@kylee07drg – Using wood for sluice gates can be dangerous. I heard about a worker who fell through rotten wooden sluice gate boards and eventually died because of this.
The sluice gate was on a cranberry farm, and the guy had to stand on top of wooden planks to use a pole to open more wooden boards in front of the gate and let the water through. He didn't know the ones he was standing on were rotten, but he found out when they broke and he fell.
He lived for a couple of months, but he caught pneumonia while trying to recover from his broken leg. He then got sepsis and died.
So, if it were up to me, I would use concrete for a sluice gate. Metal would be my second choice, but concrete sounds like the safest, sturdiest option.