‘Low energy’ sandy beaches in marine and estuarine environments: a review

This review was undertaken to identify locations where low energy beaches may occur and their diagnostic forms and process controls, including waves, tides and water levels. Examples are drawn from the sheltered coastline of Western Australia near Perth and fetch-limited estuarine environments on the northeast coast of the United States. We suggest that the term low energy be used in locations where: (1) non-storm significant wave heights are minimal (e.g. <0.25 m); (2) significant wave heights during strong onshore winds are low (e.g. <0.50 m); (3) beachface widths are narrow (e.g. <20 m in microtidal environments); and (4) morphologic features include those inherited from higher energy events. Micro-topographic features can persist in the swash zone of low energy beaches under non-storm wave conditions. There is little evidence of cyclic cross-shore sediment exchange. Bars, excepting transverse forms, located seaward of low still-water level do not appear to be part of the sediment exchange system with the foreshore. Developing a better definition of the term low energy requires understanding the occurrence and duration of morphological characteristics and the type, magnitude and frequency of hydrodynamic controls that are responsible for these characteristics. Efforts also should be directed toward: (1) discriminating between processes generated within basins (in true fetch-limited environments) and processes generated outside basins (that affect sheltered environments); (2) identifying the relative contributions of tide- and surge-related water level fluctuations on low energy beach shape; and (3) estimating thresholds for beach change.