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Title:   Author  item
                                            WEINBERG, ANDREW - Texas Water Development Boarditem
                                            BACKHOUSE, SARAH - Texas Water Development Boarditem
                                            Gitz, Dennis
  Submitted to: Government Publication/Report
                                    Publication Type: Government Publication
                                    Publication Acceptance Date: 2/3/2015
                                    Publication  Date: 2/3/2015
                                    Citation: Weinberg, A., Backhouse, S., Gitz, D.C. 2015. A water resource assessment of the playa lakes of the Texas High Plains. Texas Water Development Board. Technical Note 15-03.Interpretive Summary: The Ogallala Aquifer is an important source of water for the United States. In the Texas Panhandle, Ogallala Aquifer recharge takes place through the ephemeral Playa Wetlands, large shallow circular depressions which occupy as much as 5% of the landscape and which act as points of focus for the recharge. This study sought to reassess the amount of water collected by playas and assess how much might be available for aquifer recharge. Tools were developed to estimate recharge on a regional scale using satellites and regional weather stations. We found that while recharge is occurring, the amounts were considerably less than previously estimated. However, these tools can now be used to identify which playas should be preserved for water capture, and which might be managed for other uses.
                                Technical Abstract: Texas Water Development Board (TWDB) staff are studying the water-resource potential of playa lakes in the Texas High Plains in partnership with the U. S. Department of Agriculture— Agricultural Research Service and Texas Tech University. Phase 1 of the research seeks to measure the volume of water available in playas and current recharge rates from playas into the underlying Ogallala Aquifer. As part of Phase 1, we reconstructed the flooding history of 72 playas for an 18-year period of record using geographic information systems (GIS) analysis of
Landsat imagery. The results indicate an average annual total volume of water collected in all playas of 200,000 acre-feet. The average daily volume of water in playas declined from approximately 90,000 acre-feet in 1996 to approximately 20,000 acre-feet in 2014.
The playa water volumes estimated by this study are significantly lower than previous estimates, which ranged from two million to five million acre-feet per year. Changes in irrigation technology and agricultural practices may account for some of the difference in water volume between the current estimate and studies conducted in the 1950s and 1960s; however, changes in agricultural practices are not likely responsible for the observed decrease in playa water volume between 1996 and 2014.
Increasing evaporation rates appear to be the major factor affecting the volume of water contained in the playas over the long-term but do not provide a clear explanation of the observed decline between 1996 and 2014. TWDB data indicate that average evaporation rates have increased nearly 40 percent over the period from 1954 to present while average precipitation rates have stayed constant. Increased evaporation likely reduces runoff from playa watersheds.
And because of the broad, shallow nature of playa lakes and the relatively impervious sediments in the playa bottoms, evaporation is the dominant route of water loss from playas. Together, reduced runoff volume and increased water loss result in lower water volumes in Texas playas.
The current research program has developed screening tools to estimate playa water budgets and help select playas that may be suitable for recharge modification. A simple regression model using the mapped playa size, watershed area, and geographic longitude explains seventy percent of the observed variation in the volume of water captured by individual playas. More detailed long-term water budgets for individual playas can be developed based on a simple topographic survey coupled with analysis of existing Landsat records. These tools allow us to identify the playas that consistently capture the most water and therefor represent the best candidates for recharge modification.


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