Bonneville Bradford Fish Ladder Erosion Repair

The work includes site preparation and placement of rip-rap for armoring a slope that has recently been scoured due to high flows. Site preparation includes demolition of a grouted rip-rap layer about 3 feet thick as shown on the attached plans. Site preparation also includes demolition of the concrete slabs indicated on the latest bathymetric survey. The existing rip-rap must be removed to the slopes and elevations shown on the attached plans to allow for placement of new stone in a layer 5 feet thick. The top of the existing slope is at approximately elevation +15 feet NGVD 29. The site preparation and stone placement will extend down to an approximate elevation of -27 feet NGVD29. Government furnished stage-duration data for Bonneville Dam between Dec 1 and Feb 28 is attached. The median historical tailwater surface elevation is 15.6 feet in the month of December and 16.7 feet for the entire period. Therefore, there is a 50% chance water depth is 45 feet however the data provided indicate that larger fluctuations between 35 feet and 65 feet should be anticipated. The Government anticipates that all rock placement will occur underwater. The stone to be placed has an average weight of 3,000 pounds and diameter of 3.3 feet. The Government estimates that 4,800 tons of stone will be required to complete the work using a density of 165 PCF. Quality control on grading includes surveys before site preparation, after site preparation, and after final stone placement. These surveys may be all bathymetric in nature depending on the water surface elevations, however the entire affected area must be surveyed. Quality controls on materials and placement specifications are in Section 35 31 19 STONE, CHANNEL SHORELINE/COASTAL PROTECTION FOR STRUCTURES.