Why We Measure River Flow in Kerala

1. Where is Kerala?

Geographic Background

Kerala is a southwestern Indian state, situated roughly between 8.5°N - 12.5°N latitude and 74°E - 77°E longitude. It is characterized by a coastal strip which is thin and edged by the Arabian Sea to the west and the Western Ghats mountain range to the east. The geography of Kerala is extremely diverse, encompassing emerald green backwaters, serene beaches, and dense tropical rain forests on the slope of the Western Ghats. The tropical monsoon climate of the state is controlled by a southwest monsoon in June, July, August, and September, which brings heavy rain, often more than 75% of the annual rainfall, and a dry northeast monsoon between October and December.

Humanities and culture

Kerala has a rich and unique cultural heritage well rooted in its history. It has been a major center of trade and culture since centuries, influenced by numerous various civilizations like the Arabs, Chinese, and Europeans. The state is renowned for its folk arts such as Kathakali, a highly stylized classical dance - drama with highly ornamented costumes and cosmetics, and Mohiniyattam, a beautiful dance. Kerala also has Ayurvedic traditions, the oldest known holistic healing system worldwide. Its architecture is adorned with beautiful temples like the Padmanabhaswamy Temple at Thiruvananthapuram, which symbolizes a blend of Dravidian and indigenous styles. Kerala is culturally unique in its literacy rate and emphasis on education and social welfare.

Hydrology and River Overview

Kerala is also blessed with a series of 44 west-flowing rivers, all of which are the result of the Western Ghats. The Periyar, Bharathapuzha, and Pamba rivers are the three major river systems. The Periyar River is the longest river in Kerala and rises in the Sivagiri hills in Tamil Nadu before meandering through the central part of Kerala and emptying into the Arabian Sea off Kochi. The Bharathapuzha, or the Nila, has its source in the Anaimalai Hills and runs through Palakkad district to drain into the Arabian Sea. The Pamba River, reputed to be sacred in traditional times, originates in the Peermedu plateau and is an important water source for the eastern part of the state.

These rivers play a significant role in Kerala's ecology and human existence. Ecologically, they support a wide variety of aquatic life and act as habitats to a multitude of species of fish, birds, and wildlife. The backwaters, a unique natural feature formed due to the confluence of the rivers and the sea, are occupied by rich biodiversity of flora and fauna and have a vital role in the maintenance of the ecological balance. For human purposes, the rivers supply fresh water for household use, agriculture, and industry. They are intensively utilized for irrigation for the growing of crops like rice, rubber, and spices, which are the principal crops of the state. In industry, the majority of factories rely on river water for processes. The rivers play an important role to the extent in transportation as well, with some of the waterways being utilized for local boat traffic.

2. What is River Flow Like Near Kerala?

Determining Factors

Rainfall and Runoff

The southwest monsoon is the most prominent factor influencing river flow in Kerala. The intense and long rainfalls during this season result in a steep increase in river levels and flow velocities. The amount of rainfall could be extremely high from year to year, inducing changes in river flows. Rivers can produce high - volume runoff during years of intensive monsoon activity, thereby increasing the potential for flooding. Urbanization in Kerala has also influenced runoff since greater impervious surfaces enhance less infiltration and more surface runoff, thereby leading to faster - rising river levels. In lean years, especially when the monsoon is weak or delayed, river flows plummet, resulting in water shortage for various uses.

Bottomography and River Morphology

The steep slopes of the Western Ghats at the head of the rivers produce fast-flowing streams in the upper reaches. The rivers flowing towards the coast, the land flattens and the rate of flow decreases. The sharp valleys in the hills can make the water flow more turbulently and rapidly. The width and depth of the rivers vary along their course too. Some of the rivers are very deep and narrow in the hills, but widen in the plains. The river bed is composed of a mixture of sand, rocks, and silt, and the river bed roughness affects the flow resistance, thereby the overall flow pattern.

Reservoir Operations

There are several dams and reservoirs built across Kerala rivers, mainly for hydroelectric power generation, irrigation, and water supply. These reservoirs regulate the river flow downstream. They store excess monsoon water, thus reducing the flood hazard. They discharge water during the dry season to maintain a minimum flow, thus offering a steady supply for various uses. Mismanagement in reservoir water release, especially during heavy rainfall, can exacerbate flood conditions downstream.

