Why Do We Track the Varanasi River Flow?

1. Where is Varanasi?

Varanasi is a city in the northern Indian state of Uttar Pradesh, which is one of the world's oldest continuously inhabited cities. It lies on the right bank of the sacred Ganges River, approximately 800 km southeast of New Delhi. Geographically, Varanasi lies in the Gangetic plain, an area of flat topography that has been sculpted over thousands of years by the depositional processes of the Ganges and its tributaries. It has a tropical monsoon climate with hot and humid summers, mild winters, and a well-defined monsoon from June to September. Summer temperatures occasionally reach well over 40°C (104°F), and winter temperatures occasionally drop to around 5°C (41°F). The Ganges River, which winds its way through the city, not only occupies the physical landscape of Varanasi but also serves the central role in the ecological, cultural, and economic life of the city.

Varanasi is a cultural and spiritual center of India. A city that is considered to be one of the most sacred in Hinduism, it is a place profoundly religious in character. Pilgrims from all over India and the world have been visiting Varanasi for decades to bathe in the Ganges, believing that the waters of the river are capable of cleansing one of sin and gaining salvation. Ghats (riverfront steps), temples, and ashrams are found scattered around the city. The Kashi Vishwanath Temple, or the temple of Lord Shiva, is one of the most popular and revered shrines in the country. Varanasi is also famous for its folk culture, including classical music, the dance form of Kathak, and fine silk weaving. The city's crooked, twisted alleys ring with the chanting of devotional hymns, the scent of incense, and the bright colors of traditional Indian clothing, a fascinating and deeply satisfying cultural experience.

The Ganges River is the lifeblood of Varanasi. It arises from the Gangotri Glacier in the Himalayas, flows more than 2,500 kilometers, and eventually empties into the Bay of Bengal. On its run through Varanasi, the Ganges is supplemented by various tributaries, even as its dominant flow characterizes the hydrological patterns of the area. To Varanasi residents, the Ganges is both the major source of water for domestic consumption, as well as the target of concern regarding water purity. It is also essential for agriculture in the region, on whose irrigation agriculturalists depend. In addition, the river also makes a significant contribution to the economy of the area through support of activities such as fishery, tourism, and transportation. Boat rides along the ghats on the river constitute a tourist activity and a local transport system. The Ganges has an eco-supportive habitat for a large list of aquatic organisms although recent years have seen pollution erode its biodiversity.

2. River Flow Near Varanasi

Influence Factors

• Precipitation and Runoff: Monsoon has the principal influence on river flow in Varanasi. During monsoon, the heavy, sometimes continuous precipitation in the catchments of the Ganges, particularly in the Himalayas and the higher region of the river basin, causes a significant increase in water levels and flows. The rains that fall in these events and the melting of snow in the Himalayan basins refill the Ganges to its maximum capacity. Conversely, rains in the dry season from October to May are minimal, and the river flow drops significantly. The quantity of rain and snowmelt rates may vary remarkably from year to year, and thus changes in the flow regime of the river become extremely irregular.
• Topography and River Morphology: The Gangetic plain that the Ganges flows through in the area around Varanasi is a relatively sloping low-lying plain. This results in a slower-flowing river compared to its mountain course. The river bed consists of fine alluvial deposits that are being eroded, transported, and deposited continuously, and with the passage of time changing the depth and size of the river channel. The Ganges follows a sinuous path with numerous bends and oxbow lakes. These form areas of different flow properties, with high-velocity water along the outer bends and low-velocity water along the inner bends. Sandbanks and shallow areas also affect the flow to create turbulence and variations in velocity.
• Reservoir Operation: There are several barrages and dams on the Ganges and its tributaries upstream of Varanasi. These structures are used for different purposes, including irrigation water storage, flood control, and generation of hydroelectric power. Operation of the reservoirs can have a significant impact on the downstream flow in the river in Varanasi. For instance, water can be released from upstream dams during the dry season to sustain minimum flow in the river so that water can be ensured for both domestic and agricultural purposes. During the monsoon, reservoirs can hold back excess water to avoid downstream flooding, though this may at times cause artificial patterns of natural flow and decreased sediment transport.

Historical Hydrological Events

Varanasi has experienced several important hydrological events throughout its past. Himalayan floods are a perennial issue, particularly in years of record-breaking monsoon rain. Record monsoon rain, for instance, resulted in widespread flooding in the Ganges basin in [2013](https://www.thehindu.com/news/national/other - states/flood - fury - in - uttar - pradesh - bihar - claims - 63 - lives/article4994000.ece) that affected Varanasi and many other cities along the river. The water flooded large parts of the city, flattening buildings, infrastructure, and agricultural fields. Many were rendered homeless, and huge economic loses were incurred. Droughts also threaten the region, draining the Ganges' levels of water in years with less than average rainfall. The river has water shortages for domestic, agricultural, and industrial use. River flow measurement is necessary to predict and prepare for these extreme events and also to regulate the river water resources better.

