**7. Similarity of Lingayen Gulf and Suruga Bay in Japan**

The beach changes along the east coast in Lingayen Gulf could be compared with those measured in another bay with a similar aspect ratio and wave characteristics, such

as Suruga Bay in Japan, shown in Figure 29. When a straight line is drawn between Point Irozaki at the tip of Izu Peninsula and Point Omaezaki in Figure 29, the width of the bay mouth is approximately 50 km, and the length of the bay measured from this straight line to the bottom of the bay is 60 km, resulting in an aspect ratio of 1.2. Since the width and length of Lingayen Gulf were 44 and 58 km, respectively, and the aspect ratio is 1.3, both bays are similar to each other in terms of width, length, and aspect ratio. In addition, the west coast of Lingayen Gulf has a complicated coastline with many islands and headlands, similarly to the east coast in Suruga Bay. The development of the Balili and Aringay River deltas along the east coast of Lingayen Gulf is similar to the development of the river deltas around the Ohi and Abe Rivers with the catchment areas of 1280 and 567 km2, respectively, on the west coast in Suruga Bay. Furthermore, the formation of a sand spit at Santo Tomas is similar to the formation of the Mihono-matsubara sand spit. Thus, the morphologies of both bays resemble each other so that waves are obliquely incident to the direction normal to the shoreline, and a sand spit has been formed near the bay bottom. Therefore, much experience of beach erosion along the west coast in Suruga Bay is useful in considering measures against beach erosion on the east coasts in Lingayen Gulf.

**Figure 29.** Satellite image of Suruga Bay (for location, 34◦36 16.73" N, 138◦16 50.47" E).

Figure 30 shows the seabed contours of Suruga Bay, which faces the Pacific Ocean to the south [20], and is a deep bay with a maximum water depth of 2000 m compared with that of 100 m in Lingayen Gulf. However, the coastline configuration of the west coast of Suruga Bay resembles the east coast of Lingayen Gulf; the coastline protrudes at the mouths of the Ohi and Abe Rivers, and Mihono-matsubara sand spit develops in the bay. Owing to the wave observations offshore of the Shimizu coast, the wave height with a probability of occurrence less than 5% is 3.0 m with a wave period of 9 s [21]. This wave height is the same order of magnitude in Lingayen Gulf. The rate of longshore sand transport was estimated to be 1.3 × 105 m3/yr around the sand spit at Santo Tomas, which is in good agreement with the value of 1.3 × 105 m3/yr estimated on the Shimizu coast surrounding Mihono-matsubara sand spit in Suruga Bay [21]. On the Shimuzu coast, severe beach erosion occurred owing to the decrease in the fluvial supply of sand after extensive riverbed mining in the Abe River, which is the supply source of sand, and the movement of a sand body occurred owing to the blockage of longshore sand transport by a number of detached breakwaters as described in [20]. Thus, the experience of the

beach erosion on coasts in Suruga Bay, fully described in detail [20], is useful in explaining the beach changes along the coasts in Lingayen Gulf at least as a first step before detailed numerical simulation.

**Figure 30.** Bathymetric chart of Suruga Bay in Japan [20].
