Urban Flood Control District (UFCD) in conjunction with Adams County sought to solve ongoing problems of flooding and slope instability in a drainage corridor running right through a residential neighborhood. After a partial roadway collapse of 68th Avenue due to overtopping floodwaters, the project took UFDC priority. The landscape architect worked closely with an innovative engineering team. The design solution was split into two approaches near the inlet to the gulch and downstream of the 68th Avenue culvert (where the road failure occurred).
In the upper part of the gulch a large drainage structure, larger than your average room, was constructed below grade to handle 525 cfs, for those of you unfamiliar – that’s a giant flow of water. That inlet has an integrated drop structure to help attenuate the force of the water, then water is channeled into twin 78” pipes, through the neighborhood where constraints were so tight that previously eroding banks were already threatening backyard fences of the neighborhood. Now with the bulk of the stormwater handled subsurface, a winding at-grade swale can handle incidental flows for some infiltration. Planting screens of deciduous trees and evergreens were planted for much needed privacy between the neighbors. Wetland mitigation was necessary, so downstream of 68th Ave were constructed wetland, at a lower flattened elevation to allow for some ponding and the establishment of wetland species. A perched wetland was also constructed on the shoulder of the centerline of the stream to catch and partially treat stormwater from the adjacent road. Lastly, to deter local youth and skateboarders from the attractive nuisance of the twin 78” outfall, a large water basin was designed at a depth of about 12”. The project now provides 100 year flood prevention through this neighborhood watershed. Completed at Wenk Associates.