Document Type

Thesis - Open Access

Award Date

1974

Degree Name

Master of Science (MS)

Department

Agricultural Engineering

Abstract

South Dakota is presently planning for the irrigation of approximately one-half million acres of land in the proposed Oahe Unit located in the north central part of the state. The main body of land in the Oahe Unit is the Lake Plain area which was once the lakebed of post-glacial Lake Dakota. Approximately one-fifth of the total cost of the project will be for drainage systems. The Bureau of Reclamation is responsible for the design of the Oahe project. They are presently using a transient drainage spacing equation developed by Glover in the design of the drainage system. The use of this design equation requires the evaluation of two soil parameters; saturated soil hydraulic conductivity and drainable porosity. The auger hole method is usually used to determine the saturated soil hydraulic conductivity under saturated soil conditions. The Bureau uses a point field method called the pump-in method to estimate the saturated hydraulic conductivity of the soil under unsaturated conditions. The accuracy of the pump-in method as compared to the auger hole method has been questioned. Therefore, the Bureau of Reclamation and the South Dakota Agricultural Experiment Station decided to compare these two methods on an experimental plot at the James Valley Research and Extension Center which is within the bounds of the Oahe project. This experimental plot area contains a subsurface drainage system which was installed in 1967. Since the soils of the plot area are not completely uniform, the drain line discharges reflect an average of the soils and envelope hydraulic characteristics. An open trench construction technique was used to install the drain lines which resulted in a disturbed soil profile above the drain lines. Drainage design equations in contrast assume a homogeneous soil which means the disturbed trench soil has the same drainage characteristics as the undisturbed soil. Therefore, an investigation of the disturbed soil hydraulic conductivity was initiated to determine the effect of the trench backfill material on drain line discharges.

Library of Congress Subject Headings

Drainage

Oahe Irrigation Development

Format

application/pdf

Number of Pages

131

Publisher

South Dakota State University

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