Why Do We Measure the River Flow in Ranchi?

1. Where is Ranchi?

Ranchi, which is the capital of Jharkhand state in India, is located in the east of India. It is geographically positioned at approximately 23.35°N latitude and 85.32°E longitude. Ranchi lies on the Chota Nagpur Plateau and is famous for possessing a rolling hill topography, plateaus, and rivers and streams in hundreds. The Subarnarekha River, which is among the main water bodies of the region, and its streams play a great significance in developing the ecosystem, economy, and way of life of the city. The unique geographical setting of the city, surrounded by dense forests and natural resources, has influenced the development of the city as a major cultural, academic, and industrial center in Jharkhand.

Ranchi is culturally and historically a multicontextual heritage. It has been settled by several indigenous tribes with their own distinct traditions, languages, and arts. Some of these are the Santhal, Munda, and Oraon tribes, which have a close - rooted relationship with the land as well as its natural resources, such as the rivers. Their existence has long been based on agriculture, fishing, and forestry and has had a close association with the water bodies of the region. Ranchi also has a colonial past of British occupation. In the colonial era, it was a summer retreat of British bureaucrats, and there is some reflection of that in the architecture of the city, such as the Ranchi Club and some colonial - style bungalows. The city is renowned for its celebratory culture, commemorating the cultural diversity of the place. Festivals like Sarhul that the tribal people celebrate to welcome spring are followed by traditional dance, music, and rituals on the riverbanks, showing the importance of water in their tradition.

The Subarnarekha River is very crucial to Ranchi. The river starts on the Ranchi Plateau and flows through the state of Jharkhand and then West Bengal before emptying into the Bay of Bengal. In Ranchi, the river Subarnarekha and tributaries were exploited as a source of domestic consumption, irrigation, and industry. Historically, the river supported a dynamic agricultural economy as farmers employed its waters to cultivate such produce as paddy, maize, and vegetables. It had also been employed as a transport medium for goods and people in the past. But in recent years, the river has been severely threatened by water pollution, catchment forest destruction leading to soil erosion and sedimentation, and changes in its regime of flow due to climate change and human interventions, which have raised alarm on the water security of the city and the health of the ecosystem in the region.

2. How is the River Flow near Ranchi?

Several factors account for the river flow in Ranchi. Among these, one of the most significant is rainfall, since the region experiences a tropical wet and dry climate. The rainy season from June to September contributes to the largest proportion of rainfall in a year. The Subarnarekha River and its tributaries receive their water levels and flow rates significantly augmented during this period by runoff from the surrounding plateaus and hills into them. The heavy rains fill the rivers, enabling them to support various human activities and maintain the regional environment intact. But October to May is the dry season, and the water levels go down considerably while the rivers' velocity is considerably less. In some years, especially during severe droughts, parts of the rivers may dry up, negatively affecting the supply of water for domestic, agricultural, and industrial purposes in Ranchi. Climate change has also further added to the complexity by rendering the patterns of rainfall more erratic. Some years have intense but brief rains with flash floods, while others have prolonged dry spells, destabilizing the natural flow regime of the rivers and posing challenges to the local community and businesses.

The morphology of the river and the terrain also play a big role in deciding the flow. The upper reaches of the Subarnarekha River drain through the hilly terrain of the Chota Nagpur Plateau, where the steep slope creates rushing water with strong currents during the monsoon season. As the river descends to the plains, it spreads out to create wide and shallow reaches. The river bed consists largely of sand, gravel, and stones, subject to erosion and deposition processes. These processes can change the path of the river over time, leading to the formation of meanders and affecting its depth and breadth. Human activity has also affected the flow of the river. Ranchi has been rapidly urbanized, with the establishment of houses, roads, and other infrastructure facilities, which have disturbed the original drainage system. The increasing water requirement for housing, industrial, and agricultural purposes has led to over-extraction of water from the rivers. The quality of the water has also been reduced by industrial effluent, sewage, and agricultural runoff pollution, further affecting the environmental well-being of the river and the flow pattern.

3. How to Monitor the River Flow in Ranchi?

The surface drift buoy method and the anchored boat method are conventional techniques for river flow measurement.

