The Science of Instream Flows: A Review of the Texas Instream Flow Program (2005)

Water resources in Texas have been important in the state’s history, settlement and current economic development. Most of the state’s boundaries are defined by rivers: the Sabine River on the east, the Red River to the north, and the Rio Grande along the southwestern border with Mexico (see Figure 1-1). Within Texas, several large rivers traverse the state, generally flowing from the northwest to the southeast and emptying into the Gulf of Mexico. Texas rivers such as the Brazos, Pecos, and Trinity have served as important transportation arteries and are part of historical lore in Texas and the American West. The state also contains numerous other streams that serve as sources of water for urban populations and provide important water supplies for riverine ecosystems. In some parts of the state, especially its arid western portions, groundwater supplies have long served as important sources of water for livestock and, more recently, as sources of water for irrigated agriculture.

Like many parts of the southern and western United States, Texas experienced marked population growth during the 1980s and 1990s. The state registered a sizable 22.8 percent growth from 1990-2000, and its 2003 total population was estimated at over 22 million, second only to California’s total population¹. Such growth is projected to continue, as estimations suggest that by the year 2050 as many as 900 Texas cities will need to reduce water use or develop new supplies to meet demands during drought periods (TWDB, 2002a). Population growth and associated increasing urban demands occur simultaneously with other Texas water supplies and demands: limits on the abilities to develop new supplies or re-allocate water among existing users; legal obligations to provide flows to sustain species and habitat; and greater demands for flows to support recreational, aesthetic, and related preferences. This dynamic setting is straining the ability of Texas rivers and streams to meet these sometimes competing demands. The three state agencies responsible for water resources in Texas are the Texas Water Development Board (TWDB), the Texas Parks and Wildlife

FIGURE 1-1 Major river basins of Texas.

SOURCE: Adapted from Hayes, 2002.

Department (TPWD), and the Texas Commission on Environmental Quality (TCEQ). These three agencies are also challenged to define the state’s streamflow and related water management policies.

During the 1980s and 1990s, these three Texas state agencies began to develop programs designed to provide specific flow rates or “instream flows,” in Texas streams and rivers in order to balance competing needs for limited flows. In Texas, instream flow describes “a flow regime adequate to maintain an ecologically sound environment in streams and rivers including riparian and floodplain features and necessary for maintaining the diversity and productivity of ecologically characteristic fish and wildlife and the living resources on which they depend” or flows needed to “support economically and aesthetically important activities … [including] navigation” (TPWD, TCEQ, and TWDB, 2002).

The Texas Instream Flows Program has its roots in two State Senate Bills. Senate Bill 1 (1997), commonly referred to as the “Water Bill,” estab-

lished the state water planning process with provisions for environmental values to be considered in water development and transferal activities. Senate Bill 2 (2001) takes the state water planning process further and initiated the instream flow program. Specifically, this Bill directs the TWDB, the TPWD, and the TCEQ to “jointly establish and continuously maintain an instream flow data collection and evaluation program,” and to conduct studies that determine flow conditions in the state’s rivers and streams necessary to support a “sound ecological environment.” Senate Bill 2 stipulates that priority studies are to be completed no later than December 31, 2010.

In response to Senate Bill 2, the three Texas state agencies designed the state instream flow program and present it in two documents, the Programmatic Work Plan (PWP; TPWD, TCEQ, and TWDB, 2002) and the Technical Overview Document (TOD; TPWD, TCEQ, and TWDB, 2003). The PWP outlines the scope, timeframe, and methods that the agencies are proposing to plan, design, and implement priority flow studies. The PWP identifies the goals of an instream flow study to “determine an appropriate flow regime (quantity and timing of water in a stream or river) that conserves fish and wildlife resources while providing sustained benefits for other human uses of water resources.” Eight components give structure to Texas instream flow studies: study design, hydrology and hydraulics, biology, physical processes, water quality evaluations, integration and interpretation, study report, and monitoring and evaluation activities. For every study, the three state agencies are proposing to divide and share responsibilities among the eight elements, depending on expertise. The TOD describes the technical aspects of instream flow studies, including sampling methods for individual technical evaluations.

The Texas instream flow program design has three phases. Phase one is the drafting of the PWP and the development of the TOD (completed December 2002). The second and third phases are peer-review activities. Phase two (this National Research Council (NRC) study) entails an objective, third-party review and evaluation of the scientific basis and soundness of the scientific and engineering methods proposed for use in Texas instream flow projects. Phase three is continued peer-review by Texas river authorities and stakeholders impacted by instream flow water management decisions.

In early 2003, the TWDB requested the NRC’s Water Science and Technology Board to review the program and technical methods proposed

for establishing Texas instream flow recommendations. Later that year, a committee of experts was appointed to evaluate the scientific methods, materials, and related technical aspects of the proposed PWP and TOD for developing instream flow studies in Texas. The committee conducted its deliberations and issued its report in accordance with the task statement contained in Box 1-1.

The committee met three times in Texas between autumn 2003 and spring 2004 in Austin, San Antonio, and San Marcos. A fourth and final meeting was convened in Washington, D.C. in May 2004. Portions of the first three meetings included sessions that were open to the public, and the committee heard from a wide range of experts and citizens with interests in the Texas instream flow program and in this study. People were also invited to submit written comments for the committee’s consideration. Many individuals accepted this invitation, and these written comments were considered along with formal presentations.

The NRC study and this report are directly responsive to the needs and the request for assistance of the three Texas agencies, but this report may apply to instream flow issues beyond the borders of Texas. In Texas and other western states, demands of growth tax water supply and quality and fair water appropriation. Texas water issues are microcosmic of national water issues: uneven distribution across space and time, competing uses, increasing demands, and changes in social preferences. Therefore, Texas’ approach to instream flows may serve as a guide for other jurisdictions wrangling with similar problems.

The study’s statement of task (Box 1-1) defines the scientific and technical issues associated with instream flows in Texas that are considered in this report, and the report reflects that charge. This report provides rigorous evaluations of the PWP and TOD. During the course of committee deliberations on the scientific and technical dimensions of instream flows, the context in which such flows are implemented emerged as being very important. The report thus comments on the scientific aspects of instream flows and the decision-making context in which instream flow recommendations are implemented.

The report is presented in five additional chapters. Chapter 2 introduces the necessary context for instream flow studies in Texas, including a

description of Texas river environments across the large state, current efforts and agency programs that provide the programmatic context for the instream flow study program, and Texas water code and legislation that frame the instream flow program. A brief tutorial on instream flow science and concepts is presented in Chapter 3, including examples of instream flow studies that have been implemented. The instream flow tutorial briefly discusses the scientific bases for instream flows and the characteristics of the most effective studies.

Chapters 4 and 5 present the evaluations of the Texas PWP and accompanying TOD, respectively. The evaluation of the PWP focuses on general plans for the program as a whole as well as plans for individual river basin studies. The TOD is evaluated in its entirety and by discipline: hydrology and hydraulics, physical processes, biology, and water quality, and integration of separate discipline studies into an instream flow recommendation. These evaluations of the Texas instream flow documents constitute

the bulk of the report, findings, and recommendations. The final chapter of the report focuses on implementation aspects of the instream flow program, challenges of implementing an instream flow program in Texas, and integration of the instream flow program with existing water-related state programs.