newbe1,

Brettski makes good points relative to the reduced area of the 6 inch pipes and the 1 foot safety margin.

Often there is an opportunity for two natural spillways in a pond construction (at least in most excavated ponds I'm familiar with). They are always located where the dam tapers to meet natural ground on both sides of the pond. Sometimes the lay of the land can preclude these natural opportunities. If you have an opportunity to have one or two of these natural spillways, it could be a good thing, either as emergency or primary spillways.

It just makes me uneasy to have a plan which relies on water flowing through or over a dam to provide surge protection...of course, I live in a climate where we go from drought to 100 year floods over a weekend as is happening now in parts of Houston. Our twice a year 100 year flood is currently in progress in some parts of town.