Water Resources Collections and Archives

Rodeo Creek drains approximately 1.2 mi2 in coastal Marin County, California, debouching into the Pacific Ocean at Pt. Bonita in Golden Gate National Recreational Area. We documented the current degree of channel incision. Channel incision can lower adjacent water tables and cause bank collapse, which can increase sediment load resulting in aggradation downstream. Lower water tables can desiccate the native wetland community and allow non-native vegetation to become established. We measured eight cross sections along the length of Rodeo Creek using measuring tape and a stadia rod to measure top of bank, thalweg, high water marks, and inflection points along the banks. We made detailed sketches of channel morphology and vegetation at each cross section. We compared the resulting incision profiles of Rodeo Creek with a stream incision study of Walker Creek in northern Marin County by William Haible (1976). Rodeo Creek is less incised than Walker Creek. The most severe incision in Rodeo Creek was less than 7 ft compared to an average of 18 ft in Walker Creek. The incision in Rodeo Creek is still cutting through the alluvial fill of clays and silts as no evidence of bedrock was seen in any of the cross sections. In contrast, Walker Creek has hit bedrock. Rodeo Creek may still be in the initial stages of incision. This may indicate that more severe incision is to come as incision evolution progresses in Rodeo Creek. Clear management objectives may allow incision to progress at a more natural rate.