El Paso’s varied terrain and urbanization into the mountainous areas has increased the hydrologic and hydraulic characteristics so much that the City of El Paso sought PSC’s expertise after a high-intensity rainstorm event caused structural damage to a concrete channel and exposed a danger to property and people in the area. The local FEMA flood maps and computer models for Arroyo 1, known as Bear Ridge Channel locally, showed that the Bear Ridge Channel should have contained the 4.2-in of rain during the 24-hr 100-yr storm event within the concrete channel banks.

Time Lapse of Bear Ridge Channel During Storm from Parkhill, Smith & Cooper on Vimeo.

The computer simulations were incorrect, and reality showed that smaller storm events would leave the channel banks. The problem was a 35-ft radius, 90-degree bend in the channel. PSC’s analysis of the channel showed deficiencies in the existing constructed channel, both in geometric design and hydraulic design. PSC identified two areas in need of improvement: in the headwaters of the concrete-lined channel and 90-degree bend. PSC proposed two design alternatives to improve the channel conveyance at the 90-degree bend.

The chosen alternative consisted of a stilling basin to improve the geometric and hydraulic deficiencies in the original design. The conveyance of stormwater is now contained within the channel banks and is allowed to pass around the 90-degree bend and through the downstream culvert crossing. A sediment basin is being designed to reduce the sediment loads and restrict the flow rates into the concrete channel at the headwaters of the concrete channel.