Scour Protection for Dam Number 3, Monongahela River, Pennsylvania. Hydraulic Model Investigation.

Abstract : The section model was built to determine sizing and configuration of materials necessary to protect the downstream side of the structure from scour. Scour protection plans were developed for symmetrical distribution of discharges up to 185,000 cfs. The Type 2 riprap plan, which consisted of 3- to 4-ft-diameter stones offset 2 ft below the spillway apron and sloped downward 1V on 3H, was found to be stable for all flow conditions observed. The Type 7 scour protection plan, which consisted of grout-filled fabric bags (20.0 ft by 6.75 ft by 2.75 ft) offset 2 ft below the spillway apron and placed horizontally for 40 ft downstream of the structure and then sloped downward 1V on 3H, was also found to be stable for all flow conditions observed.