Paper No. 7
Presentation Time: 9:50 AM
INSTREAM FLOW RECOMMENDATIONS FOR THE RIO GRANDE, PECOS AND DEVILS RIVERS, TEXAS, USA
URBANCZYK, Kevin M., Department of Biological, Geological and Physical Sciences, Sul Ross State Univ, Box C-139, Alpine, TX 79832, BENNETT, Jeffery, Rio Grande Wild and Scenic River, National Park Service, BBNP-ScRM, 266 Tecolote Drive, Big Bend National Park, TX 79834, BRYANT, Gary, Texas Water Resources Institute, Texas A&M Institute of Renewable Natural Resources, PO Box 1298, Fort Stockton, TX 79735-1298, DEAN, David J., Watershed Sciences, Utah State University, 5210 Old Main Hill, Logan, UT 84322-5210, SHENG, Zhuping, El Paso Agricultural Research and Extension Center, Texas A&M Univ System, 1380 A&M Circle, El Paso, TX 79927-5020 and SMITH, Ryan, The Nature Conservancy of Texas, Freshwater Ecologist, 200 E. Grayson St, Suite 202, San Antonio, TX 78215, kevinu@sulross.edu
The Texas Environmental Flows Allocation Process is intended to determine how much water is required to sustain Texas rivers and to ensure that streamflow is protected. To accomplish the first objective for the upper Rio Grande, Pecos and Devils rivers in west Texas we have conducted an assessment of the historic data. An initial evaluation of available stream gage data allows for the selection of appropriate stream gages. The daily flow data are classified into flow components using the Indicators
of Hydrologic Alteration. The results were then statistically analyzed to develop quantitative flow recommendations using the Hydrology Based Environmental Flow Regime (HEFR, SB3 Science Advisory Committee/Texas Parks and Wildlife Department) tool.
The Big Bend Reach of the Rio Grande is plagued by an accumulation of sediment delivered by large ephemeral tributaries. Inflows from the Rio Conchos in Chihuahua, MX, large desert ephemeral tributaries, and the upper Rio Grande upstream from Presidio, TX, are not sufficient to transport this sediment downstream. Therefore, high pulse flow recommendations for the Rio Grande relied upon hydrologic analysis with a strong emphasis placed upon the study of sediment transport and analysis of geomorphology. Water quality and biology data were used to refine hydrology based recommendations for base and subsistence flow.
Recommendations for the Pecos River were completed for two separate reaches: above and below the confluence of Independence Creek. The upper reach does not currently sustain a SEE and we recommend adaptive management steps to improve ecological condition. Flow recommendations for Independence Creek and the lower Pecos reach are intended to maintain the current SEE. Habitat modeling for 10 focal fish species and water quality data was used to refine the hydrology based recommendations. The Devils River is considered pristine with exceptional water quality and an abundant and diverse aquatic and riparian ecosystem. Flow recommendations were aided by habitat modeling for local fish species to evaluate and refine the base-flow component of the hydrology-based flow regime for one of the two Devils River gages.
