Watershed Modeling in a Pseudo Alluvial Fan Area in Northeast Phoenix and Scottsdale

A hydrologic model for a portion of the Upper Indian Bend Wash watershed in northeast Phoenix and Scottsdale is prepared to obtain realistic flows for natural washes north of the Central Arizona Project (CAP) dikes. The model is based on unit hydrograph and approximate field survey procedures. The ephemeral Sonoran desert washes descend on a semi-alluvial fan area from the McDowell Mountains and have a tendency to split and combine on their way south to the CAP dikes. Existing and on-going urbanization and the paved and unpaved roads have altered the pattern and amount of flow. Aerial photogrammetry, detailed contour maps, Geophysical Survey instruments and field visits were used to identify the location of the washes. Hand level and measuring tape were used to approximately define the geometry of the split flow, combined flow and channel sections. The resulting flows are significantly different from the previous hydrologic studies based on United States Geological Survey (USGS) quadrangle maps, field data and "engineering judgement" calls on drainage area delineations, flow splits and combinations.