A proposal to build a 31-mile water tunnel under the Grand Coulee was made by Frank Harris, a civil engineer from Renton. His plan, publicly announced in December 1935, was to expedite the irrigation of approximately 500,000 acres of land in the Columbia Basin by a gravity system, without waiting for Grand Coulee power. He figured that the amount of water required to lift and fill what is now Banks Lake would be 20,320,000,000 cubic feet before any could flow out into the main distributing canals. Frank reasoned the expense of this could be avoided by constructing a water tunnel approximately 300 feet below the floor of the upper coulee from the dam to below Dry Falls, using the chain of lakes in the lower coulee for reservoir purposes. To build the tunnel, shafts could be sunk every four or five miles, and drilling could proceed in two directions from each shaft, making it possible to complete in three years. Such a tunnel would cost $18,000,000 and would deliver water to the land by 1940, without wasting water or energy. This would have converted the high dam into a semi-gravity project. It is not known when this proposal died.

Dan Bolyard, Them Dam Writers online 2020