Conference program and abstracts - Coastal-Change.Org

Investigating inter--‐annual and multi-‐decadal signals in
tide gauge records from Vietnam; Implications for sea
level and coastal hazard studies
Dat T. Pham 1 , Adam D. Switzer 1,2 , Aron J. Meltzner 1,2
1
Division of Earth Sciences, Nanyang Technological University,
Singapore.
2
Earth Observatory of Singapore, Singapore, Singapore.
ABSTRACT
Coastal flooding commonly causes property and economic damage
and the loss of lives in low--‐lying and densely populated coastal
areas. Tidal variations and sea level variability are two of the primary
local factors that can enhance the risk of coastal flooding in
decades to come. On inter--‐annual time scales, tidal variations are
affected by two important cycles, name--‐ ly, the nodal 18.6--‐year lunar
nodal cycle and the 8.85--‐year cycle of lunar perigee. Investigating
these tidal modulations would allows potentially predicting periods
when enhanced risk of coastal flooding is likely.
In this study, we focused on high tide levels and extreme sea levels
which have not been extensively studied. We investigated sea level
data from three tide gauges distributed evenly along the Vietnam
coastline to define: 1) the inter--‐annual modulation signals (targeting
the nodal and perigee cycles) on high tide levels and 2) the long-
-‐term variations of extreme sea levels. We applied the percentile
time--‐series analysis method to figure out tidal modulations and least
squared equations to study the long--‐term rate of sea level change.
The results revealed that the nodal cycle predominates at Hon Dau,
which has a diurnal tide regime. In contrast the mixed tide regions of
Son Tra and Vung Tau showed no effects of either cycles. Regarding
long--‐term rates of mean sea level changes at all three stations, the re--‐
sults are fairly consistent with previous studies. Extreme levels at Hon
Dau show higher rates than the rate of mean sea level whereas at
Vung Tau, the rates for all levels are similar. The complicated variations
of extreme levels are found at Son Tra and it suggests further
investigation should be carried out.
The Fourth IGCP 588: PREPARING FOR COASTAL CHANGE 33