Abstract
Human activities within a watershed, such as agriculture, urbanization, and dam building, may affect the sediment yield from the watershed. Because the equilibrium geomorphic form of an estuary is dependent in part on the sediment supply from the watershed, anthropogenic activities within the watershed have the potential to affect estuary geomorphology. The Sacramento River drains the northern half of California’s Central Valley and is the primary source of sediment to San Francisco Bay. In this paper, it is shown that the delivery of suspended-sediment from the Sacramento River to San Francisco Bay has decreased by about one-half during the period 1957 to 2001. Many factors may be contributing to the trend in sediment yield, including the depletion of erodible sediment from hydraulic mining in the late 1800s, trapping of sediment in reservoirs, riverbank protection, altered land-uses (such as agriculture, grazing, urbanization, and logging), and levees. This finding has implications for planned tidal wetland restoration activities around San Francisco Bay, where an adequate sediment supply will be needed to build subsided areas to elevations typical of tidal wetlands as well as to keep pace with projected sea-level rise. In a broader context, the study underscores the need to address anthropogenic impacts on watershed sediment yield when considering actions such as restoration within downstream depositional areas.
Highlights
River systems transport sediment from erosional areas of watersheds to depositional areas, such as lowland floodplains and estuaries
Kendall’s τ and Spearman’s ρ are non-parametric correlation coefficients that measure the correlation between two continuous variables (Helsel and Hirsch 1992), such as time and sediment yield
Peak concentrations during the largest floods of the time period appear to have decreased with time, corroborating the finding of decreasing suspended-sediment discharge
Summary
River systems transport sediment from erosional areas of watersheds to depositional areas, such as lowland floodplains and estuaries. Over long-term geomorphic time scales, the processes of erosion and deposition, along with sea-level change, likely attain some form of geomorphic equilibrium that includes the landforms found in estuaries, such as tidal wetlands. Humans have the potential to disrupt this balance by altering the processes on either end of the system. Changes in land-use activities within the watershed, such as urbanization, agriculture, and dam building, have the potential to alter the sediment yield from erosional areas. The effects of human development on the sediment yield of the Sacramento River are studied by examining suspended-sediment records for 1957 through 2001
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