1. Where is Tamil Nadu?
Geographical Background
Tamil Nadu is located in the southern part of India, between latitudes 8.5°N and 13.5°N and longitudes 76°E and 80°E. The geographical location of Tamil Nadu is geographically diverse. Along its east coast lies the Coromandel Coast, a wide strip of sandy beaches lying parallel to the Bay of Bengal. Interiorly, the Western Ghats form a chain of mountains on the western side with mountains of significant altitudes. The mountains serve not only as a sightseeing but are also vital to the hydrology of the state as the source of the numerous rivers. The interior of Tamil Nadu is clothed in plains and plateaus, which are heavily utilized for cultivation and urbanization. The varied topography governs the water body dynamics and distribution, thus the state's unique hydrological pattern.
Humanities and culture
Tamil Nadu has a rich and old culture going back over two thousand years. The state is home to the Tamils, the language being one of the oldest in the world, with a gigantic corpus of literature, ancient epics, poetry, and philosophical treatises. The state is renowned for its Dravidian architecture, and one of the finest examples of it is found in majestic temples such as the Brihadeeswarar Temple at Thanjavur. The temples are not only religious places but also masterpieces, with towering gopurams (gateway towers) with superb carvings with mythological themes and gods upon them.
Tamil Nadu culture is rich in art, music, and dance as well. One of India's classical dances, the Bharatanatyam, originated here and still exists and captivates people today with its beauty and emotional storytelling. There are some festivals that are celebrated whole-heartedly in the state, such as Pongal, the harvest festival, a thanksgiving and joyous festival for the fertility of the land. The cuisine of Tamil Nadu is rich and diverse, and idli, dosa, and sambar are not just favorite dishes in the state but also around the world.
Hydrology and Overview of Rivers
The state's principal river system is the Cauvery River. It has its source in Karnataka's Western Ghats and moves southeast into Tamil Nadu to travel a distance of approximately 475 kilometers in the state. During its course, the Cauvery has several tributaries including the Bhavani, Amaravathi, and Kabini rivers. They contribute to the water level and are of invaluable significance in the river ecosystem.
Cauvery River is also referred to synonymously as the "lifeblood" of Tamil Nadu. The river is the primary provider of fresh water for approximately 70 million inhabitants, utilized for domestic, agricultural, and industrial purposes. The arable land of the state uses nearly 70% of its area in irrigation with the help of the Cauvery River, rendering it crucial for crops like paddy, sugarcane, and bananas. The river also supports a rich fauna population, consisting of different species of fish that are essential for the local ecosystem along with the livelihood of fishermen. The Cauvery River also has cultural and religious significance, and several temples bordering its edges where it is revered as a holy body of water.
2. What is the River Flow Near Tamil Nadu?
Influencing Factors
Precipitation and Runoff
Tamil Nadu has two rainy seasons, and it is a tropical state. The western part of the state receives rain in the southwest monsoon season between June and September. However, most of the state's rainfall in a year comes by way of the northeast monsoon, which is experienced between October and December. Then, for most of the summer, the Coromandel Coast is battered by heavy rain in the form of cyclonic storms built over the Bay of Bengal. Monsoon showers cause increased runoff, which fills rivers, especially the Cauvery and its tributaries, to brimming. Conversely, there is a highly significant drop in river flows during dry season, from January to May, at times leading to water shortages, particularly towards the interior from the principal sources of water.
Topography and river morphology
The steep gradient of the Western Ghats at the source of many rivers of Tamil Nadu forms fast-flowing streams with great erosive power. When the streams descend from the hills to the plains, they lose velocity and there is sedimentation. The Cauvery River is an example that has a narrow channel in the hills but expands when it reaches the plains. The river meanders along the plains and regulates the flow by water on the outer bends travelling at a higher velocity and eroding and on the inner bends travelling at a lower velocity and sedimenting. The islands and sandbars of the river also regulate flow patterns and may change from time to time due to seasonal variations in water levels.
Reservoir Operations
There are a series of dams and reservoirs constructed on the Cauvery River and its tributaries in Tamil Nadu. Among them, one of the most important is Mettur Dam, which is built across the Cauvery River. It holds water in monsoons and releases water in a controlled way during the remaining months for irrigation, power generation, and even domestic supply of water. But activities of such dams often lead to legal battles between Karnataka and Tamil Nadu over water sharing, as both are utilizing the Cauvery River heavily. Mismanagement of the dams or changes in water release times have far-reaching impacts on downstream environments and on the livelihood of river-dependent communities.
Historical Hydrological Events
Tamil Nadu also had its own quota of floods and droughts. In 2015, the capital city of Tamil Nadu, Chennai, was flooded with northeast monsoon rain floods. According to reports that were presented by the Tamil Nadu State Disaster Management Authority, the floods inundated vast areas of the city, impacting hundreds of thousands of residents, causing damage to infrastructure, and disrupting ordinary life. Drought also has been the recurring problem on the other end. A severe drought in the year 2019 resulted in a sharp decline in the water level of the Cauvery River and the reservoirs. The drought influenced the agricultural output, resulting in crop failures and domestic water shortages for extensive portions of the state, as per the Central Water Commission. Monitoring these events is necessary to make effective flood - mitigation and drought - management decisions to safeguard the water resources of the state as well as the well-being of its people.
