Masters Theses

Date of Award

8-2024

Degree Type

Thesis

Degree Name

Master of Science

Major

Biosystems Engineering

Major Professor

Andrea L. Ludwig

Committee Members

Lori A. Duncan, Jon M. Hathaway

Abstract

Streambank erosion has become an escalating concern due to climate change and increased land development. This erosion adversely affects human populations and aquatic ecosystems, yet there are limited incentives to stabilize eroding shorelines. Traditionally, shorelines have been protected using hard armoring techniques with materials such as rock or concrete. While these methods are effective, there are growing shifts towards bioengineered or vegetated methods of shoreline stabilization. Recently, the Tennessee Department of Environment and Conservation (TDEC) approved bioengineered bank stabilization as an acceptable stormwater mitigation technique due to its water infiltration benefits. This research, conducted in Knoxville, TN, aims to enhance stormwater mitigation programs by establishing a basis for crediting bioengineered bank stabilization for erosion prevention rather than infiltration. The study focused on three objectives: comparing erosion monitoring methods, evaluating the relationship between watershed imperviousness and stream dimensions, and assessing the benefits of bioengineering methods for bank stabilization. The assessment of bank pins, two-dimensional surveying, the Bank Stability and Toe Erosion Model (BSTEM), and historical aerial photography revealed no significant correlations between any two methods of erosion measurement. These findings underscore the necessity of employing multiple erosion monitoring methods to increase accuracy. Additionally, the study explored the relationship between impervious surfaces and stream dimensions for outlet streams of watersheds with a range of area and imperviousness. Due to a limited data set it was determined that there was a need for further investigation into the impacts of urbanization as well as deforestation. Riprap and brush mattresses were evaluated for their ecological impact using various ecosystem service indicators, including soil microbial activity (Tea Bag Index), erosion risk (Bank Erosion Hazard Index), green canopy coverage (Foliage), habitat quality (TDEC habitat assessment), and economic feasibility (NRCS cost estimations). Bioengineering methods outperformed hard armoring in all assessed areas, demonstrating a 17% higher habitat quality, moderate to high erosion risk (compared to very high risk in riprapped areas), higher microbial activity, 43% more green canopy cover, and lower installation costs ($49/linear foot versus $245/linear foot for hard armoring). These findings indicate that bioengineered methods provide superior ecosystem functions and services compared to hard armoring techniques.

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