Pond Boss Forums POND CONSTRUCTION Selecting a site Creek/Spring hole...fill or no? New Pond question

Hello. I am new here and I am afraid I might have to fix my brand new pond (it should end up being about 3 acres / 17 feet deep near dam). My dam was just finished about three weeks ago. We have had virtually no rain since then (less than one inch). I put a dam across a stream that ran about two-thirds of the year (run off from fields/pasture). But, the creek bed stayed mushy/swampy year-round. We speculated on whether a spring existed. When my contractor started the dam, he filled in the creek back about 50 feet from the dam and water started accumulating at that point so he dug a hole -like 3 to 4 feet deep to marshall the water in the hole. At first it was just about 5 feet in diameter. Now its about 15 feet in diameter and rising even though we have had little if any rain (and I have been sucking the water out with a pump to irrigate the grass seed on the dam). I am wondering whether I ought to have that hole filled in and put some more clay on the bottom? Something that has me worried is that on the downstream part of the creek (On the "dry" side of the dam), the creek I dammed and another creek join, which then goes parallel with the dam. That creek seems to have a lot more water in it than the rest of the creek (in fact, most of the creek is bone dry). I don't know what is causing that. Since we have had no rain, and the pond basically has no water in it other than the aforementioned hole, I cannot see how the dam would have anything to do with the extra water in the creek. One theory I have is that it may be from all the irrigation I have done on the dam. Maybe the water from the irrigation has worked its way down to the creek bed. Is there is a more sinister possibility? There is a core trench between 4' to 6' deep and there was no water in the trench when it was compacted.

Roxman71, welcome to the forum!

You might have quite a cunundrum there. If the water is in fact a spring, it can take away water as well as provide it.

Did your dam core reach good clay the entire length and up the sides to above full pool level? If the builder cut off the creek where the dam was built and dug down to good heavy clay and compacted the full length of the dam, the water backing up into the pond would be due to it not being able to flow past the dam.

Did the creek you blocked have spots where waater would seem to go "underground" and pop back up further downstream? If so, you dammed what is called a "losing" stream and about the only way to seal them is to line the entire pool area waith a good thick layer of compacted clay.

My first inclination would be to fill the hole with compacted clay, but experience tells me to wait and see if the pond fills considerably after a couple good rains and holds it's level well above where it is now. You will need to allow for some notable drops in water level to seep into the surrounding soils to saturate the ground after each rain and level rise. If the water level drops back to where it is now (or several feet) after a few days, a leak would be virtually certain then.

Thanks Rainman. I do think on the pool side of the dam, there was some areas where the stream I dammed went underground. However, all that (the marshy soil) was 30 yards or so from the where the dam is located and I never saw any evidence of a spring or underground water downstream. In other words, below the marshy area the creek bore into the ground about 5 feet deeper and resumed a normal hard bed. I wish I would have studied these forums more before I started the dam. I think I would have had the core dug deeper and would have gotten more soil testing. My contractor is going to look at the situation today. I thought about asking him to dig around with his backhoe on the back side of the dam, near the creek bank, to see if he can find any water flowing into the creek from under the surface - but, again, since there is no water in the pond yet, I don't know why there would be...