Extreme Estuarine Flooding Leading to Estuary
Transverse Flow Salinity Intrusion
Nuryazmeen Farhan Haron, Wardah Tahir, Lee Wei Koon
Abstract
—The objective of this paper is to explain the extent of estuarine flooding to estuary transverse flow salinity intrusion. Water quality along the estuary is influenced by salinity intrusion during normal flow condition. However, during the extreme estuarine flooding, the water quality will deteriorate, due to the effect of the transverse flow salinity intrusion. This will reduce the productions of aquatic life. Animals, humans, and plants will also be affected. This paper also discusses a preliminary study on transverse flow salinity intrusion model in estuarine systems due to estuarine flooding. This paper is part of water quality aspects and flood risk management to keep water clean, especially in estuaries.Index Term
- estuarine flooding, transverse flow, salinity intrusion, estuaryI.
I
NT RODUCT IONEstuary is defined as an area where two waters namely
semi-enclosed seawater or freshwater (river) and open sea or
saltwater (ocean) meet [1]. During the process, distribution of
salinity in the estuary changes gradually depending on various
factors such as
space, time, movement of tides in the estuarine
system, fresh water discharge from river, difference in fluid
density, shape of estuary, wind effect, and Coriolis effects.
Since long time ago, the estuary has been the main focus of
human as a route of communication and trade, especially for
people in rural areas far from the coast. Recently, in Malaysia,
there has been rapid development of industrial and power
generation activities taking place in the estu arine system.
These have brought great changes to the natural balance in the
estuarine topography due to the dredging of shipping lanes
along the bottom estuarine, and the disposal of industrial
wastes into the water system.
Furthermore, the pollution in the estuary and the
surrounding area will become more serious during flood.
Flood events involve areas where there is changing of wet and
dry conditions, which are a common situation in the estuaries,
lagoons and rivers, or floods resulting from dam breaks and
prolonged rainfall, or any flows of shallow water exposed to
large changes of its free surface [2]. Extreme flood events in
Malaysia, specifically in Johor at the end of the year 2006 that
lasted until early 2007 as well as in Pahang in 2001 and 2007,
had impacted the estuaries; the salinity level in the areas had
decreased dramatically.
When such phenomenon occurs, aquatic life along the
estuaries and river area will be affected due to the decline of
water quality level. Eventually, low water quality can cause
many adverse effects to animals, plants, and especially to
humans. For example, when a person takes or uses
contaminated water, various kinds of diseases can be
transmitted from the contaminated water, such as hepatitis A,
blue baby syndrome, and food poisoning.
This paper presents the preliminary study on extreme
estuarine flooding and the estuary transverse flow salinity
intrusion caused by it.
II.
E
XTREM EE
STUARINEF
LOODINGANDT
RANSVERSEF
LOWS
ALINITYI
NTRUSIONA.
Extreme Estuarine Flooding
The extreme flood events in Johor at the end of the year
2006, which lasted until early 2007, had impacted the Pulai
River estuary; the salinity level in the estuary decreased
dramatically. When the salinity level decreased, the dissolved
oxygen (DO) level increased, as also reported in the study by
[3] at Neuse River estuary, North Carolina, USA. This
phenomenon had eventually impacted Johor’s economy. The
centre of shellfish and aquaculture industry in Western Johor
Strait suffered significantly from the storm-driven low salinity
event [4]. In addition, the production of mussels in the Johor
Straits declined due to high fresh water inflow (Fig. 1). The
mussel production must meet a minimum quality requirement
or standard in order to get a certificate for export purposes.
Fig. 1. T he decline in mussels production on Johor Straits due to flood event (Source: Berita Harian, Feb. 2007).
B.
Transverse Flow Salinity Intrusion
Many studies have been done to evaluate the estuarine
characteristics such as changes in estuarine salinity [5-13],
sediment from various aspects of the shear effect [14-22],
influence of wind [23-28], tidal effects [29-34], and runoff
T his work was supported in part by the Ministry of Higher Education(MOHE) and Universiti T eknologi MARA (UiT M), Malaysia under Grant Research Acculturation Grant Scheme (RAGS). F. H. Nuryazmeen is the PhD Candidate, Faculty of Civil Engineering, Universiti T eknologi MARA 40450 Shah Alam, Selangor, Malaysia
(email: neemzay@yahoo.com).
effects [7, 8, 28, 35], using numerical modelling. However,
there is a lack of research to see the mixing process between
saltwater and freshwater in estuaries during the normal flow
and high flow in a transverse flow.
The extreme estuarine flooding does not only affect the area
along the estuary (longitudinal or x-direction), but it also
affects the land due to the transverse flow (y-direction) (Fig. 2).
