L - Alaska Energy Data Inventory

WATANADAMThe crest length of the dam has changed from 3,450 feet to 3,765feet, based upon new topography.As a result of explorations in the river bottom, the foundationexcavation has been revised. The river alluvium will be removed tobedrock under the cam. A grout gallery, excavated into rock, has beenadded to insure adequate treatment of the permanently frozen bedrock.The 1976 Interim Feasibility Report presented an earthfill damutilizing local gravel deposits for shell material. Explorations haverevealed that there are insufficient gravel deposits within economichaul distances. Since a large amount of sound rock will be generatedfrom spillway excavation and an excellent quarry source is availableimmediately adjacent to the damsite, the design has been revised tosubstitute rockfill for gravel in the upstream and downstream shells.Field explorations revealed an abundance of glacial till in the areasuitable for use as core material. For this reason, a semiperviouszone has been added to use the less expensive glacial material ratherthan quarried rock. The filters have also been revised to take advantageof adequate quantities of gravelly sand and the readily availablerock quarry (see Plate B-3). The gravelly sand from Borrow Pit E, nearthe mouth of Tsusena Creek, will be used for the fine filter, and rockfill,in the smaller sizes from the quarry, will be used for the coarsefilter. Details of the revisions are discussed in Appendix D, Foundationsand Materials.SPILLWAYThe saddle spillway centerline has been moved approximately 800feet southwest (see Plates B-2 and B-5). The foundation explorationsmore definitely located top of rock in this area; therefore, the spillwaywas relocated to insure construction in rock. Crest gate widthswere reduced from 59 feet to 55 feet after additional hydraulic calculations.The concrete lined downstream channel section was lengthenedfrom 150 feet to 800 feet to protect against rock plucking caused byhigh water velocities. The length of channel divergence was revisedfrom 930 feet downstream of the crest to 1,360 feet to improve hydraulics.The spillway channel slope was revised, requiring excavation its fulllength, so that it emerges at the Tsusena Creek level to reduce environmentaldamage expected from the 400-foot vertical water drop over naturalterrain with the original spillway design. This substantially increasesexcavation; however, almost all of the material will be used in the damembankment.B-3