**3. Morphological Characteristics of Lingayen Gulf**

Lingayen Gulf, with a width of 44 km and a length of 58 km, has an aspect ratio of 1.3 and opens to the South China Sea in the direction of N20◦W, as shown in Figure 1. This gulf has a semicircular embayment located on the northwestern coast of Luzon [10]. This area has two seasons—the wet season, from April to October, and the dry season, from November to March. Annual average rainfall in this area is 2500 mm with an average peak of 800 mm in August and a low of 1 mm in January. The mountains protect the province from the northeast monsoon and the trade winds but do not spare it from floods during the wet season. The west coast of this gulf has a complicated shoreline with many islands and headlands, whereas alluvial fans have developed along the east coast (Figure 1). A headland protrudes at San Fernando at the north end of the gulf, and the Balili River with a catchment area of 518 km<sup>2</sup> flows into the gulf 9.6 km south of San Fernando. Furthermore, the Aringay River with a catchment area of 405 km<sup>2</sup> flows into the gulf south of the Balili River, forming a delta. In addition, an elongated sand spit forms at Santo Tomas 18 km southeast of the Aringay River. In this gulf, incident waves have a strong directionality; waves are obliquely incident at a large angle relative to the direction normal to the shoreline because of the slender shape, so shoreline undulations due to high-angle wave instability [1] may have occurred.

The wave characteristics of this area can be estimated by the Global Wave Statistics [8]. In this report, the wave statistics in each area, separated into 104 subregions of all the world's oceans, are shown based on the wave observation data and the hindcast of ocean waves. The area offshore of Lingayen Gulf belongs to subregion No. 40, and the results are summarized in Table 1; wave height with a probability of occurrence less than 5% ranges between 4.26 and 5.71 m with the maximum of 5.71 m in the direction of N. This result corresponds to the wave climate in South China Sea offshore of Lingayen Gulf, so the wave height in Lingayen Gulf is reduced, subject to the wave-sheltering effect.

**Table 1.** Wave climate offshore of Lingayen Gulf [8].


Figure 2 shows the seabed topography of Lingayen Gulf with an average depth of 46 m and a maximum charted depth of about 100 m along its northern boundary [10]. Although a 20 m depth contour runs smoothly along the east coast, the contours shallower than 10 m in depth protrude around the Aringay River mouth and offshore of a sand spit at Santo Tomas. The formation of a sand spit on the bottom of the gulf clearly indicates the predominance of southward longshore sand transport under the oblique wave incidence from the north. On this coast with these characteristics, severe beach erosion occurs along the east coast because of the spatial imbalance in southward longshore sand transport.

**Figure 2.** Bathymetric chart of Lingayen Gulf in the Philippines (modified from [10]).
