Jim and BranClan,
Good luck on your projects. Getting past the COE is only the first step.
As Dave points out, "impeding flood plains" almost certainly puts you on the radar of a multitude of regulatory agencies.
I don't know the rules in Texas, but here is the Kansas list of activities in floodplains that draw scrutiny and potential fines.
(c) “Development” means any man-made change to real estate, including, but not limited
to:
(1) buildings or other structures;
(2) mining;
(3) dredging;
(4) filling;
(5) grading;
(6) paving;
(7) excavation or drilling; or
(8) storage of equipment or materials.
After you get past the floodplain management regulations, you run into the levee regulations.
Basically, it is normally easy to get approval to grade your gravel driveway in the floodplain - but do not stockpile topsoil and gravel. You can probably get approval to dig a Texas "tank" style pond in the floodplain, but if you raise an embankment for the pond more than a foot above grade, then you trigger a slew of levee regulations. If you are impeding the floodplain, near homes or a city, then the review could get expensive very quickly.
My advice, get all of your approvals FIRST during the design phase of your project before you start spending money moving any dirt.