The surface drift buoy method is a simple technique in which floats are placed on the surface of the river and their movement over a known distance and period is determined. This is used to estimate the surface velocity of the flow. However, this is an inaccurate technique. It measures the flow only at the surface, which may not be the same as the rest of the water column. Wind, waves, and surface-level perturbations also can distort buoy motion, rendering the reading inaccurate.

The anchored boat technique is to moor a boat at a fixed position in the river. A current meter is then lowered into the water at various depths to measure the flow velocity. This method gives a better profile of the flow at the point. It is, however, time - consuming, labor - intensive, and unsafe in terms of safety in cases where the water is turbulent or flowing quickly. A significant amount of manpower and resources are required to make measurements at many points using the method.

Acoustic Doppler Current Profilers (ADCPs) offer a more advanced and efficient alternative. ADCPs can quantify the water velocity at various depths across the entire body of water without making contact, hence being non-invasive. They can quickly create high-resolution flow profiles across large areas of the river within a brief amount of time. This makes them highly suitable for monitoring complex and dynamic river flows around Ranchi.

4. How Do ADCPs, According to the Doppler Principle, Operate?

ADCPs operate on the Doppler principle. They are emitting acoustic pulses into the water. These pulses travel through the water and strike moving particles, such as suspended sediment, plankton, or microscopic organisms. When the signals bounce off of these traveling particles, the signal frequency varies as a function of the speed of the particles relative to the ADCP current meter. By analyzing these changes in frequency, the ADCP can calculate the water speed at different depths, creating a snapshot of the river flow. This enables flow rates, directions, and overall river dynamics to be measured precisely, which provides valuable data for hydrological studies and water management.

5. What is Required for High-Quality Measurement of River Flow in Ranchi?

In order to apply ADCP to high-quality river flow measurement in Ranchi, certain equipment properties are necessary. Durability of the material is of prime importance. The ADCP profiler should have the ability to withstand the rugged river environment, which includes exposure to sediment-laden water, variable water temperature, and the potential collision with floating objects. Corrosion-resistant high-grade materials such as titanium or specialty polymers ensure the durability and long-term operation of the device.

Size and weight are also critical factors. Light and small ADCP is easier to transport and install, especially in the narrow and sometimes hard - to - reach river sections near Ranchi. This ease allows more mobile data collection in other areas of the river.

Cost - effectiveness is also a consideration. For long - term or large - scale monitoring exercises in Ranchi, a performance - yielding ADCP at a reasonable price is a good idea. This enables effective monitoring of the river flow without draining the bank, enabling regular and fine - grained observation of the river response.

6. How to Select the Correct Current Measurement Instrument?

Deployment Methods

• Mobile boat ADCP: Applicable for conducting surveys, analyzing river discharges, and creating detailed flow maps of the Subarnarekha River and its tributaries. It can cover extensive areas quickly, allowing accurate data acquisition at various sites and providing a comprehensive picture of the river flow pattern.
• Bottom - mounted (fixed) ADCP: Suitable for long - term continuous monitoring at fixed locations in the rivers. Once installed on the river bed, it can provide data for a long duration, giving valuable information on long - term trends and variations of the river flow.
• Cableway ADCP: Where there is a cableway on parts of rivers, a cableway ADCP can be utilized to measure the flow across the river at a specific point. It is an efficient method of obtaining accurate and reliable measurements of flow at crucial locations in the river for comparison purposes to calibrate and validate other means of measurement.

Working Frequency

The working frequency of an ADCP determines its range as well as resolution. A 600 kHz ADCP with the range to 70 meters is well suited for reasonably shallow reaches of the rivers surrounding Ranchi or for obtaining high-resolution observations in deeper reaches. A 300 kHz ADCP with a range of up to 110 meters is better suited for the deeper reaches of the rivers. The frequency choice is made based on the inherent characteristics of the river and the measurement requirements, e.g., required resolution and maximum water column depth for measure.

Recommended Brands

Teledyne RDI, Nortek, and SonTek are reputable global ADCP brands that are famous for their high - quality and reliable products used in a broad variety of hydrological investigation and observation applications. For an inexpensive one, the ADCP manufacturer Chinese brand’s "China Sonar Panda ADCP" is a top choice. Made of all-titanium alloy, it is extremely resilient and dependable, and thus fit to withstand the inhospitable river conditions in the environs of Ranchi. An "affordable ADCP", it provides excellent performance at a low price. For more information, visit https://china-sonar.com/.

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