HYDROLOGY AND POLICY IN THE UPPER RIO GRANDE: THE BASIN TO BAY EXPERT SCIENCE TEAM

Senate Bills 2 and 3 of the 77^th and 80^th Texas Legislatures created a legal framework for the development of science-based, minimum in-stream flow recommendations to support “sound ecological environments” in Texas rivers. Two of the most advanced statewide laws related to environmental flows in river basins in the country, implementation of the Texas Instream Flow Program and Senate Bill 3 are bound to raise some interesting legal issues and some challenging questions for scientists and agencies tasked with defining, monitoring and compliance.The area of study for the Upper Rio Grande Basin to Bay Expert Science Team (BBEST) is the reach of the Rio Grande/Rio Bravo from the confluence with the Rio Conchos below Fort Quitman to Amistad reservoir including the contributions of the Pecos River below Red Bluff and the Devils River.

A “sound ecological environment” is broadly defined to sustain the full complement of the current suite of native species in perpetuity, or at least support the reintroduction of extirpated species, sustain key habitat features required by these species and retain key features of the natural flow regime required to complete their life cycles. Furthermore, these flows sustain key ecosystem processes and services, such as elemental cycling and the productivity of important plant and animal populations. Each BBEST defines conditions from known historic flow regimes or develops parameters using available science.In developing analyses and recommendations, the science team must consider all reasonably available science, without regard to the need for the water for other uses. The science team's recommendations must be based solely on the best science available. Per statute, any uses attributable to Mexican water flows must be excluded from environmental flow regime recommendations. Methods include applied modeling programs such as Indicators of Hydrologic Analysis (IHA) and Hydrology Based Environmental Flow Regime (HEFR) using periods of record extracted from historic IBWC and USGS stream gage data and include collecting survey and field data which are applied to correlated cross-section and habitat suitability analyses.