Okay Theo!! You are making my mind think!
A primary spillway and an emergency spillway!!

Primary set to handle overflow from the pump and dump excess and the emergency one set higher in the dike/ridge to handle rain excess. Gotcha... am I right? Can they both go to the same ditch? I'm thinking so since initially the geothermal guy said that all of the pump and dump water could go to the ditch (we've had several heavy floods since we've lived here the most recent - if you've followed the news - this year without any of our ditches filling with water -- just slightly soggy for a day or so).

What size pipe should suffice for each spillway?

And yeah on the bright side for the POND (not our electric bill \:D ) the geothermal should run during peak evap. periods -- plus I have M.S. so keeping it cool is a necissity in the hot times -- though I will probably not be able to drop the temp. down to 68 degrees in the winter anymore when I'm home alone since geothermal is most efficient when kept at a constant temp. -- ah well I suppose I can always wear shorts and a tee shirt).
Thanks!
I love this site!