I have seen this problem in a few ponds that I ended up getting the job of rebuilding.The way that it was thought 30to40 years ago that sending the overflow pipe straight down the dam at such an angle that it was running with enough pressure to move a house right off the foundation.Now with the new style pipes it makes the job of installing a good solid overflow system much easier.The problem with the steel pipes was the corrugation the vibration of the water from start to finish would not only cut the flow rate in half but in most cases if there was a coupling joining the pipes together it would shake them apart.Lets not forget that copper sulfate has been around since the beginning of time and the damage that it can do to steel goes without saying.The cheapest way that I can think of with no risk of problems down the road 5to10 years is take some firehose cap one end fill it with water throw it in the pond uncap the end behind the dam below the water level or the desired level that you want and watch the level go down.If you have alot of flow add another hose when your done hang the hose in the shed. It won't end up costing you a dime in the future. Anyway, there are alot of options out there to get the draw down that you need without putting a large amount of dollars out of your pocket that you could use on beer.DOC

Doc