A control structure is normally built with reinforced concrete and treated timbers. The major benefits the manufactured stoplog control structures have over the field constructed types are that they are light weight, inexpensive, and allow for easy water level adjustments. The other common type of drop structure is the swiveling pipe structure. The inlet is a swiveling arm placed inside the drop structure. The water level is regulated by simply rotating the swivel arm.
Beaver activity can cause major problems in a restored wetland.
The blockage of the principal spillways by beavers raises the water level and can flood near by lands. This results in constant maintenance of removing debris from inlets. To control the beaver problem than can be removed by the same methods as muskrats. Since this is only a temporary solution the wetland should be made as beaver proof as possible, if the project exists in an area known to be home to beaver. Trash guards or grates should be installed at the inlet of principal spillways to restrict debris from flowing into the piping and restricting water flow.