Thanks for the quick reply. I guess my main question is designing the diversion ditch around the main pond. The ditch would actually have water flowing through it more often than the typical emergency spillway. I'm guessing with a 2-3" rain it would have water going through he diversion ditch because the 8" PVC won't handle much more than the normal flow of the stream. My main worry is the diversion ditch handling a lot of flow that I know I can see. I don't have a lot of room due to the terrain of the land but I want to make the diversion ditch as large as possible 30-40' with flat bottom and 3-4' foot sides. I'm guessing a highly erosion resistant grass would be the best for the bottom. The sediment pond would have 4' or so of free board in hopes of absorbing some flow before it went around. I think I can have as much as 450CFM of flow with a 6-7" rain.
