I am in a duck club that uses the dual wall HDPE pipe in several locations under levees to hold and drain water. We just replaced a 24" one which developed a split after 17 years and eroded a "suck hole" in the top of the levee which I found when it collapsed under my Ranger. Personally I would not use it for a pond spillway in preference for schedule 40 PVC or smooth steel. 18" PVC may cost close to ductile steel anyway. Certainly in your case of a 36' high dam follow the engineering recommendations.

Last edited by Redonthehead; 03/14/17 06:59 PM.
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