twinstack - I've built several myself, supervised the construction of a few and inspect a few now. (All of the above not meant to infer that i know anything about it, but will post a few random comments

- In my opinion, there's too much Government at every level, but you may want to find out if your State DNR or DEQ requires a permit to enlarge your pond (I wouldn't make a formal request, because the Beauracrats will usually say yes even if not required by law)
- If this is just a fun project, using your own equipment, have at it. Use impervious material for your dike. You intend to provide for an overflow, Riprap the outlet so it won't erode the dike.
- If a Big Deal Formal Project, then yes, have a qualified Engineer Design it, help you with the required permits and supervise consruction. He will design an Emergency Spillway so you don't lose it during the 100 year storm (or earlier)
- If you want to attract Puddle Ducks (Mallards, etc.) leave one area about 2' deep so they can feed off the bottom.
- If you go the formal route, there may be Grant Funds available if you call it a "Wildlife Impoundment"
First picture is of a pond I had dug last Fall, just before snowfall. Have to dress it up and seed this spring. It's spring fed, so plan to plant some Rainbow Trout for the Grandkids to catch.
2nd and 3rd pics are of a "Wildlife Impondment I built several years ago". Received a Grant for 50% of the costs, but had so many permits and Government types involved it was unbelievable - all just so a couple of Mallards and/or Woodducks could do their reproduction thing. Max. 4'head at the dike - floods 1 acre.
penokee /forums/images/graemlins/smile.gif