The salinity distribution and salinity intrusion length may be
considered as major environmental factors affecting the
existence and distribution of organisms in estuaries. The
extreme estuarine flooding and transverse flow salinity
intrusion affect the water quality and the environment —the
productions of aquatic life will eventually decline, and humans,
animals, and mangrove areas will also be affected.
Fig. 2. An example of transverse flow (y-direction) in estuary due to extreme flood event.
III.
T
HEE
XAM PLE OFE
STUARINEF
LOODINGAT
S
UNGAIP
AHANGE
STUARINES
YSTEMSungai Pahang, which flows for a length of 440 km, is the
longest river in Peninsular Malaysia (Fig. 3). It has a
catchment area of 29,300 km
2with an average annual rainfall
of between 2000 and 3000 mm. The tidal influence of this
river extends about 25 km upstream from the estuary. Severe
flood occurred in 1967, 1971, 1999, 2001 and 2007, where
houses at the estuarine and coastal areas were hit by the
combined effect of high tides and flood discharge (Fig. 4 and
5). The joint occurrence of severe flood discharge from
upstream of the river with high seawater level caused the
historical major flood in Pekan town and areas close to the
estuary. The estuary area was flooded even though there was
no rain before or during the flood occurrence.
Siltations at the river mouth also contribute to the flooding
especially during the northeast monsoon season. Other than
that, salinity level in estuarine system also changes during
flood. Salinity level declines dramatically during monsoon
season, for examples, in 2001 and 2007. Fig. 6 and Fig. 7
show the locations of water quality monitoring stations at
Sungai Pahang estuary, and the graph of salinity level near
Sungai Pahang estuary at eight river stations from 2001 until
2011 respectively. Meanwhile, Fig. 8 and 9 show hydrological
stations in Pahang, and the hydrograph near Sungai Pahang
basin from 2000 to 2012, respectively.
Fig. 3. View of Sungai Pahang estuary.
Fig. 4. View of flooding in Pekan T own near Sungai Pahang Estuary.
Fig. 6. Locations of water quality monitoring stations at Sungai Pahang estuary (Source: http://www.enviromalaysia.com.my/wqm_pahang.php).
Fig. 7. Salinity level near Sungai Pahang estuary at 8 river stations from 2001 until 2011 (Source: DOE Malaysia).
Fig. 8. Hydrological stations in Pahang (Source: DID Malaysia).
Fig. 9. Hydrograph near Sungai Pahang basin from 2000 to 2012 (Source: DID Malaysia).
IV.
M
ODELLING THEE
STUARINEF
LOODINGW
ITHS
ALINITYI
NTRUSION INT
RANSVERSEF
LOWEstuarine flooding and transverse flow salinity intrusion in
estuarine system can be modelled
using the Shallow Water
Equations (SWEs). Most previous studies only develop
1-Dimensional (1D) [36, 37] or 2-1-Dimensional (2D) [20, 38-44]
model using SWEs for several cases such as improving the
grid-based, studying the general fluid density differences, and
studying the s ediment transport. Other than that, previous
studies have built models using SWEs for solving problems
such as wetting-drying fronts [39, 45, 46], dam breaks [45,
47,48], one-layer flows [48, 49], two-layer flows [43, 50-52],
and mud flow intrusions [49, 52, 53]. It is applied to the
various conditions in many rivers, lakes, and the sea.
However, these previous studies do not investigate the
problem of salinity intrusion in the estuary during flood.
Therefore, the use of SWEs to develop Shallow Water
Modelling (SWM) is expected to reveal the flood
hydrodynamics and salinity intrusion in the estuary and their
impact on the water quality and the environment.
The Shallow Water Equations (SWEs) are a model of
hyperbolic partial differential equations (PDEs) governing
fluid flow in the oceans, coastal regions, estuaries, rivers, and
channels. The SWEs can be used to predict tides, storm surge
levels, and coastline changes from hurricanes, as well as ocean
currents. This model can also be used to study the dredging
feasibility. The principles of conservation of mass and
conservation of momentum have been used in deriving the
Navier-Stokes equations. Vertical integration allows the
vertical velocity to be removed from the SWEs because
the
value of the parameter in z-direction is much smaller than the
value of the parameter in y-direction.
and vh, the PDEs in case of no Coriolis, frictional or viscous
forces are:
(1)
(2)
(3)
V.
