Water supply assessment and ranking of watershed dams in Georgia

Abstract

Jordan, Jones & Goulding, Inc. (JJG, teamed with Schnabel Engineering, LLC) was selected by the Georgia Soil and Water Conservation Commission (Commission) to inventory and evaluate the water supply potential for 166 existing Watershed Dams in Georgia. Because of tremendous growth in the past several decades, water supply sources are increasingly in demand in Georgia, particularly in North Georgia. Also, environmental permitting requirements associated with constructing new reservoirs are increasingly stringent. Expansion of existing reservoir structures may be more acceptable to resource agencies, because many of the environmental impacts associated with existing reservoirs have already occurred. The Commission wanted a methodology to assess its existing dams and to rank their relative suitability for water supply; but inventory, assessment and ranking of 166 dams and their potential for expansion is no small task. JJG employed a GIS-based approach to the inventory and evaluation process. Available data resources were accessed and pertinent information on many factors was obtained, including wetlands, streams (including trout streams), protected species, cultural resources, numbers of affected structures and roads, impaired streams [303(d) or 305(b) listed], and distance to existing surface water intakes. Use of these data coverages made the organization of this huge amount of information manageable. The available environmental resource data was compared to potential reservoir yields, potential for pumpedstorage operation, and distance/cost of pumping to existing water systems. This information was assembled into an electronic matrix that enabled ranking of the various economic and non-economic factors according to their perceived importance. By iterations of the matrix, sensitivity analyses of the alternatives were done to look at their robustness under various yields and operating conditions. The top twenty alternatives that emerged from the ranking process were physically surveyed by JJG ecologists and engineers to refine the previously-collected data under “real-world” field conditions. Field data sets were collected using global positioning system (GPS) equipment, enabling the more accurate information to be downloaded directly into the GIS database. This in turn enabled a rapid re-evaluation of the rankings of the 20 most suitable alternatives.