstream. After conferring with the Larimer County floodplain administrator, the team successfully submitted a Conditional Letter of Map Revision (CLOMR) for the structures design, using the 2013 pre-flood condition as the baseline HEC-RAS model.

To upgrade the road to appropriate Larimer County and AASHTO standards, the overall pavement section design for the repair was wider than the original road. Ayres’ HEC-RAS modeling showed the proposed design would encroach into the channel and cause an unacceptable rise unless retaining walls were used. The proposed design now incorporates retaining walls along most of the repair length. Ayres assembled and submitted the CLOMR package to the Federal Emergency Management Agency in spring 2015, and the CLOMR was approved within five months.

Project Information

Client's Name

Larimer County Engineering Department


Larimer County, CO

Primary Service

River Engineering + Water Resources


Local Government