South Atlantic Water Science Center - South Carolina
USGS staff collecting water-column samples on Bushy Park Reservoir.
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Investigation of Flow Patterns, Water–Quantity, and Water-Quality Conditions in the Bushy Park Reservoir, Charleston, South Carolina
Project Number: FDF1000, FDF2000, FDF3000
The U.S. Geological Survey South Atlantic Water Science Center - South Carolina (USGS-SCWSC), in cooperation with Charleston Water System (CWS), is evaluating the hydrodynamics of the Bushy Park Reservoir to determine the effects on water-quality conditions. Specifically, the CWS has three areas of concern that this investigation will address: (1) hydrologic monitoring of the reservoir to establish a water budget, (2) water-quality sampling, profiling, and continuous monitoring to evaluate the causes of taste-and-odor occurrence, and (3) technical evaluation of appropriate hydrodynamic and water-quality simulation models for the reservoir.
Data collection will include real-time continuous monitoring, discrete water-quality sampling, and vertical and longitudinal profiling by using an Autonomous Underwater Vehicle (AUV). The data-collection effort will help to identify probable “hot spots” of elevated chlorophyll and blue-green algae (BGA) concentrations within the reservoir and give insight to the principal causes of the Bushy Park Reservoir taste-and-odor episodes.
Periods of elevated trans-1, 10-dimethyl-trans-decalol (geosmin) and 2-methylisoborneol (MIB) concentrations have occurred in the Bushy Park Reservoir including an extreme case during the spring of 2012. Occurrence of geosmin and MIB, which produce musty, earthy tastes and odors, are one of the primary causes of taste-and-odor episodes in drinking water. Although not a human health problem, geosmin and MIB are problematic because the human taste-and-odor detection threshold for these compounds is extremely low and conventional water-treatment procedures such as particle separation, oxidation, and adsorption typically do not reduce concentrations below the threshold level. Geosmin- and MIB-producing BGA blooms are attributed to a range of environmental factors, including nutrient concentrations and ratios, light availability, water temperatures, water-column stability, and reservoir flushing rates. Remediation efforts of reservoir conditions where BGA dominance occurred has hinged upon a strong scientific understanding of the mechanisms controlling the algal community.
Evaluating the physical and chemical conditions within the Bushy Park Reservoir with respect to changes in BGA concentration may provide CWS a basis to further modify management strategies to reduce taste-and-odor occurrence. Management strategies can be implemented long-term to prevent conditions under which BGA dominate and additional treatment technologies, like the powdered activated carbon that CWS currently (2014) utilizes, can be implemented short-term to reduce or remove the taste-and-odor compounds.
The data to determine the water budget and reservoir circulation dynamics of Bushy Park Reservoir will include measurements of the volume of the reservoir and the inflows and outflows to the reservoir; bathymetric data collected using an AUV; withdrawal information collected from area industries and CWS; water-level data from the new installation of a continuous real-time water-level gage located near the Bushy Park Reservoir dam; and collection of index velocity measurements at the Durham Canal gage and at temporary locations throughout the reservoir. To measure the flow in the water tunnels, real-time monitoring stations will be established and acoustic Doppler velocity meters will be located in the tunnels.
To analyze the possible convergence of conditions that cause taste-and-odor problems, data will be collected over a two-year period. A combination of continuous monitoring of water-quality and meteorological parameters, longitudinal water-quality profiling of the reservoir and tributaries, and discrete water-quality sampling will be used to capture the temporal and spatial water-quality dynamics of Bushy Park Reservoir.
The previously documented three dimensional Environmental Fluid Dynamics Code (EFDC) model for both hydrodynamics and water quality (Tetra Tech and Jordan Jones and Goulding, 2008; Hamrick, 1992; Park and others, 1995; Cerco and Cole, 1993) will be evaluated to 1) determine if the calibration is adequate to use as a planning tool for the Bushy Park Reservoir and 2) if the model calibration is not adequate, determine the modifications to the model application that would be necessary for recalibration and application as a planning tool. The EFDC model will be evaluated with existing data and the data collected during this investigation. If necessary, a list of recommended changes to the model and the level of effort required will be generated. A thorough reconfiguration and recalibration of the model is not part of this investigation. Making a limited number of changes to the model will help to inform the level of effort needed to develop a good reservoir management models. In addition, preliminary reservoir management scenario simulations will provide information on the feasibility of alternative management options. The following modifications to the model will be made:
RELEVENCE AND BENEFITS
Evaluating the physical and chemical conditions within the Bushy Park Reservoir with respect to changes in BGA concentration may provide CWS a basis to further modify management strategies to reduce taste-and-odor occurrence. Management strategies can be implemented long-term to reduce the frequency of conditions under which BGA dominate and additional treatment technologies to those currently (2014) being used can be implemented short-term to reduce or remove the taste-and-odor compounds.
The results of this work will be documented in two USGS Scientific Investigations Reports and made available to the general public at the USGS publication website https://water.usgs.gov/pubs. The reports will describe the data-collection effort, interpretation of the data, and technical evaluation of the hydrodynamic and water-quality simulation models for the reservoir.
Cerco, C. F., and T. Cole, 1993, Three-dimensional eutrophication model of Chesapeake Bay, J. Environ. Engnr., 119, 1006-1025.
Hamrick, J. M., 1992, A Three-Dimensional Environmental Fluid Dynamics Computer Code: Theoretical and Computational Aspects. The College of William and Mary, Virginia Institute of Marine Science, Special Report 317.
Park, K., Kuo, A.Y., Shen, J., and Hamrick, J.M., 1995, A Three-Dimensional Hydrodynamic-Eutrophication Model (HEM-3D): Description of Water Quality and Sediment Process Submodels (EFDC Water Quality Model). The College of William and Mary, Virginia Institute of Marine Science, Special Report 327.
Tetra Tech and Jordan, Jones & Goulding, 2008, 3-D Modeling Report for the Charleston Harbor System, prepared for Berkeley-Charleston-Dorchester Council of Governments, 455 pp.
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