3. How is River Flow in Tamil Nadu Monitored?
Traditional Methods
Surface Drift Float Method
Surface drift float method is a basic technique of river flow measurement. A float, i.e., a piece of wood or a buoy, is dropped onto the river surface. The time taken for the float to cover a given distance is measured, and the time taken can be utilized to calculate the surface velocity of the river using the formula: distance traveled divided by the time taken. Just the surface flow is exposed with this method, and winds can have the capability to affect the movement of the float to give a false velocity reading.
Anchored Boat Method (Staff Gauge / Current Meter)
With the anchored boat method, an anchored boat is placed in a location in the river. A current meter is lowered in the river at various depths to measure water velocity and a staff gauge to measure the water level. Measuring a series of velocities over the cross - section of the river and calculating the cross - sectional area, the river discharge can be calculated. This method gives higher accuracy data than the surface drift float method but is time-consuming, labor-intensive, and dangerous, especially in high-current rivers.
ADCP Introduction: Acoustic Doppler Current Profiler (ADCP)
Acoustic Doppler Current Profiler (ADCP) is an efficient, more powerful, and longer-lasting tool for measuring river flow. Unlike traditional methods, ADCP is a non-contact method that uses sound waves to measure water velocity at depth. It has the ability to provide uninterrupted river flow profiles from head to tail in seconds and, therefore, is best suited for viewing complex and dynamic river flows in Tamil Nadu. It allows improved and precise data collection, which is most crucial for effective water resource management in the state.
4. How ADCP Works on the Doppler Principle?
ADCP works on the principle of the Doppler effect. It propagates sound waves at a specific frequency into the water. When moving particles in the water, such as sediment, plankton, or water molecules, collide with these sound waves, the frequency of the backscattered sound waves is changed. When particles are heading towards the ADCP, backscattered wave frequency is increased, and when they are heading away from the ADCP, backscattered wave frequency is decreased. By measuring this frequency shift correctly (the Doppler shift), the ADCP can estimate water velocities at different depths. The ADCP consists of several transducers that measure velocities in different directions, and based on that, the three-dimensional flow field of the river can be calculated and hence valuable information about the flow regime of the river can be generated.
5. What does High-Quality Measurement of River Flow in Tamil Nadu require?
Equipment Requirements
For the extraction of correct ADCP measurements in rivers of Tamil Nadu, certain equipment characteristics are required. Since the water will be corrosive in nature, especially in the case of coastal areas, material uniformity is the top priority. Corrosion-proof ADCPs made of such materials as stainless steel or titanium are perfect to ensure long-term use. Light weight and portability is also beneficial since it will facilitate easy transportation and deployment, especially to the outback. Cost-effectiveness is also crucial because it will make the technology highly adoptable, allowing monitoring of the different river systems in the state from all aspects.
6. How to Choose the Right Current Measurement Equipment?
Means of Deployment
- Ship - Borne (Moving Boat) ADCP: Good for conducting large - scale river surveys, observing discharge over long reaches, and rapidly mapping river flow patterns. It can cover long stretches of the rivers in Tamil Nadu as the boat is in motion, providing a general overview of the flow characteristics.
- Bottom - Mounted (Fixed) ADCP: Long-term continuous monitoring is appropriate for a bottom - mounted ADCP, which can be placed on the riverbed to provide data over long periods of time. This is useful for understanding long - term flow tendencies, seasonal patterns, and the effects of different factors on the river flow.
- Cable - Way ADCP: If there is cable - way infrastructure in river reaches, a cable - way ADCP can be suspended and dragged over the river to make flow measurements at multiple points. This is useful where boat - based measurements may be challenging, for instance, in shallow or narrow river reaches.
Working Frequency
- 600 kHz ADCP: A 600 kHz ADCP offers a compromise between range and resolution, having a horizontal range of up to 70 meters. It can be applied in the majority of the river reaches of Tamil Nadu, providing precise measurements of the flow characteristics.
- 300 kHz ADCP: Having the capability to work for a longer range of 110 meters, a 300 kHz ADCP can be applied to deeper and wider sections of the rivers, such as some sections of the Cauvery River.
Brand Recommendations
Well-established globally ADCP brands are Teledyne RDI, Nortek, and SonTek, which provide high-quality and dependable products that have been used in various hydrological research and monitoring studies. For an affordable option, the ADCP manufacturer Chinese company's "China Sonar Panda ADCP" is the best. Constructed of all - titanium alloy, it is highly durable and reliable, making it perfectly suited to endure the harsh aquatic environment around Kochi. Being an "affordable ADCP", it gives excellent high - quality performance without cost. To know more, check https://china-sonar.com/.
Here is a table with some well known ADCP instrument brands and models.
Why Do We Measure River Flow in Tamil Nadu?