Electrical Power for Valdez and the Copper River Basin-1981

PROJECT DESCRIPTIONThe proposed Allison Lake hydropower facility will consist of a laketap at 1,250 feet elevation, a rock tunnel from this level to 1,220feet elevation, and a 48~inch penstock reaching from the lake tapthrough the rock tunnel to one of the two proposed powerhouse alternatives(Figures 2 and 3). Both proposed powerhouse alternativesare located on Alyeska Pipeline Service Company property and eitherwould occupy about 1.5 acres. The Alyeska terminal site road wouldprovide access to either site, with only an additional 50-100 feetof road construction required.Powerhouse alternative #1 is proposed above the existing weir inAllison Creek, which was constructed by the Alyeska Pipeline ServiceCompany for a partial source of water for the terminal of the Trans­Alaska Pipeline. The proposed powerhouse is at an approximateelevation of 100 feet (Figure 2). The tailrace would run directlyinto Allison Creek at this location. The CE has not proposed a dualtailrace configuration at this site as described below for powerhousealternative #2; however, further consideration of such a feature atthis site is contained in the discussion section of this report.Powerhouse alternative #2 is proposed near tidewater at an approximateelevation of 10 feet (Figure 3). A combination of two tailraces areproposed by the CE for this powerhouse. One would discharge directlyinto Port Valdez, the other would discharge into Allison Creek nearthe proposed powerhouse. CE personnel have stated that the dischargefrom the proposed powerhouse could be regulated through each tailraceindependently or through each simultaneously. For example, flowthrough one tailrace could be constant while flow through the otherwould vary according to power generation requirements. In addition,a six-inch steel diversion pipe is proposed from the penstock toAllison Creek above the existing weir to provide supplemental waterif the tributary flow to the creek is not sufficient for the needsof Alyeska, and resident and anadromous fish.To allow disposal of the proposed spoil, excavated from the rocktunnel, an access road approximately 500 feet long will be constructedfrom the lower end of the rock tunnel at 1,220 feetelevation due east to the edge of a cliff. About 45,000 cubic yardsof rock is proposed to be dumped over this cliff and into a deepgorge.The proposed transmission line will run 3.5 miles from one of theproposed powerhouse sites to the Solomon Gulch substation of theSolomon Gulch hydropower facility, now under construction by theCopper Valley Electric Association. It will closely follow theroute of the existing Dayville Road along Port Valdez.RESOURCE INVENTORYLower elevations of thi/coastal forest in this region support densestands of Sitka spruce- and mountain hemlock with an understory of_T I' Common names of plant and animal species are used throughout t hi sreport. A list of scientific names is given in APPENDIX A.