arch dam backstop bamboo curtain bank bar barrage barricade barrier bear-trap dam beaver dam blank wall block blockade boom breakwater breastwork brick wall buffer bulkhead bulwark cofferdam dam defense dike ditch earthwork embankment fence gate gravity dam groin hydraulic-fill dam iron curtain jam jetty leaping weir levee logjam milldam moat mole mound parapet portcullis rampart rock-fill dam seawall shutter dam stone wall stop wall weir wicket dam work