Date Thesis Awarded

4-2019

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Geology

Advisor

Dr. Gregory Hancock

Committee Members

Dr. James Kaste

Dr. Robert Rose

Abstract

Retention ponds are commonly used to mitigate the negative effects of the increased volume of surface runoff produced by urbanization. Many studies, however, suggest that these ponds are not actually effective at protecting the downstream channel from the changes in channel morphology and degradation of water quality driven by urbanization. The goal of this study is to evaluate how well a retention pond located in James City County, Virginia protects the downstream channel from changes in sediment transport regime and fluctuations in salinity and water temperature. Discharge, salinity, and water temperature data from adjacent watersheds, one urbanized with a retention pond and one predominantly forested without a retention pond, were compared to assess the impacts of urbanization on water quality. Longitudinal profiles of both stream channels were compared in order to analyze alterations in channel morphology caused by urbanization. Over the summer months, the retention pond was, on average, 5.5°C warmer than the stream draining the forested watershed. Daily fluctuations of 5°C were observed in the pond, while daily temperature fluctuations were on the order of 1-2°C in the forested watershed. Storm-based changes in salinity were observed in the stream draining the pond but not in the stream draining the forested watershed. Additionally, when comparing the two channel profiles, the stream draining the retention pond displayed an area of higher slope near its headwaters, decreasing 25 feet in elevation over the first 30 meters of the channel. The stream in the forested watershed had a more consistent slope along the length of the channel. From the differences in the data from the two streams, it is clear that the retention pond is not protecting the downstream channel from erosion near its headwaters or from significant fluctuations in water temperature and salinity.

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