One of my small ponds has a grate over the drain culverts and it would completely cover with debris. I ended up putting a piece of fencing in front of it at a steep angle with the top just above the grate level this catches the debris before it gets to the drain and is able to gather more debris than the grate would clog up with. When the water level gets to the culvert it is flowing over the fence but all the debris is held in the fence.