A linear regression fit gives rates of relative sea level rise of 12.6 and
14.8 mm/yr at Bangkok Bar and Pom Prachun respectively. These large
rises were not observed at group 1B stations, not even at Ko Sichang,
which is located nearby, 45 km to the southeast. Geological settings
provide an explanation for these differences. All group 1B stations are
situated on outcrop islands (Ko Sichang, Ko Lak and KoMattaphon) or in
areas of shallow bedrock (Sattahip). In contrast, both Bangkok Bar and
Pom Phrachun are situated in the estuary of the Chao Phraya River,
which is an area of nearly 2000m thick alternating layers of soft clay,
stiff clay and sand. With such sediment depths, it is not economically
feasible to construct the foundations of any building or structure on the
bedrock. Instead, a structure load needs to be supported by piles
standing on a sand layer around 20m beneath the surface. It was first
reported in 1968 that Bangkok was subsiding, and pronounced land
subsidence of the city started in the 1970s (Phien-wej et al., 2006). The
trend lines of Bangkok Bar and PomPhrachun exhibit faster relative sea