Two sectional models were used to check performance of the proposed spillway for John Day Dam and to develop improvements if necessary. A three-bay section of the 20-bay spillway was studied in a 1:41.14-scale model. A two-bay section of the 17 low bays to be used during second-step construction was reproduced in a 1:24-scale model. Modifications of the crest piers to reduce the danger of cavitation during unusually large spillway flows were recommended. Discharge ratings in the three-bay model indicated that capacity of the spillway was slightly greater than computed for the design flow of 2,250,000 cfs. A 185-ft-long stilling basin at elev 114 performed as well as a 210-ft-long basin at elev 118. Three 10-ft-high baffle piers produced desired flow conditions in bay 2 of the stilling basin.

Two sectional models were used to check performance of the proposed spillway for John Day Dam and to develop improvements if necessary. A three-bay section of the 20-bay spillway was studied in a 1:41.14-scale model. A two-bay section of the 17 low bays to be used during second-step construction was reproduced in a 1:24-scale model. Modifications of the crest piers to reduce the danger of cavitation during unusually large spillway flows were recommended. Discharge ratings in the three-bay model indicated that capacity of the spillway was slightly greater than computed for the design flow of 2,250,000 cfs. A 185-ft-long stilling basin at elev 114 performed as well as a 210-ft-long basin at elev 118. Three 10-ft-high baffle piers produced desired flow conditions in bay 2 of the stilling basin.

The concrete-gravity ogee spillway of The Dalles Dam contains twenty-three 50-ft-wide bays separated by 10-ft-wide crest piers. The crest is designed to pass 2,290,000 cfs under a total head of 61.3 ft; the crest shape is designed for 75 per cent of maximum head or 46.0 ft. A 170-ft-long, hydraulic jump-type stilling basin, with one row of 9-ft-high baffle piers and a 13-ft-high end sill, will dissipate excess energy of spillway flows to and including the project design discharge of 2,290,000 cfs. The hydraulic performance of various elements for the spillway and stilling basin was studied in a 1:36-scale model.