Why Do We Measure River Flow in Banjarmasin?

1. Where is Banjarmasin?

Background Geography

Banjarmasin, the capital of Indonesia's South Kalimantan province, lies on the southern bank of Borneo, in the extensive delta of the Barito River. It extends over roughly 98.4 square kilometers, and the city is a low-lying river system, canals, and swamps, never more than 3 meters above sea level—so-called "Venice of Borneo." The topography is characterized by tidal flats and mangrove forests, with the Barito River branching into dozens of distributaries as it flows into the Java Sea.

The equatorial climate is characterized by an average temperature of 27–30°C all year round and 3,000–3,500 mm of rain, all occurring during the northwest monsoon months (November to March). The Meratus Mountains slope gently to the north, their slopes feeding the rivers that bisect Banjarmasin, while the south flows into the shallow waters of the Java Sea.

Human/Cultural Aspect

Banjarmasin is a vibrant cultural city of over 625,000 people, consisting of Banjar, Malay, Chinese, and Dayak groups. The city has been influenced by the Banjar, indigenous people, for centuries whose culture and language dominate daily life. The city is also a common history with the Banjar Sultanate of the 16th to 19th centuries, a commercial giant whose tradition lives on in the form of structures like the 17th-century Sultan Suriansyah Mosque, one of the oldest Islamic monuments in Indonesia.

Water dominates life in Banjarmasin: over 40% of the population live in stilt houses (rumah lanting) above rivers, and floating markets like Pasar Terapung Lok Baintan make up the center of commerce. Vendors sell freshwater fish, tropical fruit, and hand-woven kain songket fabric from wooden boats. Cultural activities range from dansa banjar (traditional dance) and gambus (Islamic music) to festivals like Hari Raya Idul Fitri and Pesta Barito (Barito Festival), celebrating the city's riverine heritage.

Overview of River and Hydrology

Banjarmasin's lifeblood is the Barito River, which runs 900 kilometers from the Muller Mountains to the Java Sea. The river divides into major distributaries like the Martapura and Landak Rivers when it passes through the city, creating a system of rivers constituting Banjarmasin's city center. Tributaries like the Tabalong and Kapuas Murung Rivers feed the system, draining over 100,000 square kilometers of the South Kalimantan interior.

For Banjarmasin, the Barito system is lifeblood. It supplies 95% of the city's fresh water, sustains fisheries that produce 50% of the local protein supply, and serves as the principal transport system—boats and klotok (motorized canoes) outnumber automobiles in much of the city. From an ecological perspective, the river delta is a valuable mangrove haven for endangered species like the proboscis monkey and the saltwater crocodile, and its peat swamps are significant carbon sinks. Seasonal flooding, even though disruptive, provides agricultural land with nutrient-rich sediment, which enables rice to be cultivated in the surrounding lands. Deforestation and palm oil development in the upper catchment have supplemented sedimentation, whereas urbanization has constricted river channels, leaving the area exposed to increased flood danger.

2. What is the River Flow near Banjarmasin like?

Factors that Control

Precipitation and Runoff

The monsoon cycle dominates the precipitation regime of Banjarmasin. Rainy season (November–March) is associated with intense rain with rainfall of 400–500 mm/month, leading to rapid runoff from the Meratus Mountains. This raises the Barito's water level in Banjarmasin by 2–4 meters, flow rates of 0.8–1.5 m/s, inundating stilt-house settlements and floating markets. Dry season (April–October) limits rain to 150–200 mm/month, slowing the flow to 0.3–0.7 m/s, though tidal forces keep relatively stable water levels.

Terrain and River Morphology

Barito River flows through a deltaic flat plain in Banjarmasin with only 0.0005% slope, having slow, curved currents. The bottom of the river is covered by soft mud and silt and temporary sandbars that shift the channel course when flooding occurs in the river. Tidal flows in the Java Sea radiate 120 kilometers upstream to Banjarmasin, generating 1.5–2.5 meter daily water level fluctuations—some of Kalimantan's highest. This tidal "bore" twice daily briefly reverses river flow, generating complex currents that mix freshwater and saltwater in downstream sections, affecting water quality for use and irrigation.

