30-year response to damming of a Mediterranean river in California, USA

Abstract

Dry Creek is a major tributary of the Russian River in Northern California (USA) that has experienced hydrologic and morphologic alterations after the closure of Warm Springs Dam in 1983. Our objective is to present a detailed diagnosis of the modification of the creek’s flow and sediment regimes, and interpret the alterations regarding the ecomorphologic evolution previously observed in the creek. Statistical analysis of the river’s flow and sediment series indicates that dam operation has had significant impacts on the magnitude and frequency of occurrence of the highest floods, and the magnitude, variability, and duration of low and very low flows. Similarly, sediment concentration and discharge have also experienced major alterations. Loss of habitat complexity for native flora and fauna (especially endangered salmonids), channel incision, and vegetation encroachment are some of the negative trends found for the creek over the last 30 years, since river regulation began. We discuss the present dynamics of the river and propose, on that basis, the improvement of its hydromorphic functioning as part of future large-scale restoration initiatives.

Keywords:

• Dry Creek
• Russian River
• river regulation
• fluvial geomorphology
• hydrologic alteration
• flow regime

Acknowledgements

The grantees stayed as visiting scholars at the Institute or Urban and Regional Development, Department of Landscape Architecture and Environmental Planning (University of California, Berkeley, USA). We also want to acknowledge Dr. J. Toby Minear (USGS), who provided helpful insights into the hydrological and ecological functioning of Dry Creek and Russian River, Denis O’Halloran (USGS, California Water Science Center) for providing relevant information about the sediment sampling techniques in the Russian River basin, and also the very insightful comments and valuable suggestions provided by three anonymous referees on the submitted manuscript draft.