Why Do We Measure River Flow in Palembang?

1. Where is Palembang?

Geographical Background

Palembang, the capital of Indonesia's South Sumatra province, sits on the east coast of Sumatra, in the vast Musi River catchment. The city is around 400 square kilometers broad, from 2 to 10 meters above sea level, and highly susceptible to flooding. To its west, there are gently sloping Bukit Barisan mountains and to the east, the landscape is extended into vast wetlands and deltaic plains towards the Bangka Strait. Its tropical climate is warm and humid at all times, and it rains about 2,800 mm annually, supporting high-density rainforests and fertile agricultural lands on its outskirts.

Human/Cultural Aspect

Palembang is one of Southeast Asia's oldest cities, with a history dating back to the Srivijaya Empire (7th–13th centuries), a maritime empire that dominated regional trade. This history is embedded in such icons as the Kuto Besak Fort, a 17th-century Dutch-built river fort on the Musi River, and the nearby Candi Muara Takus, a Hindu-Buddhist temple complex. The city's cultural identity is Malay, Chinese, and indigenous in nature, as witnessed by its cuisine—pempek (fish cakes) and tekwan (fish soup) are common street foods—and celebrations such as Lebaran and Cap Go Meh. The people of Palembang have a deep bonding with the Musi River that has shaped their lifestyle and culture for millennia.

Hydrology and River Overview

The Musi River is Palembang's defining waterway, spanning 750 kilometers from its source in the Barisan Mountains to its mouth in the Bangka Strait. It is fed by tributaries like the Ogan and Komering Rivers and forms a huge basin of 50,000 square kilometers. In Palembang city, when flowing, the Musi widens to 400–600 meters and is thus one of Sumatra's widest rivers.

For Palembang's 1.7 million people, the Musi is vital. It supplies 95% of the freshwater to the city, irrigates 80,000 hectares of oil palm and rice plantations in surrounding regencies, and is home to river transport—the key to goods and human movement. Ecologically, its floodplains are essential for fish breeding, while its delta mangroves protect coastal areas from erosion. Its seasonal floods, though challenging, contribute nutrient sediment that fertilizes agricultural land, and hence an equilibrium of threat and yield.

2. River Flow around Palembang

Influencing Factors

Precipitation and Runoff

The weather of Palembang is dominated by monsoons: the rainy season (November–March) brings high levels of rain, with monthly rainfall in excess of 400 mm, while the dry season (April–October) drops rainfall to 100–200 mm. This determines remarkable fluctuations in the river flow of the Musi. Runoff during rainy months augments runoff from the Barisan Mountains, raising levels by 6–10 meters and raising velocities to 2–3 m/s. Palembang lowlands are commonly flooded, a natural occurrence that locals have adapted to for centuries. Dry months reduce flow to 0.3–0.8 m/s, lowering water levels 4–7 meters, exposing gigantic sandbars and straining water supply.

Terrain and River Morphology

Its flow regime is controlled by the Musi river route to Palembang. It moves in mountain gorges with turbulent streams in the upper regions, but as it approaches the eastern plain, it expands into a winding stream with a bed of silt-clay. On the approach to Palembang, the river's width varies from 400 meters in narrower sections to 600 meters in broader channels, and 8 to 15 meters deep. Meanders create uneven flow: faster currents erode outer banks (threatening infrastructure like the Ampera Bridge), while slower inner currents deposit sediment, forming islands like Kemaro Island—a cultural and ecological landmark. These features generate complex eddies and cross-currents, complicating flow measurement.

Reservoir Operations

Upstream reservoirs, such as the Rajabasa Dam on the Ogan River, help regulate the Musi’s flow. Built to control floods and irrigate, they store excess water in wet years when there is plenty of water to avoid flooding downstream of Palembang. They have a limited storage capacity, however: record rains in 2020 filled the dam too full, spilling over into the Musi river and inundating 40% of the city (as estimated by South Sumatra's Disaster Agency). Regulated releases from lesser dams during dry periods maintain minimum flows, providing enough water for agriculture and residences.

Past Hydrological Events

There has been extensive hydrological disaster following in Palembang. The 2007 flood was most intense: monsoon rains swept the city's Musi 8 meters, inundating 60% of the city, displacing 300,000 people, and destroying 25,000 homes (The Jakarta Post). Economic losses exceeded $50 million, with infrastructure and agriculture being notably affected.

Droughts have also struck: the 2019 dry season saw rainfall drop by 60%, reducing the Musi’s flow to 25% of average. Palembang imposed water rationing, and rice yields in surrounding areas fell by 40% (per a 2020 study by the Indonesian Ministry of Agriculture). These events underscore the urgency of accurate flow monitoring to mitigate risks.

3. How is River Flow in Palembang Observed?

Traditional Methods

Surface Drift Buoy Method

For decades, officials used wooden rafts or barrels to estimate surface velocity by taking time to pass between markers. Such a frugal technique did not reveal subsurface currents—critical in the Musi, where depth changes create radical contrasts of top and bottom flow. Wind and drifting matter, common during rainy spells, further bent findings.

The technique involves mooring a boat and lowered current meters to measure velocity at depth intervals. It provides high-resolution profiles but is labor-intensive: one cross-river survey may be made by a single cross-river surveying 5–6 personnel taking 8–10 hours. Flood stage conditions are hazardous—during the 2013 flood, a boat belonging to one team was destroyed by floating material, shortening measurements at maximum flood stage.

ADCP Introduction

Acoustic Doppler Current Profilers (ADCPs) transformed Palembang's flood monitoring. ADCPs must utilize sound waves to measure velocity from top to bottom of the Musi, without intruding into the river and in real time. Unlike traditional techniques, ADCPs are able to capture 3D patterns of flow, even in the wide, curved sections of the river. A 600-meter-wide area is measured in 45 minutes, providing critical information for flood forecasting. Palembang deployed 8 ADCPs along the Musi after 2007, cutting the response time for flood by 60%.

4. How Does ADCP Work?

ADCPs leverage the Doppler effect: they emit acoustic pulses (300–1200 kHz) that bounce off suspended particles. The frequency shift of reflected pulses reveals particle speed, translating to water velocity. By sampling at multiple depths, ADCPs create a complete flow profile. Modern 4-beam designs capture 3D currents, essential for mapping the Musi’s complex eddies and meanders.

5. What’s Needed for High-Quality Measurements?

• Material Reliability: Corrosion resistance in the sediment-laden, brackish lower reaches of the Musi.
• Portability: Light (less than 8kg) for deployment from small boats in urban reaches.
• Cost-Effectiveness: Reasonable enough for Palembang's budget, with long battery life (12+ hours) for long surveys.

6. Selecting the Best Equipment

Deployment Techniques

• Boat-Mounted ADCPs: Best suited for quick flood surveys, getting across Palembang's urban reaches easily.
• Bottom-Mounted ADCPs: Deployed near the city center for 24/7 data, critical for early warnings.
• Cableway ADCPs: Used upstream where boats struggle, measuring flow in narrow, fast sections.

Working Frequency

• 600 kHz ADCP: Offers a reasonable trade-off between range and resolution, with a horizontal range of up to 70 meters. It is suitable for most of the rivers in Johor Bahru, and it will provide us with accurate readings of flow velocity at different depths.
• 300 kHz ADCP: With a greater range of up to 110 meters, it would be more appropriate for deeper and wider sections of the rivers, i.e., near the estuary or in areas of huge tidal activity.

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.