Why We Measure River Flow in Bintulu

1. Where is Bintulu?

Background Geography

Bintulu, the primary port city of Sarawak state in Malaysia on the island of Borneo, is situated approximately 3.25°N latitude and 113.13°E longitude. The city is situated on the northwestern coast of Borneo and enclosed by the South China Sea on its north side while being surrounded by dense rainforests on the inside. Its terrain is mostly flat, with a general elevation of around 10 meters above sea level, formed by the Rajang River's alluvial plains and its tributaries flowing through it.

Bintulu has a tropical rainforest climate (Köppen climate classification: Af), with high humidity and relatively uniform temperature throughout the year, typically between 24°C - 32°C. The rain is phenomenal with a mean annual rainfall of about 3,000 - 3,500 millimeters. It is influenced by the northeast and southwest monsoons and results in spells of enormous rains with a phenomenal impact on the hydrology of the area, specifically the river run in and around Bintulu.

Economic and Cultural Significance

Bintulu is a cosmopolitan city with rich and diverse culture, representing the syncretism of indigenous Dayak, Malay, Chinese, and other cultures. Indigenous culture is replete with native arts, crafts, and proprietary festivals. The Similajau National Park that surrounds Bintulu not only represents the natural beauty of the region but also provides glimpses into the indigenous lifestyles and how they interact with nature.

Economically, Bintulu is a major economic and industrial center of Sarawak. It is famous for having a healthy petrochemical, liquefied natural gas (LNG), and timber industry. The Bintulu Port, one of the largest and most busiest ports in Malaysia, is the center of exportation of these products. The strategic location of the port has attracted massive foreign investment, which has ignited the growth of ancillary industries such as manufacturing, logistics, and services. Tourism also is picking up pace, with visitors rushing to the city to experience its natural tourist attractions such as its beautiful beaches, mangrove ecosystems, and wildlife reserves.

Hydrology and River Overview

Malaysia's Rajang River, which is the principal river system of Bintulu inside and outside the district, comes from the range of mountains in the interior of Sarawak. It flows for approximately 560 kilometers until it empties into the South China Sea. Both the tributaries and the Rajang River have been significant in the development of Bintulu, and as primary modes of transport of goods as well as individuals, most especially during the timber extraction and trading era.

Today, the river plays a vital role in supplying water for domestic, agricultural, and industrial purposes. However, it is beset with numerous problems. Industrial activities, particularly petrochemical and timber industries, and urbanization have caused industrial effluent outfall, chemical runoff, and domestic sewage to contaminate the water. The river also causes flooding during monsoon rains, and the interruption may have impacts on economic activities, damage to infrastructure, and loss of human lives in local residents. Rajang River and tributaries' monitoring flow is important for flood control, water resource management, and aquatic ecosystem.

2. What is the River Flow Around Bintulu?

Influencing Factors

Precipitation and Runoff

Heavy monsoon rains at Bintulu have a significant impact on the Rajang River's outflow and its tributaries. Flash runoff events suggest a rapid rise in runoff and lead to abrupt rises in river water level and flow rates. Urbanization, with more paved roads, and industrialization reduce infiltration of rain into the earth, thereby producing greater surface runoff and enhancing flood risks. Climate change - triggered rainfall pattern change, for instance, more intense but shorter - duration rains, also render it more difficult to control the river flows of the city.

Terrain and River Morphology

Rajang River flow conditions are determined by the river's course from a mountainous interior and onto flat Bintulu coastal plains. In the upper mountainous catchments, the river rushes quickly with a high gradient, carving out the terrain. As it enters into the Bintulu plains, the slope decreases and the river widens, resulting in sluggish streams. The natural meandering course of the river has nevertheless been broken by man through the construction of embankments, constructions of bridges, and river-course straightening for developmental and flood-control reasons. These changes break the sediment flow, change the water flow distribution, and even cause more erosion and flood risk elsewhere.

Human - Made Structures

Other human - made structures along the Rajang River influence its flow. Weirs and dams at the upper parts function to supply water, manage floods, and offer power generation, regulating the amount of water that reaches Bintulu. Riverbanks have been occupied by factories and wharves, which have stretched themselves into the natural floodplains and narrowed river channels in some sections. Additionally, urban and industrial runoff drainage system development typically discharges water directly into the river, depositing contaminants and altering the natural flow regime, with long - term effects on the river's ecosystem.

