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.'1.'" , nn'S"8 ,~ ~ .jJ' ~ .' .. i 'J - ,_ -0' Wetland Mitigation A- 9 i effects on wetland growth. However, the project will also contribute water during the spring. The growing season in the UncompahgTe Valley starts in late March. However, due to the high elevation of much of the drainage, the spring runoff does not usually come until early June. Between late March and early June, the Uncompahgre has historically flowed at very low levels (50 to 150 cfs). By consistently bringing significant amounts of water into the system during the early growing season, the project is expected to help 'jump-start' hydrophytic vegetation that may not otherwise have any water until mid-June. The situation is similar in the late growing season, when the project will again be delivering additional water into a stream that is otherwise largely dry. "Backwaters, recharge" effects are similar to those identified in enhanced and diminished diversity. The latter analysis is, however, limited to the water conveyance area defined by the HEC-2 model. There are significant numbers of abandoned back channels, gravel mines, sloughs and other low areas that are not part of the HEC-2 conveyance. These areas can be expected to fill through groundwater recharge and overbank flow during the winter and early spring months. As hydropower flows drop in the spring, they will leave behind willow pools and moisture. Wetland plants in these backwater areas will have the benefit of more moisture for growth. At present, water is limited in these areas, since flows are naturally low in winter and spring. Sponsors believe this benefit could yield creation or enhancement of 20 to 50 acres of wetlands; however, since these figures are not scientifically quantified, the benefit is not included in Table 1, above. Agricultural and commercial development along the Uncompahgre is located on and above the geomorphic terraces. Below this line, in the floodplain, land is generally used for wildlife, wetlands, calving or, for many agricultural owners, waste ground. Greystone's field delineations showed that less than 1/2 of this floodplain area is currently wetland. IncTeased water availability has the potential to add substantially to the wetland area between the terraces. Since there is no development in these lowlands, such wetland enhancement can come without adversely affecting cropland or infrastructure. Sponsors believe that portions of the widened channel will develop annually-emergent, hydrophytic vegetation as the spring flows recede. If approximately 20% of the widened channel develops such vegetation, it will increase net project benefits by another 8 acres for the 750-cfs project, 9 acres for the 850-cfs project, or 10 acres for the 950-cfs facility. Since only experience will show the true extent to which such vegetation actually develops, this potential benefit is also not included in Table 1. Please see Section X.C of the 1995 Final Report on Bank Stabilization, and Response USFWS-5 through USFWS-I0 in Applicants' Response to Public Comments for additional, detailed discussion of these and related effects. AS Lateral Hydropower Project July 2000 .f: . . " - ~"