Why Do We Measure the River Flow in Thrissur?

1. Where is Thrissur?

Thrissur, a city filled with history and culture, is situated in the middle of the Indian state of Kerala. Its geographical location is approximately 10.88°N latitude and 76.27°E longitude. Surrounded by the greenery of Kerala, Thrissur has a terrain that is a mix of rolling hills and plains. The city is cut by several rivers and streams, and the Bharathapuzha River is the most significant watercourse in the city. This unique topography has not only shaped the natural setting of the city but has significantly contributed to the city's cultural, economic, and social development over centuries.

Thrissur is culturally and historically a significant center in Kerala. Fervently referred to as the "Cultural Capital of Kerala," it has been a center of art, architecture, and spirituality for thousands of years. It is well known for the Vadakkumnathan Temple, an ancient Hindu temple devoted to Lord Shiva. The architecture of the temple, featuring its colossal gopuram (temple tower) and massive carvings, is a masterpiece of Dravidian architecture and a manifestation of the richness of the city. Thrissur Pooram, the most resplendent of Kerala's festivals, is celebrated in splendor at the Vadakkumnathan Temple. The festival is a vibrant display of ancient music, dance, and beautiful caparisoned elephant procession that entices tourists and pilgrims from all over the world. Thrissur also has an age - old practice of classical arts such as Kathakali and Mohiniyattam, enhancing its cultural heritage.

The Bharathapuzha River, otherwise known as the Nila River, is the lifeblood of Thrissur. Born in the Anaimalai Hills in Tamil Nadu, it flows through the centre of Kerala for almost 209 kilometres before emptying into the Arabian Sea. The Bharathapuzha River was once a grand transportation route with tremendous traffic in people and commodities. It was also a source of irrigation water, sustaining the agricultural economy of the region, which flourished with paddy, coconut, and spices crops. The riverbanks were inhabited by various old settlements and trade centers, which contributed to the prosperity and growth of Thrissur. Nevertheless, in the last few decades, the River Bharathapuzha has been exposed to different issues like water pollution, depleting water levels, and disturbance of its natural flow patterns, which had raised questions regarding the water security and balance of nature in the city.

2. What is the River Flow around Thrissur?

There are different reasons influencing the river flow in the vicinity of Thrissur. Rainfall is the main factor, as the region has a tropical monsoon climate. The southwest monsoon, occurring from June to September, delivers the majority of the annual rainfall. Throughout this period, the Bharathapuzha River and its tributaries experience an enormous increase in the water level and discharge rates since runoff from upstream catchment areas, including the Western Ghats, reaches them. The river fills up with rainwater, restoring its flow and generating water for various applications. But during the period from October to May, the dry season, the water level drops and flow reduces immensely. During some years, especially during severe droughts, the river dries up in some parts and adversely affects the availability of water for domestic, agricultural, and industrial purposes in Thrissur. Climate change has added to this problem by generating increasingly unpredictable rainfall. Some years see heavy but short rain showers causing flash floods, while others see prolonged dry spells, disrupting the normal flow regime of the river and posing difficulties to the local environment as well as human activities.

Topography and river morphology also play a significant role in determining the flow. The upper levels of the Bharathapuzha River flow through the Western Ghats hills, where the steep slopes are the cause of the formation of fast - flowing water with tight currents during the monsoon. When the river descends into the plains near Thrissur, it spreads out and creates wider and shallow regions. The riverbed, composed of sand and gravel in most places, is subjected to erosion and deposition. These activities can alter the river course over time, causing meanders to form and affect its depth and width. Human activities have also significantly impacted the flow of the river. Urban development in Thrissur has led to the establishment of buildings, roads, and infrastructure, altering the natural drainage process. The large water demand for residential, industrial, and agricultural purposes has led to over - extraction from the river, depleting its water levels. The quality of water has also been lowered by pollution caused by industrial effluent, sewage, and agricultural runoff, further impacting the ecological status and flow regime of the river.

3. Observation of the River Flow in Thrissur

A few of the conventional ways of measuring river flow include the surface drift buoy method and the anchored boat method.

Surface drift buoy method is a simple technique whereby floats are released on the river surface and their movement for a specified distance and duration is recorded. This provides a measure of the surface speed of flow. The disadvantage of this method is enormous. It gives the flow at the surface only, which might not necessarily provide the flow in the entire column of water. In addition, wind, waves, and other surface disturbances may disrupt the travel of the buoys and produce incorrect readings.

