Why Measure the River Flow in Guwahati?

1. Where is Guwahati?

Guwahati, the largest city in the Indian province of Assam, is geographically located in the northeastern part of India. At approximately 26.14°N latitude and 91.75°E longitude, it is located on the southern banks of the Brahmaputra River, which is one of Asia's largest rivers. The city is placed in a setting that possesses the immensity of the Brahmaputra Valley, and behind it, the foothills of the Himalayas. This specific geographic setting not only provided the city with a natural setting but also shaped how it has developed as a chief economic, cultural, and transit hub in the region.

Historically and culturally, Guwahati is a culturally diverse melting pot that possesses a distinct rich heritage. It has been the cultural center of Assamese people for generations. Guwahati is renowned for its heritage festivals and the most prominent among them is Bihu. It is celebrated with utmost excitement through folk dances, songs, and colorful attire, illustrating the energetic nature of Assamese people. Guwahati is also rich in religious origins as the city is home to various ancient and historic temples. The Kamakhya Temple, where goddess Kamakhya is worshipped, is one of the holiest Shakti Peethas in Hinduism and is visited by thousands of pilgrims each year. Guwahati has witnessed the rise and fall of various kingdoms and dynasties over the ages, including the Ahom Kingdom, which still influences the art, architecture, and administration of the land.

The Brahmaputra River is the lifeline of Guwahati. Originating in the Chemayungdung Glacier of Tibet, China, as Yarlung Tsangpo River, it flows east in Tibet before making an abrupt change of direction to flow into India via Arunachal Pradesh, and then it is called the Brahmaputra. The river then meanders through Assam for about 725 kilometers before flowing into Bangladesh. In Guwahati, the Brahmaputra River is used for numerous purposes. It is a valuable source of water for domestic, agricultural, and industrial uses. It was a major route of trade in the past, with inter-regional trade and cultural exchanges. The river supports a healthy environment, and there are various fish species, birds, and other water animals. But the Brahmaputra has also a whimsical nature, and it frequently brings ruinous floods that pose dangers to the city and its inhabitants as well.

2. What is the River Flow around Guwahati?

There are several factors governing river flow around Guwahati. Precipitation and runoff are the governing factors. The climate surrounding the area is tropical monsoon, and monsoon dominates from June to September. There is heavy and persistent rainfall during this time, particularly in the upstream catchment regions in the Himalayas and the surrounding mountains. The rain- induced runoff inflates the Brahmaputra River, leading to a considerable rise in water levels and flow speeds. In opposition to this, during the dry season that lasts from October to May, the water levels are significantly low, and the flow is much reduced. Climate change has contributed to the issue, leading to more variable and intense monsoons, increasing the frequency and magnitude of flooding.

The topography and river morphology are also critical considerations in controlling the flow. The Brahmaputra River traverses an area with steep gorges in its upper reaches and wide, flat floodplains near Guwahati. As it enters the city, the river broadens, with a mean width of a series of kilometers in some reaches. The sand and sedimentary riverbed is eroding and depositing perpetually, changing the course of the river over time. The presence of numerous tributaries, such as the Barak River and their various distributaries, also has a significant contribution to the complex flow pattern near Guwahati, as they add to the water content and modify the flow patterns.

Upstream, the Brahmaputra has tributaries with dams and barrages for water discharge regulation. They are used mainly for power generation through hydropower, irrigation, and flood control. Their operation may have negative as well as positive impacts on the downstream flow. Even though they help in reducing the severity of floods to some extent, improper management or instant heavy rain can lead to sudden water level surges, which are dangerous to the city.

Historical

hydrological events have had a considerable impact on Guwahati. The Brahmaputra River experienced a critical flood in 2012 that affected extensive parts of Assam, including Guwahati. Accounts by the Assam State Disaster Management Authority are that the flood covered extensive tracts of the city, damaged infrastructure, and rendered hundreds of thousands of residents homeless (Source: Assam State Disaster Management Authority, 2012). Such events highlight the need for closely monitoring the river flow in order to develop effective flood mitigation strategies and protect the life and belongings of the residents.

3. How to Monitor the River Flow in Guwahati?

A few of the conventional techniques used to measure river flow include the surface drift buoy method and the anchored boat method.

