Why We Measure River Flow in Bandung

1. Where is Bandung?

Geographical Background

Bandung, the capital of Indonesia's West Java province, is situated in the center of the Bandung Basin—a fertile valley surrounded by the volcanic ridges of the Parahyangan Highlands. The city is at an elevation of 768 meters above sea level and approximately 167 square kilometers in width, with the altitudes ranging from 600 to 1,000 meters. In the north, an erupting volcano, Mount Tangkuban Perahu, pierces the skyline, and to the south, the horizon is rimmed by the Pangrango and Gede mountains. This mountainous terrain makes Bandung less tropical in climate than Indonesia's urban coastal cities, with temperatures averaging 23°C, earning it the sobriquet "Paris of Java." The basin's topography constitutes a natural drainage system, as rivers slice through lush valleys and city districts.

Human/Cultural Aspect

Bandung is a city of history and creativity, where indigenous Sundanese culture meets colonial legacy and modern innovation. It was founded as a Dutch colonial resort town during the 19th century, grown as a center of education and activism, and served as a center for the independence movement of Indonesia. Its architectural heritage includes Art Deco treasures such as the Savoy Homann Hotel and the Bandung Institute of Technology, a hub of scientific inquiry. Sundanese culture thrives in performances of kecak dance, angklung ensembles, and dishes such as soto bandung (hot soup) and kue cubit (small pancakes). With over 2.5 million inhabitants, Bandung is a fashion, textile, and digital start-up hub, but it remains closely connected to its mountain rivers.

Hydrology and River Overview

The Citarum River, Bandung's most significant watercourse, originates in the highlands to the south of the city, near Mount Gede. The river, which is 300 kilometers long, flows north out of the Bandung Basin, via highly populated areas like Cibiru and Bojongsoang, before continuing through West Java's lowlands to empty into the Java Sea. Great tributaries like the Cikapundung, Cimahi, and Cikaret form a vast network draining volcanic slopes and urban areas within the basin.

For Bandung, the Citarum system is essential. It supplies 80% of Bandung's fresh water, irrigates 200,000 hectares of paddy fields spreading across the surrounding plains, and powers hydroelectric stations that generate 15% of West Java's electricity. Ecologically, its upper catchment holds threatened species like the Javan hawk-eagle, and its floodplains hold high biodiversity. However, rapid urbanization pressed the system—industrial waste and household sewage have contaminated water, and flow monitoring became essential for resource management as well as pollution management. The monsoon rains that create seasonal changes in the river decide Bandung's water security, and accurate measurement is essential.

2. How is the River Flow near Bandung?

Influencing Factors

Precipitation and Runoff

Bandung's climate features two distinctly recognizable seasons: the wet season (October–April) and dry season (May–September). During the wet season, heavy rainfall in the Parahyangan Highlands has monthly totals of more than 400 mm. This leads to heavy runoff, flooding the Citarum and its tributaries. River levels can rise by 4–6 meters, and flow velocities increase to 2–3 m/s, posing flood hazards to Bandung's lowlands. Rainfall drops to 100–150 mm per month during the dry season, reducing flows to 0.5–1 m/s. This volatility is a source of issues: floods during the wet season and dry-season deficits, both of which must be watched closely.

Terrain and River Morphology

The Citarum and its tributaries within Bandung are shaped by the basin's volcanic terrain. Cikapundung, which flows through the city center, has a high slope (0.5%) in its headwaters, resulting in quick, turbulent flow, before it flattens to 0.1% within the city center and slows to a sluggish current. Urbanization has altered the rivers: concrete channeling has reduced the Cikapundung from 30 meters to 15 meters in places, reducing its capacity. Volcanic ash sedimentation and deforestation have decreased the depth of the river with an average depth of 2–3 meters (down from 5 meters in the 1970s). Bottlenecks are formed by these changes, increasing flood risk during heavy rain.

