Document Type

Thesis - Open Access

Award Date

2017

Degree Name

Doctor of Philosophy (PhD)

Department

Agricultural and Biosystems Engineering

First Advisor

Todd Trooien

Keywords

drainage intensity, drainage system, drainmod, hydrological impact, hydrological modelling, subsurface drainage

Abstract

Subsurface drainage in agricultural land changes the field water balance by providing an alternate pathway for subsurface water. Determining the effects of subsurface drainage on downstream hydrology requires quantifying the components of the water balance. A number of studies have looked at the hydrological impacts of subsurface drainage. However, the effects are complex and difficult to generalize. The complex interaction involves the interrelation among variables such as soil type and properties, climate (rainfall and evapotranspiration), and drainage design configuration (drainage intensity and drainage coefficient), which all are local in nature. Additionally, most studies have been conducted in humid climates, whereas eastern South Dakota is located in a transitional dry subhumid climate. The objective of this study was to determine the impact of subsurface drainage on water yield (runoff plus drain flow) at the field scale in eastern South Dakota in terms of soil type, weather, and drainage design (drain depth and spacing). Long-term simulations were performed in DRAINMOD, a field scale deterministic process based hydrological model, to quantify each component involved in the water balance. The hydrologic outputs (daily, monthly, and yearly) of DRAINMOD were used to determine the impact of subsurface drainage for various scenarios of selected soil type, climatic condition, and drainage design that are typical for the study area. The results of the impacts of tile drainage on water yield at the field scale were presented as functions of soil, climate, and drainage design. The results showed the water yield increased with increased drainage intensity (DI) for all selected soils. The subsurface drainage amounts also increased with increased DI. The results also showed that runoff decreased with increased in DI within the same soil type. Also, the proportion of drainage to water yield increased with increased DI. Water yield decreased as saturated hydraulic conductivity increased. Improved understanding of impacts at the field scale is an important first step towards understanding the impacts of subsurface drainage on stream flow.

Library of Congress Subject Headings

Subsurface drainage -- South Dakota.
Water balance (Hydrology) -- South Dakota.
Hydrology -- South Dakota.
Hydrologic models.
DRAINMOD.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

117

Publisher

South Dakota State University

Rights

Copyright © 2017 Govinda Karki

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