This is what I currently have. It is a 6" Sch40 PVC Pipe, 40' Long that goes through my berm. At full pool it will be about 3' under water. I have a "T" on the end with a female clean out adapter, which I will put the plug in when the water gets high enough to run out the pipe. Currently water is flowing into the pond through the pipe, helping it fill.
Here is what I am planning on doing. Coming off the top of the "T" will be a 6 to 8 reducer. The standpipe will be 8" SCH40. Over that I will slide a section of 12" Irrigation pipe so that water overflowing into the pipe will come from lower in the water column instead of off the surface. It hold the 12" inplace, I will use 3/8" stainless bolts through the 12", double nutted in place holding a bind against the 8" at the bottom (so no holes are in the 8" under water). At the top the 3/8" bolts will go into the side wall of the 8" to hold the 12" in place. The 12" pipe will be 2" taller that the 8" so that if the water rises enough it will bypass 12". 2" from the top of the 8" will be two 2" holes that will handle the water flow from normal rain events. The top of the 12" will be capped with a brass trash screen I am making from some scrap 1/4" brass rod and brass plate.
This setup should give me a 4 stage overflow system along with the arability to pull the 6" clean out cap and drop 3-4' of water.
Normal rain event, water will go between the 8 and 12" and through the two 2" holes.
Heavy rain event the water will go between the 8 and 12" and through the two 2" holes, while spilling over the top of the 8" pipe.
Severe rain event, water will spill over 12" pipe, through the trash rack, and directly into the 8" pipe.
Extreme rain event, emergency spillway will see water.
The pond is 1.5 acres with about a 1:3 to 1:4 watershed.
Any comments? suggestions? My main concerns are if the 2" difference in pipe height is enough or should it be greater and about the two 2" holes, are they the correct size?