C
ONCLUSIONIn this ongoing research, a Shallow Water Modelling
(SWM) for salinity intrusion in estuarine system will be
developed in order to see the impact of flood and salinity
intrusion in transverse flow on the water quality of the estuary
and on the surrounding area. A relationship between salinity
intrusion and various flow parameters can be established using
the model. The model simulation of SWM using real-time data
in any estuarine system can be used to analyze the process of
transverse flow salinity intrusion and the impacts on the water
quality and the surrounding area when the fresh water flow
varies. The model will be useful in predicting the affected area
by measuring the transverse flow salinity intrusion during an
extreme flood event. SWEs will be used in order to develop
the flood and salinity intrusion model accurately and
efficiently for the Government and private use in the future.
A
CKNOWLEDGMENTThe first author is a PhD candidate of Faculty of Civil
Engineering, Universiti Teknologi MARA, Malaysia and this
paper is partially of her research.
R
EFERENCES[1] D. W. Pritchard, ― Observations of circulation in
[2] coastal plain estuaries,‖ Estuaries, no. SS-83, pp. 37– 44, 1967. [3] J. M. Zokagoa and A. Soulaïmani, ―Modeling of wetting–
drying transitions in free surface flows over complex
topographies,‖ Computer Methods in Applied Mechanics and Engineering, vol. 199, pp. 2281–2304, Jul. 2010. [4] J. V. Reynolds-Fleming and R. A. Luettich Jr,
―Wind-driven lateral variability in a partially mixed estuary,‖ Estuarine, Coastal and Shelf Science, vol. 60, no. 3, pp. 395–407, 2004. Berita Harian, Newspaper of Malaysia, Feb. 2007.
[5] W. C. Liu, M. H. Hsu, A. Y. Kuo, and J. T . Kuo, ―T he Influence of River Discharge on Salinity Intrusion in the T anshui Estuary, T aiwan,‖ Journal of Coastal Research, vol. 17, no. 3, pp. 544–552, 2001.
[6] R. A. Locarnini, L. P. Atkinson, and A. Valle- Levinson, ―Estimating the mean temperature and salinity of the Chesapeake Bay mouth,‖ Estuaries, vol. 25, no. 1, pp. 1– 5, 2002.
[7] M. Larson, R. Bellanca, L. Jönsson, C. Chen, and P. Shi, ― A Model of the 3D Circulation, Salinity Distribution, and T ransport Pattern in the Pearl River Estuary, China,‖ Journal of Coastal Research, vol. 21, no. 5, pp. 896– 908, 2005.
[8] J. Cao, R. Li, and Y. Zhu, ―Study on Saltwater Intrusion in the Yangtze River Estuary by 3D Numerical Model,‖ in Education Technology and Training, 2008. and 2008
International Workshop on Geoscience and Remote Sensing. ETT and GRS 2008. International Workshop on, 2008, vol. 2, pp. 81–84.
[9] L. G. Fang, S. S. Chen, H. L. Li, and C. D. Gu, ― Monitoring water constituents and salinity variations of saltwater using EO-1 Hyperion satellite imagery in the Pearl River Estuary , China,‖ in IGARSS, 2008, pp. 438–441. [10]M. L. Becker, R. A. Luettich Jr., and M. A. Mallin,
―Hydrodynamic behavior of the Cape Fear River and estuarine system: A synthesis and observational investigation of discharge–salinity intrusion relationships,‖ Estuarine, Coastal and Shelf Science, vol. 88, no. 3, pp. 407–418, 2010.
[11]K. Kuijper and L. C. V. Rijn, ―Analytical and numerical analysis of tides and salinities in estuaries; part II: salinity distributions in prismatic and convergent tidal channels,‖ Ocean Dynamics, vol. 61, pp. 1743–1765, Jul. 2011. [12]J. Parsa and A. Etemad-Shahidi, ―An empirical model for
salinity intrusion in alluvial estuaries,‖ Ocean Dynamics, vol. 61, no. 10, pp. 1619–1628, Jul. 2011.
[13]J. Lee and A. Valle-Levinson, ― Influence of bathymetry on hydrography and circulation in the region between an estuary mouth and the adjacent continental shelf,‖ Continental Shelf Research, 2012.
[14]J. A. Lerczak and W. R. Geyer, ― Modeling the lateral circulation in straight, stratified estuaries,‖ Journal of Physical
Oceanography, vol. 34, pp. 1410–1428, 2004.
[15]K. M. H. Huijts, H. M. Schuttelaars, H. E. D. Swart, and A. Valle-Levinson, ―Lateral entrapment of sediment in tidal estuaries: An idealized model study,‖ Journal of Geophysical Research, vol. 111, no. C12, Dec. 2006.
[16]K. E. K. Abderrezzak, A. Paquier, and E. Mignot, ―Modelling flash flood propagation in urban areas using a two-dimensional numerical model,‖ Natural Hazards, vol. 50, pp. 433–460, 2009.
