Abstract
Studies of land use impacts, frequency-magnitude issues and the influence of basin scale on sediment delivery are impeded by the lack of sediment yield data from small watersheds. In this study, sediments from Thompson Lake, Virginia (United States), are used to study the last 30 years of sediment yield from the 3.8 km2 contributing catchment. Sediment yield changes at this site are found to be related primarily to precipitation history, rather than to gradual environmental change in the uplands, although even the low sediment yields reported here may be elevated as a result of former land use. This result as well as an established relationship between sediment magnetism and particle size allow for a simple evaluation of sediment yield frequency and magnitude. Two magnetic susceptibility peaks identified in the sediment record are hypothesized to represent discrete flood sediment strata, one resulting from Hurricane Agnes in 1972. Given this association, storm sediment yield at Thompson Lake accords with the classical expectation of moderate-event preeminence with regard to long-term sediment export. However, the Agnes event was found to be more important with regard to total sediment yield in this headwater basin than in larger trunk-streams elsewhere in the affected region. [Key words: sediment yield, lake sediment, frequency-magnitude, magnetic susceptibility.]
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