My vote is fail. Why not use this instead? Block is much more porous than concrete. If you are determined to go with an open topped system, I'd pour a concrete chute with a concrete footing and have a groove for the boards in the walls and the bottom of the chute.

https://www.agridrain.com/shop/c85/...1/inline-water-level-control-structures/


www.hoosierpondpros.com

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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).