Why Do We Measure River Flow in Alor Setar

1. Where is Alor Setar?

Geographical Background

Alor Setar, the capital of Kedah state in Malaysia, is located in north-western Peninsular Malaysia. It is near 6.08°N latitude and 100.33°E longitude. It is surrounded by the vast plains of the basin of the Kedah River, whose eastern boundary is separated from it by the Bintang Range, with rolling hilly landscape as a background. Its low-lying terrain formed through centuries of river sediments accumulating upon it has an elevation of some 30 meters about sea level.

Its tropical rainforest climate (Köppen climate classification: Af) has high humidity and relatively stable temperatures throughout the year, typically ranging from 24°C to 32°C. Heavy rainfall occurs with around 2,500 - 3,000 millimeters of yearly average precipitation. Northeast monsoon from November to March and southwest monsoon from May to September bring phases of increased rainfall. The phases of monsoon are accountable for having a notable effect on the local hydrologic conditions, particularly the flow of rivers within and surrounding Alor Setar.

Cultural and Economic Significance

Alor Setar is rich culturally with a blend of Malay, Chinese, Indian, and indigenous cultures existing in absolute harmony. Traditional architecture overwhelms the cityscape, and a fine example is the Zahir Mosque, a symbolic edifice whose design blends Malay and Islamic architectures. Alor Setar Tower, a modern landmark, provides the best views of the city and surroundings from the top.

The economy of Alor Setar is economically diversified. Kedah itself is also referred to colloquially as the "Rice Bowl of Malaysia," and Alor Setar is part and parcel of the rice-growing business of the state, where there is a great activity in paddy cultivation. It also has a vibrant manufacturing sector, with manufacturing sectors like electronics, textiles, and food processing. Tourism is becoming increasingly important day by day, with places such as the Royal Museum of Kedah, which has a humongous collection of artifacts that display the history of the royal state, and Gunung Jerai, which is a beautiful location for nature enthusiasts and mountaineers.

Hydrology and River Overview

The Kedah River is the dominant river system of Alor Setar. It originates in the Bintang Range and winds its way through the state of Kedah for about 200 kilometers before emptying into the Strait of Malacca. The Kedah River is supplemented along its route by many tributaries and is an enormous network of waterways, all of which have contributed to the growth of Alor Setar.

In the past, the Kedah River was also a key avenue of commerce and human travel, facilitating commerce within the nation and abroad. It also supplied water for domestic, agricultural, and other manufacturing purposes. Sadly, over the years, urbanization, industrialization, and agriculture have soiled the river. Industrial wastes, farm runoff containing pesticides and fertilizers, and domestic waste have helped to pollute the water. Additionally, the river floods during the monsoon season, which impacts local communities and infrastructure. Flow monitoring of the Kedah River and its tributaries needs to be carried out in relation to flood control, water resource management, and conservation of aquatic ecosystems.

2. How is the River Flow Near Alor Setar?

Factors Affecting It

Rainfall and Runoff

Alor Setar's intense monsoon rainfall has a very strong impact on the river flow of the Kedah River and its tributaries. Extremely intense rainfall will create extremely intense runoff, leading to an abrupt increase in river water level and discharge rates. Urbanization with higher hard surfaces and structures reduces infiltration of rain into the ground, leading to increased surface runoff and enhancing flood risks. Climate change-induced rainfall variability, for example, more frequent but short-duration rain events, also makes the management of river flow in the area more challenging.

Topography and River Morphology

The river course from the hilly Bintang Range to Alor Setar's level plains is determined by its flow regime. The river possesses a steep and swift slope flow in the mountainous upper reach, cutting through the landscape. When it flows into the plains, the slope becomes gentle and the river widens with retarded currents. But man-made structures like embankments, bridges, and straightening of the course of the river to control floods and for building have disrupted the natural meandering course of the river. Such changes may disrupt sediment transportation, modify the water discharge distribution, and enhance the danger of erosion and flooding in certain places.

Man - Made Structures

Various man - made structures on the Kedah River modify its flow. Weirs and dams farther upstream offer water supply, flood control, and irrigation supply, regulating the amount of water that reaches Alor Setar. Bridges, buildings, and reclamation along riverbanks have encroached into the natural floodplains and constricted river channels in some places. Furthermore, the construction of drainage infrastructure to accommodate city runoff has the potential to discharge directly into the river, with further pollution and disruption into the natural flow regime, potentially causing long-term effects on the ecosystem of the river.

