Small rivers in tectonically active regions deliver a disproportionate amount of sediment to the oceans relative to the area they drain (Milliman and Syvitski, 1992). The abundant sediment deposited at the mouths of mountainous streams provides an unique opportunity to infer the primary controls on basin evolution (Wheatcroft et al., 1996; Wheatcroft et al., 1997). Although the sedimentary record at the mouths of small, mountainous streams is extensive, the majority of sediment carried by them is deposited upstream from the basin mouth (Trimble, 1977; Ichim, 1990; Milliman and Syvitski, 1992; Mertes and Warrick, 2001). As a result, many studies now focus on floodplain sedimentation as a means of determining geomorphic response to environmental change (Assleman and Middelkoop, 1995; Walling et al., 1997; Goodbred and Kuehl, 1998). Current methods used to determine rates of floodplain sedimentation, however, do not provide high-resolution data over varying time scales necessary to understand the importance of anthropogenic effects on the landscape, especially in relation to climate and tectonics.

Furthermore, simply measuring rates of overbank sedimentation on any particular floodplain may not be enough to understand the relationship between sediment storage and environmental change in a small, mountainous catchment. In general, sediment yield increases with decreasing stream order (Trimble, 1977; Ichim, 1990) and the differences in sediment yield across stream orders may result in different responses to environmental change across the watershed (Graf, 1983). As a result of the spatial variances in sediment yield, it can be expected that rates of overbank deposition on floodplains adjacent to different stream orders will be different as well. Although some studies (Walling et al., 1996; Walling and He, 1998) found no significant longitudinal trend in overbank deposition rates, examining changes in sedimentation as a function of stream order may provide insight into the variability of subbasin response to environmental change.

This web site is meant to provide an overview of a three-year study of the sedimentation dynamics of the Navarro watershed of Northern California (Fig. 1). Our goal was to determine the controls of floodplain sedimentation and to use that understanding to generate insight of the role that anthropogenic effects have on basin evolution in context of climate and tectonics. Located adjacent to the San Andreas fault system, the watershed provides a great opportunity to examine the role of tectonics in controlling basin sediment yield. The highly detailed anthropogenic history also provides a framework from which to examine how different forms of land-use influence sedimentation patterns. Study of the Navarro watershed is particularly important because it represents the southernmost extent of natural spawning ground for the endangered coho salmon (Oncorhynchus kisutch). Intensive land use and the highly erodible nature of the underlying Franciscan Complex have led the Environmental Protection Agency to establish strict sediment regulations for the Navarro basin in an effort to protect coho salmon and the threatened steelhead trout (Oncorhynchus mykiss) (http://www.epa.gov/region09/water/tmdl/navarro/navarro.pdf).

For the purpose of this web site, our investigation is divided into three separate parts. Each part is meant to provide greater detail into the questions we examined and the methods employed in an attempt to answer them.

References: