Electrical Power for Valdez and the Copper River Basin-1981

Discharge measurements are sparse and; according to the CE, accuratepredictions of the amount of water flowing through the powerhousecannot yet be determined. Daily discharge measurements of AllisonCreek should be taken for a minimum of one year, beginning as soonas possible. However, collection of data for two years or more isrecommended. These data should be provided to the FWS quarterly toassist in refining discharge flow schedules through the proposedpowerhouse to Allison Creek.The CE has stated that tributary and groundwater flow to AllisonCreek will contribute seasonally to base flow in the creek afterproject operation. The specific amount of this flow is needed foranalysis in the development of flow recommendations to Allison Creekfrom the powerhouse. The CE expects that tributary and groundwaterflow will maintain adequate flow in that reach of the stream belowthe weir; however, during the low flow period of late winter andearly spring it may be necessary to supplement instream flow belowthe weir to 5.0 cubic feet per second (cfs). The proposed 6 inchdiversion pipe should be adequate to accomplish this.Temperature profile data of Allison Creek is needed to assessimpacts. The CE should conduct temperature profiles in Allison Laketo the proposed lake tap intake depth for a period of one yearbeginning as soon as possible. A minimum sampling effort shouldinclude the months of March, June, September, and December.Concurrently, water samples for testing dissolved oxygen, pH, heavymetal, and turbidity levels, should also be taken at the surface andat the same depth and general location of the proposed lake tap. Itmay be feasible for the CE to model or accurately predict the thermalregime of Allison Lake with data available for similar alpine lakes.If dissolved oyxgen concentrations are below 6.0 mg/l, correctivemeasures may be necessary if the dissipators do not insure dissolvedoxygen readings of 6.0 mg/l or above. A temperature probe or similarrecording device should be installed in the gravel where intertidalspawning occurs to record intragravel temperature for the same timeperiod. The thermograph now installed in Allison Creek should alsobe maintained throughout the same one-year period.With knowledge of the existing temperature regime for Allison Creek,the temperature of the water coming from the powerplant, the anticipatedbase flow, and the anticipated flow schedules for projectoperation, the temperature in the spawning beds could be predictedand the effects on developing salmon embryos calculated. Until theextent of adverse impacts can be identified, it is difficult topredict if any other form of mitigation may be appropriate. Itcould be determined that regulation of the thermal regime of AllisonCreek may be required to protect fish resourCeS.During the first year of project operations, daily temperaturereadings should be taken in Allison Creek below the tailrace dischargeand provided monthly to the FWS and the ADF&G. Depending onthe temperatures, it may be feasible that refinement of dischargerecommendations could further mitigate potential impacts due to