Why Do We Measure the River Flow in Allahabad?

1. Where is Allahabad?

Allahabad, officially renamed Prayagraj, is situated in the northern Indian state of Uttar Pradesh. Situated at the conjunction of the Ganges, Yamuna, and the mythological Saraswati rivers, it holds a unique geographical position. It is situated geographically at around 25.43°N latitude and 81.84°E longitude. Allahabad lies in the fertile Indo - Gangetic Plain area, with low lying country allowing for centuries of development of mass produce agricultural and urbanisation.

Allahabad is one of India's most culturally and historically significant cities. For thousands of years, it has been a centre of religious and cultural life. The Kumbh Mela, which occurs every 12 years at the sangam (meeting of the rivers), is the world's largest peaceful pilgrim congregation. Millions of pilgrims come to it from all over the world during this festival to bathe in the holy waters in the belief that it would wash away their sins. The city also has a rich history going back to prehistoric times, having been governed by some of the greatest empires like the Mauryan, Gupta, and Mughal empires. Dynasties have come and gone in the city, and its architecture reflects a fusion of different influences.

The Allahabad river systems are of extreme importance. The Ganges, which takes its origin in the Gangotri Glacier of the Himalayas, is one of the most famous and longest rivers of India. It stretches for about 2,525 kilometers across the northern Indian plains. The Yamuna, as mentioned earlier, takes its origin from the Yamunotri Glacier and flows through several states before it meets the Ganges at Allahabad. The confluence of these two massive rivers and mythological Saraswati is an ecologically and spiritually hot spot. The rivers are utilized to provide water for household uses, agriculture, and industry surrounding and within Allahabad. They also have a diverse aquatic life, contributing to the ecological composition of the region. The rivers were employed as primary means of trade and transport historically, triggering economic growth and cultural exchange.

2. What is the River Flow around Allahabad?

There are numerous factors that influence the river flow around Allahabad. Precipitation and runoff are of utmost significance. Monsoon weather is faced by the area during June to September, where it rains continuously and in big amounts. This results in an enormous increase in the water levels and rates of the Ganges and Yamuna rivers. The runoff from the surrounding hill regions in the north and others makes a high contribution of water to the rivers. Conversely, during the dry season between October and May, water level drops, and flow becomes slower. The change in rainfall pattern due to climate change also affects the well-established flow regimes, making the river flow more fluctuating in recent decades.

The river morphology and terrain also affect the flow. The flat plains enable the rivers to meander and spread out, with broad and shallow parts alternating with narrower and deeper channels. The riverbed consists of sediment, and the deposition and erosion processes repeatedly alter the depth and shape of the rivers and thereby influence the local flow patterns. The zone of confluence at Sangam has a unique hydrological situation where the differing characters of waters of the Ganges and Yamuna get mixed up, creating complex patterns of flow.

Upstream on both Yamuna and the Ganges there are numerous dams, barrages, and reservoirs. For example, Tehri Dam on Bhagirathi River (a major tributary of the Ganges) and Hathnikund Barrage on Yamuna regulate water discharge. Such reservoirs store water during the monsoon and release it slowly in the dry periods to maintain at least a minimum level of flow downstream and meet the requirements of various activities. However, improper management or unforeseen circumstances may lead to sudden fluctuation in water release, and this would result in flood or water shortage in the downstream area, e.g., Allahabad.

Regarding previous hydrological events, Allahabad has witnessed several major floods. One of the worst floods happened in 2013. In a report by India's Central Water Commission, excessive monsoon rains in the upper catchment regions of the Ganges and Yamuna caused a huge amount of water to flow, causing the rivers to burst their banks in Allahabad. The flood submerged huge parts of the city, damaged infrastructure, including roads, bridges, and buildings, and rendered thousands homeless (Source: Central Water Commission, India, 2013). For facilitating planning of flood - control facilities, protection of the lives and property of the residents, and efficient management of water resources in a sustainable way, monitoring these events must be done.

