Welsh Journals

Beach Morphology Changes at Ynyslas Spit, Dyfed, Wales. A.T.WILLIAMS N.E.CALDWELL A.P.YULE Polytechnic of Wales, Pontypridd. (received March 1980; in revised form November 1980) Abstract 12 profiles at Ynyslas Spit were surveyed over a 2 year period. Sedi- ment samples were obtained from fixed positions on these profiles dunes, high-tide, mid-tide and low-tide, and standard statistical parameters calculated. Mean grain size of the sand samples was found to increase seawards due to higher energy levels. Standard deviation values were found to be similar for the dune/high-tide zones and for the mid-tide/low-tide zones. 4 storms affected the beach morphology during the study period and a wave refraction model was used to study one of these events. Wave orthogonal convergence was observed at the northern end of the Spit. Volumetric data obtained for the storms indicated that changes were not the result of chance. The longshore energy flux factor for the major storm was 45,000 watts per metre. Introduction A detailed 2 year investigation (1976-78) into beach change of state was carried out at Ynyslas Spit, Dyfed, Wales (Figure 1). This beach is considered stable and 23 surveys of 12 profiles were undertaken during the investigation. The project was aimed at relating changes in beach volume and sediment characteristics to sea wave informat- ion. Unfortunately, the experimental period included only one storm of note from 11.11.77 to 13.11.77. However, a large amount of data related to the stability of the beach/dune interface was gathered over this period. Such information is required for coastal planning and engineering, especially the relationship between volumetric and strandline change, and wave energy. Beach slope responds to wave action by graduating to an equilibrium state under constant wave conditions (Sonu, 1973). Wave field growth acting on an equilib- rium profile causes erosion, the opposite causes deposition.