McNary Dam, Columbia River, Oregon and Washington; Hydraulic Model Investigation.

The hydraulic model investigations described herein were conducted on a 1100-scale general model and were concerned with flow conditions at McNary Dam during the construction period and after the permanent structures were completed. Studies of flow conditions during the construction period resulted in the adoption of a plan that required only two main cofferdams for the river closure. The first-step cofferdam enclosed the north 13 bays of the spillway the second-step cofferdam enclosed the balance of the 22-bay spillway and the 14-unit powerhouse. As a result of the tests, the woodcrib method of closing the main river channel at the upstream leg of the second-step cofferdam was abandoned in favor of a rock and concrete tetrahedron fill.