Wittman Geomorphic and Sediment Yield Analysis (AZ)
WEST Consultants, Inc. conducted a geomorphic and sediment yield analysis of the Wittmann area for the Maricopa County Flood Control District as a part of a team conducting the Wittmann Area Drainage Master Plan Update. The Wittmann study analyzed the majority of the 310 square mile drainage area for flood hazards and unstable landforms. The work performed by WEST involved collection of existing data on soils, surficial geology, land use / land cover, projected land uses, slope, geology and available aerial photos. This data was placed into a GIS database and analyzed to determine stability of the various landforms in the Wittmann study area. The results of the study will used to aid the flood control district in regulating expected development in the area. The geomorphic analysis was also used to aid in the delineation of floodplains and in the delineation of areas that can be developed without additional, detailed geomorphic analysis. Development in areas noted as unstable or needing further study will be required to conduct further analysis to determine stability or to stabilize the areas. Several areas were classified as active alluvial fans and development was not recommended on these active areas.

WEST conducted the analysis utilizing a series of historical photos dating back to the 1930’s as well as recent black and white and color aerial photography. The color photography was found to be valuable in differentiating soil coloration from changes in vegetative density or desert pavement.

The basic data used for the geomorphic analysis was also incorporated into GIS analysis of the sediment yield of the portion of the study area draining into McMicken Dam. Sediment yield was calculated using a number of methods which were then compared with the original estimates for the dam. Sediment retention in the dam was also estimated by calculating the differences between topographic surveys approximately 40 years apart. The sediment retention analysis was similar enough to the values calculated to provide support for the methodology used in application of the various methods to the area. The sediment yield data was incorporated into the alternative analysis for modifications to McMicken Dam.