Human Impact on Flow

Land use change and urbanization have had profound effects on river dynamics. Its urbanized area has risen 60% since 1990, riverbanks and canals being reclaimed for roads and housing—the functional width of the Barito within the city center reduced by 30%. Land clearing by palm oil estates (those with 800,000 hectares of South Kalimantan) increased sedimentation, where the Banjarmasin river depth decreased by 1–2 meters since 2000, based on a 2021 Indonesian Institute of Sciences (LIPI) report. This diminished flood-carrying capacity and enhanced erosion of pilings of stilt-houses.

Historical Hydrological Events

Banjarmasin knows floods, but these are now complemented by human actions. The floods of 2020 were especially dramatic: 75 consecutive days of monsoon rain had swelled the Barito by 5 meters, sweeping through 90% of the city, displacing 150,000 people, and demolishing 8,000 stilt houses (according to Antara News). Floating markets vanished, and 60% of rice paddies in adjacent regencies were devastated, creating shortages.

Drought is unusual in the region. The 2016 El Niño reduced rainfall by 55%, reducing the Barito's flow to 20% of its normal level. This exposed riverbeds, grounding boats and forcing residents to dig shallow wells, salinating groundwater. Fish catches declined 80%, putting the livelihoods of 20,000 fishers at risk (2017 LIPI report).

3. How is River Flow in Banjarmasin Measured?

Traditional Methods

Pole Gauge Measurements

For decades, city governments gauged water levels at points along the riverbanks using depth markers on wooden poles. It was a rough but easy method: it provided surface height but not velocity, and gauges themselves were often destroyed by floating debris during floods. Tidal fluctuations also complicated the distinction of natural cycles from flood events.

Rowboat Current Timing

Fishermen and officials estimated flow speed by timing rowboats along fixed distances between landmarks. This was highly subjective, as rowing effort varied, and it ignored subsurface currents—of extreme significance in Banjarmasin's tidal rivers, where water near the riverbed often flows in the opposite direction to surface water.

Introduction of ADCP

Acoustic Doppler Current Profilers (ADCPs) transformed Banjarmasin's flow monitoring in 2017. Mounted on small motorized vessels, the instruments use sound waves to measure velocity across the entire water column in real time, even in muddy and shallow water. A 200-meter section of the Barito is surveyed in 30 minutes, capturing complex tidal flows and eddies that escaped traditional techniques.

The city's water agency operates 6 ADCP units, which are placed in strategic locations like the Barito Bridge and near main floating markets. Data from these devices have improved flood forecasting by 60% and enabled selective dredging to protect stilt-house settlements (South Kalimantan's Water Resources Department).

4. How Does ADCP Work?

ADCPs emit high-frequency acoustic pulses (300–1200 kHz) that bounce off suspended particles—organic material, silt, and plankton—in the water. The Doppler shift causes the returned pulse frequency to change: higher if particles are moving toward the instrument, lower if moving away. The ADCP measures these changes and calculates velocity at 0.3–0.5-meter depth intervals, creating a 3D flow profile from river surface to bottom.

The newer ADCPs used in Banjarmasin consist of four transducers that are angled 25 degrees, allowing them to capture reversing currents from tides. The measurements are stored on the instrument or transmitted to a central station, where real-time monitoring can be achieved during periods of flood or low flow.

5. What's Needed for Good Quality Measurements in Banjarmasin?

Equipment Requirements

• Shallow-Water Capability: Operable at depths as low as 1 meter, common in Banjarmasin's distributaries during dry seasons.
• Resistance to Fouling: Protected against algae and barnacle growth, which are abundant in the warm, nutrient-rich Barito River.
• Battery Durability: Minimum 12-hour life to cover entire tidal cycles (12.4 hours in Banjarmasin), with waterproof casings to protect against splashing.
• Portability: Lightweight (less than 8kg) for easy transport between stilt-house docks and small boats.

6. Choosing the Right Equipment

Methods of Deployment

• Boat-Mounted ADCPs: Primary means of surveying Banjarmasin's main river channels, with the capability to take measurements in different distributaries.
• Fixed ADCPs: Deployed on stilt-house pilings at floating markets to obtain continuous data on tidal and flood flows.
• Handheld ADCPs: Used in narrow canals (sungai kecil) that cannot be entered by boats, providing information on how floodwaters move through the neighborhoods.

Working Frequency

• 1200 kHz ADCPs: Applicable in shallow canals and distributaries (depth <5 meters) like the Landak River, offering high resolution to quantify near-bed currents.
• 600 kHz ADCPs: Used in the main channel of the Barito (depth 5–15 meters), trading off range and resolution to quantify tidal reversals.

Brand Recommendations

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