For my 1.8 Acre BOW, I have a 20' wide spillway, with 3-4" tall bermuda grass. 6" in 2-3 hours off of 35-40 Acres of watershed ( all grassland ) , 3 days of overflow and the bermuda acting like over lapped shingles , NO damage, no ruts, it never clogs . Very happy with my spillway . But, the dynamics of each pond , of each watershed is different . It all depends , probably applies . I've hired a professional dam builder for both of my ponds, who's primary income for last 50 years has been Federal water shed control dams .
Hire a professional . If going with spillway, maintain it .


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