Lake Darling Spillway, Souris River, North Dakota. Report 2. Modified Spillway, Hydraulic Model Investigation.

The existing general spillway model of Lake Darling Dam was modified using the original linear scale ratio of 1:36. With modifications, the model reproduced the topography in an area extending 750 ft upstream, 1,700 ft downstream from the axis of the dam 485 ft to the left and 460 ft to the right of the center line of the spillway. Model analysis of its performance was desired to evaluate stilling basin action and riprap requirements and to obtain discharge characteristics of the relocated structure. This model investigation was particularly concerned with flow conditions in the approach and exit channels, spillway capacity, hydraulic performance of the stilling basin, and channel protective stone requirements. The hydraulic performance of the stilling basin was evaluated by conducting hydraulic jump sweep out tests to determine the factor of safety of the design for holding the jump in the basin by lowering the tailwater below the minimum expected tailwater elevation for various discharges. Velocities and center-line water-surface elevations were measured in the approach and exit channels for various conditions.