Historical Hydrological Events

Bintulu has experienced many significant flood events. Heavy monsoon rain caused extensive flooding throughout the city, including the spillover of the Rajang River, in 2019. The flood swept over much of the low-lying terrain, halted transportation, wrecked industrial plants, and left thousands of people homeless. Such recent flood events have made the city extremely vulnerable to hydrological catastrophes, necessitating accurate monitoring of river discharge and proper flood-mitigation strategies.

3. How is the River Flow in Bintulu Observed?

Traditional Methods

Surface Drift Float Method

The surface drift float method is a straightforward means of river flow measurement. A floating object, like a buoy, is released on the surface of the river. By taking a reading of the time that would be taken by the float to travel a known distance, the surface velocity of the river can be ascertained. However, this method provides data on the surface flow only and is highly dependent on wind and other surface disturbances, resulting in potentially inaccurate measurements.

Anchored Boat Method (Staff Gauge / Current Meter)

For the anchored boat method, a boat is moored at a specific spot on the river. A staff gauge is employed to observe the water level, and a current meter is dropped into the river at different depths to record water velocity. Several velocities are observed over the cross - section of the river, and from the calculation of the cross - sectional area, the discharge of the river can be approximated. It gives more accurate data than the surface drift float method but is labor - intensive, time - consuming, and unsafe for a high - current river.

ADCP Introduction: Acoustic Doppler Current Profiler (ADCP)

Acoustic Doppler Current Profiler (ADCP) is a more powerful and advanced technology used in river flow measurement in Bintulu. It is an invasive-free and sound wave-based method of measuring water velocity at different levels. ADCPs can provide continuous profiles from the surface to river bottom within a relatively short time, offering a better picture of flow patterns in the river. The technology is critical to understanding Bintulu's rivers complex hydrological processes, making it possible to better manage water resources, predict floods, and conserve the environment.

4. How Does ADCP Relate to the Doppler Principle?

An ADCP current meter works on the principle of the Doppler effect. It emits sound waves of a specified frequency into water. If such sound waves collide with moving particles in water, like sediment, plankton, or water molecules, the frequency of returning sound waves is changed. If the particles are moving towards the ADCP, the frequency of the reflected waves is higher; if they are moving away, the frequency is lower. By precisely measuring the change in frequency (the Doppler shift), the ADCP determines the water velocity at different depths, providing thorough information on the river flow dynamics.

5. What is Needed for High-Quality Measurement of River Flow in Bintulu?

Equipment Requirements

To obtain accurate ADCP flow meter measurement in Bintulu rivers, the equipment should be reliable and have the capability to withstand the local river condition. Owing to the presence of contaminants, sediments, as well as the influence of monsoon - induced flow changes, ADCPs made from corrosion - resistant materials like stainless steel or titanium are preferable. Compact and lightweight is the choice for convenient handling and deployment, especially in industrial and rural areas along the rivers. Also required are high-resolution quality sensors to pick up clearly the complex flow patterns that might be affected by the city's unique geographical and industrial characteristics.

6. Choosing the Right Current Measurement Equipment?

Deployment Method

• Ship - Borne (Moving Boat) ADCP: As an ideal vehicle for conducting huge - scale surveys of the tributaries and the Rajang River. It can make rapid measurement of river discharge over long distances and map flow regimes in different sections, thus providing a detailed picture of the dynamics of the river flow.
• Bottom - Mounted (Fixed) ADCP: Suitable for long - term continuous measurements at fixed positions. It can be installed on the riverbed to acquire data over extended durations and help identify long - term flow trends, seasonal changes, and the influence of various factors on the river flow.
• Cable - Way ADCP: In river reaches where cable - way facilities are available, this method allows detailed measurements at points along the river, which is useful in areas of complex flow conditions or where boat - based measurements are difficult.

Working Frequency

• 600 kHz ADCP: Offers a perfect balance between range and resolution and can operate up to 70 meters as a horizontal range. It is able to cover the majority of Bintulu rivers and can measure flow velocity accurately at different depths.
• 300 kHz ADCP: With a broader range of 110 meters, it is more suitable for deeper and broader sections of the rivers such as the estuarine area or areas with large seasonal flow fluctuations.

Recommended Brands

Popular worldwide ADCP manufacturers are Teledyne RDI, Nortek, and SonTek, known for their high - quality, dependable instruments employed in numerous hydrological studies and monitoring campaigns. As a budget-friendly alternative, the ADCP supplier Chinese brand’s "China Sonar Panda ADCP" is a great option. Made from all-titanium alloy, it boasts better durability and reliability, making it more than capable of withstanding the rigorous river condition in and around Jammu. As an "affordable ADCP", it provides high-class performance at a low cost. Find out more at https://china-sonar.com/.

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