Sediment Regimes under Different Slope and Surface Hydrologic Conditions

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AbstractDuring rainfall events, many physical processes occur simultaneously. Conceptual frameworks for infiltration, runoff, surface sealing, sediment detachment, transport, and deposition processes have long been recognized. Nevertheless, interactions between hydrologic and sediment regimes and how they are affected by changes in slope steepness, soil erodibility, and rainfall erosivity have not been evaluated. A laboratory study on the Glynwood clay loam (fine, illitic, mesic Aquic Hapludalf) was designed to demonstrate interactions between hydrologic and sediment regimes. Four rainfall intensities, from 30 to 120 mm h−1, and two inflows, equivalent to 30 and 60 mm h−1 rainfall, were applied to create different combinations of rainfall detachment and shallow flow transport. Sediment delivery was quantified from two rainfall events: first on freshly packed soil under free drainage and later on the eroded surface under seepage. During the first rainfall event, average sediment deliveries from 30 to 100 mm h−1 runoff were 1.8, 3.4, and 3.3 kg m−2 h−1 for slopes of 5, 10, and 15%, respectively. The lack of slope effects from 10 to 15% slope indicates the shift from a transport‐limiting sediment regime at low slopes to a detachment‐limiting sediment regime at high slopes. Under the potentially more erodible seepage condition, the second rainfall event produced only 1.3, 1.8, and 1.5 kg m−2 h−1 sediment from the same range of slopes and runoff rates. Reduction in sediment delivery during the second run was caused by removal of the easily erodible fraction during the first run. Increased profile drainage at the 15% slope further limited sediment detachment. These results show interactions between surface hydrologic conditions and erosion processes and the importance of understanding dominant sediment regimes in developing erosion prediction models.