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This Article Full Text (PDF) All Versions of this Article: B26452.1v1 121/7-8/1054    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Warrick, J. A Articles by Mertes, L. A.K Search for Related Content GeoRef GeoRef Citation

Sediment yield from the tectonically active semiarid Western Transverse Ranges of California

¹ USGS Western Coastal and Marine Geology, 400 Natural Bridges Drive, Santa Cruz, California 95060, USA
² Department of Geography and Institute for Computational Earth System Science, University of California, Santa Barbara, California 93106

Sediment yields from the world's rivers are generally highest from steep drainage basins with weak lithology, active tectonics, or severe land-use impacts. Here, we evaluate sediment yields from the Western Transverse Ranges of California in an attempt to explain why they are 2- to 10-fold greater than the surrounding areas of California. We found that suspended-sediment yields across the gauged basins of the Western Transverse Range during 1969-1999 varied by approximately an order of magnitude (740-5300 t/km²/yr). Similarly, fine-sediment concentrations for normalized discharge rates varied by almost two orders of magnitude (e.g., 1.3-110 g/L for the mean annual flood) for 11 previously unmonitored drainages of the Santa Ynez Mountains. Areas with high sediment yields consistently have weakly consolidated bedrock (Quaternary-Pliocene marine formations) and are associated with the highest rates of tectonic uplift of the region (>5 mm/yr). These regions are important to the sediment discharge budgets, because 50% of the total suspended-sediment discharge from the Western Transverse Range is estimated to be generated within these regions, even though they represent only 10% of the total watershed area. Previous estimates of suspended-sediment discharge from the Ventura River have likely been underestimated by 50% because the gauging station is located immediately upstream of a high sediment yield region. We also found a significant and positive correlation between sediment yield and the percentage of a watershed with grassland and agricultural land use. These results suggest that there is adequate variation within the lithology, tectonics, and land use of the broader Western Transverse Range geologic province to induce large variations in sediment yield at the local scale.