Groundwater Studies

Hydrologic Investigations

The first step in any hydrologic investigation is characterization of the resource. Initially, upper, lower, and lateral boundaries of the groundwater basin are delineated, and then aquifer properties—such as saturated thickness, hydraulic conductivity, transmissivity (the rate at which water moves through a formation), specific yield, and storage coefficient—are determined to understand the storage and yield capacity of the basin. Unlike oil reservoirs, which are static, groundwater basins are dynamic. Aquifers adjust constantly to short- and long-term changes in climate, groundwater withdrawals, and land uses. Thus, the amount of water entering the basin (recharge) and the amount of water leaving the basin (discharge) are also important factors in the evaluation of groundwater availability. Finally, assessing the quality of the basin helps to identify natural pollution sources, potential impacts of pumping on groundwater and surface water quality, and groundwater flow regimes.

Many properties vital to groundwater evaluation remain very difficult to quantify. Hydrogeologists use a variety of methods to estimate aquifer parameters, recharge, discharge, and water quality of the basins. These include physical measurements, such as water levels in wells, stream flow measurements, aquifer performance tests, tracer tests, and water quality sampling. Other methods are indirect, such as developing water budgets and utilizing computer groundwater flow models. Computer models enhance our understanding of current conditions as well as assist in the prediction of aquifer response to future climatic or land use changes.

Groundwater Allocation

Consistent with state law, the OWRB conducts maximum annual yield studies to determine amounts of water that may be withdrawn from Oklahoma's groundwater basins by permitted water users. The resulting figure is considered to be the amount of water that can be safely withdrawn from an aquifer to ensure a minimum basin life of 20 years.

To arrive at a basin's maximum annual yield, investigators map the total land overlying the basin-often divided into sub-basins for yield determinations-and estimate the amount of water in storage. Next, they determine the rate of natural recharge and total discharge, transmissivity, and potential for pollution from natural sources. The balance of the available water is then allocated proportionately to each acre of land overlying the basin. Prior to final consideration of this prorated amount, hearings are held to allow public input into the determinations.

To date, hydrogeologic investigations have been completed on five major bedrock aquifers and 10 major alluvial and terrace formations; four studies are underway on bedrock aquifers while three are pending on alluvial/terrace formations. Seventeen minor basin studies have either been completed or are near completion.

Current Studies

• Congress included approximately $700,000 in the Bureau of Reclamation's FY-2004 budget for the OWRB to conduct the second year of a comprehensive cost-share study of south central Oklahoma's Arbuckle-Simpson Aquifer. This $5 million, multi-year hydrologic investigation represents the most comprehensive study of water resources-especially concerning complex surface and groundwater relationships-ever undertaken by the State of Oklahoma. The aquifer supplies flow to many area rivers and streams-including Byrd's Mill Spring and the Blue River, the drinking water source for the City of Ada-but more information is required to properly manage and protect the region's water resources. Study results will provide state and local decisionmakers with the necessary information to determine how water resources in the region should best be utilized while protecting area springs and streams. Ongoing field work includes installation of stream gages, updating the current inventory of water wells and springs, and collecting measurements and samples from wells, springs, and streams in the study area. Special emphasis is being afforded to deep wells, on which a variety of hydrologic tests will be performed