A Statewide Evaluation of Excess Water Availability for Aquifer Storage and Recovery Projects or Aquifer Recharge Projects in Texas
Abstract
Texas is repeatedly subjected to long-term droughts interspersed with intense floods. Storing excess flood water for use during droughts is one approach for water suppliers to adapt to these climate extremes. In 2019, the Texas legislature passed House Bill 720 authorizing the use of state water, including flood water, for aquifer recharge and House Bill 721 requiring a statewide survey of aquifer suitability for Aquifer Storage and Recovery (ASR) or Aquifer Recharge (AR) projects. One objective of this study was to evaluate the availability of excess water sources for ASR or AR projects based on volume, frequency, and duration of the excess water source. Excess water sources evaluated in the survey include surface water, reclaimed water, and groundwater.
Excess surface water consists of surplus appropriated surface water from reservoirs and run-of-river sources and unappropriated streamflow, the streamflow remaining after all existing water rights and environmental flow requirements are satisfied. Surplus appropriated surface water was estimated as the projected reservoir and run-of-river surplus supplies remaining after considering projected water demands and recommended Water Management Strategies that would utilize appropriated supplies. The Texas Commission on Environmental Quality (TCEQ) water availability models (WAMs) with a monthly timestep under full authorization (Run 3) were applied to estimate the monthly unappropriated streamflow (including floodwater) at model control points located across the State. The WAMs were modified as necessary to consider environmental flow needs where the TCEQ adopted instream flow standards were not included in the models. A previous floodwater analysis conducted by Yang and Scanlon (2019) quantified the daily floodwater (≥95th percentile of daily discharge) volume at the outlet of ten major river basins in Texas, showing that large volumes of unappropriated floodwater (37 km3, 30 million acre feet) in 2015 - 2017, corresponding to ~ 2× water use in the State. Those floodwaters are co-located with Texas Gulf Coast Aquifer and Trinity Aquifers systems that have reported reduced groundwater levels with historical use, underscoring the potential for storing excess floodwater in depleted aquifers through ASR and AR. Comparison between the current and the previous floodwater study shows that at the outlet of Nueces, San Antonio, Lavaca, Colorado, and San Jacinto river basins, floodwater represented 50% - 100% of the unappropriated flow by volume. However, at the outlets of the other five basins, floodwater only represented a small portion of the unappropriated flow (15% - 30%). The annual duration and monthly frequency metrics used in the current analysis were appropriate for a regional-scale analysis at the statewide level. A daily analysis of floodwater, especially its duration and frequency, would increase the accuracy of floodwater analysis but is not practicable at a statewide level. The availability of excess reclaimed water was evaluated by obtaining historical effluent discharge data for the 2015-2019 period from the EPA Enforcement and Compliance History Online database. County population estimates from the Texas Water Development Board 2022 State Water Plan database (TWDB DB22) were then used to project annual available reclaimed water to 2070. Excess groundwater was estimated to be the amount of Modeled Available Groundwater remaining after existing groundwater use and recommended Water Management Strategies identified in the TWDB DB22 have been satisfied. The results of each of the excess water sources evaluated in this study were then integrated in an excess water screening tool that provides a composite score for all water sources on a grid of 1500 x 1500 m (~50,000 x 50,000 feet) cells, a key screening metric used by the TWDB to evaluate aquifer suitability for ASR and AR projects in Texas.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMH189...02Y
- Keywords:
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- 1630 Impacts of global change;
- GLOBAL CHANGE;
- 1880 Water management;
- HYDROLOGY;
- 1884 Water supply;
- HYDROLOGY;
- 1990 Uncertainty;
- INFORMATICS