The present invention is directed toward various valving arrangements to control the flow of granular material. In one embodiment, a valve is provided which facilitates flow of the material in one direction, but resists flow in another direction. In another embodiment, a retaining wall is provided with a plurality of generally horizontal passageways, which, under normal circumstances, resist passage of the flowable granular material positioned therebehind and, under modified circumstances, can serve as relief valves to avoid pressure on the wall which might cause the wall to move in an undesirable manner. In a third embodiment, a plurality of valving units is provided for beach retention of sand through efficient separation of sand from incoming waves.