Morphodynamic response of
estuaries to climate change
YUNZHU YIN
3rd year of PhD
Supervisors:
Dr. Harshinie Karunarathna
Prof. Dominic Reeve
2015 - 2016
Research project summary
My PhD research is to investigate the morphological changes in estuaries with the
impact of climate changes. The estuarine morphology is predominantly affected by
the environmental variables such as waves, tides and river discharges. However, the
sea level rising should also be taken into account when considering morphodynamic
change in the timescale of decades or hundred years. This research is to use a
process-based model Delft 3D to explore the differences in morphological changes
between current climate conditions and future climate conditions. The future sea
levels and storm climate will be taken into account to investigate future morphological
change.
Research activities
1. Site study
Objectives for the current period
1)
To set up the numerical model;
2)
To calibrate the model;
3)
To validate the hydrodynamic, wave and morphodynamic model.
1) Validation
The validations of the models were carried out by using measured tide, wave and bathymetry data.
The results show that the hydrodynamic, wave and morphodynamic modules of Delft 3D were able
to reproduce the measured conditions very well.
The Deben Estuary, which is located Suffolk, in southeast England, is my study area (Fig 1). The
reason for choosing this site is following:
1) The estuary is well-documented in field data that can be compared with the simulated results for
the purpose of model validation.
2) The vulnerable morphology makes this site as a good case to investigate the impact of climate
changes.
3) Waves play an important role in morphodynamic change. Although a series of offshore
sandbanks located at the mouth of the estuary are predominantly controlled by tide, the storm wave
climate of the southern North Sea has a great contribution on the adjacent coast (Burningham,
2006).
The offshore seabed of Deben estuary has a mixture of mud, fine sand and broken shell (HR
Wallingford, 2002) with the tidal range varying from 3.2m to 3.6m and predominant wave coming
from northeast.
Figure 3 Wave height validation at Point 2 (the position is in Figure.1 ) Figure 4 The measured (left) and resulted bathymetry (right)
2) Scenarios
Three sea level rising rates are considered including the minimum sea level, mean sea level rising
and maximum sea level rising (IPCC, 2001).
Felixstowe wave rider (Point 2)
Figure 1 interested places and domains
2. Methodology
This study uses the process-based model Delft 3D which has been developed by Deltares (Lesser
et al, 2004). The Delft 3D model consists of a number of integrated modules which allow simulation
of hydrodynamic flow (under the shallow water assumption), waves, sediment transport and
morphological changes. Therefore, this model is widely applied to river, estuarine and coastal
situations. The main idea was shown in the diagram Figure 2.
Tide
Sea level (rising)
Model
Sediment Transport
Wave
Figure 5 Modelled bathymetry based on the current sea level (left) and minimum future sea level (right)
Figure 5 shows the comparison of the bathymetry between the current sea level and future sea level
after taking into account the minimum sea level rising (increased by 0.2m) based on the average
wave data. It is shown that if the sea level has been rising with its lowest rate, the Deben estuary
would have a significant differences in current and future morphology change.
Average
Extreme
Bathymetry
Updating
morphology
New bathymetry
Figure 2 Two model storylines (Left: present scenarios model diagram; Right: future scenarios model diagram)
3. Results
The morphodynamic module was set up with wave model coupled into the hydrodynamic module.
Figure 6 The comparison of the erosion and accretion on the two points EBB (left) and HORSE (right) (Note: blue line: current sea
level; red line: future sea level based on the 0.2m increase; positions are shown in Figure 1)
Figure 6 shows that the ebb delta (EBB) will become more shallow and expansion when the sea
level has risen while the flood tidal delta (HORSE) in the inner estuary will not have a significant
difference in the aspect of bed level although there is still some erosions.
Conclusions and objectives for the next research period
1) The validated Delft 3D morphological model can been used to explore the morphodynamic problems in estuaries;
2) According to the preliminary results, the differences of estuarine morphology may happen between the current condition and the future conditions resulted from
the climate changes. So this will be an encouragement for the later work that investigating the further morphodynamics due to the extreme changes on climate.
3) The following work will force on the investigation of morphological changes due to other sea level rising scenarios and extreme storm conditions based on
future climate scenarios.