Electrical Power for Valdez and the Copper River Basin-1981

occur, and may allow the rock to blend in with the surroundings. within several years. Blasting for tunnel construction couldtemporarily disturb resident wildlife. The above ground portion ofthe penstock will be a permanent scar on the hillside.Increased erosion and subsequent stream sedimentation may resultfrom cleared areas. The extent of this occurrence will be directlyrelated to construction techniques and can be avoided. Adverseimpacts which can occur to aquatic species as a result of siltationare numerous and well documented. Major impacts from siltation, as aresult of construction of the proposed project, include decreasedvigor or death of incubating salmon eggs by interfering with orpreventing respiration, loss of spawning gravels, and physicaldisturbance to both adult salmon and other resident species.Clearing of approximately 21.5 acres of vegetation would be requiredfor the transmission line. Visual impact would be significant.Clearing and construction activities could disturb nesting eagleswhich may result in desertion of eggs and young. Bird collisions·with power lines will result in mortality. Transmission poles couldbe the tallest object in the immediate vicinity and may commonly beused by raptors as a perch. Improper line spacing presents thehazard of electrocution to large raptors.Construction activities will disturb terrestrial wildlife and maycause avoidance of the area while construction is occuring. Thisimpact should be minor as no wildlife concentrations or criticalhabitat areas are known to occur in the immediate area.To prevent debris from reaching the turbines, construction of ascreen over the penstock intake at the lake will be necessary andcould require lake drawdown to the lake tap inlet. This will result·in dewatering the upper reaches of Allison Creek. If discharge didnot occur directly to Port Valdez or occur in a carefully controlledmanner it could create excessive discharge into the lower stream;possible scouring of the streambed; and depending when this occurred,above normal stream velocities could either prevent returning adultsfrom entering the stream or expose incubating eggs. Also, residentDolly Varden could be flushed out of the system to marine waters.Operation and Maintenance: During project operation, the lake levelwould be drawn down as much as 100 feet, primarily over the wintermonths. Biological impacts to the lake resulting from this drawdownwould probably be minor, although the aesthetic impact would besignificant. Fortunately, the lake itself is not visible from thetown of Valdez. Fluctuating lake levels could cause lake shoreerosion leading to landslides in steeper areas with accompanyinghabitat degradation. During winter, shelf ice formed by thedropping lake level could impede movement of mountain goats. Thelow number of goats in the area reduces the extent of this occurrence.The impacts which would result from project operation have thegreatest potential for adversely affecting the environment ofAllison Creek. The drawdown would dewater Allison Creek at its