I am not sure how to post a drawing but did find a link showing a poor example of a "Kansas kettle" on page 11.
http://aquanic.org/publicat/govagen/ncae/redtmd.pdf
Most I have seen are much longer from the levee side out into the pond. Perhaps four times long as wide.
Basically it is the drainage structure for an aquaculture pond that facilitates safe removal of live healthy fish. It is sort of like a small raceway set in the bottom of pond, below the level of the pond bottom. Very similar to the drain trough in the above photos except it is much wider. Nearly 2 meters (I am thinking six feet) wide plus or minus some.
Then there is the wall in the center that is attached to the drain outlet side of the structure and extends nearly 3/4 's of the length of the raceway towards the pond. So essentially you have a "U" shaped raceway. On one side of the raceway wall closest to the pond levee is a fresh water supply. On the other side is the drain opening and a screen. The idea is that the live fish have no choice but to go into the raceway and then the flowing water keeps them alive and healthy until they are netted out and loaded into livehaul trucks or put on ice. We have two state fish hatcheries in MS with this type structure. It makes pond harvest much easier.
sorry you asked?
