THE INFLUENCE OF WEATHERING ON HEADCUT EROSION

Authors: Robinson, Kerry; Bennett, Sean; Hanson, Gregory; Kadavy, Kem

Submitted to: American Society of Agri Engineers Special Meetings and Conferences Papers
Publication Type: Proceedings
Publication Acceptance Date: 7/9/2000
Publication Date: 7/9/2000
Citation: Robinson, K.M., Bennett, S.J., Hanson, G.J., Kadavy, K.C. 2000. The influence of weathering on headcut erosion. American Society of Agricultural Engineers Meetings. Paper #002066. 10 p.

Interpretive Summary: The forces exerted by flowing water cause soil erosion. Different types of hydraulic forces can act to remove individual soil particles and larger aggregates. These forces are particularly different upstream and downstream of a gully overfall. Weathering of the soil surface has been observed to accelerate these erosion processes. Wetting and drying, freezing and thawing, crust formation, and surface cracking are just of few of the weathering processes that can attack the soil surface. This research found that weathering weakened a soil surface layer ranging from 25 to 50 mm (1 to 2 in) in thickness. This material was quickly removed when the soil was exposed to flowing water. A large test section of soil that included a gully overfall was exposed to numerous weathering cycles for approximately one month between each flow event. Weathering caused about half of the observed soil erosion. This information should be of interest to researchers and/or engineers responsible for predicting soil erosion, reducing sediment loading, and improving water quality. Little information presently exists about the impact of weathering processes on soil erosion.

Technical Abstract: Surface weathering accelerates soil erosion, and weathering processes can contribute to increased scour in the vicinity of a headcut. Normally erosion-resistant materials may be susceptible to dessication cracking as the material dries between runoff events. Additionally, tension cracking near an overfall, crust formation, and freeze-thaw cycles can cause increased erosion. This paper examines the impact of weathering cycles on headcut erosion in a compacted cohesive soil exposed to intermittent flows. A 1.8-m wide and 29-m long flume with 2.4-m tall walls was used to contain a test section of compacted cohesive soil. The soil was exposed to normal weathering cycles for approximately one month between each flow event. Dessication cracks developed quickly after cessation of flow. A surface layer 25 to 50 mm in depth was quickly removed when the flow was reintroduced. After this initial period of rapid erosion, the soil surface became much more stable. Therefore the sediment concentration in the flow was initially high and then rapidly decreased. Weathering processes appeared to cause approximately half as much erosion as plunge pool scour processes. The paper describes and presents measurements of the observed erosion. This research enhances our understanding of how weathering cycles can influence soil erosion.