I just recently aquired property behind my house (20 acres) that has a deeeep ravine, the creek sides are 12-15 ft tall. I had the NCRS man take a look and he told me that the ravine drains 320 acres and it was on the verge of being a flood control project. Said I could get done for 250,000 lol!! I decided to build a little pond instead. Is he right or do I need a second opinion?

It depends on how fast those acres drain, but that is a lot of land draining into your ravine. If it were mine, I'd watch it for a few years and get some pictures during flood events. Our stream (legal drain) drains close to a square mile and I could not afford to install a proper dam (even if they let me). The amount of water that runs through during a flood is impressive.

The NCRS man is correct as a trickle won't cut banks that deep. Maybe you could put a small pond to the side of the ravine and feed it from the ravine when it has water in it. Good luck.

I would agree with kenc. Without getting into to much minutia, water is relentless and always tries to go in a straight line unless it hits a diversion. If the creek banks are gradually V shaped and meander, then I would be less worried than if they're steep and fairly straight. Historical water flow can be read, but it doesn't sound good.

My two thoughts are, yes get a second opinion from a reputable pond builder, and whatever water comes in a pond has to go out. Building an overflow/drain system adequate enough to handle that much water could be a nightmare, and very expensive.

Silt and nutrient load from that much water could be an issue also.

Good luck, and keep swinging at it. I bet there's a solution somewhere.

To get a more accurate description, you really need to look at the peak flow from a given inch rain. A 300 acre flat, sandy watershed will flow much less runoff than a steep, predominantly clay 300 acre watershed. The NRCS guy is most likely correct though. 300 plus acres will likely be a lot of water in an 8 inch rainfall event.

My advice is to look for a smaller watershed to build on. Generally, a 300 acre drain will have a smaller tributary drain coming into it from the side that you could safely construct a dam across.

I agreement it into my bottom that out-of-the-way from a least slope for a level waste drain line, there is as well a utmost. The plan being that if there is too much slope, the solid will drain left more rapidly than the solids and as a result the solids may sling up in the line.