Tennessee Valley Authority. Construction of Douglas Dam. Hot tar tank tender at the site of TVA's new Douglas Dam on the French Broad River. His job is to supply hot tar used to fill cavaties in the bed rock. This dam will be 161 feet high and 1,682 feet long, with a 31,600 acre reservoir area extending forty-three miles upstream. With a useful storage capacity of approximately 1,330,00 acre feet, this reservoir will make possible the addition of nearly 100,000 kilowatts of continuous power to the TVA system in dry years and almost 170,000 kilowatts in the average year