TRANSPORT AND DEPOSITION OF SOIL PARTICLES BY SHALLOW FLOW ON CONCAVE SLOPES (SEDIMENT, COHESIVE BED-LOAD)
Abstract
Sediment eroded from soil on an upslope source area was discharged with flow onto a concave bed where deposition occurred. Sediment in these experiments was a nonuniform mixture of primary particles (sand, silt, clay) and aggregates (conglomerates of primary particles), typical of that eroded from most soils by sheet and rill erosion. Deposition and transport rates for 11 sediment fractions and depth of deposited sediment were measured with time. Flow velocity was measured by timing the advance of a dye front. The study produced several important results. Increasing rainfall intensity for a given discharge rate significantly increased sediment transport and reduced deposition. Large, 2-8 mm diameter, primary particles were deposited at the upslope edge of deposition as expected. However, the flow rolled similar sized, lightweight, soil aggregates and deposited them much further downslope than where large primary particles were deposited. Although large particles tended to be deposited at the upper edge of deposition, small sand and silt sized particles were deposited everywhere along the deposition area. The Yalin equation adequately described observed total load transport. A multi-particle deposition model based on existing transport theory adequately described profile shape development and total load as a function of time for "no rain" conditions. Modification of the Yalin constant allowed the model to successfully predict deposition profile shape and total transport rates but not the transport of smaller size fractions early in profile development. Transport capacity was found to be a function of rainfall intensity.
Degree
Ph.D.
Subject Area
Agricultural engineering
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