SALTWATER INTRUSION MANAGEMENT IN COASTAL GEORGIA:
Research Group: Elçin Kentel, Harold Gill and Mustafa M. Aral
Long-term pumping from the Upper Floridan Aquifer (UFA) in the Savannah, Georgia area has lowered groundwater piezometric heads significantly in the region. This resulted in saltwater intrusion and brackish water contamination of the aquifer at Hilton Head Island, S.C. The aquifer is a primary source of drinking and industrial process water in the region, and various categories of users routinely apply to the State of Georgia Environmental Protection Division for groundwater withdrawal permits. The Georgia Environmental Protection Division (EPD) is a state agency, which is in charge of the management of the groundwater resources of the region for the benefit of all of its users. These users include the municipalities in the region, the industry, the agricultural users as well as the individuals residing in the area. In achieving this objective EPD's goal is the development of a long term groundwater management strategy, which will protect the UFA from further saltwater intrusion at the coastline while allowing additional groundwater withdrawals from the aquifer. To aid in this effort, in addition to their in house research activities, EPD has solicited the United States Geological Survey’s (USGS) support to conduct various studies in the Savannah region. Ga. EPD used the results of these studies to evaluate groundwater withdrawal permit requests and to formulate interim water management strategies [EPD 1997] for coastal Georgia. These studies were based on the results of various groundwater flow simulations done for the Floridan aquifer system in the region and did not intend to evaluate spatial distribution of optimal additional groundwater withdrawals that may be available in the region, nor did they include regional management concerns other than the hydraulic management of the aquifer system. In this study, we propose a coupled simulation-optimization model to evaluate additional groundwater withdrawal potential from the UFA in the Savannah region. As an extension of this approach, we also provide a methodology, which incorporates management criteria other than the hydraulic management of the aquifer system into the decision making process for selecting the best groundwater management strategy. In doing so, we provide a review of the current knowledge on the hydrogeology of the region as well as other studies that addressed this problem.
The results of the simulation-optimization model given in this report may be used as preliminary guidance for groundwater withdrawal permit evaluation in the region. The Lower Floridan Aquifer (LFA) is identified as an alternative groundwater source to the region by EPD. Accordingly, we considered groundwater withdrawal from the UFA, the LFA, and the UFA and the LFA together (i.e., UFA+LFA) as alternative groundwater management strategies. These three principal management strategies, i.e. groundwater withdrawal from the UFA, the LFA, and UFA+LFA, should also be evaluated giving consideration to various additional criteria.
These criteria can be identified as:
(i) satisfying the additional water demand in the region (i.e., with respect to groundwater withdrawal permit applications);
(ii) providing equal opportunity for each user in the region;
(iii) maintenance of minimal drawdowns at some other critical locations on the coastline that may have high risk of saltwater contamination; and
(iv) maintenance of low cost solution for the water supply deficit to the communities and the industry in the region which may be interpreted as an inhibiting factor for the development of the region.
Since in most cases these complex criteria, identified in (i) through (iv) above are rather vague, it is naturally easier to represent these objectives as heuristic objectives (by heuristic objectives we mean objectives that are identified in linguistic terms) in terms of "fuzzy sets." In this study, based on this innovative approach, a fuzzy multi-objective decision making framework, which imbeds the optimal hydraulic management framework into it is proposed. We believe that integrated utilization of simulation-optimization model results and the decision making procedure proposed here, when combined with expert knowledge to identify the appropriate membership functions of the fuzzy objectives, will enable the water resources managers to objectively evaluate the management alternatives in the Savannah region of the State of Georgia.
References:
Kentel, E., Gill, H. and Aral, M. M. (2005). "Evaluation of Groundwater Resources Potential of Savannah Georgia Region," Multimedia Environmental Simulations Laboratory, Report No. MESL-01-05, 104p. (This report can be requested from MESL under publications link.)