Historical Hydrological Events

One of the worst floods in Kerala happened in 2018. During August to September, unusually high southwest monsoon rains, with rivers overflowing and release of water from dams, resulted in widespread flooding. The Kerala State Disaster Management Authority reported that a total of 483 people were fatalities, and more than a million people were left homeless. Large areas of the state, including some of the main cities such as Kochi and Thrissur, were inundated. The crop lands, especially those that produced cash crops such as rubber and spices, were ravaged. Road, bridge, and power line facilities were severely damaged. Monitoring such events is essential as it helps in creating better flood-mitigation strategies, refining early-warning systems, and making the state more resilient to future hydrological calamities.

3. How is the River Flow in Kerala Monitored?

Traditional Methods

Surface Drift Float Buoy Method

The surface drift float buoy method involves the launching of a buoy on the river surface and tracking its journey over a measured distance and time. The buoy speed is taken to be the river surface velocity. This is a simple, low-budget method using simple equipment like a buoy and a stopwatch. It only provides an estimate of the surface flow, taking no account of the velocity variation with depth. Further, the wind and other surface - level disturbance can contribute even more to making the measurements quite inaccurate.

Anchored Boat Method (Staff Gauge/Current Meter)

In anchored boat measurement, a boat is anchored at a single location in the river. A current meter is lowered to different depths to measure the velocity of the water, with a staff gauge employed to measure the water level. This measurement gives accurate velocity profiles at a single point but takes time, requires a lot of labor, and has safety risks, especially in wide rivers or in high - speed rivers.

ADCP Introduction: Acoustic Doppler Current Profiler (ADCP)

Acoustic Doppler Current Profiler (ADCP) offers a better and more efficient method of measuring river flow. It is capable of producing continuous velocity profiles from surface to bottom of the river in a non-invasive way. ADCPs are able to quickly survey large river sections, which makes them ideal for general flow estimation, such as for floods or long-term hydrology in Kerala's complex river networks.

4. An ADCP Operation According to the Doppler Principle

An ADCP profiler operates on the Doppler principle. It transmits sound waves at a specified frequency. When the sound waves impact moving entities in water, such as sediment or plankton, the frequency of the returning waves changes with the relative motion of the entities. When the particles are heading towards the ADCP, return signal frequency is higher; when moving away, lower. By calculating the frequency differences, the ADCP calculates the water velocity at various depths. With greater than one transducer angled differently, it records velocity components in three dimensions so that the total water flow pattern can be accurately determined.

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

Equipment Requirements

Material Reliability

The warm tropical climate of Kerala and the corrosive nature of the water, especially near the coast, necessitate ADCPs to be designed with highly resistant materials. Stainless steel or special alloys and hard plastics make equipment durable in the harsh environmental conditions.

Small Size and Lightweight

The sinuous and constricted path of some rivers in Kerala, added to the need for rapid deployment at various locations, makes compact and lightweight ADCPs more convenient. They may be easily carried and shifted, either on small boats or at hard - to - access locations.

Cost-Effectiveness

For mass and long-term monitoring projects in Kerala, affordable ADCPs are a requirement. A device that offers quality performance at a reasonable cost enables wider deployment on the state's numerous rivers so that cross-section data are available.

6. How to Choose the Best Current Measuring Equipment?

Deployment Techniques

Boat-Mounted (Floating Boat) ADCP

Boat-mounted ADCP current profiler is best suited for making detailed river-section surveys. It can quickly make measurements of discharge and map the flow characteristics across the river width, which is useful in flood-response operations and basic river-flow investigations.

Bottom - Mounted (Fixed) ADCP

Most appropriate for continuous long-term monitoring, bottom-mounted ADCP can be mounted on the river bed to observe flow data for an extended period of time. This provides observation of seasonal as well as long-term trends in river flow in Kerala.

Cableway ADCP

In regions where cableways are present, the river flow can be measured using a cableway ADCP. This technique is applicable in reaches where boat deployment is complicated or where a fixed-bottom installation is not feasible.

Working Frequency

For Kerala rivers, a 600 kHz ADCP would normally be an ideal choice as it provides a good range (up to 70 meters in the horizontal direction) and resolution for the state's medium-sized rivers. A 300 kHz ADCP with greater range up to 110 meters may be employed for deeper or wider river stretches but with lower resolution.

Brand Recommendations

Well - recognized international ADCP brands are Teledyne RDI, Nortek, and SonTek, with high - quality and reliable products. The ADCP manufacturer Chinese company’s "China Sonar Panda ADCP" can be referred to as an affordable Chinese brand. Made of all - titanium alloy, it offers excellent corrosion resistance and durability at extremely competitive prices. More information is available at https://china-sonar.com/.

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