mag

Malaysia Water Research Journal
BED LOAD CHANGES IN ESTUARY DUE TO SEA LEVEL RISE AND
HYDRODYNAMIC REACTION
Anizawati Ahmad (1) , Wan Hanna Melini Wan Mohtar (2) &
Nor Aslinda Awang (3)
(1,3)
1National Hydraulic Research Institute of Malaysia (NAHRIM), Seri Kembangan,
Malaysia,
e-mail: anizawati@nahrim.gov.my
(2)
Department of Civil & Structural Engineering, Faculty of Engineering and Built
Environment, Universiti Kebangsaan Malaysia 43600, Bandar Baru Bangi, Malaysia,
e-mail: hanna@ukm.edu.my
ABSTRACT
The complexity of estuarine hydrodynamics is due to the continuous interaction
between freshwater and saltwater. The hydrodynamic process is influenced
by marine factors such as tides, waves, salt water intrusion, river discharge,
sediment type and shape of the mouth. This research attempts to investigate
the bed changes at Kuala Pahang due to sea level rise-induced hydrodynamic
reactions. The study area experiences dominant mixed semidiurnal tides and is
projected to be hit with sea level rise of 0.034, 0.144 and 0.307 m in years 2020,
2060 and 2100, respectively. The rate of sea level rising is the third highest, at the
East Coast of Malaysia after Kelantan and Terengganu. The increase in sea level
caused changes in water depth, bathymetry and hydrodynamic pattern. The
increase in flow velocity promotes erosion and the reduction in flow velocity lead
to sediment deposition. MIKE 21 software was used in the numerical modeling
to analyse the hydrodynamic processes while Sand Transport (ST) module was
used to study the sediment transport. The sea level rise factor was combined
to obtain the changes in the study area. The study is limited to the southwest
monsoon. Modelling work was conducted for a temporal scale of 14 days, taking
into account a full tidal cycle. The historical analysis of bathymetry changes
was done by comparing the bathymetry data in 1952 and 2014 using ArcGIS
software. The analysis showed that the bathymetry has changed between -0.08
to +2.9856 m in the last 62 years. Hydrodynamic modeling results indicate that
the flow velocity changed between -0.01 - +0.18 m/s on average, and maximum
between -0.06 - +0.2 m/s. Sediment transport modeling shows the average rate
of bed level change is between 0.2 to 0.6 m/dy and average bed load changes
was between 0.0002 - 0.0008 m3/s /m. Analysis has shown the southern part
of estuaries, meanders of rivers and near island experienced decrease in flow
velocity which indicate sedimentation.
Keywords: sea level rise, hydrodynamic, bed load changes
Institut Penyelidikan Hidraulik Kebangsaan Malaysia (NAHRIM)
13
National Hydraulic Institute of Malaysia (NAHRIM)