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

BOX ES-1
Statement of Task for Texas Instream Flows

The committee will appraise the scientific and engineering methods used to help establish instream flow recommendations in Texas rivers, and focus on the soundness and adequacy of the Programmatic Work Plan for developing instream flow studies developed by the TWDB, TCEQ, and TPWD. Specifically, the NRC committee will:

Evaluate the key documents that explain these scientific and engineering methods and their applications in setting instream flow recommendations. These documents are a) the 2002 Programmatic Work Plan, and b) a supplementary technical volume that describes these methods in greater detail.
Review and provide advice on several scientific and technical matters relevant to instream flow studies and recommendations, including:
1. appropriate spatial scales of analyses in hydrologic and related models;
2. use of habitat-flow relations in setting instream flow requirements;
3. use of landscape ecology metrics in setting instream flow requirements;
4. range of biophysical model parameters employed in the Texas State TMDL program;
5. applicability of water quality models used in the Texas State TMDL program to instream flow studies.

Evaluate findings and recommendations of Tasks 1 and 2 for consistency with the requirements of Texas law for the study of instream flows

relatively new, and basic premises of this field continue to evolve. How flow regimes influence the structure of aquatic and riparian ecosystems is largely unknown, although the management of these ecosystems is dependent on this knowledge (NRC, 2004a). Most instream flow programs specify a single, minimum value of stream flow that is required to (1) meet a legal standard or (2) sustain an endangered species or some other flow-dependent resource(s). However, current trends in instream flow programs are moving away from these single values and towards comprehensive river science. For example, instream flow hydrology and hydraulics now include the hydrologic regime with seasonal and inter-annual variation and not only a minimum flow value; biological aspects account for aquatic and riparian ecosystems and not just a single-species target species. In-channel and out-of-channel riverine physical processes are also considered, such as sediment dynamics and geomorphic processes, and water quality considerations in-

Table of Contents

Front Matter R1-R12

Executive Summary 1-15

1 Introduction 16-21

2 Scientific and Program Context for the Texas Instream Flow Program 22-31

3 An Introduction to Instream Flow Science and Programs 32-57

4 Evaluation of the Texas Instream Flow Programmatic Work Plan 58-74

5 Evaluation of the Texas Instream Flow Technical Overview Document 75-109

6 Implementation Issues 110-128

References 129-134

Acronyms 135-136

Appendix A Glossary 137-142

Appendix B Water Science and Technology Board 143-144

Appendix C Biographical Sketches for Committee on Review of Methods for Establishing Instream Flows for Texas 145-150