Field guide to a dynamic distributary drainage system: Tiger Wash, western Arizona

Management of flood hazards on piedmonts of the western United States is increasingly important as urban development expands into these areas. In the western United States, the term piedmont describes the low-relief, gently sloping plains between mountain ranges and the streams or playas that occupy the lowest portions of the valleys. Distributary, downstream- branching fluvial systems are common in piedmont areas, and all or parts of many of these distributary systems are active alluvial fans. Management of flood hazards on active alluvial fans is particularly challenging because of complex flow patterns, widespread inundation, local high-velocity flow, and the potential for development of new channels during floods. Geologic and geomorphologic analyses provide insights into the fluvial processes on piedmonts and thus can be invaluable in assessing flood hazards (Pearthree, 1989; Baker and others, 1990; Field and Pearthree, 1991; Hjalmarson and Kemna, 1991; Pearthree and others, 1992; Hjalmarson, 1994; Field, 1994a; 1994b; National Research Council, 1996; Field and Pearthree, 1997; Pearthree and others, in press). This field guide provides an overview of investigations of the Tiger Wash distributary drainage system in western Arizona, which experienced an extreme flood in late September, 1997. (34 pages)