Reductions in Fluvial Sediment Discharge by Coastal Dams in California and Implications for Beach Sustainability | doi.page

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Reductions in Fluvial Sediment Discharge by Coastal Dams in California and Implications for Beach Sustainability

The Journal of Geology2003Vol. 111(2), pp. 167–182

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Cope M. Willis, Gary Griggs

Abstract

The long‐term sustainability of California’s beaches depends on periodic deliveries of sand and gravel from coastal rivers and streams. To assess the long‐term health of California’s beaches, this study characterized the current state of fluvial sediment delivery and quantified, on a littoral cell basis, the cumulative impacts of dams in decreasing annual discharge. Presently, more than 500 dams impound more than 42,000 km2 (or 38%) of California’s coastal watershed area. Flow modeling suggests that by diminishing flood hydrographs, these dams have reduced the average annual sand and gravel flux to 20 major littoral cells by 2.8 million m3/yr (or 25%). In 70% of the streams considered in this study, suspended sediment loads during equivalent discharge events have declined over the past three decades, which indicates that dams have also significantly reduced downstream sediment supplies. Approximately 23% (or 274 km) of the 1193 km of beaches in California are downcoast from rivers that have had sediment supplies diminished by one‐third or more. Moreover, 192 km (or 70%) of these threatened beaches are located in southern California, where most of the state’s beach recreation and tourism activities are concentrated. Although past large‐scale nourishment activities associated with coastal construction and harbor dredging have offset fluvial sediment supply reductions, particularly in southern California, many of these threatened beaches can be expected to undergo long‐term erosion in the future.

Citations Over TimeTop 10% of 2003 papers

Abstract

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