The Effects of Hurricane Nora on Eomorphic Characteristics of Yuma Wash, Yuma Proving Ground, Arizona.

A baseline survey of Yuma Wash conducted in 1995 was used to assess channel changes associated with flooding from Hurricane Nora in September 1997. Repeat surveys conducted in January 1998 were compared to the 1995 survey to measure areas of cross-sectional scour and fill, net change in channel area, and change in thalweg depth along the channel. One-dimensional hydraulics modeling was used to estimate flood peak discharge and hydraulic variables. Statistical analyses were used to determine which physical drainage basin and channel attributes, and which hydraulic variables, best explained observed changes in channel geometry. September 1997 flood peak discharge varied from 16 to 237 cu ms, increasing rapidly downstream. Older high-water marks probably from 1972 recorded a peak discharge of 1280 cu ms. Channel change ranged from a maximum of -10 sq m of degradation to 33 sq m of aggradation. Cross sections with wider valleys, numerous multiple channels, and less vegetation aggraded, whereas cross sections in narrower valleys with fewer channels and more vegetation degraded. Cross sections with greater maximum flow depth also aggraded those with lower flow depth degraded.