I am hoping to build a 7 acre lake by damming up a small creek that runs most of the year. Normal flow is just a trickle in the bottom of the creek bed, but during a rain the water rises very, very quickly and will fill my 48" culvert two or three times a year. In the last 10 years, my road over the 48" culvert has washed out twice. These rapid rises don't last long, and the water level in the creek will fall back to just a trickle within a few hours after the rain stops. The natural creek bank is about 6' to 8' wide at the bottom and ranges from 3' to 6' deep. The lake would be about 125 yards wide at the dam and close to 400 yards long. I know I would need a wide emergency spillway to handle the big rains. What I can't decide is how big of a spillway pipe I should install. I'm planning for at least 4' of free board, but that may not be enough either. I shot the elevations with a transit and found that the natural creek bed falls 9 feet from the dam site to where I want to back up the water. I'm new here, so please, experts chime in.
