1 - Alaska Energy Data Inventory

C. Trashrack.(1) Losses - The primary trashrack has a gross cross-sect i ana 1area of 361 ft2 based on its 19 ft x 19 ft shape. The rat i 0 of the nettrashrack area to the gross area was estimated at 0.67 (the same ratio forthe intake trashrack at Long Lake) resulting in a net trashrack area of.67 x 361 ft2 = 241.9 ft2. With the maximum' expected discharge of518 ft 3 /s the maximum velocities through the net and gross trashrackareas are 2.14 ftls and 1.44 ftls respectively with the trashrack at 4.0 ftfrom the orifice. A flow net indicates that flow paSSing through thetrashrack utilizes a portion of the trashrack approximately 16 ft indiameter, resulting in functional gross and net trashrack areas of 201.1ft2 and 134.7 ft2 respectively. Maximum velocities through these areasare 2.58 ftls and 3.85 ft/s respectively. References 9 and 16 indicatethat the maximum velocity through the gross area of the rack should beabout 2.5 ftls with velocities of up to 5.0 ftlsec being acceptable forracks which are accessible for cleaning.To avoid damaging the turbine the trashrack will be put in place overthe orifice after the final lake tap blast and before any discharge ispermitted through the power conduit.(2) Hydraulic Losses Through the Trashrack - When considering thetotal trashrack (gross area 361.0 ft2 and net area, 241.9 ft2 with amaximum discharge of 518 ft 3 /S) the losses are:Trashrack ConditionNo clogging25% clogging50% cloggingHydraulic Losses0.05 fto. 12 ft0.34 ftIf we consider the 16 ft diameter area resulting from a flow net study(gross area, 201.1 ft2 and net area 134.7 ft 2 ), the hydraulic lossesare:Bl-42