Date of Award:

5-2019

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Watershed Sciences

Advisor/Chair:

Patrick Belmont

Co-Advisor/Chair:

Peter Wilcock

Third Advisor:

Efi Foufoula-Geogiou

Abstract

Rivers create beautiful patterns and provide drinking water to millions. However an alarming number of rivers in the US and globally are threatened by excess sediment and nutrients. Agricultural rivers draining erodible soils are particularly vulnerable. Rivers of southern Minnesota provide a unique opportunity to study water and sediment dynamics in a naturally vulnerable system. Sediment reduction strategies are needed to ensure biological integrity and adequate water quality. Here, I address the questions: 1) have climate, land use practices, or both affected streamflows in Midwest agricultural rivers?, 2) which streamflows set the rate of river bluff erosion?, and 3) how do sediment supply and transport influence the form and behavior of the lower Minnesota River? Chapter 2 demonstrates, in three agricultural basins, that artificial drainage practices have decreased soil moisture, contributing to increases in streamflow. Chapter 3 quantifies river bluff erosion and identifies erosion by streamflows as the dominant erosion process. Erosion by common floods accomplishes the most cumulative bluff erosion. Bluff erosion contributes sediment to the Minnesota River. Chapter 4 shows how this coarse sediment influences the form and behavior of the Minnesota River. Therefore if flows were reduced, bluff erosion would slow, and the supply sediment to the Minnesota would slow, leading to less streambank erosion. Since streamflows have been increased by agricultural drainage practices, water retention solutions are needed to reduce high flows.

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