[17]S. N. Chen and L. P. Sanford, ―Lateral circulation driven by boundary mixing and the associated transport of sediments in idealized partially mixed estuaries,‖ Continental Shelf Research, vol. 29, no. 1, pp. 101–118, 2009.
[18]S. N. Chen, L. P. Sanford, and D. K. Ralston, ―Lateral circulation and sediment transport driven by axial winds in an idealized, partially mixed estuary,‖ Journal of Geophysical Research, vol. 114, no. C12, pp. 1–18, Dec. 2009. [19]A. G. L. Borthwick, S. C. Leon, and J. Jozsa, ―Adaptive
quadtree model of shallow-flow hydrodynamics,‖ Journal of Hydraulic Research, vol. 39, no. 4, pp. 413–424, 2010. [20]W. Wu, A. Sanchez, and M. Zhang, ―An implicit 2-D
depth-averaged finite-volume model of flow and sediment transport in coastal waters,‖ in Coastal Engineering, 2010, pp. 1–13. [21]L. C. Rijn, ―Analytical and numerical analysis of tides and
salinities in estuaries; part I: tidal wave propagation in convergent estuaries,‖ Ocean Dynam ics, vol. 61, no. 11, pp. 1719–1741, Jul. 2011.
[22]J. Murillo, B. Latorre, and P. García-Navarro, ―A Riemann solver for unsteady computation of 2D shallow flows with variable density,‖ Journal of Com putational Physics, vol. 231, pp. 4775–4807, 2012.
[23]C. D. Winant, ―Three-dimensional wind-driven flow in an elongated , rotating basin,‖ Journal of Physical Oceanography, vol. 34, pp. 462–476, 2004.
[24]Q. Liang, A. G. L. Borthwick, and P. H. T aylor, ―Chaotic mixing in a basin due to a sinusoidal wind field,‖ International Journal for Numerical Methods in Fluids, vol. 47, pp. 871–877, 2005.
[25]X. Guo and A. Valle-Levinson, ― Wind effects on the lateral structure of density-driven circulation in Chesapeake Bay,‖ Continental Shelf Research, vol. 28, no. 17, pp. 2450–2471, Oct. 2008.
River,‖ Journal of Geophysical Research, vol. 113, no. C9, pp. 1–9, Sep. 2008.
[27]S. Popinet, R. M. Gorman, G. J. Rickard, and H. L. T olman, ―A quadtree-adaptive spectral wave model,‖ vol. 34, pp. 36–49, 2010.
[28]R. J. Uncles and J. A. Stephens, ―The effects of wind, runoff and tides on salinity in a strongly tidal sub- estuary,‖ Estuaries and Coasts, vol. 34, pp. 758–774, 2011.
[29]R. J. Chant, ―Secondary circulation in a region of flow curvature: Relationship with tidal forcing and river discharge,‖ Journal of Geophysical Research, vol. 107, no. C9, pp. 1–11, 2002.
[30]X. Guo and A. Valle-Levinson, ―Tidal effects on estuarine circulation and outflow plume in the Chesapeake Bay,‖ Continental Shelf Research, vol. 27, no. 1, pp. 20–42, Jan. 2007. [31]P. Cheng and A. Valle-Levinson, ―Influence of lateral
advection on residual currents in microtidal estuaries,‖ Journal of Physical Oceanography, vol. 39, pp. 3177–3190, Dec. 2009. [32]J. Parsa and A. E. Shahidi, ―Prediction of tidal excursion
length in estuaries due to the environmental changes,‖ International Journal of Environmental Science and Technology, vol. 7, no. 4, pp. 675–686, 2010.
[33]I. Safak, a. Sheremet, a. Valle-Levinson, and a. F. Waterhouse, ―Variation of overtides by wave enhanced bottom drag in a North Florida tidal inlet,‖ Continental Shelf Research, vol. 30, no. 18, pp. 1963–1970, Oct. 2010.
[34]P. Cheng, A. Valle-Levinson, and H. E. D. Swart, ― A numerical study of residual circulation induced by asymmetric tidal mixing in tidally dominated estuaries,‖ Journal of
Geophysical Research, vol. 116, no. C1, pp. 1–13, Jan. 2011. [35]J. C. Warner, W. R. Geyer, and J. A. Lerczak, ― Numerical
modeling of an estuary: A comprehensive skill assessment,‖ Journal of Geophysical Research, vol. 110, no. C5, pp. 1–13,
2005.
