Pond Boss Forums GENERAL QUESTIONS Property Projects & Construction Pond Build Planting Question

First off, WELCOME TO PONDBOSS and welcome to the forum!

Foolish question here.. I can't see where the culvert is but now it sounds like it is too your advantage to keep it plugged (or finish plugging it somehow) Or at least use it to your advantage. If the street runoff can be directed via this culvert to your pond great. Or if hampering the culvert's success adds more surface runoff of the street to your pond, then take it. I'm in a similar way that any road or surface run off I can capture is hundred of thousands of gallons of free, mostly clean water that comes into my pond. Once the streets are cleaned with a couple downpours the water rushing over the asphalt into the pond is pretty clean.

If you aren't sure about soil composition or how much clay is in the retention pond you may consider a small investment into a single unit (2 bags) of a 2 part polymer called soilfloc. Lots of good info and threads on PB forum with a local expert willing to advise. The beauty of using it now is that you have a freshly dug pond with no vegetation or leaf matter in the soil. You can till the dry soilfloc polymer (mixing part A and B) and scatter over the dirt and then till it under with rototiller or even with landscape rake. Or you can wait till it is mostly full or full and apply on the water and let it sink. This polymer will help clear the water, capture the suspended dirt/clay and pull to the bottom. Then the water pressure above and the moving 'silt' and polymer will find its way traveling into any cracks or veins and embed itself. It then expands and helps fill the cracks.

You don't have to decide now, you certainly can let it fill naturally with rain and runoff and then gauge how much it will lose through the ground and through evaporation and apply it next season. IT does seem to work a little better in warm water rather than cold water conditions. It is a fairly cheap product and adds good 'insurance' that you will seal the bottom better from the beginning and not lose so much water in between rain spells and to evaporation. Ground water ponds that rely on run off or rain are tricky and levels fluctuate widely. If it does fluctuate, at some point you may want to add a pond-side stab well or shallow well if water table is not too far down to help you add water when needed.

I'm sorry I can't be of much help with planting grass IN the pond bowl. My concern would be that anything that takes off in the bottom of the pond soon will be under water and will immediately die. Thinking positive for you hopefully with some fall rains you only will have to worry about seeding the edges and maybe the top few feet of the banks and the underwater portion of the pond?