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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,

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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, estuary

I.

I

NT RODUCT ION

Estuary 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 E

E

STUARINE

F

LOODINGAND

T

RANSVERSE

F

LOW

S

ALINITY

I

NTRUSION

A.

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).

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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

HE

E

XAM PLE OF

E

STUARINE

F

LOODING

AT

S

UNGAI

P

AHANG

E

STUARINE

S

YSTEM

Sungai 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

2

with 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.

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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 THE

E

STUARINE

F

LOODING

W

ITH

S

ALINITY

I

NTRUSION IN

T

RANSVERSE

F

LOW

Estuarine 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.

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and vh, the PDEs in case of no Coriolis, frictional or viscous

forces are:

(1)

(2)

(3)

V.

C

ONCLUSION

In 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

CKNOWLEDGMENT

The first author is a PhD candidate of Faculty of Civil

Engineering, Universiti Teknologi MARA, Malaysia and this

paper is partially of her research.

R

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Nuryaz me e n Farhan Haron was

Figure

Fig. 1. The decline in mussels production on Johor Straits due to flood event  (Source: Berita Harian, Feb
Fig. 4. View of flooding in Pekan Town 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)

References

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