arch dam backstop balustrade bamboo curtain bank bar barrage barrier bear-trap dam beaver dam boom boundary 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 rail railing rampart roadblock rock-fill dam seawall shutter dam wall weir wicket dam work