Soil erosion on upland areas is a highly complex phenomenon involving detachment and transport of soil particles, storage and runoff of rainwater, and infiltration. The relative magnitude of these processes depends on the antecedent conditions and scale of operations. In describing and predicting these processes, one often resorts to the appealing but simplifying concepts of rill and interrill areas. Within these areas, homogeneity of processes is assumed. Yet simplifying representations can often lead to substantial errors. In this study a series of experiments are conducted to determine the soil loss and runoff response on a small upland area of 0.60 m by 3.75 m to different rainstorm regimes, overland flows, surface roughness, slope steepnesses, and subsurface water pressures under highly controlled laboratory conditions using a flume and rainfall simulator as water applications and a laser-microreliefmeter and tensiometric system as soil response measuring devices. The objective is to obtain a better understanding of the role of these different conditions on soil erosion processes. The soil chosen in this study was a Grenada slit loam (Glossic Fragiudalf, a highly erodible material commonly found on Bluff Line Watersheds in the lower Mississippi Delta. The results show: 1) smooth, uniform surfaces yield less soil loss than rough surfaces on this sealing susceptible soil; 2) a sequence of rainstorms of decreasing intensity cause more soil loss than a sequence of similar storms of increasing intensity; 3) Changes in subsurface soil water pressure substantially affect sediment concentration in runoff but impacted only marginally the runoff amounts; 4) drainage networks of the eroding, initially rough surfaces are similar to those of large river basins.
Key Words:Erosion processes, Sediment concentration, Drainage networks, Surface microrelief, Roughness, Seepage.
Publications:Römkens, M. J. M., Prasad, S. N., Helming, K. 1996. Sediment concentration in relation to surface and subsurface hydrologic soil conditions. Porch. of the 6th Fed. Interagency Sedimentation Conf., Las Vegas, Nevada. Vol. 2, pp IX9-lXl 6.
Helming, K., Römkens, M. J. M., Prasad, S. N. 1997. Roughness and sealing effect on soil and infiltration on a low slope. Proc. International Soil Conservation, organization. (In press).
Helming, K., Römkens,M. J. M., Prasad, S. N., and Sommer, H. 1997. Erosional development of small scale drainage networks. In "Lecture Notes in Earth Sciences. Springer Vedag, Berlin, Germany, (In press).
Römkens, M. J. M., Prasad, S. N, and Helming, K. 1997. Effect of negative pore pressures on sediment concentration in runoff. Proc. of the MLDCI Conf, Oxford, MS. (In press)
Helming, K., Prasad, S. N., Römkens, M. J. M. 1997. Drainage network characteristics on eroding soil surfaces. Proc. of the MLDCI Conf, Oxford, MS. (In press).