Semi diurnal variability of Weligama beach due to tidal and wave actions

Abstract

The effect of the tidal and wave action on the Weligama beach in the vicinity of the Polwatta River mouth is studied for the first time. The Weligama bay is located in the southern coast of Sri Lanka at approximate coordinates of 80.45E and 5.95N. The changes of the beach and the changing water level at the river mouth during the tide were monitored for two consecutive days in June 10-11, 2006. The high tide on June 10* was in the afternoon around 2.30. The water level was increased by about 20 cm at the high tide. Increase of the tidal action due to full moon was observed on the June 11* and the maximum rise of the water level was about 30 cm. The short-term variation of beach accretion/erosion due to wave action was measured at two location tracks on the beach and it was found to be within + 10 cm. Accretion takes place onshore locations at both tracks during early afternoon on June 11*. Strong positive correlation (over 60%) between beach profile data and tide data is found at onshore locations during accretion on track B on June 11 *. Negative correlation of around 50% between the two data sets is observed at onshore locations when more erosion takes place on track B on June 10*.