Effects of Drawdown on Water Quality and Temperature in Duke University's Chiller Pond

Abstract

The Duke Pond (or chiller pond) collects runoff from 20% of the Duke University campus and serves as a water source to the adjacent evaporative cooling plant. Due to frequent water withdrawals from the chiller plant, the water levels are expected to fluctuate anywhere from one to four feet daily (1.22 m). This project aims to (1) calculate a water budget for the pond, (2) determine the effects of fluctuating water levels on various water quality parameters, (3) assess whether the pond is compliant with state water quality standards, and (4) determine whether the stream temperature is significantly different at the inflow versus the outflow to the pond. An additional goal was to develop a GIS tool that estimates the annual sediment yield from the Duke pond’s watershed using the Universal Soil Loss Equation (USLE). After the pond stabilized I found that dissolved oxygen, pH, temperature, and specific conductance decrease with increasing water levels in the pond. The temperature is not significantly different at the outflow compared to the inflow stream. For the majority of the 8-month sampling period, dissolved oxygen and pH remain compliant with the state standards. Chlorophyll-a had one occurrence where it exceeded the standard. The USLE tool accurately delineates the watershed for the pond and calculates an annual sediment loss of 168.2 lb/ac/yr.