A gated, or controlled, spillway has floodgates. Stage the height of a water surface above an established datum plane. See gage height. Surface Area indicates the size of the surface of the lake at the level shown, in acres. Tail Level indicates the water surface elevation on the downstream side of the dam, in feet msl.
Volume indicates the amount of water in the lake at the head level shown, in acre-feet.
10 Year Flood a flood which has a ten percent chance of occurring in any given year. 50 Year Flood a flood which has a two percent chance of occurring in any given year. Several 100-year floods can occur within the same year or within a few short years. Also called the base flood . 500 Year Flood a flood which has a two-tenths of one percent chance of occurring in any given year.