Masters Theses

Date of Award

8-2006

Degree Type

Thesis

Degree Name

Master of Science

Major

Environmental Engineering

Major Professor

John Schwartz

Committee Members

Randall Gentry, David Feldman

Abstract

Beaver Creek is located in Knox County, Tennessee and is on the 303d list for impairment due to phosphorus, nitrate, Escherichia coli, loss of biological integrity due to siltation, and habitat loss due to impacts from urbanization. The Beaver Creek watershed is rapidly urbanizing, but is still composed primarily of agricultural and forested lands. The watershed also has a large residential area. The purpose of this research is to provide a better understanding to the following questions:

• How does sediment yield change in watersheds as a function of urbanization?

• How do sediment yields change in watersheds as a function of land disturbance coverage and distribution?

• How do sediment yields change in watersheds as a function of Best Management Practices effectiveness, within a framework of land disturbance coverage and distribution?

These questions were explored by performing simulations with the Annualized Agricultural Non-Point Source Pollutant (AnnAGNPS) loading model. AnnAGNPS is a dynamic sediment delivery model that was developed by the United States Department of Agriculture, National Sedimentation Laboratory. There were four experiments that were performed using AnnAGNPS to model different simulation scenarios in the watershed. The experiments are:

• Experiment 1: Effect of increased urbanization on sediment yield with and without bank erosion simulated.

• Experiment 2: Effect of increased disturbed land in the watershed on sediment yield, and its distribution within the watershed.

• Experiment 3: Effect of increased disturbed land on sediment yield distributed on lowland versus hill slope.

• Experiment 4: Effect of BMP effectiveness on sediment yield in the watershed.

The results of this thesis have shown the impacts of urbanization and disturbed lands on sediment yield. Urbanization in Beaver Creek watershed resulted in an increase in the amount or runoff. This increase in runoff resulted in a greater sediment yield when including bank erosion. However, when bank erosion was not included in the calculation of sediment yield, the sediment erosion from the landscape was reduced when urbanization was increased.

A model simulation for sediment yield when the land base was completely undeveloped provides a frame of reference to compare the results of the four experimental simulations. At this point, the sediment yield including bank erosion was 137.47 T/day. This is the natural occurring level of sediment in the watershed mostly consisting of bank eroded sediments.

Increasing the amount of disturbed lands in the watershed has been shown to approximately double the amount of sediment yield. When the spatial location of disturbed lands in the watershed was modeled in AnnAGNPS, the results showed that development concentrated in the lower watershed generated more sediment yield than when concentrated in the mid and upper areas of the watershed.

Experiment 3 simulated the effects of concentrating the disturbed lands on the hillslopes and lowlands. Concentrating the disturbed lands on the hillslopes had the greatest impact on sediment yield. When the disturbed lands were concentrated on the lowlands, the results were near the sediment yield for disturbed lands equally distributed on the lowlands and hillslopes.

Experiment 4 was to determine how BMPs effectiveness would affect sediment yield. The BMPs effectiveness was modeled at increasing amounts of disturbed lands. As the efficiency of the BMPs increased, the sediment yield decreased. Through the effective use of BMPs in Beaver Creek watershed, more development could occur without having a significant increase in sediment yield.

Ultimately, a watershed management plan will be developed by the Beaver Creek Taskforce (BCTF). The BCTF can use the reference point (137.47 T/day) for naturally occurring sediment in the watershed to determine what level of sediment they prefer to manage. Listed below are the recommendations for Beaver Creek to use in establishing the watershed management plan.

• Set the maximum level of development that can occur if it is equally distributed in the watershed.

• Limit development when it is concentrated in either the lower or the upper watershed.

• Limit development on the hillslopes.

• When developing on the hillslopes, strictly enforce the use of BMPs.

• Use BMPs with higher effectiveness if more development is desired in the watershed.



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