Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/1996
Publication Date: N/A
Interpretive Summary: Where erosion rates on agricultural lands are severe, rills are active. Rills are small, ephemeral surface water channels which occur in fields during rainstorms, and are typically covered by farmers with tillage. Rills function as both a source of erosion and the delivery system for carrying soil and sediment from hillslopes, and thus are very important erosional features. This research was conducted to investigate rill erosion. Several experiments using several different soils were conducted in the field and in the laboratory to better understand the factors which influence the velocity of water in the rills, and the amount of sediment produced by erosion in the rills. This information will be used in the development of soil erosion models which are used to make soil conservation plans for farmers and to conduct soil erosion inventories. The information will help soil conservationists make more informed decisions on soil conservation planning.
Technical Abstract: Rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes. Six experiments were conducted on two soils and a uniform sand using three experimental methodologies. The results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills. Velocity did not vary with slope, and Reynolds number was not a consistent predictor of hydraulic friction. This result was due to interactions of slope gradient, flow rate, erosion, and the formation of rill roughness, bed structures, and headcuts. An alternative relationship for rill flow velocities was proposed. Stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set, while other hydraulic variables were not. The data for stream power and sediment load fit the form of a logistic curve (r**2=0.93), which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory.