Willis Properties | Casa Grande, AZ
The Villa Arroyo development is a 240-acre residential sub-division under development by Willis Properties with approximately 830 single family lots planned. The developer retained the EPS Group team to study the existing watershed and the corresponding drainage impacts of the planned development, as well as to design the drainage infrastructure required to handle stormwater as it flows through the site.
The property is located at the southeast corner of Val Vista and Trekell Roads in Casa Grande. Runoff from the 7.6 square mile watershed originates in the Sacaton Mountain range and flows southwest across Highway 387 and Interstate 10 before reaching the site. The watershed is mostly undeveloped rangeland with shallow natural washes and some wildcat residential developments.
EPS Group developed a two-dimensional hydrologic model (FLO-2D) to account for the distributed flow patterns, attenuation at roadways, and within developed areas of the watershed.
The model accounted for spatially varied rainfall depths, infiltration loss parameters, 45 existing culverts, and included over 532,000 20-ft grid cells with elevations set using available 0.5-m LiDAR topographic data.
Our team also developed a separate two-dimensional model using HEC-RAS to analyze the existing site conditions and to size and design the proposed drainage infrastructure at the site. The “RAS2D” model uses upstream inflow hydrographs from pre-defined FLO-2D floodplain cross-sections and also accounts for local rainfall runoff using the “Rain-On-Grid” precipitation based upon excess rainfall depths. We updated the local RAS2D model with detailed breaklines and proposed terrain grading models to provide more accurate flow depths and velocities for the grading design. Site modifications were made to account for potential erosive areas with adequate freeboard adjacent to conveyance corridors.
With a sound hydrologic analysis and appropriate drainage infrastructure design, Villa Arroyo will bring much-needed housing to Arizona’s expanding population while maintaining the safety of our neighborhoods and the integrity of our watershed.