Drilled shafts installed in lakes or rivers require use of a casing placed from above the water surface to a minimum embedment into the river or lake bottom. Do not define the top of the drilled shaft in the normal manner (a set distance below finished grade). Define the top of the drilled shaft as 1 to 2 ft. above the normal water elevation. If the water level is variable, add a provision allowing the top of the drilled shaft to be adjusted based on water level at the time of construction. Allow casing required for construction to remain in place at the option of the contractor. Typically, casings left in place look no worse than the stained concrete shaft that will be visible if casings are removed. If casing is to be left in place, disregard skin friction along the length of the casing. If permanent casing is used in standing water, consideration should be given to painting the portion of casing extending above the mud line.