GRAIN SIZE CHARACTERISTICS OF NATIVE AND NOURISHED BEACHES IN TERNATE, CAVITE, PHILIPPINES

Abstract

 Sediment compatibility refers to the sediments ability to perform well compared to that of the native sand. It is often based on the granulometric similarity of the sand originally present in the beach and the sand that is used in the beach nourishment.Various methods are used to obtain this compatibility and the method used in the study is the median (D₅₀) grain size distribution. Two beaches (one native and the other nourished) located in Luzon, specifically in Ternate, Cavite, Philippines were investigated according to the characteristics of sand grain size. Specifically, the study aims to; (1) compare the median grain size (D₅₀) distribution of both nourished and native sand, (2) generate spatial distribution with respect to beach profile, and (3) identify the effects of sediment compatibility. Results of the sieve analysis range revealed that median grain size (D₅₀) of the nourished beach sand (0.5mm - 1.2mm) is greater than that of the native beach sand (0.19mm - 0.47mm). Based on the concept of sediment compatibility, the material used for nourishment in Puerto Azul area is not compatible as the nourished beach has significantly larger D₅₀ values. Both the dry and wet areas of the beach produced the largest values of D₅₀ ranging from 0.65mm to 1.2mm for the nourished beach and 0.21mm to 0.48mm for the native beach. The swash area produced the finest grain size among all the areas with D₅₀ ranging from 0.5mm to 1mm in the nourished beach and 0.19mm to 0.43mm in the native beach. The average slope of the nourished beach (15.5:100) is almost twice the average slope of the native beach (8:100), which supports the grain size characteristic of the study area that larger grain size develops a steeper slope compared to smaller grain size. The transport of the nourished sediments may be due to the incompatibility as well as the difference in specific gravity with the native sand.