So going with option 1, the least cost method of excavating and hauling earthfill short distances is with large scrapers, which can carry up to 20 cubic yards per trip – and doing the math, there would be over 51 million such trips. Converting 634,000 acre feet to cubic yards (the common unit of measure for volume when excavating or dredging) yields just under 1,023,000,000 cubic yards. There are two primary ways to accomplish that: 1) excavation “in the dry” between the current water surface and the maximum water surface elevation with earthmoving equipment, or 2) hydraulic dredging, whereby a barge with a mechanical cutter head removes material from the lakebed and pumps it as a slurry through a pipeline to a disposal area where the excess water is removed and the material remains.Īn an acre-foot is an acre of land covered by a foot of water (43,560 cubic feet). To gain equivalent storage capacity, that volume of earth would have to be removed from the reservoir basin below the maximum water surface elevation and transported to an area above it. Raising the dam 18.5 feet would provide an additional 634,000 acre-feet of storage, and would cost an estimated $1.2 billion. It’s a matter of the huge volume of material that would need to be removed to gain the same storage volume as raising the dam. Yes, dredging and other means of excavating material from the reservoir footprint were considered as an alternative, but even a cursory look at the effort and the cost removes the idea from further consideration very quickly. Collins’ question is entirely logical and one that we’ve been asked periodically since the study began. Bill Collins, asked why Saturday’s column didn’t address the idea of dredging the lake to create additional storage space. Here's a response from the top engineer at the dam, posted last September: Twice in recent days people have asked the question.
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