Pond Boss Forums POND CONSTRUCTION Building a dam Overflow Pipe or Not

Some more info on spillways from another PBoss article.
From: "Spillways .... Avoid The Flood" by Mike Otto. PBoss Mag Nov-Dec 2007. Mike discusses spillway options for excavated ponds and ponds with dams. Here are some pertinent points from the artcle.

Spillway pipe is the principal or primary spillway. When the primary spillway cannot drain all the water, the pond fills to the secondary spillway called the emergency spillway whose job it is to quickly release huge amounts of water during heavy rains. The excess water should always flow through the spillway and not across the top of the dam. Excavated ponds are usually dug on flat ground and do not have spillway pipes because massive amounts of water in these ponds drains across the top and out, not downward through a pipe or over a dam. How do you wash out just a hole in the ground?. However most all ponds have some sort of dam unless the pond is built on very flat ground where the water fills the hole and out the top.
Reasons for a spillway pipe are: 1. Water management –release of bottom water or water drawdown. 2. Manage ordinary rainfall and protect emergency spillway from erosion damage. The emergency spillway should not be on top of the dam unless the spillway is rock or concrete. Small terrace can be used to divert water away from the backside slope of the dam . Thus if any erosion damage occurs it is to the spillway and not the dam.