Influence of groundwater on the beach profile change

Abstract

Relationships of hydrological parameters which are groundwater level, rainfall, and tides to the beach profile change of a beach are examined in order to advance understanding on swash zone morphology. Heavy rainfall and drought affect the groundwater level in Malaysia during two seasons. First, heavy rainfall and storms contribute to higher groundwater level during the wet season; thereby enhance the erosion rate. Second, lesser rainfall or no rain during the dry season will drop the groundwater level and enhances the accretion rate. According to this phenomenon, seasonal variation factor has significant impact to the sediment transport due to the groundwater level effects. A field investigation is conducted at Desaru beach with three monitoring wells are installed cross shore to the beach along with a rain gauge at the upslope. A tide gauge is installed at jetty Tanjung Balau in order to record the water level. Two field works are done for one week during spring and neap tides for both seasons. From the analysis obtained, Desaru is categorised as medium-sandy beach with the mean of medium grain size, d50 = 0.37 mm. It is found that the highest rainfall occurred on July while the driest month occurred on April with no rainfall at all. Observations from both monitoring wells show that the groundwater surface is generally not flat but fluctuated with time from the Southwest to the Northeast monsoon. The beach groundwater levels in the two monitoring wells were affected by rainfall however groundwater level in the well that located near to the shore is highly affected by tidal fluctuation. Finally, it is found that beach with high groundwater level tends to erode and producing flatter gradient.