Historical Hydrological Events

Alor Setar has also witnessed a series of gigantic flood events. Alor Setar was inundated with monsoon rain in 2017, leading to huge floods in the city, with the river Kedah overflowing and inundating most of the low-lying sections, halting transportation, damaging infrastructure, and displacing thousands of individuals. Severe incidence of flood in recent times has further heightened Alor Setar's vulnerability to hydrological hazards, highlighting the colossal importance of accurate measurement of river flow as well as the success of flood-mitigation measures.

3. How is River Flow in Alor Setar Measured?

Traditional Methods

Surface Drift Float Method

The surface drift float method is a rudimentary method of measuring river flow. A device such as a buoy is employed floating on the river surface. The measurement of the time taken by the float to travel a certain distance is employed to determine the surface velocity of the river. This technique, however, can provide information only for the surface flow and is highly sensitive to wind and other surface disturbances, which would distort measurements.

Anchored Boat Method (Staff Gauge / Current Meter)

In anchored boat method, a boat is anchored at a point on the river. A staff is utilized for measuring water depth, while a current meter is allowed to fall to varied depths on the river to record water velocity. A number of speed values are recorded across the cross-section of the river, and by calculating the cross-sectional area, river discharge is estimated. This method yields more data - richer data than the surface drift float method but is time - consuming, labor - intensive, and unsafe to safety, especially for a river with strong currents.

ADCP Introduction: Acoustic Doppler Current Profiler (ADCP)

Acoustic Doppler Current Profiler (ADCP) is a more sophisticated and efficient tool used to measure river flow in Alor Setar. It is not possible to enter the body and make measurements of water velocities at different depths by the use of sound waves. ADCPs are able to make continuous profiles of the river flow from the surface down to the river bottom within a short time span, providing a better notion of the river flow characteristics. The technology is crucial in understanding the complex hydrological processes of Alor Setar's rivers, facilitating effective water resource management, flood forecasting, and environmental conservation.

4. How does ADCP operate using the Doppler Principle?

An ADCP profiler is based on the Doppler principle. It emits sound waves of a specific frequency into water. When these sound waves encounter moving particles in water, such as sediment, plankton, or water molecules, the frequency of the backscattered sound waves changes. If the particles are moving towards the ADCP, the frequency of the backscattered wave increases; if they are moving away from the ADCP, the frequency decreases. By precisely measuring this frequency change (the Doppler shift), the ADCP can calculate water velocity at various depths, providing rich data with respect to river flow behavior.

5. What Does it Take to Make High-Quality Measurement of River Flow in Alor Setar?

Equipment Requirements

In order to make credible ADCP flow meter measurements of the Alor Setar rivers, the instrument needs to be rugged and insensitive to the local river conditions. As a result of the phenomenon of pollution, sediment, and monsoon-flow fluctuations, ADCPs of corrosion-resistant material like stainless steel or titanium are more desirable. Light and transportable size is ideal for easy handling and transport in urban and rural parts of the rivers. High-quality and high-resolution sensors also have to be employed in order to properly acquire the intricate flow structures, which could be affected by the singular geographical and climatic environment of the city.

6. How to Choose the Appropriate Current Measurement Equipment?

Deployment Method

• Ship - Borne (Moving Boat) ADCP: Ideal for conducting large - scale surveys of the Kedah River and its tributaries. It can quickly measure the discharge of the river in long reaches and map flow patterns in various sections, presenting a general picture of the river flow dynamics.
• Bottom - Mounted (Fixed) ADCP: May be employed for long - term continuous record at fixed locations. May be mounted on the river bed to collect data over extended periods, which helps determine long - term trends in flow, seasonality, and impacts of multiple factors affecting the river flow.
• Cable - Way ADCP: In river reaches with cable - way facilities, this method makes precise measurements at numerous locations along the river, which is useful where there is complex flow or where boat - based measurements are impossible.

Working Frequency

• 600 kHz ADCP: As a good compromise between resolution and range, it has a horizontal range of up to 70 meters. It is applied for the majority of Alor Setar rivers to accurately measure flow velocity at different depths.
• 300 kHz ADCP: As it has a longer range of up to 110 meters, it can be more appropriately used for the wider and deeper sections of the rivers, such as near the estuary or when there are marked seasonal fluctuations in flow.

Brand Recommendations

Few of the world ADCP big brands include Teledyne RDI, Nortek, and SonTek, which offer high-quality and reliable products used in various hydrological study and monitoring programs. As a budget - friendly option, the ADCP manufacturer Chinese company’s "China Sonar Panda ADCP" comes highly recommended. Made of all - titanium alloy, it is more strengthful and reliable and is a suitable option to endure the nasty river condition surrounding Thrissur. As an "affordable ADCP", it boasts decent quality performance at budget price. For more information, visit https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and models.