Priority Groundwater Management Areas Studies (PGMAs)

Evaluation of Selected Natural Resources in Parts of the Rolling Plains Region of North-Central Texas

by Daniel W. Moulton and Alison Baird, Texas Parks and Wildlife Department, Austin, Texas. April 1998.

Executive Summary

This report evaluates the potential effects of the designation of a Priority Groundwater Management Area (PGMA) on some of the natural resources of the North Texas Alluvium and Paleozoic Outcrop (North Texas) study area (PGMA study number 16). The report is in response to Senate Bill 1 (75th Texas Legislature, 1997) which placed priority on the completion of pending PGMA studies mandated by House Bill 2 (69th Texas Legislature) in 1985. The purpose of the PGMA process is to identify and evaluate areas of Texas that are experiencing, or are expected to experience, critical groundwater problems within the 25-year planning horizon. The PGMA process is intended to encourage local and regional governments to address identified groundwater problems and consider appropriate management options.

The North Texas study area includes parts of the drainage basins of the upper Red River, the upper Brazos River, and a very small portion of the upper Trinity River. The area lies within the Mesquite Plains subregion of the Rolling Plains Natural Region and includes Archer, Baylor, Childress, Clay, Collingsworth, Cottle, Dickens, Fisher, Foard, Hall, Hardeman, Haskell, Jack, Jones, Kent, King, Knox, Motley, Palo Pinto, Shackelford, Stephens, Stonewall, Throckmorton, Wichita, Wilbarger, and Young Counties; an area slightly less than 15 million acres. The ecology of the Rolling Plains today reflects a history of human disturbance including over-grazing, soil erosion, lowered water tables in some areas, declining native grasslands, and altered river ecosystems. The historic tall and midgrass prairies have become a mesquite-short grass savanna.

The human population density of the 26-county area is quite low (~ 13 people/square mile) and not projected to increase much by 2050. The most-likely-scenario projection for the area in 2050 is 320,000 people. However, the population of the Dallas-Fort Worth Metroplex, just east of the study area, is projected to exceed 8 million people by 2050. In the future, it is this enormous population that will impose ever-increasing demands and pressures upon the water-based natural and recreational resources of the study area. As the recreational demands of the Metroplex population grow, the water-based recreational resources of the study area will become more valuable to the people of the region. If the region's water resources are conserved and appropriately managed, the economic value of water-based recreational resources will greatly exceed present value and have the potential to become a major component of the study area's economy.

It is the quality, not the quantity, of some of the area's groundwater and surface-water resources that is of concern in the region. The high salinity of much of the area's water resources, largely due to natural salt deposits, presents a challenge to natural resource planners and managers. Municipal, agricultural, and industrial water users would like to lower the salinity of certain surface-water supplies. One way this is done is by intercepting and disposing of the highly saline flows of certain streams, usually issuing from natural salt springs and seeps, in order to improve the quality of downstream surface-water supplies. There are several such chloride control projects, both existing and proposed, in the study area. These highly saline flows are natural in the region and have existed for millennia. Our native prairie stream fish faunas have evolved under these conditions and are uniquely adapted for life in these harsh aquatic ecosystems. The interception of saline flows can also significantly reduce the base flows of streams and rivers. Reduction of base flows alters aquatic ecosystems in many ways. These changes, as well as the segmentation of rivers by impoundments, have resulted in a decline in diversity and abundance of our native prairie stream fishes.

In the study area as elsewhere, groundwater and surface-water resources are not separate and cannot be managed separately without adverse environmental impacts. The potential for and desirability of conjunctive use of groundwater and surface-water resources in the study area was discussed in Texas Water Development Board Report 337. Conjunctive use ideally involves proactive management of all water resources to achieve maximum sustainable utilization of total water resources in the most economic and equitable manner. In the study area, where the quality of some groundwater and surface-water supplies is substandard for treatment and use, substantial benefits could result from conjunctive management of total water resources. The PGMA process should not overlook the economic and other values of the water-based natural and recreational resources of the study area. To do so would not be in the best long-term economic or other interests of the region's people.