Queen Valley Flood Mitigation Project (AZ)
The Pinal County Flood Control District (PCFCD) requested that WEST Consultants, Inc. (WEST) conduct a reconnaissance level investigation of flooding issues in Queen Valley, a retirement community located in the north central region of Pinal County, Arizona, adjacent to Queen Creek. WEST performed the following tasks: a) provide a detailed field reconnaissance and survey of the key areas in the region; b) utilize these data to develop updated hydrologic and hydraulic models of Queen Creek; and then c) reassess the mitigation techniques from an earlier study in light of the updated models.

Following the extensive field survey, hydrologic and hydraulic models of the Queen Valley area were constructed through rigorous analysis of historical records, GIS mapping, and other procedures in adherence with the scope of work provided by PCFCD. The hydrologic model was used to predict 10-year, 100-year, and other return period storm flows. These flows were used in the steady-state hydraulic model of the Queen Valley watercourses in order to predict flooding extents. Model verification was implied by the match between predicted results and both the historical records and the field observations.
Extensive flooding is predicted during the 100-year storm event, primarily at the wash crossings of the existing roads. Along the West Branch, Allison Drivecan passes approximately the 1-year event, Donna Drive passes the 3-year event, and Diane Drive passes the 10-year event. On Queen Creek, Sharon Drive is only able to pass the 1-year event. Queen Anne Drive is able to pass slightly less than the 10-year event. The Queen Creek Drive Bridge is able to pass the 70-year event.

The following flooding mitigation strategies were then investigated: a) Improve road crossings (i.e., upsize the culverts, remove obstructions); b) widen the existing channels; c) reduce channel roughness by clearing debris and / or resurfacing; and d) reduce flow by constructing a detention basin in the northwest area of Queen Valley. The results of this investigation indicated that the best strategy is widening existing channels and improving all road crossings. Indeed, even limiting these efforts to the present extents of the washes allows conveyance of flows as high as the 10-year event without overtopping.