Why We Measure River Flow in Jambi City?

1. Where is Jambi City?

Geographical Background

Jambi City, the capital of Indonesia's province of Jambi, is located on Sumatra's eastern coast, within the Batanghari River basin long lowland region. It is surrounded by unpenetrated tropical rain forest and immense palm oil plantation and is approximately 175 square kilometers in size at altitudes of between 5 and 20 meters above sea level. To the west of it is far-off ridgeline of the Bukit Barisan hills, but to the east the ground falls flat to create the immense wetlands of the Batanghari delta. As an equatorial city anywhere, it has hot, humid climates throughout the year, 2,500–3,000 mm average annual rainfall that keeps the rich biodiversity of the area in place.

Human/Cultural Aspect

Jambi City is a melting pot with deep-rooted cultures, the old capital of medieval Melayu Kingdom (7th–14th centuries), a grand sea kingdom wherein it dominated trade in the Strait of Malacca. Its cultural identity today is a mixture of Malay tradition and Javanese, Chinese, and indigenous influences. The city's heritage is preserved in such landmarks as the Mpu Tantular Museum, where the artifacts of the Melayu Kingdom are preserved, and such festive celebrations as Hari Raya Aidilfitri and Karnaval Budaya Jambi, where such old dances as zapin and ronggeng are performed. Handicraft fabrics, scented spices, and newly caught river fish are the foundation of the city's markets, which will inevitably be a reflection of the city's close affinity with the river and jungle that encircle it.

Hydrology and River Overview

The Batanghari River, the longest in Sumatra, is the heart and soul of the city of Jambi. The 1,143-kilometer river originates in the mountain highlands of the Barisan Mountains and flows east through thick rainforests, emerald valleys, and cityscapes, including Jambi City, before emptying into the Java Sea via a ginormous delta. Large tributaries like Batang Merangin and Batang Tembesi flow into it, giving it a ginormous drainage system that drains over 100,000 square kilometers of Sumatra.

Batanghari is a significant one for Jambi City. It supplies 90% of the city's potable water to 600,000 citizens, floods 60,000 hectares of rice and rubber plantations in surrounding regencies, and drives domestic fisheries that give thousands their livelihood. Ecologically, the river delta and flood plains are valuable habitats to the Sumatran tiger and the false gharial, both being listed endangered species, and coastal areas are afforded shielding by its mangroves against erosion. Besides Jambi City, the river branches out to 200–300 meters in breadth, and its average depth is 8–12 meters, with seasonal floods regulating its flow with nutrient sediment that is needed for agricultural purposes but risky for the city.

2. How is the River Flow around Jambi City?

Influencing Factors

Precipitation and Runoff

Jambi City experiences a monsoonal climate: extremely heavy rains during the rainy period (October–April) with monthly flows typically exceeding 400 mm and dry period (May–September) when it is reduced to 100–150 mm. The seasonal nature results in extremely rapid change in Batanghari stream flow. During the rainy season, the Barisan Mountains release a huge runoff of torrent rains, elevating river levels by 5–8 meters and stream flow rates to 2–4 m/s. Flood waters frequently overflow into Jambi City's low-lying residential suburbs, an ancient natural process that has shaped local residents' mode of life. During dry season, the river discharge decreases to 0.5–1 m/s with 3–5 meters of water level reduction, exposing sandbars and reducing the supply of irrigation water.

Terrain and River Morphology

The course of Batanghari to Jambi City determines its unique pattern of flow. Further upstream, it creates deep gorges in mountainous terrain with turbulent currents of high speed.

The above information describes the unique features of Batanghari river. When it flows into the east lowlands to the south of Jambi, the river spreads, its rock channel turning into silt and clay, and meanders. The meanders produce irregular flow: water surges around exterior bends, eroding riverbanks (placing such structures as bridges and dikes in danger), while interior bends lose sediment, forming islands and sandbars that isolate the channel. Near Jambi City, river width varies between 200 meters in the narrow parts to 300 meters in the wide parts, and the depths vary from 5 meters in shoals to 15 meters in the channel. All these physical values create complex flow patterns with eddies and cross-currents that are difficult to measure accurately.

