Stream: Animas River (Lower Segement) Executive Summary

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Biological Data This segment of the Animas River is a moderate gradient stream with moderate to large substrate size, often punctuated by large boulders within the stream channel. Many portions of the stream channel have been affected by historic mining that moved bedload materials. Natural hydrologic processes since the mining activity ceased have created a natural stream channel, but some portions of the river are still highly braided and lack good width to depth ratios. Water quality in the stream segment is affected by heavy metals from both natural sources and historic mining activities within the watershed. Minnie Gulch, Maggie Gulch and Cunningham Creek contribute water to the river that has lower concentrations of heavy metals, so water quality improves as you move downstream through the reach. Fish surveys have documented naturally reproducing populations of brook trout in this reach. Brook trout are the trout species that are most tolerant of heavy metal loads, but they indicate that the stream has sufficient macroinvertebrates to provide for fish forage, and that the stream has basic ecologic functions. Brook trout are not found below this reach, indicating that downstream heavy metal loads are once again too high for fish habitat. The riparian community consists primarily of willows and potentilla. The riparian community in this reach is vigorous and has succeeded in converting the stream from a braided system to a channelized environment that is more favorable to fish populations. Field Survey Data BLM staff used the R2Cross methodology to quantify the amount of water required to preserve the natural environment to a reasonable degree. The R2Cross method requires that stream discharge and channel profile data be collected in a riffle stream habitat type. Riffles are most easily visualized, as the stream habitat types that would dry up first should streamflow cease. This type of hydraulic data collection consists of setting up a transect, surveying the stream channel geometry, and measuring the stream discharge. Biological Flow Recommendation The CWCB staff relied upon the biological expertise of the cooperating agencies to interpret output from the R2Cross data collected to develop the initial, biologic instream flow recommendation. This initial recommendation is designed to address the unique biologic requirements of each stream without regard to water availability. Three instream flow hydraulic parameters, average depth, percent wetted perimeter, and average velocity are used to develop biologic instream flow recommendations. The CDOW has determined that maintaining these three hydraulic parameters at adequate levels across riffle habitat types, aquatic habitat in pools and runs will also be maintained for most life stages of fish and aquatic invertebrates (Nehring 1979; Espegren 1996). For this segment of stream, five data sets were collected with the results shown in Table 1 below. Table 1 shows who collected the data (Party), the date the data was collected (Date), the measured discharge at the time of the survey (Q), the accuracy range of the predicted flows based on Manning's Equation (240% and 40% of Q), the summer flow recommendation based on meeting 3 of 3 hydraulic criteria and the winter flow recommendation based upon 2 of 3 -3-