Electrical Power for Valdez and the Copper River Basin-1981

I NTRODUCTI ONThe area considered for possible hydroelectric alternatives includedthe coastal area around Valdez, the Chugach Mountains, and portions ofthe Copper River Basin. This area corresponds roughly to the servicearea bf Copper Valley Electric Association, over whose powerlines theelectricity from any potential hydropower development would betransmi tted.This appendix describes the climate of the study area and thestreamflows derived for the five sites considered as hydropoweralternatives. These sites include Allison Lake, Tsina River, TiekelRiver, Tonsina River, and Klutina River. They are shown on the basinlocation map, Figurp 1 page 24 of the main report. The final page ofthis appendix is a plate which portrays reservoir regulation, includingestimated lake elevations, regulated and unregulated streamflows, as wellas firm and secondary energy for the favored development at AllisonLake. This was done on a monthly hasis for the years 1948 to 1977.CLIMATEThere is a wide variation in climate throughout the study area. Theregion adjacent to the coast is under maritime influence, with highprecipitation and relatively mild temperatures. The interior area hasmore of a continental climate, with extreme temperatures and lessprecipitation. Between these two areas is a mountainous transitionregion whose climate is a hydbrid of maritime and continentalconditions.Valrlez, the primary load center of the coastal region, is located ona well sheltered extension of Prince William Sound. Snowcapped mountainscontaini~g extensiv~ glacier areas surround Valdez on three sides, withrugged but unglaciated mountains to the south and southwest. Activeglaciers extend t~ within 5 to 10 miles of old Valdez to the north andreach down to the level of the glacial plain on which old Valdez islocated. This level glacial plain is a well forested area except for thetidal marshes south~/est and the glacial drainage area to the east. Theterrain surrounding Valdez exerts a pronounced influence on practicallyall aspects of the local weather and climate. The sheltering effects ofsurrounding mountains channel local winds into two distinct channels.From October through April prevailing winds are from the northeast; fromMay through September prevailing winds are from the southwest.Precipitation is abundant year-round, but builds up noticeably during thelate summer and fall. The heaviest precipitation usually occurs inSeptember and October; almost 25 percent of the total annual rainfalloccurs in these 2 months. Snowfall during the winter months is veryheavy. There is considerable cloudiness during the entire year, butslightly less tha~ is realized at Alaskan points farther southeast.About 1 day in 6 can be classified as clear. Although the high mountainridges to the north provide considerable barrier to the flow of coldcontinental air from the interior during the winter months, there is adefinite off setting factor in the downslope drainage from the highA-l