Effects of multiple small stock-pond dams in a coastal watershed in central California: Implications for removing small dams for restoration
Published:January 01, 2013
J.L. Florsheim, A. Chin, A. Nichols, 2013. "Effects of multiple small stock-pond dams in a coastal watershed in central California: Implications for removing small dams for restoration", The Challenges of Dam Removal and River Restoration, Jerome V. De Graff, James E. Evans
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Small dams are often situated on low-order tributaries that drain grazed hill-slopes in dry regions of the western United States. In this paper, we use remote-sensing techniques in a case study to explore the effects of multiple small stock-pond dams on tributaries to Chileno Creek, a coastal watershed in central California. Dam density, or number of dams per drainage area, is 0.76 dams per km2, with most of the tributaries containing one or more dams. The total eroding channel length downstream of dams is ∼11% greater than total eroding length upstream. The relatively high density of the small stock-pond dams leads to cumulative effects that elevate the magnitude of (1) increased downstream erosion and (2) fragmentation of longitudinal connectivity between tributary headwaters and the main channel. The total headwater area producing sediment blocked by small dams equals 30% of the Chileno watershed. From these data, we infer that reduced sediment load due to the presence of the dams slows downstream riparian recovery. Results of the Chileno Creek case study emphasize that basin-scale management approaches and restoration strategies to restore connectivity are imperative in watersheds with high dam density. Uncertainty related to the biophysical effects of small dams and their removal may be investigated through analysis of baseline and long-term monitoring data, and adaptive assessment and management.
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The Challenges of Dam Removal and River Restoration
River restoration is a societal goal in the United States. This collection of 14 research papers focuses on our current understanding of the impacts of removing dams and the role of dam removal in the larger context of river restoration. The chapters are grouped by topic: (1) assessment of existing dams, strategies to determine impounded legacy sediments, and evaluating whether or not to remove the dams; (2) case studies of the hydrologic, sediment, and ecosystem impacts of recent dam removals; (3) assessment of river restoration by modifying flows or removing dams; and (4) the concept of river restoration in the context of historic changes in river systems.