Quick update. I got a 3/4" rain Friday night with the water level very close to the breach hole in the dam. I had the 2" drain running the whole weekend and it didn't drop water level, but water never came up enough to flow out the breach. I want to avoid breach flow of course. I left the valve partially open as runoff keeps flowing in.
From Weds midnight to Friday, they are predicting 3" more. It has me concerned, so I am going to get a 100' roll of corrugated 4" pipe and put it thru the breach hole. I hope to have a temporary overflow to help the 2" drain. There is an earthen bridge across the breach as there was a good bit of freeboard designed in. Soil has dropped from the underside of that bridge and mounded up, so I am leery about hand digging a trench thru. Just trying to find more ways to unload water without cutting more soil away.
Anyone ever successfully do a siphon going 5-6' above water level with flexible pipe? I'll be doing this alone, so can't get too fancy but thinking about trying. You can't seal seams (on a T) well, so may cap the bottom end and try to fill it from the pond entry up on top of dam, then pull it down to water level and uncap back end.
I have the fabric sleeve left over from the french drain project, so thinking 10' of perforated pipe and sock over the last 12', tied off at the end.. should prevent fish intake.