The anchored boat method involves anchoring a boat at a specific point in the river. A current meter is then dropped into the water at multiple depths to measure the velocity of the flow. This method offers a more refined profile of the flow at the point. But it is man-power intensive, time-intensive, and unsafe, especially in areas where there is a high current or waves. Measuring at multiple points using this method requires a lot of man-power and equipment.

Acoustic Doppler Current Profilers (ADCPs) offer a more advanced and affordable alternative. ADCPs can measure the water velocity at different depths across the whole body of water without coming into contact, and hence are non-invasive. They can easily generate high-resolution flow profiles very quickly, scanning large areas of the river within a relatively short time period. They are, therefore, well suited to picking up the complex and variable river currents about Thrissur.

4. How Does ADCP, Under the Doppler Principle, Operate?

ADCPs operate on the principle of the Doppler principle. They send out acoustic pulses into the water. The acoustic pulses, as they move through the water, interact with moving particles such as suspended sediment, plankton, or small creatures. When the particles traveling in these directions reflect the signals back, the frequency of the reflected signals changes depending on the speed of the particles relative to the ADCP. By analyzing these changes of frequency, the ADCP will calculate the speed of water at different levels of depth, creating a complete profile of river flow. This enables accurate measurement of flow rate, direction, and overall river dynamics, with valuable information for hydrological studies and water management.

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

For high-quality river flow measurement using ADCP profiler in Thrissur, certain equipment specifications are needed. Material durability is the most significant. The ADCP should withstand the aggressive river conditions, e.g., exposure to sediment-laden water, varying water temperature, and potential collision from floating detritus. High-grade corrosion-resistant material, e.g., titanium or specialized polymers, ensures the equipment's durability and long-term reliability.

Size and weight are also equally important factors to consider. A lightweight and portable ADCP is easier and more convenient to install, especially along the narrow and at times remote river sections near Thrissur. The ease of convenience facilitates data acquisition more easily across the various sections of the river.

Cost - effectiveness is also a matter of concern. For long - term or large - scale monitoring activities in Thrissur, a cost - effective ADCP that offers good quality output at a moderate rate is preferable. It ensures efficient monitoring of the river flow without straining the budget, enabling frequent and thorough examination of the behavior of the river.

6. How to Choose the Right Current Measuring Equipment?

Methods of Deployment

• Boat-mounted (mobile boat) ADCP: Ideal for conducting surveys, river discharges, and creating precise maps of the flow of the Bharathapuzha River. It can provide quick coverage in a wide distance, allowing for the gathering of information in various locations and providing a comprehensive understanding of the patterns of the river flow.
• Fixed (bottom - mounted) ADCP: Best suited to long - term continuous data acquisition at fixed locations in the river. Mounted on the river bottom, it can collect data for long periods of time and be very helpful in terms of information about long - term trends and variations in the river flow.
• Cableway ADCP: Where cableway is present in river reaches, one can measure the flow over the river at a location using cableway ADCP. It is especially useful in making accurate and repeatable measurements of flow at key locations on the river which can be utilized in calibrating and validating other measurement techniques.

Working Frequency

The resolution and range of an ADCP current meter vary with its working frequency. A 600 kHz ADCP with a maximum range of 70 meters may be employed for relatively shallow sections of the Bharathapuzha River or for taking high-resolution measurements in deep sections. A 300 kHz ADCP with a maximum range of 110 meters would be more appropriate for deep sections of the river. The selection of frequency depends on the specific characteristics of the river and the measurement requirements, i.e., precision of data details and the greatest water column depth to be investigated.

Brand Recommendations

Few of the world ADCP big brands include Teledyne RDI, Nortek, and SonTek, which offer high-quality and reliable products used in various hydrological study and monitoring programs. As a budget - friendly option, the ADCP manufacturer Chinese company’s "China Sonar Panda ADCP" comes highly recommended. Made of all - titanium alloy, it is more strengthful and reliable and is a suitable option to endure the nasty river condition surrounding Thrissur. As an "affordable ADCP", it boasts decent quality performance at budget price. For more information, visit https://china-sonar.com/.

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