I recently completed a 5 acre pond that is holding water great and is about 12-16" from the spillway overfow elevation. Part of the watershed is a 15 acre pasture hill and we installed a 16" culvert x 100' long along with a berm to catch the water flowing from this hill and route to the pond. My contractor was supposed to install the culvert invert (bottom) elevation of the outlet at the same elevation as the spillway.

Since the water level has risen with recent rains, I now find the water level is at the outlet invert elevation and stil have at least a foot, probably around 18" to go before reaching the spillway overflow elevation. He tells me there is an 18" drop in elevation from inlet invert to the outlet invert elevation of the culvert.

It seems to me that as long as the inlet invert elevation is higher than the top of culvert elevation at the outlet, that water will stil flow but it sounds like it will be very close. Even if it does flow, I'm wondering if having the culvert outlet almost or completely below water at full pool will cause any other issues? Any input is much appreciated. Although time will tell with more rainfall, I'd like to have a preliminary plan.

Sorry if this gives you a headache to try and understand!

If you plan on having CC in the pond, the culvert might make good spawning habitat for them if it's under water. I don't know how that fits into your fishery plans.

Even with the elevation drop from inlet to outlet, depending on where you are measuring the water (bottom or top of inlet pipe?) at spillway level you potentially could be also dumping water out of that pipe.

Also, depeinding on the water level in the pipe, any stagnant water creates a good breeding ground for mosquitos. I don't know if they'll fly 90 feet to the water, but they surely will fly 5 feet or so, possibly more to get to the stagnant water inside the pipe to lay their eggs.

Nope, no CC, only CNBG, RES, and LMB. The bottom of the inlet culvert (away from pond) should be higher than the spillway, so I shouldn't get back flow thru the cuvert if this is the case. If its not, the culvert will surely have to be reworked. During a heavy rain there is a ton of water that flows through that 16" culvert and it it wont flow freely, the berm will be topped and washed severly for about 100' all the way to the pond.

Another heavy rain or 2 should answer the question. I have a fairly robust warranty provision in the Contract, so my contractor will be required to fix at his cost. Bottom of the outlet culvert elevation (at the pond) was supposed to be the exact same elevation as the spillway.

Whether he chooses to do so is another matter, but I believe he would.

Thanks for the response esshup.