Mancos Watershed Functional Assessment

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Mancos Valley since the late 1870’s. We conducted seventeen surveys at different locations spaced regularly throughout the valley and on the major tributaries. Each reach that was surveyed exhibited a specific set of characteristics that was unique to that particular part of the river, and these surveys should be consulted when considering future management or restoration plans for that reach. However, because we sampled many different reaches within the study area, we were able to detect geographic trends and patterns in the surveys that are useful in describing the overall condition of the Mancos River in the study area, and that will help provide a guide to restoration planning for this watershed in the future. We found that despite the long history of intensive human use, many aspects of the stream-riparian ecosystem of the Mancos River in the Mancos Valley and the surrounding areas are currently in good or very good functional condition, especially when compared to similar sized river systems elsewhere in the American Southwest. Water quality in the watershed as measured by the RSRA protocol was generally good, although there was a relatively high amount of algae in the lower Valley that suggests that there may be some nutrient loading into the river from agricultural run-off in this area. There was little active bank erosion or channel downcutting in the main river or the major tributaries. Mud Creek was the primary exception to this pattern, where there was considerable current erosion. Fine sediment deposition on the channel bottom of the main river and the major tributaries was limited, except in the lower Valley, where there may be a lack of regular scouring flows that would remove normal sediment loads. The diversity of aquatic macroinvertebrate within the river was mostly excellent, except again in the most downstream reaches. The presence of a good macroinvertbrate fauna was another indicator of good water quality and a lack of heavy sedimentation. Aquatic insects also serve as key source of food for native fish, including trout. The riparian vegetation in the flood plain adjacent to the river was generally abundant and vigorous in most reaches. Although there was an absence of dense shrubs and tall trees in the reaches that have historically been used as pastures for livestock grazing, new seedling recruitment for most riparian woody species was very good throughout the Valley. The presence of seedlings indicates that the woody component of the riparian system has the potential to recover rapidly in the future. When this happens, dense shrubs and trees along the stream banks will create additional shading and will reduce evaporation and current water loss from the river channel. It will also provide more and better habitat for wildlife species. Finally, there were very few non-native or exotic shrubs and trees, such as saltcedar (Tamarix ramosissima) and Russian olive (Elaeagnus angustifolia), in most of the reaches, except in a few locations in the lower part of the Valley. The lack of invasion of the riparian zone by exotic woody plants is exceptional for river systems like the Mancos in the American southwest. The removal of the non- native species at the few sites where they now occur, such as has already been conducted by Mesa Verde National Park, should be effective in stopping further encroachment in the future. The RSRA surveys also revealed several challenges to maintaining and potentially improving the stream riparian ecosystem in the Mancos Valley and the surrounding areas. First, the levees that line one or both banks in many reaches in the middle and upper part of the valley have isolated the river from its historic flood plain, and they have stopped the important natural processes such as regular over-bank flooding into the flood plain in these reaches. The levees also reduce the quality of the Mancos River as habitat for native fish, because they have prevented the development of important channel and bank structural features needed by the fish, including underbank cover, and frequent deep water pools and riffles. Instead, where there are levees, the channel is uniformly wide and shallow, with steep, cobble- lined, banks. The addition of woody debris to the river in these reaches could result in a significant improvement in fish habitat, and thereby increase the overall ability of the Mancos River to support a healthy and large fish population. Second, it appears that much of the moisture that has created the vigorous riparian plant community that occurs within the historic flood plain in the Mancos Valley is the result of leakage from unlined irrigation ditches that run throughout the valley, and does not derive primarily from the river itself. A key challenge to sustain the overall long-term healthy condition of the Mancos River will be to find ways to 4