Submitted to: International Soil Conservation Organization Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/4/1997
Publication Date: N/A
Citation: N/A Interpretive Summary: Soil erosion on agricultural lands is impacted by the degree of surface roughness. Little information is available how different degrees of surface roughness affect erosion processes, such as rilling, soil detachment and transport, and infiltration. In this publication, results of an experimental study are reported which examines the effect of a series of rainstorms of decreasing intensity on surface roughness changes, rilling, soil loss, and infiltration. Results indicate that roughness affects flow distribution, which in turn affects soil loss. A smooth surface had the lowest soil loss, while a rough surface showed the largest soil loss. These results stand in stark contrast to accepted notions.
Technical Abstract: Rills are the major source of soil loss from sloping fields. Fields have various degrees of roughness. It is generally accepted that soil surface roughness reduces runoff and soil loss. Yet, little quantitative information is available about the effect of roughness on infiltration, soil loss, and rilling. This study investigates the effect of soil surface roughness on infiltration and soil loss during the stages of seal development and runoff generation, steady-state flow conditions, and rilling. Flume studies using a rainfall simulator consisted of applying (i) a sequence of four rainstorms of constant rainfall amount with decreasing intensity, and (ii) two 30 min overland flow regimes to a loess soil of 2% slope. Treatments consisted of rough, medium rough and smooth soil surface conditions. During the initial stage of seal development and runoff generation, roughness affected the time of incipient runoff and the reduction in the seal hydraulic conductance. Additionally, runoff distribution patters led to high soil losses for rough surface conditions. The second stage was characterized by near steady-state values of infiltration and soil loss rates during the low intensity rainstorms. The effect of surface roughness on infiltration and soil loss was minor. The third stage represented high overland flow rates that induced flow concentration. Whereas soil loss increased on the smooth surface due to rill formation that was characterized by the development of headcuts, no rills developed on the rough surfaces, though preferred pathways for flow were evident. The results suggest that surface roughness may be a factor in reducing the risk of rill development and soil erosion on low slopes.