HR: 09:30h
AN: NB21F-05    [Abstracts]
TI: Effect of Increases in Peak Flows and Imperviousness on Stream Morphology of Ephemeral Streams in Southern California
AU: * Stein, E D
EM: erics@sccwrp.org
AF: Southern California Coastal Water Research Project, 7171 Fenwick Lane, Westminster, CA 92683 United States
AB: The relationship between increased basin imperviousness, increased effective runoff, and stream channel degradation has been well documented. In 2003 the Center for Watershed Protection reviewed over 220 studies on this topic and developed an Impervious Cover Model (ICM) as a key paradigm to explain and sometimes predict how indicators of stream quality change in response to different levels of watershed development. The ICM predicts that stream quality indicators will decline when watershed impervious cover exceeds 10% and that severe degradation will occur above 25% impervious cover. However, one of the major gaps in the ICM is that it has not been tested in the southwestern U.S. and it is not certain how well the existing ICM predicts stream stability in arid and semi-arid climates. The goal of this study was to begin filling this knowledge gap by investigating the relationship between basin imperviousness and stability of ephemeral streams in southern California. A combination of historic and current field geomorphic analysis was conducted on ten sites to establish a relationship between increases in basin imperviousness and peak flow and changes in stream channel morphology, given the boundary resistance in each stream. This data was used to generate an enlargement curve for southern California streams and compare that to relationships observed in other portions of the country. The apparent threshold of response for southern California's ephemeral streams in less than 5%, substantially lower than observed in other regions of the country. Furthermore, ephemeral streams appear to be less resilient than similarly sized perennial streams. Although all channels appear to have an inherent rate of degradation, the rate increases substantially when basin imperviousness exceeds 2-3%. This study constitutes the first step toward building a regional ICM for arid and semi-arid areas
DE: 1803 Anthropogenic effects
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly