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EXECUTIVE SUMMARY <br />WINDY GAP FIRMING PROJECT DRAFT ENVIRONMENTAL IMPACT STATEMENT <br />• Ammonia concentrations in St. Vrain Creek, Big Dry Creek, and Coal Creek would increase under all <br />of the alternatives. The potential for exceedance of the water quality standard is possible for some <br />locations. <br />• In Carter Lake and Horsetooth Reservoir, total phosphorus, total nitrogen, and chlorophyll a <br />concentrations would increase, and DO concentrations would decrease. Lower DO concentrations in <br />Horsetooth Reservoir would contribute to continued exceedance of the manganese standard. <br />Aquatic Resources <br />The assessment of effects to fish habitat along the Colorado River was modeled following the concepts of the <br />Instream Flow Incremental Methodology (IFIM). This approach combines stream hydraulics, habitat use <br />criteria, and hydrology to predict fish habitat as a function of streamflow. Fish community and fish <br />populations were assessed based on changes in physical habitat, as well as projected water quality changes <br />within those systems in rivers and reservoirs. The changes were compared to the existing conditions to <br />determine if there would be factors that affect fish populations at the acute or chronic level. Major effects are <br />summarized below: <br />The amount and frequency of available fish habitat in the Colorado River would decrease under all <br />alternatives from reductions in streamflow. The greatest change would occur under the action <br />alternatives, where up to a 24 percent decrease in adult rainbow trout habitat just upstream of the <br />Williams Fork confluence would occur in 4 out of 10 years. Under the No Action alternative, the <br />maximum decrease in habitat at this location would be 9 percent in 3 out of 10 years. Effects to <br />juvenile rainbow trout and juvenile and adult brown trout would be less under all alternatives. The <br />greatest reductions in fish habitat would occur during high runoff for a few months in the early spring <br />and summer when Windy Gap diversions occur. A decrease in habitat at this time would have less <br />impact than changes in flow during other times of the year when Windy Gap does not affect flows <br />and less habitat is available. <br />• No adverse impacts to spring spawning rainbow trout or fall spawning brown trout are predicted for <br />any of the alternatives. <br />• The potential for exceedance of the aquatic life temperature standard would increase at lower flows in <br />the summer, but measurable impacts to fish populations are not expected because flow reductions in <br />July and August would be infrequent. <br />• The amount and frequency of available fish habitat in Willow Creek would decrease from reduced <br />summer flows. <br />• Lower water levels and changes in water quality in Granby Reservoir, Carter Lake, and Horsetooth <br />Reservoir are unlikely to impact fish. <br />• Increased East Slope streamflows would slightly enhance fish habitat in the Big Thompson River, St. <br />Vrain Creek, Big Dry Creek, and Coal Creek. <br />• Flow changes in North St. Vrain Creek under the No Action alternative would affect fish habitat both <br />positively and negatively depending on storage and release from Ralph Price Reservoir. <br />Vegetation and Wetlands <br />Permanent effects to vegetation and wetland resources would occur in areas that would be inundated by a <br />reservoir or located within the footprint of dams, roads, relocated transmission line, or other facilities. <br />ES -14 <br />