Document Type

Dissertation - Open Access

Award Date

1972

Degree Name

Doctor of Philosophy (PhD)

Department / School

Agricultural Engineering

First Advisor

John L. Wiersma

Abstract

Soil erosion caused by rainfall is a very complex physical process. To evaluate the mechanism of erosion so that an assessment can be made of the extent to which it may be controlled necessarily begins with an understanding of the basic fundamental factors involved. The purpose of this study involves the development of an insight of the relative importance of the roles played by various contributors to the erosion process. Particular emphasis is placed on the contribution of rainfall detached soil to total soil loss. Three soil types, Barnes loam, Crofton silt loam and Central sandy loam, were prepared with preformed rills in a laboratory plot and subjected to simulated rainfall. During rainfall application, determinations were made of the exact source of all soil that was detached and carried off the plot. The mode of transport by splash or by surface flow, of that detached soil, was ascertained. Since transportation of most detached soil particles is directly related to runoff, the role of infiltration and runoff was also investigated extensively. Infiltration rates were found to vary, being greater in plot areas within the rills than between the rills. This appeared to be a result of rainfall impact forming a well defined and impervious surface seal in the areas outside the rills. Within the rills, a layer of flowing runoff water acted as a buffer between the soil surface and the impacting waterdrops, thus impeding the formation of an effective surface seal. In order to determine if rainfall impact or surface runoff was the prime source of energy for soil detachment, simulated rainfall was applied both with natural energy and with most of the energy removed. Removal of 89 percent of the energy of impact without reducing the application rate decreased soil losses by 90 percent or more, indicating that the energy of impact of falling raindrops is the major force initiating soil detachment. Erosion rates within the rills were nearly identical to the rates of erosion in the areas between the rills when using a cohesive soil such as a Barnes loam. For less cohesive soils, such as Crofton silt loam and Central sandy loam, flowing water increased the rates of erosion in the rills over that in areas between rills. However, even on these soils rainfall energy was still the dominant force initiating erosion. Mode of transport of detached soil particles was separated into two portions, that transported in drop splash alone and that transported by a combined action of surface flow and splash. Even though the normal rainfall impact energy was reduced, at least 80 to 90 percent of the soil transported off the areas between the rills was carried by combined surface flow end splash. This was transported either to the rills or off the lower end of the plot. The remainder was transported by splash action alone. The susceptibility of a soil to splash erosion or rill erosion is an important physical parameter of a soil. The three soils tested in this study included a wide range of physical characteristics, with no single measured parameter being sufficient to adequately indicate a soil's susceptibility to splash or rill erosion. The characteristic of cohesiveness of a soil provides a superior single indicator of this. However, if such a parameter is to be used, there is a need for a means of accurately describing the cohesive properties of a soil.

Library of Congress Subject Headings

Hydraulics
Rain and rainfall
Runoff

Format

application/pdf

Number of Pages

158

Publisher

South Dakota State University

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