My pond is going to be excavated and not have a regular dam, just an overflow drain and emergency spillway. I’m going to repurpose the current drain in the area that’s currently used for downspout and sump pump discharge and runs down to a culvert. The downspout and sump will be rerouted into the pond. My concern is the elevation of everything, especially since the line for sump and pond drain are at basically the same depth. How do I have the pond pipe drain and emergency spillway drain without back flowing into the sump/downspout line?
I had considered having the sump at or very near the water surface with a back lower preventer but wasn’t sure that would consistently drain the pipes and/or be safe in flood times if the emergency spillway was in use.
Never say never but the pond will be about 1/4 acre and will only be fed through runoff (about 2 acres of watershed) and the sump/downspout so I don’t expect the emergency drain drain would be used much at all.

I think the primary question is what kind of stuff might go into the pond from your downspouts and sump?

I’m not expecting any issues with that water assuming it’s as clean or cleaner than the runoff that will go in the pond. But I can always redirect down the road if it becomes an issue.

I would think that those sources would be decent sources for pretty clean rain water to be fed to the pond.... In my opinion, I would prefer my pond be fed clean water from off of a roof and / or ground water from a sump vs. runoff the from a field with possible chemicals contaminants etc.. so no problem with that as i see it.

Do you have a transit / laser level to confirm elevations? The way I see it, the sump pump is going to be able to pump into the pond no matter what level the pond is at..... The check valve will always prevent backflow. Now with that said, check valves and sump pumps do fail so it would be good to verify elevations in case it fails during a flood or you have to change out the sump pump during a flood.. As long as the gutter downspout entry point is higher than the pond water level, the water will go to the pond... if they are not, then they back up, fill the drain tile around the house and at that point the sump pump would be responsible for all of that water plus any other ground water.

I'm not expert but that is my thought