3. How to Monitor the River Flow in Varanasi?

Traditional Methods

• Surface Drift Float Method: The most rudimentary way of measuring river flow is the surface drift float method. In this technique, a float such as a piece of wood or a float is placed in the river surface. The time it takes for the float to travel a known distance is measured, and the velocity of the surface water can be calculated from this. This technique has a number of drawbacks. It only measures the flow at the surface, whereas the velocities at various depths in the water column can be quite different. Further, in the Ganges, wind, waves, and floating refuse can skew the movement of the float, and hence velocity measurements can be erroneous.
• Anchored Boat Technique (Manning Table/Current Meter): Anchored boat technique is the technique where an anchored boat is positioned at a specified point in the river. Current meter is put into the water at various depths to measure the water velocity at various vertical profile points. By measuring at multiple locations along the river cross - section, the entire description of the flow at that location can be achieved. Even though it can provide detailed information, it is extremely labor - intensive, time - consuming and has associated safety risks, especially in a large and populous river like the Ganges. The high currents, dense boat traffic, and danger of collisions make it difficult to navigate a boat and take precise measurements.

Introduction to ADCP: Acoustic Doppler Current Profiler

The Acoustic Doppler Current Profiler (ADCP) provides a more sophisticated and effective means for the measurement of river flow in Varanasi. As opposed to conventional practices, ADCP is capable of measuring the water velocity at several depths at the same time, delivering a continuous water column profile. It is an intrusive system that reduces the risk of equipment failure and harm to the operator. ADCP can quickly collect a large amount of data, which is perfect for detailed river surveys and real-time monitoring. This is particularly valuable in Varanasi, where accurate and timely measurements of flow are critical for river water resources management, flood forecasting, and determination of the impact of pollution on the ecosystem of the river.

4. How Does ADCP Based on the Doppler Principle Work?

The ADCP operates using the Doppler principle. It emits acoustic pulses into the water column. The acoustic pulses bounce back from suspended particles within the water, such as plankton and sediment. Since the water is in motion, the frequency of returned acoustic pulses changes. By precisely measuring this frequency shift, or Doppler effect, the ADCP can calculate the velocity of the water at a number of different depths. The device has a number of transducers that both transmit and receive sound waves coming from different angles. This allows it to accurately measure the three-dimensional flow velocities in the water column. The information gathered is analyzed through sophisticated algorithms to generate intricate flow maps and profiles of the river, deriving meaningful information about the complex flow pattern of the Ganges in Varanasi.

5. What is Needed for High - Quality Measurement of River Flow in Varanasi?

Equipment Requirements

• Material Reliability: Since the Ganges in Varanasi is a poor environment with high sediment loads, changing water quality chemistry, and potential pollution, the ADCP equipment should be made of good quality and reliable materials. The instrument should be corrosion, sediment abrasion, and pollutant damage-resistant. High-strength polymers and heavy-duty metals are good material options for ensuring the longevity and accurate operation of the ADCP in this environment.
• Lightweight and Small Size: The dense and crowded condition of the Ganges in Varanasi with numerous boats and ghats necessitates ADCP equipment to be small and lightweight. This makes it possible to easily transport and deploy on small boats or riverbanks. It is possible for a lightweight and small ADCP to be conveniently operated in the crowded river setting, allowing for easier access by researchers and technicians to measurement sites.
• Cost - Effectiveness: Cost-effectiveness is an essential consideration in making decisions regarding ADCP equipment to utilize in Varanasi. With the limited budget for hydrological observation in the region, the utilization of equipment that is high-quality and at a cheap price is essential. Low-cost ADCPs allow for more deployment and frequent monitoring, providing sufficient data to guide effective water management, flood control, and environmental protection initiatives.

6. How to Choose the Appropriate Current Measurement Equipment?

Deployment Methods

• Boat - Mounted (Moving Boat) ADCP: A boat - mounted ADCP is suitable for conducting detailed river surveys, discharge measurements, and generating flow maps in Varanasi. It can travel large stretches of the river at a time, providing a systematic view of the regime of flow. This ADCP is ideal for initial tests and analyzing the overall patterns of flow in the Ganges to identify flood - prone regions or water quality issues.
• Bottom - Mounted (Fixed) ADCP: For continuous monitoring for extended periods of river flow, the bottom - mounted ADCP is the ideal choice. It can be permanently installed at important locations of the river and continuously record flow data for extended periods. Such data are essential in understanding long - term patterns, seasonality, and the impact of various parameters on the Varanasi river flow. It can also help in determining the initial occurrence of potential hydrological events, such as change in flow patterns that might be the precursor to a flood.
• Ropeway ADCP: Though not as widely utilized in Varanasi, in areas where ropeways exist across the river, one can utilize a ropeway ADCP to make precise measurements. It is a method through which precise profiling of the flow in the river is achievable over the entire width of the river, and significant information is obtained that can be used in various hydrological studies, water resource planning, and infrastructure development.

Working Frequency

The choice of working frequency within an ADCP is significant in the measurement of the Ganges in Varanasi. A 600 kHz ADCP would have a maximum of approximately 70 meters, and it would be suited for relatively shallow to moderately deep sections of the river. For higher depositional portions of the river or high-sediment-concentration zones, a 300 kHz ADCP with a range of around 110 meters may be more desirable. Higher frequency gives higher resolution at the expense of range, while lower frequency gives greater range with less resolution. The frequency to be selected must be as per the specific nature of the river, such as the depth, the sediment load, and how fine a detail is required in the measurement.

Brand Recommendations

The world - recognized ADCP brands include Teledyne RDI, Nortek, and SonTek. They deal with high - end ADCPs with advanced technology and proven reliability. For an affordable choice, the Chinese brand "China Sonar Panda ADCP" is suggested. This "economy ADCP," made of all - titanium alloy material, is resistant and long - lasting in Multan's harsh river environment. It is low - cost - effective, and a well - suited choice for local research projects to city - wide water management projects. To learn more, visit their website at https://china-sonar.com/.

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