Mancos Watershed Functional Assessment

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METHODS The Rapid Stream-Riparian Assessment (RSRA) Method The RSRA protocol (Stacey et al. 2006) was developed to provide a mechanism to objectively determine the functional condition of both the aquatic and riparian components of small and medium sized streams and rivers in the American Southwest and in other similar arid and semi-arid regions. It provides a standardized method to evaluate the existing conditions along a particular reach of the river, to determine which components of the stream-riparian ecosystem differ from what would be expected within the reach under geomorphicly similar but unimpacted reference conditions, and to create a yardstick to objectively monitor any future changes within the system that result either from active restoration programs or from allowing the system to follow its current trajectory under existing management programs. Because the protocol can be completed in a relatively short time and does not require specialized and expensive equipment, it is possible to efficiently survey a number of different reaches within a particular watershed. This then can provide an understanding of both the variation in conditions within a particular watershed, as well as any trends that might exist as one moves through the watershed that might indicate cumulative impacts of various activities upon the stream-riparian ecosystem. The RSRA method thus provides an effective tool to assess the current overall health of a river system at the level of the entire watershed. The RSRA utilizes a primarily qualitative assessment based on quantitative measurements made in the field. It focuses upon five functional components of the stream-riparian ecosystem that provide important benefits to humans and wildlife, and which, on public lands, are often the subject of government regulation and standards. These components are: 1) non-chemical water quality and pollution, 2) stream channel and flood plain morphology and the ability of the system to limit erosion and withstand flooding without damage, 3) the presence of habitat for native fish and other aquatic species, 4) vegetation structure and composition, including the occurrence and relative dominance of exotic or non- native species, and 5) suitability as habitat for terrestrial wildlife, including threatened or endangered species. Within each of these areas, the RSRA evaluates between two and seven variables which reflect the overall function and health of the stream-riparian ecosystem. Each variable and the basis for its inclusion in the protocol are briefly summarized in Table 1. Variables are measured either along the entire study reach (usually around 1 kilometer in length, depending on local conditions) or along 200 meter sample transects. Each variable is then assigned a score from “1" to “5", using predefined scoring levels that can be scaled to the individual geomorphic and ecological conditions of that particular reach. A score of “1" would indicate that the ecosystem is highly impacted and non-functional for that variable, while the other extreme, a score of “5", would indicate the system is healthy and is functioning in a way that would be found in a reference stream that has not been impacted by human activities. A complete description of the variables and the methods used to collect and score them is contained in Stacey et al., 2006). Assumptions and Limitations of the RSRA Method. In interpreting the results of a RSRA survey, several features of the protocol should be kept in mind. First, the protocol considers features or variables that not only indicate the ability of the system to provide specific functions, but ones that also reflect important ecological processes within the stream-riparian system. For example, the fish habitat section includes a measure of the relative amount of undercut banks along the reach. Undercut banks not only provide important habitat and hiding cover for fish and other aquatic species, but their presence along a reach indicates that the banks themselves are well vegetated, and that there is sufficient root mass from vegetation to allow the development of the hour-glass shape channel cross-section that is typical of most healthy stream systems. The presence of this channel shape would in turn indicate that the fluvial 12