Lydia Detention Pond
Lafayette, Colorado  –  2013

Lydia Detention Pond is located just south of the Lydia Drive - Etna Drive intersection. Poor hydraulics at the pond entrance as well as within the detention pond caused ponding water which resulted in maintenance and safety issues for the City and Home Owner Association. Brown Civil Engineering was tasked by the City with providing analysis and design to mitigate the drainage problems related to the unsatisfactory conditions at the existing detention pond.

Analysis showed that storm drainage from the surrounding area collected at the intersection of Lydia Drive and Etna Drive. From there, the runoff was conveyed to the detention pond via a concrete pan which connected to a flared end section. The flared end section had been modified to include a drop structure. Flat grades in the street coupled with poor pipe entrance and outfall hydraulics caused water to pond in the intersection to levels that caused driving hazards. Once runoff entered the pond, low flows in the detention pond pooled due to flat grades that were inadequate to convey flows across a grass turf area to the pond outlet. The ponding water resulted in soggy play areas and created maintenance problems.

Design solutions to mitigate the drainage problems included pipe entrance modifications that improved hydraulic flows. The intersection pavement at Lydia Drive and the concrete pan area were regraded to provide smooth flows to the pipe entrance. The pipe, located within a 30-ft. drainage easement between two homes, was removed and replaced with a low-profile horizontal elliptical pipe due to lack of adequate cover to sustain vegetative growth. The new pipe was installed at a slope designed to work well hydraulically with the new entrance grading. Within the pond, a concrete trickle channel was installed to convey low flows from the entrance pipe to the outlet channel, thus eliminating standing water in the pond. Water quality for the drainage area is addressed outside of this detention facility.

Brown Civil Engineering provided complete Bidding and Construction Administration services for the project, including project close out. Construction was completed in the summer of 2013. Post construction documentation shows that ponding in the street has been greatly reduced during rainfall events, and flow into the entrance pipe is smooth. .

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