MORPHOLOGIC CHANGES OF A MICRO-TIDAL, LOW WAVE ENERGY BEACH FACE DURING A SPRING-NEAP TIDE CYCLE, RHONE-DELTA, FRANCE

Detailed profiles of the beach face at the micro-tidal, low wave energ y shoreline of the Rhone-Delta were measured up to three times daily d uring one spring-neap tide cycle. Samples of sedimentary structures an d quantitative data of tides, wind, waves, swash and backwash, beach g roundwater levels and sediment transport were collected simultaneously . A qualitative model for morphologic changes of the beach face in the Rhone-Delta is based on these data. As the study period did not inclu de storms, the results are only applicable to low wave energy conditio ns. The morphologic changes of the beach face can be schematized as an alternation of three profile types: (1) straight, (2) concave and (3) convex-concave. The straight profile develops under lower energy cond itions (H-b < 0.25 m), while the convex-concave profile develops under higher energy conditions (H-b > 0.35 m). The concave profile takes an intermediate position. The influence of the micro-tidal cycle (mean r ange 0.21 m) on the beach face morphology is expressed by the exact po sition of the step and the berm crest. Slight variations of the three profile types develop under conditions of strong offshore winds result ing in eolian sediment transport towards the beach face and during hig h groundwater levels relative to sea-level leading to localized mid-be ach face erosion caused by impermeability of this part of the beach fa ce. Sedimentary structures were classified according to the observed m orphologic zones in the beach face environment.