3. How to Observe the River Flow in Allahabad?

Anchored boat and surface drift buoy techniques are older techniques for river flow measurement.

The surface drift buoy technique is a simple but straightforward technique. Floats are placed on the river surface, and their movement along a known distance and time is measured. This will provide an estimate of the surface flow velocity. But it is restricted in that it can only quantify the surface flow and is heavily reliant on wind, thus potentially causing the buoys not to trace the actual direction of the water flow and, as a result, giving wrong readings.

The anchored boat method employs anchoring a boat at a location in the river. A current meter is then dropped into the water at different depths to estimate the flow velocity. It gives a better description of the flow at that particular point. But it is manpower - intensive, time - consuming, and poses risks to safety, especially in turbulent or fast - flowing waters. It requires a lot of manpower and resources as well to take measurements at different points.

Acoustic Doppler Current Profilers (ADCPs) offer a more advanced and efficient alternative. ADCPs can measure the velocity of water at different depths along the entire water column without coming into contact, hence they are non-invasive. They can quickly produce accurate flow profiles, sweeping large parts of the river in a few minutes. They are most suitable for surveying and monitoring of the complex river currents around Allahabad.

4. How Does ADCP, Which Is Based on the Doppler Principle, Function?

ADCPs are based on the Doppler principle. They emit sound waves into the water. As the sound waves pass through the water, they encounter moving particles such as suspended sediment, plankton, or small animals. When the signals are bounced off these moving particles, the frequency of the returned signals changes depending on the particles' velocity relative to the ADCP. By examining the variations in frequency, the ADCP can calculate the velocity of the water at different depths and construct a comprehensive profile of the river flow. With it, one can precisely measure the rate of flow, direction, and overall river dynamics.

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

For reliable river flow measurement using ADCP in Allahabad, there are certain equipment characteristics that are needed. The most critical is material reliability as the ADCP will have to resist the harsh river environment, including exposure to water, sediment abrasion, and varying water temperature. The durability and longevity of the device can be ensured through the use of a robust and corrosion-resistant material such as titanium or high-grade plastics.

Size and weight are also considerations. A lightweight and compact ADCP is easier to transport and deploy to different locations, particularly in difficult river conditions or where access is limited, such as in the case of Allahabad's complex river system.

Cost-effectiveness is another important consideration. For big-scale or long-term monitoring tasks, a high-quality ADCP that is affordable is desirable. This makes it possible to cover more area and take measurements more often without breaking the bank.

6. How to Choose the Right Current Measurement Equipment?

Deployment Methods

• Boat-mounted (mobile boat) ADCP: It is appropriate for surveying, determination of river discharges, and development of maps of flow. It quickly surveys large river stretches, thus can be employed in the Allahabad surrounding large-scale river systems. It is able to sample data at more than one point, providing an overall river flow pattern.
• Bottom - mounted (fixed) ADCP: In the case of continuous long - term monitoring, a bottom - mounted ADCP is the best choice. Once fixed on the river bed, it may collect data for long periods, providing useful information regarding the long - term alterations and trends in the river flow. This is useful in studying the hydrological and ecological changes in the Allahabad rivers.
• Cableway ADCP: Where a cableway is available in river reaches, a cableway ADCP can be used. It is hanged overhead suspended above the river and can measure the flow across the river at one fixed point. This method is suitable for making accurate and consistent flow measurements at strategic points in the river.

Working Frequency

An ADCP's range and resolution are affected by its working frequency. A 600 kHz ADCP usually has a maximum range of 70 meters, which is appropriate for comparatively shallow rivers or for getting high-resolution measurements in very deep rivers. A 300 kHz ADCP can measure a maximum of 110 meters and thus is more appropriate for deep rivers like the Ganges and Yamuna near Allahabad. Higher frequencies provide greater resolution but with a limited range, while lower frequency has greater range but reduced resolution. The frequency to be used depends on the precise measurement requirements, including the river depth and desired detail level.

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.