Surface drift buoy method is a simple method. Floats are deployed on the river surface, and their displacement over a predetermined distance and time is monitored. This gives an approximation of the surface flow velocity. This technique is seriously flawed. It will provide only the flow at the surface, which could be quite different from the flow in the entire water column. Also, wind and other interference at the surface level is able to affect the movement of the buoys, causing misreading.

The boat anchor technique involves mooring a boat in one location in the river. A current meter is lowered into the water from several different depths in an effort to measure the velocity of flow. This method gives a more precise flow profile at the point. Nevertheless, it is labor - intensive, time - consuming, and risky, especially in the turbulent and swift - moving waters of the Brahmaputra. It requires a considerable amount of labor and resources to take measurements at multiple points.

Acoustic Doppler Current Profilers (ADCPs) offer a more advanced and affordable alternative. ADCPs can measure the water velocity at various depths across the entire water column with no contact, they are therefore non - invasive. They can deliver high-resolution flow profiles quickly, mapping out large sections of the river within a short time frame. This makes them incredibly well-positioned to track the complex and dynamic river flows around Guwahati.

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

ADCPs work based on the Doppler principle. ADCPs emit acoustic pulses into the water. As these pulses are traveling through the water, they encounter moving particles, such as suspended sediment, plankton, or small animals. When the signals reflect off these moving particles, the frequency of the reflected signals changes with the velocity of the particles relative to the ADCP. Through inspection of the frequency shifts, the ADCP is able to calculate the velocity of the water at different depths, creating a complete profile of the river flow. This makes it possible to measure exactly flow rates, directions, and the river's dynamics as a whole, providing valuable information for hydrological studies and water management.

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

For precise river flow measurement using ADCP in Guwahati, some equipment features are needed. Reliability of materials is most critical. The ADCP needs to withstand the harsh river environment, including exposure to sediment - water, high currents, and varying water temperatures. High-grade, corrosion-resistant materials such as titanium or specially engineered polymers confer the device's ruggedness and long-term functionality.

Weight and size are also important factors to consider. A light and small-sized ADCP is more convenient for transportation and deployment, especially in the context of the challenging river conditions in the Guwahati region. It allows for data gathering in various river sections, including remote ones.

Cost-effectiveness is another important factor. In large-scale or long-term monitoring ventures in Guwahati, a cost-effective ADCP that provides high-quality performance at an affordable price is ideal. This provides all-round monitoring of the river flow without burning a hole in the pocket, making it easy to conduct frequent and detailed evaluations of the river's pattern of behavior.

6. How to Choose the Right Current Measurement Equipment?

Methods of Deployment

• Boat-mounted (mobile boat) ADCP: Ideal for conducting surveys, estimation of river discharges, and flow detailed maps. It possesses the ability to traverse extensive areas of the Brahmaputra River in the Guwahati region and has the ability to gather data from several points to provide a general picture of the river flow patterns.
• Bottom - mounted (fixed) ADCP: Most suitable for long - term continuous measurements. It can be fixed to the river bottom and take measurements for extended periods, giving good information on long - term variation and trends of the river flow. This is beneficial in studying the ecological impacts of water management activities and climate change impacts on the river.
• Cableway ADCP: Where a cableway is present in river reaches, a cableway ADCP may be utilized. It is placed above the river and can measure the flow over the river at a given point. This is an appropriate way of taking precise and credible flow measurements at major points in the river, which may be used for calibration and validation of other measurement techniques.

Working Frequency

The operational frequency of an ADCP influences its range and resolution. A 600 kHz ADCP, with a maximum range of 70 meters, can be used for fairly shallow parts of the Brahmaputra River or for the purpose of taking high-resolution measurements in deeper portions. A 300 kHz ADCP, with a measurement range of up to 110 meters, can be used in deeper parts of the river. The frequency choice is determined by the specific river conditions and needs of the measurements, i.e., the desired detail and the maximum depth of the water column to be measured.

Brand Recommendations

World - leading ADCP brands include Teledyne RDI, Nortek, and SonTek, with high - quality products, advanced technology, and excellent reliability. For a cost - effective budget, ADCP manufacturer Chinese brand "China Sonar Panda ADCP" is also very good. Made of all-titanium alloy material, this "economy ADCP" is extremely durable and resistant to corrosion, well-suited to the harsh environment of the Soan River. Its high cost-effectiveness makes it within the budget of a range of users, from small-scale research projects in the vicinity to city-scale water management initiatives. To find out more, visit their website at https://china-sonar.com/.

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