Abstract
Abstract. Erosion and sedimentation pose ubiquitous problems for land and watershed managers, requiring delineation of sediment sources and sinks across landscapes. However, the technical complexity of many spatially explicit erosion models precludes their use by practitioners. To address this critical gap, we demonstrate a contemporary use of applied geomorphometry through a straightforward GIS analysis of sediment sources in the San Francisco Bay Area in California, USA, designed to support erosion reduction strategies. Using 2 m lidar digital elevation models, we delineated the entire river network in the Arroyo Mocho watershed (573 km2) at the scale of ∼ 30 m segments and identified incised landforms using a combination of hillslope gradient and planform curvature. Chronic erosion to the channel network was estimated based on these topographic attributes and the size of vegetation, and calibrated to sediment gage data, providing a spatially explicit estimate of sediment yield from incised channels across the basin. Rates of erosion were summarized downstream through the channel network, revealing patterns of sediment supply at the reach scale. Erosion and sediment supply were also aggregated to subbasins, allowing comparative analyses at the scale of tributaries. The erosion patterns delineated using this approach provide land use planners with a robust framework to design erosion reduction strategies. More broadly, the study demonstrates a modern analysis of important geomorphic processes affected by land use that is easily applied by agencies to solve common problems in watersheds, improving the integration between science and environmental management.
Highlights
Introduction and objectiveChannel incision is a common erosional response to natural or anthropogenic forcing that poses challenges to watershed management across the globe (Schumm et al, 1984; Schumm, 1999, 2007)
We estimated the specific sediment yield for each reach to illustrate how sediment yield varies downstream through the channel network
Viewing the generic erosion potential (GEP) layer draped over high-resolution aerial imagery along roughly 50 % of the channel network, we consistently observed steep eroding banks in areas with high GEP values throughout the watershed
Summary
Introduction and objectiveChannel incision is a common erosional response to natural or anthropogenic forcing that poses challenges to watershed management across the globe (Schumm et al, 1984; Schumm, 1999, 2007). Incision caused by humans can include urbanization that greatly increases runoff and sediment transport (Booth, 1991), or dams and gravel mining that reduce sediment supply (Kondolf, 1997; Surian and Rinaldi, 2003). Examples of natural causes of incision include change to a wetter climate that increases runoff (Balling and Wells, 1990) and catastrophic events that increase sediment supply from volcanic eruptions (Simon, 1992), extreme precipitation (Miller and Benda, 2000), or following wildfire (Benda et al, 1998). In some environments, incised channels are part of a natural alternating cycle of aggradation and degradation in response to episodic sediment supply (Bull, 1997). Channel incision creates a variety of problems including destruction of valley bottoms (arable land) and in-
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