staumauer bitburger dam on river prum

architecture background barrier bitburg bitburger blocking bridge canal concept dam day dike downstream dyke energy engineering environment europe flood floodgate flow flowing gate gateway germany green hydraulic industry lake landscape leafy levees lock passage power protect prum reflection reservoir rill river rural scenic sluice spillway spring staumauer stausee stream summer sunny surface system tree trees vehicular wall water watercourse watergate waterway waterworks weir