Nearshore Evidence in Support of the Bruun Rule on Shore Erosion

The Bruun Rule on shore erosion states that for a beach and nearshore profile at equilibrium, as water level rises, sediments are eroded from the beach and deposited in the nearshore zone; in turn, the nearshore bottom is elevated in direct proportion to the rise in water level. The Rule was tested under field conditions. At Terry Andrae State Park, Wisconsin, nearshore profiles in Lake Michigan were surveyed once a week from April through July, 1971 as lake water level seasonally rose. The nearshore zone consists of two longshore bars which parallel the shore. The Bruun Rule is applicable in the zone of the first longshore bar system. As lake water level rose, the bars advanced landward, and from the base of the foreshore to the crest of the first bar, the elevation of the nearshore bottom increased. On the lakeward slope of the first bar crest, no deposition or erosion occurred. The elevation of the second bar crest remained constant as water level rose.