Electrical Power for Valdez and the Copper River Basin-1981

As stated previously, two alternative sites have been proposed forthe powerhouse. Either site would require clearing of approximately1.5 acres for construction purposes. Some alteration of the streambankand streambed will result from installation of the tailrace andsedimentation could occur. The magnitude of these impacts could bereduced significantly depending on the construction techniquesutilized and the time of work.Impacts which would result from either of the proposed powerhousealternatives were described above. Those impacts which would vary,depending on the site selected, are described below.Powerhouse Alternative Itl: The discharge of flow from this alternativeis proposed by·the CE directly from the tailrace into AllisonCreek. Radical flow changes would result and all adverse impactsdescribed previously for alteration of flow would occur. In addition,if instream flows were totally dependent on power generation needs,periods of very low flow could result when the power plant was shutdown for maintenance or other reasons.The discharge of all project flows into Allison Creek at this sitewould also result in temperature and possibly dissolved oxygenimpacts occurring in the total reach of Allison Creek utilized byf ish. Flows in the creek above this site may not have any appreciablebuffering effect for maintenance of natural water qualitysince they would be low in relation to the flow through the powerhouse.Powerhouse Alternative 1t2: Impacts described above for site Itl mayalso be applicable to this alternative. This alternative has twotailraces proposed. If the tailrace waters were discharged directlyinto Port Valdez during the summer months, a portion of the salmonpopulation could be diverted away from spawning areas in the naturalstream by the larger quantities of Allison Creek water issuing fromthe tailrace into Port Valdez. Diverting water from the powerhousethrough the tailrace positioned in Allison Creek would alleviatethis impact; however, those impacts discussed above under powerhouse1t1 would occur. Hhen the discharge is diverted back through thetailrace into Port Valdez, some of the redds could be dewatered.Also, the discharge could prove to be such an attractant to adultsalmon that they would pool up below the discharge and not utilizeother portions of the stream or intertidal area for spawning.Periods of very low flow during powerhouse shut down could alsoresult from this alternative. The proposed 6 inch diversion pipecould be used to add supplemental water to the creek. However, theuse of the diversion pipe for long periods to supply water to thestream or as a substantial supplement to natural flows could alsocause early fry emergence as dicussed earlier.Diversion of flows directly into Port Valdez during most of the yearwould result in a reduction of water velocity in the natural stream~bed which could result in sedimentation of the spawning gravel.