Reservoir Operations

The reservoirs upstream, such as the Saguling and Cirata Dams on the Citarum River, are critical to flow regulation. Built in the 1980s, these dams store water during the wet season to prevent downstream flooding in Bandung and discharge water in the dry season to maintain irrigation and hydropower. Sedimentation has reduced their capacity by 30% over the past 40 years. In 2019, heavy rains and unexpected dam releases overflowed the Cikapundung, flooding 15% of Bandung (West Java's Disaster Management Agency). This highlights the importance of reliable flow data for reconciling reservoir operation and city security.

Historical Hydrological Events

Bandung has had severe hydrological hardship. The most severe were the 2009 floods: monsoon rain poured in endlessly over the Cikapundung and Cimahi Rivers, overflowing their courses and flooding 25% of the city. Over 30 lives were claimed, 100,000 were evacuated, and economic loss exceeded $200 million (Antara News). Roads and schools were severely damaged.

Droughts have also impacted the region: the 2015 El Niño reduced rainfall by 50%, cutting the Citarum's flow to 40% of normal. Bandung imposed water rationing, and rice yields in surrounding areas dropped by 30% (per a 2016 report by the Indonesian Ministry of Agriculture). These events underscore the importance of monitoring river flow to mitigate risk.

3. How is River Flow in Bandung Observed?

Traditional Methods

Surface Drift Buoy Method

Local governments used plastic or wooden boards to estimate surface speed by tracing them over specified distances for decades. It was cheap but unreliable as it excluded subsurface currents—essential in Bandung rivers, where depth variation creates distinct flow layers. Wind and volcanic ash, ubiquitous in the Citarum, also skewed results, and thus it was unsuitable for flood forecasting.

Anchored Boat Method

It involved mooring a boat and recording velocity at different depths with a current meter. It produced accurate profiles but was very labor-intensive: a single Cikapundung survey for example involved 4–5 individuals and 5–7 hours. It had high safety risks in rainy periods, with boats struggling against strong currents. In 2017, a survey crew had to suspend work after their boat struck an obscured volcanic boulder, indicating the limitation of the technique.

ADCP Introduction

Acoustic Doppler Current Profilers (ADCPs) transformed flow monitoring in Bandung. ADCPs use sound waves to measure velocity across the entire water column, in real time and non-invasively. 3D flow patterns, such as the turbulent upper reaches of the Citarum, are captured by ADCPs unlike other techniques. 50 meters of the Cikapundung can be surveyed in 20 minutes and data used in flood forecasting and water management is critical. Since 2010, Bandung water authority has installed 10 ADCPs, which have reduced the times of flood responses by 30%.

4. How Does ADCP Work?

ADCPs are based on the Doppler effect: they transmit high-frequency sound pulses (300–1200 kHz) that bounce off suspended particles, such as volcanic sediment. Returned pulses shift frequency with particle motion—higher if towards the instrument, lower if away from it. By calculating these shifts, ADCPs determine velocity at multiple depths, delivering a complete flow profile. New 4-beam designs sample 3D currents, essential to chart the Citarum's eddies.

5. What Does Bandung Need for High-Quality Measurements?

Equipment Needs

• Material Durability: Needs to be resistant to corrosion in the mineral-rich waters of the Citarum, where volcanic sediments enhance wear. Has to be stainless steel or titanium components.
• Portability: Light weight (under 6kg) to utilize in narrow, urban rivers like the Cikapundung.
• Cost-Effectiveness: Affordable for Bandung's budget, with long-running batteries (8+ hours) for extended surveys during monsoons.

6. Choosing Appropriate Equipment

Deployment Methods

• Boat-Mounted ADCPs: Great for quick flood surveys, taking boats through Bandung's city rivers to gather real-time data.
• Bottom-Mounted ADCPs: Placed at strategic points, e.g., beneath bridges, for around-the-clock data that can be used for early flood warnings.
• Cableway ADCPs: Deployed in volcanic gorges upstream where boats cannot travel, to monitor flow in steep and narrow reaches.

Working Frequency

• 600 kHz ADCPs: Best for shallow, 70-meter-wide rivers like the Cimahi with high-resolution details to distinguish sediment layers.
• 300 kHz ADCPs: Applicable for wider sections of the Citarum (110 meters maximum), for taking measurements of deeper flows.

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.