Reservoir Operations

Upper reservoirs like the Koto Panjang Dam (300 km north of Jambi) also control Batanghari flow. Constructed for hydroelectric power supply and flood protection, the dam discharges excess water during peak monsoon seasons to prevent flooding downstream in Jambi City. Though limited in function by river size: in 2021, torrential rain overwhelmed the capacity of the dam, creating massive flooding in Jambi (Disaster Management Agency of Jambi Province). Spilling under control from small dams such as Batang Merangin during periods of drought helps preserve base flows, provides irrigation and domestic water.

Historical Hydrological Events

Jambi City also has a rich heritage of riverine tragedy. A record monsoon flood in 2007 submerged the Batanghari, flooding 70% of the city, 150,000 inhabitants, and 10,000 homes (Kompas newspaper). Crops lost more than $20 million, and floodwaters became tainted to trigger outbreaks of leptospirosis,.

Droughts have also left their mark. The 2015 El Niño event reduced rainfall by 70%, cutting the Batanghari’s flow to 30% of its average. Jambi City imposed strict water rationing, with residents queuing for hours at communal taps, while rice yields in the surrounding areas dropped by 50% (per a 2016 study by the Indonesian Ministry of Agriculture). These events highlight the critical need for accurate flow data to manage risks and resources.

3. How River Flow in Jambi City is Monitored?

Traditional Techniques

Surface Drift Buoy Technique

Local government officials have used crude equipment like plastic bottles or bamboo rafts to estimate surface velocity by watching them float over measured distances over years. This is inexpensive and easy but extremely untrustworthy: it can't measure flows below the surface (which can vary by 40% from surface flows) and can be distorted by floating debris and wind—common in the devastating wet-season floods of the Batanghari.

Anchored Boat Method

This technique is to tie a boat in mid-river and suspend a mechanical current meter to measure velocity at various depths. It provides excellent vertical profiles but requires much drudgery: one cross-river survey uses 4–5 individuals and 6–8 hours, with risk at high discharges. In an unexpected flood surge in 2019, a survey crew just avoided capsizing, which highlighted the method's weakness.

ADCP Introduction

Acoustic Doppler Current Profilers (ADCPs) have revolutionized flow measurement in Jambi City. The ADCPs use the sound waves to determine velocity through the entire depth of the river, non-intrusively and in real time. Other sensors gather data in only one or two dimensions, but ADCPs record 3D flow patterns, including the intricate meanders and flood conditions of the Batanghari. It can monitor a 300-meter-wide area in 30 minutes, providing critical information for forecasting floods and water resource management. After 2007, the Jambi water company installed 6 ADCPs along the river and improved flood response time by 50%.

4. How Does ADCP Work?

ADCPs use the Doppler effect: they send high-frequency acoustic pulses (300–1200 kHz) that rebound off suspended particles in water. The frequency of the reflected pulses changes depending on particle motion—higher when moving towards the device, lower when moving away. By calculating these shifts, the ADCP determines velocity at multiple depths, creating a complete flow profile from surface to riverbed. Modern ADCPs use 4 beams to measure 3D flow, essential for capturing the Batanghari’s complex currents.

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

• Material Reliability: Resistant to corrosion in the Batanghari’s sediment-laden waters.
• Portability: Lightweight (under 7kg) for deployment from small boats in narrow sections.
• Cost-Effectiveness: Affordable for Jambi’s limited budget, with durable batteries (10+ hours) for extended surveys.

6. Choosing the Right Equipment

Deployment Methods

• Boat-Mounted ADCPs: Ideal for rapid flood surveys, covering Jambi’s urban river sections in 30–60 minutes.
• Bottom-Mounted ADCPs: Installed near the city center to offer 24/7 data through satellite for issuance of early flood warnings.
• Cableway ADCPs: Installed in upstream gorges where boats cannot pass, measuring flow in thin, fast sections.

Working Frequency

• 600 kHz ADCPs: Suitable for shallow, 70-meter-wide sections in the outskirt of Jambi.
• 300 kHz ADCPs: Suitable for the 110-meter-wide main channel around the city center, observing deeper flows.

Brand Recommendations

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