Date of Award

5-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Earth and Environmental Studies

Thesis Sponsor/Dissertation Chair/Project Chair

Josh Galster

Committee Member

Clement Alo

Committee Member

Duke Ophori

Abstract

The ability of drinking water reservoirs to retain a large amount of runoff during a storm event may allow them to be used as flood mitigation infrastructure. These types of reservoirs are not typically considered for flood mitigation because they are primarily thought of as a resource for drinking water, irrigation, or recreation. Flood mitigation is a secondary or tertiary use. But conscripting them for flood mitigation creates a flexible water resource system and may provide a simpler and more inexpensive solution to flooding than alternative methods since nothing new would need to be constructed.

The process of determining the potential viability of drinking water reservoirs for flood mitigation is also straightforward. Digital elevation models (DEMs) were utilized to determine the watershed boundaries upstream of the reservoirs. The land use of the reservoir’s watershed was classified using data from the National Land Cover Database. The runoff volume from precipitation events was calculated using the curve number method which is based on land use, hydrologic soil type, and amount of precipitation. The runoff volume was compared to the bonus capacity (the difference between the maximum and normal capacities) of the reservoir. Values for normal and maximum capacity were obtained from the United States Geological Survey. Additionally, discharge and flood height data from a river gage downstream of the reservoir was used to determine if the absorption of that volume of water by the reservoir would change the amount of flooding downstream of the reservoir.

Runoff from the 5-year storm could be absorbed by the bonus capacities of five of the six reservoirs with the Wanaque Reservoir being the exception. Runoff from the 10- year storm event could be absorbed by the bonus capacities of Lake Tappan, Greenwood Lake, and Lake Hopatcong. Runoff from the 50- and 100-year storms could not be absorbed by the bonus capacities of any of the six study reservoirs.

Installation of permeable pavement was modelled by reducing the curve number values of developed lands upstream of each reservoir by 37 or 50 percent, depending on the starting curve number values in the watershed. Permeable pavement, though an admittedly expensive solution, could reduce runoff in all of the six reservoir watersheds for all four storm events. However, only runoff from the 50-year storm (1.24xl07 cubic meters) for Lake Tappan was able to be reduced (1.03xl07 cubic meters) to within the reservoir’s bonus capacity (1.08xl07 cubic meters). This large reduction in runoff was due to the high percentage of developed land within Lake Tappan’s watershed.

Two of the six study reservoirs, the Wanaque Reservoir and Lake Hopatcong, were shown to have the capability to absorb enough runoff to mitigate flooding downstream during high precipitation storm events. The Wanaque Reservoir had enough available storage space (~1.90xl07 cubic meters) to absorb the flood volumes from Hurricane Irene (4.62xl06 cubic meters) and Tropical Storm Lee (3.96xl06 cubic meters). Lake Hopatcong also had enough available storage space (~4.1 lxlO7 cubic meters) to absorb the flood volumes from Hurricane Irene (1.75xl06 cubic meters) and Tropical Storm Lee (3.06x106 cubic meters). The Wanaque Reservoir and Lake Hopatcong historically have both shown to have similar available storage space amounts to absorb comparable flood volumes. With proper modification and more flexible management strategies, these reservoirs may be used more effectively for flood mitigation.

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