thanks for all the great info..........here are a few more details........it's gona be a pond for cows........but i also semi pro bass fish wanna be,,,,,,,so i have gave alot to making under points......sharp turns & fast ledges plus i will be putting in a windmill & bottom air.......i live in east texas.....we have great clay here ....can i use a pipe to controll most of rainfall......& a spillway for the flood waters......this tank is fed by a ditch & when it rain good it's moving some water.......if i put a pipe thru dam [ 6 inch] & put a 8 inch pipe on a tee with the tee being at water level .how far below & how far above with the 8 inch pipe do i go...thanks guys