134 Hydrogeology II: Groundwater Management

Tuesday, 6 November 2012
8:00 AM - 12:00 PM
212AB

INSTREAM FLOW RECOMMENDATIONS FOR THE RIO GRANDE, PECOS AND DEVILS RIVERS, TEXAS, USA

Paper number: 134-9
Program: Technical Sessions
Time: 9:50 AM – 10:05 AM

Authors

Abstract

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.