Upper Washita River Alluvial Aquifer Study

Science Center Objects

This project is a detailed study of the groundwater and surface water, the hydrogeology, climate, and base flow to streams, and the effects of water use and changes in weather and climate on the hydrologic system. The study includes field collection of groundwater and streamflow data, mapping the water table, aquifer base, and water use.

Map showing location and deposits that make up Reach 1 of the Washita alluvial aquifer, western Oklahoma.

Map showing location and deposits that make up Reach 1 of the Washita alluvial aquifer, western Oklahoma.(Public domain.)

SUMMARY

The Oklahoma Water Resources Board (OWRB) requires a detailed hydrogeological study and numerical groundwater-flow model analysis for determination of the Equal Proportionate Share (EPS) pumping rate and effects of pumping and climate scenarios on water resources to manage future water use for Reach 1 of the Washita River alluvial aquifer, here referred to as the WRA (Oklahoma Water Resources Board, 2012). The EPS is defined as "the maximum annual yield of water from a groundwater basin or subbasin which shall be allocated to each acre of land overlying such basin or subbasin". (Oklahoma Statutes Title 785, Chapter 30, 2011).

The objectives of this proposed study are to (1) describe the hydrologic system of the WRA, (2) describe the conceptual flow model, and (3) provide estimates of the response of the aquifer to transient stresses under various pumping and climate scenarios. This proposed study will provide useful information about the hydrogeologic characteristics of the WRA, which will benefit water managers and water users, and provide information that can be used to manage future water supplies. The numerical groundwater-flow model will provide a decision-support system for analysis of the effects of future water demands. This study supports the U.S. Geological Survey (USGS) Strategic Science Direction of building a water census of the United States, particularly determining “changes over time in freshwater quantity and quality in response to changes in climate, land use and land cover, and human and environmental water needs” (U.S. Geological Survey, 2007).

This proposed study will be a collaborative project of the USGS Oklahoma Water Science Center (OKWSC) with the OWRB. USGS staff will perform field work, data collection and interpretation, and numerical groundwater-flow model development, with support from OWRB staff for access to hydrological and hydrogeological background, tabular and geographical data, water-level collection, and direction for the emphasis of this study. USGS and OWRB staff will contribute to report writing. The proposed study will commence during February, 2015 and conclude in November, 2017.

The Washita River Alluvial aquifer is subdivided into four sections, termed “reaches” by the OWRB (Oklahoma Water Resources Board, 2012). The WRA is the westernmost and upstream section and is the focus of this study. The WRA is defined as the unconsolidated Quaternary-age deposits underlying the Washita River in Roger Mills and Custer Counties, Oklahoma (fig. 1).

USGS scientists conduct passive seismic study in the Washita Reach 1 study area.

USGS scientists conduct passive seismic study in the Washita Reach 1 study area.(Public domain.)

This study will use all available literature, geographic, and tabular data with new field data to describe the climate, water use, water quality, and construct the hydrogeologic framework and conceptual flow model of the WRA. To quantify the groundwater-flow system a new numerical groundwater-flow model will be constructed, calibrated, and used to calculate the EPS and effects of drought and future water use on amounts of available groundwater. Additional field data will include as many as 50 direct-push Hydraulic Profiling Tool (HPT) profiles and as many as one aquifer test to estimate hydraulic conductivity. Field data collection will include installation of as many as 3 observation wells, measurement of water levels in accessible existing wells including a synoptic water-level measurement effort, and using water-level loggers to collect time-series data from at least 3 wells.

This study will be reviewed according to USGS Fundamental Science Practices (Fundamental Science Practices Advisory Committee, 2011). Groundwater measurements will be collected using technical procedures described in Cunningham and Schalk (2011). All data collected will be entered into the USGS National Water Information System (NWIS; USGS, 2012) database and quality assured per system data entry requirements. The results of the study will be published in a USGS Scientific Investigation Report.

PROBLEM

  To manage future water use for the WRA the OWRB requires a detailed hydrogeological study and numerical groundwater-flow model analysis for determination of the Equal Proportionate Share (EPS) pumping rate and effects of pumping and climate scenarios on water resources (Oklahoma Water Resources Board, 2012). The EPS is defined as "the maximum annual yield of water from a groundwater basin or subbasin which shall be allocated to each acre of land overlying such basin or subbasin". (Oklahoma Statutes Title 785 Chapter 30, 2011). There is limited information on the hydrogeologic characteristics and the groundwater-flow system as well as on the behavior of the groundwater system under transient stresses. Existing numerical flow models for the WRA are out of date and can be greatly improved. Thus, to effectively manage the groundwater resources of the WRA, a study is needed to improve understanding of hydrogeology of the groundwater-flow system and interactions with surface water. An updated numerical groundwater-flow model is also needed to evaluate the behavior of the local groundwater system under stresses such as water withdrawal and extended drought periods.

OBJECTIVES AND SCOPE

he objectives of this proposed study are to (1) describe the hydrologic system of the WRA, (2) describe the conceptual flow model, and (3) to provide estimates of the response of the aquifer to transient stresses under various pumping and climate scenarios.

RELEVANCE AND BENEFITS

This study will provide useful information about the hydrogeologic characteristics of the WRA, which will benefit OWRB water managers and water users, and help to inform management plans that will ensure sustainable water supplies. The numerical groundwater-flow model will provide a decision-support system for analysis of future water demands that can be used to determine effects of a variety of future water-use and climate scenarios and management plans. This study supports the U.S. Geological Survey (USGS) Strategic Science Direction of building a water census of the United States, particularly determining “changes over time in freshwater quantity and quality in response to changes in climate, land use and land cover, and human and environmental water needs."