1 - Alaska Energy Data Inventory

for an 11 ft tunnel and a then current tank design volume of 61,586 ft 3(final design volume is 65,508 ft 3 for an 11 ft diameter power tunnel).Minimum water surface elevation on demand varied by only 0.06 ft betweenthe upstream and downstream locations. This minimal change would notaffect the final design.During preliminary calculations, a variety of transient calculationswere made for the air chamber 200 ft upstream and downstream from therecommended location. These calculations showed that only water hammer wassignificantly affected by relocating the air chamber. As a result only therejection condition was run for the upstream and downstream locations forthe design tank.These runs were based on the nominal ll-ft diameter power tunnel.results are as follows:TheMax. Hydraul ic GradientElevation at Air ChamberSurge Tank (ft)Additional WaterHammer (ft)Max. Hydraulic GradientElevation at Unit (ft)200 ftUpstream1,126.8255.21,382.0Tank LocationRecommendedLocation1,128.4201.01,324.4200 ftDownstream1,130.2165.41,295.6K. Air Chamber Air Loss - Potential loss of air from the air chamberis an important consideration. Air can be lost in three possible ways:1 ) Air leakage through the rock, 2) air entrapment in the air chamberwater, and 3) air leakage into the rock trap and power tunnel through asevere downsurge. Only points 1 and 2 above are considered in this sectionsince the air chamber surge tank has been designed to retain approximatelya 3 ft depth of water under the maximum expected downsurge condition.B4-18