Pond Boss Forums POND CONSTRUCTION Building a dam If your dam is wide enough...?

At what point do I not even have to bother with a core trench or worry about my dam size? If your daming up a creek and its solid clay soil and its 30-40 foot wide at the top and 90-100 foot wide at the bottom 1 to 3 ratio...There so much clay dirt there?....Do I need to even worry?

You core to make sure there isn't a seam or layer that water could seep through.
If there aren't any seams or porus materials below where you start adding fill it shouldn't leak.
Part of coring a dam is exploring. Digging down and looking for porus layers.
Borings offer guidelines into whether there are porus layers or not. Keep in mind that a million year old gravel stream channel that's not all that wide (might be missed by borings) might be under there. Or might not be.
Not being familiar with your area I wouldn't say whether you should core or not, just wanted to offer some general info.

See this for some of the whys.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=3;t=000167;p=1

FWIW: My big pond's dam is approximately 212 feet thick (700 wide, don't remember how tall) at base. They still did a keyway. In fact, where the ditch ran through, they did several keyways just to minimize the possibility of a seep or leak. Seems to have worked. Didn't add that much to time or cost. I'm glad they did it.

On the question of excavating the south side, if your material is good enough there is no reason to remove it, however, if any of the material is undesirable it needs to be removed. On the question of the core trench, your soil sounds ideal, however make sure that the old and new dirt gets sewn in. It is really not a very large expense for a core trench and is usually worth it.

For face72-on the tree excavation question, all the books say outside of the tree drip line.