From the ponds that I've seen with properly installed overflow pipes, I recommend them instead or relying on an earthen spillway. We're talking about years and years of usage, and soil will erode, no matter what vegetation is growing on it. I am of the opinion that if you build it right, you only have to build it once.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).