Welcome, Mac15. While this is not my area of experience, I have to agree that your drainage area sounds awfully large for the size of pond involved. If there was no other water control feature other than letting it overtop the dam, that overflow standpipe may well make a big difference when you rebuild. I would think you'd want to ensure that you have a very capable secondary spillway to handle heavy rain events, one that is sufficiently constructed to withstand a potentially high volume of water flowing over it for an extended period.

Be patient and some others will come along who have plenty of experience to offer you some insights on the project. Do you have any pictures of the area you could share? How about aerial/satellite photos or topo maps?

Todd La Neve

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1.5 & .5 ac ponds - LMB, BG, RES, YP, GC, HSB