[36]M. Castro, J. Macias, and C. Pares, ―A Q-scheme for a class of systems of coupled conservation laws with source term. Application to a two-layer 1-D shallow water system,‖ ESAIM: M2AN, vol. 35, no. 1, pp. 107–127, 2001. [37]M. J. Castro, J. A. Garcia-Rodriguez, J. M. Gonzalez- Vida, J.
Macias, C. Pares, and M. E. Cazquez- Cendon, ―Numerical simulation of two-layer shallow water flows through channels with irregular geometry,‖ Journal of Computational Physics, vol. 195, pp. 1–31, 2004.
[38] K. Anastasiou and C. T . Chan, ― Solution of the 2D shallow water equations using the finite volume method on unstructured t riangular meshes,‖ International Journal for Num erical Methods in Fluids, vol. 24, no. 11, pp. 1225– 1245, 1997.
[39]Q. Liang and A. G. L. Borthwick, ―Simple treatment of non-aligned boundaries in a Cartesian grid shallow flow model,‖ International Journal for Numerical Methods in Fluids, vol. 56, pp. 2091–2110, 2008.
[40]Q. Liang, G. Du, J. W. Hall, and A. G. L. Borthwick, ― Flood inundation modeling with an adaptive quadtree grid shallow water equation solver,‖ Journal of Hydraulic Engineering, vol. 134, no. 11, pp. 1603– 1610, 2008.
[41]A. Kurganov and G. Petrova, ―Central-upwind schemes for two-layer shallow water equations,‖ SIAM Journal on Scientific Com puting, vol. 31, no. 3, pp. 1742–1773, 2009. [42]J. M. Zokagoa and A. Soulaïmani, ―Modeling of wetting–
drying transitions in free surface flows over complex
topographies,‖ Computer Methods in Applied Mechanics and Engineering, vol. 199, pp. 2281–2304, Jul. 2010.
[43]W.-K. Lee, A. G. L. Borthwick, and P. H. Taylor, ― A fast adaptive quadtree scheme for a two-layer shallow water model,‖ Journal of Computational Physics, vol. 230, no. 12, pp. 4848–4870, Jun. 2011.
[44]G. Kesserwani and Q. Liang, ―Dynamically adaptive grid based discontinuous Galerkin shallow water model,‖ Advances in Water Resources, vol. 37, pp. 23–39, Mar. 2012.
[45]Q. Liang and A. G. L. Borthwick, ―Adaptive quadtree simulation of shallow flows with wet –dry fronts over complex topography,‖ Com puters & Fluids, vol. 38, no. 2, pp. 221–234, Feb. 2009. [46]Q. Liang, ―Flood simulation using a well-balanced shallow
flow model,‖ Journal of Hydraulic Engineering, vol. 136, pp. 669–675, 2010.
[47]Q. Liang, A. G. L. Borthwick, and G. Stelling, ―Simulation of dam- and dyke-break hydrodynamics on dynamically adaptive quadtree grids,‖ International Journal for Num erical Methods in Fluids, vol. 46, pp. 127–162, 2004.
[48]M. J. Castro, A. M. Ferreiro Ferreiro, J. A. García- Rodríguez, J. M. González-Vida, J. Macías, C. Parés, and M. Elena Vázquez-Cendón, ― The numerical treatment of wet/dry fronts in shallow flows: application to one-layer and two-layer systems,‖ Mathem atical and Computer Modelling, vol. 42, no. 3–4, pp. 419–439, Aug. 2005.
[49]S. C. Chen, S. H. Peng, and H. Capart, ―Two-layer shallow water computation of mud flow intrusions into quiescent water,‖ Journal of Hydraulic Research, vol. 45, pp. 13–25, Jan. 2007. [50]R. Abgrall and S. Karni, ―Two-layer shallow water system: A
relaxation approach,‖ SIAM Journal on Scientific Com puting, vol. 31, no. 3, pp. 1603–1627, Jan. 2009.
[51]B. Spinewine, V. Guinot, S. Soares-Frazão, and Y. Zech, ―Solution properties and approximate Riemann solvers for two-layer shallow flow models,‖ Com puters & Fluids, vol. 44, no. 1, pp. 202–220, May 2011.
[52]A. Canestrelli, S. Fagherazzi, and S. Lanzoni, ―A mass-conservative centered finite volume model for solving two-dimensional two-layer shallow water equations for fluid mud propagation over varying topography and dry areas,‖ Advances in Water Resources, vol. 40, pp. 54–70, May 2012. [53]S. C. Chen And S. H. Peng, ―Two-Dimensional Numerical
Model Of T wo-Layer Shallow Water Equations For Confluence Simulation,‖ Advances In Water Resources, Vol. 29, Pp. 1608–1617, Nov. 2006.
Nuryaz me e n Farhan Haron was