Geomorphic Context , Constraints , and Change in the lower Brazos and Navasota Rivers , Texas FINAL REPORT September 2006

Submitted to the Texas Water Development Board 2 PREFACE This report is submitted in fulfillment of contract no. 2005-483-564 between the Texas Water Development Board and Jonathan Phillips (doing business as Copperhead Road Geoscience). The report is presented in two more-or-less independent parts, reflecting the Scope of Work for the project. The first is a review and evaluation of geomorphic stream channel classifications in the context of the Texas Instream Flow Program: Geomorphic Classification, Geomorphology, and Water Resource Management in Fluvial Systems: The Texas Context. Part 2 is a geomorphic assessment of the lower Brazos and Navasota Rivers, based on application of River Styles. Part 2 is presented in several subchapters. Each part has a separate list of references cited. INTRODUCTION Geomorphology—encompassing landforms, channel and valley morphology, processes of erosion, transport, deposition, and bank failure/stability—is vital for the management of river and stream systems. River engineering, aquatic and riparian ecosystem management, and water resource management all depend on characterization and understanding of fluvial geomorphology. In response to these needs a number of river and stream classifications and characterizations based on, or incorporating, geomorphology have been developed. The purpose of this paper is to review the geomorphological basis of classification and 7 characterization schemes, and to evaluate them with respect to two criteria— relevance to instream flow assessment and management programs, and appropriateness for application in the Texas coastal plain. The most obvious differences between fluvial systems—or different portions of the same fluvial system—are geomorphological. Aspects such as channel width and depth, bank type and steepness, floodplain morphology, slope, bed and bank material, valley wall confinement, etc. are clearly critical not only to fluvial geomorphologists, but also to river engineering and to any human access to or use of river resources. Fluvial geomorphology also affects, and reflects, hydrologic processes and regimes. The type and quality of aquatic and riparian habitats are also directly related to specific landforms and geomorphic processes There is little or no dispute of this contention. Statements such as Montgomery's (1999), for example, that " spatial variation in geomorphic processes governs temporal patterns of disturbances that influence ecosystem structure and dynamics, " have never been seriously challenged. Evidence showing specific relationships between stream geomorphology and aquatic macroivertebrate habitat quality, densities, and diversity is presented by Sullivan et al. (2004). The widespread acceptance of geomorphology-based classification systems by ecologists, hydrologists, and water resource managers is evidence of the general …