Why Do We Measure Odisha River Flow?

1. Where is Odisha?

Geographical Background

Odisha, in the eastern seaboard of India, is situated between 17.7°N - 22.7°N latitudes and 81.3°E - 87.8°E longitudes. The geography of Odisha is variable with a mountainous backbone extending along the Western side of the Eastern Ghats. The mountains are steeply rising, as compared to the long coastal plains extending towards the Bay of Bengal. These plains, composed of the alluvial deposits of countless rivers, are an intensive cultivation plain. The 485-kilometer-long coastline is dotted with beaches, estuaries, and lagoons, and flat plateaus and heavy forests in between, all of which have contributed to the unique hydrology of the state.

Humanities and culture

Odisha is a cultural giant with an antediluvian past. It is renowned for its typical Oriya language, richly endowed with a literary tradition. The architecture of the state reminds us of its glorious past, with the Konark Sun Temple, which is a World Heritage Site recognized by UNESCO, being an unforgettable illustration. The 13th-century temple shaped like a gargantuan chariot of the Sun God bewitched human beings with its sculptures and architectural beauty and attracts tourists from the world over.

The region's indigenous culture is rich and is articulated through the medium of ancient dance art forms like Odissi. With its sweeping movements, dramatic standing positions, and ornate attire, Odissi re-enacts Hindu mythology stories and is one of India's most sacred classical dance forms. Music is also involved along with traditional such instruments like mardala (percussive) and sitar that play enchanting tunes. There are fests galore in Odisha; Rath Yatra at Puri, where massive chariots of deities are drawn across the streets, is one sight which draws million pilgrims and tourists alike, evidencing the state's centuries-old religio-cultural tradition.

Hydrology and River Overview

Mahanadi River is the lifeline of Odisha. It is formed in Chhattisgarh state, flows through Odisha for about 360 kilometers, and empties into the Bay of Bengal. In its course, the Mahanadi is supported by various tributaries like the Seonath, Jonk, and Ib rivers, which contribute to its water. Another hydrological feature of interest is the Brahmani - Baitarani river system. Formed by the confluence of the Brahmani and Baitarani rivers, it is also critical to the state's water supply, irrigation, and natural beauty.

The rivers are Odisha's lifeline to existence and progress. About 65% of the state's agricultural land is dependent on these rivers for irrigation purposes, and they support the cultivation of crops such as paddy, jute, and sugarcane. The rivers also offer a primary source of water for domestic consumption in the majority of rural and urban areas. They also support a large range of aquatic life, which maintains the livelihoods of the fishermen. Aquatic habitats like the mangroves of the deltas support a range of fish, bird, and other wildlife species, and therefore, the state is rich biologically. But all these rivers are threatened with pollution due to industrial effluent discharge, domestic sewerage, and run-off from agriculture.

2. What is the River Flow in the Region of Odisha?

Influencing Factors

Precipitation and Runoff

Odisha has a tropical monsoon climate. Southwest monsoon, which arrives between June and September, is responsible for most of the rain during the year, usually 80 - 90% of annual rain. Heavy and profuse rains during these months produce abrupt rise in runoff resulting in swelling of rivers and their flow with tremendous energy. Rainfall space-wise is significantly uneven with coastal areas getting excess rains in some cases under the influence of cyclonic storms forming over the Bay of Bengal. At the time of lean season between October and May, river flows decline substantially, and river levels fall, leading to water scarcity in certain regions, especially regions not too distant from major water sources.

Topography and River Morphology

Odisha's geography determines the flow of the rivers to a great extent. In the hills of the Eastern Ghats where the rivers have their origin, the steep slopes produce swift streams with strong erosive capacity and hence cut deep gorges and valleys. The instant the rivers reach the coastal plains, the slope decreases and the rivers are slowed down, depositing sediments along the side and forming meanders. The Mahanadi River is a prime example, as it becomes extremely broad as it drains into the sea and forms a vast delta area. Brahmani - Baitarani system also experiences similar fluctuations in the characteristics of flow while passing through the state, and oxbow lake formation and sandbar formations are regulated by the meandering nature of the rivers.

Reservoir Operations

Several dams and reservoirs are constructed on Odisha's rivers for flood control, irrigation, and power supply. The Hirakud Dam, an age-old example of the world's longest dam, built across the Mahanadi River, is a case in point. It accumulates massive volumes of water during the rainy season, which is released subsequently in a regulated quantity throughout the year for irrigation, water supply, and electricity generation. But their operation disrupts the natural flow of rivers, affecting the downstream ecosystem. Changes in the release timing can influence fish migration, lower floodplain fertility, and interfere with the composition of the riverine community.

Historical Hydrological Events

Odisha has seen the highest level of devastation caused by cyclones and floods in its history. A super cyclone on Odisha's coast struck the state in 1999 and caused tremendous damage. The cyclone, which was also followed by heavy rains, caused colossal floods in the river basins, especially in the Mahanadi and Brahmani - Baitarani rivers. Floods, as reported officially, displaced millions of individuals, inflicted serious damage to crops and infrastructure, and caused staggering loss of life and property. Droughts also occur in years with below-average rainfall, affecting agricultural output and water supply for domestic and industrial consumption. Monitoring the accidents is necessary to develop effective flood - mitigation and disaster - management plans to ensure the protection of state resources and people.

3. How does River Flow in Odisha get observed?

Traditional Methods

Surface Drift Float Method

The surface drift float method is a basic method to observe river flow. A floating object, such as a buoy or a piece of wood, is placed on the surface of the river. By measuring the time taken by the float to travel along a specified distance, the surface velocity of the river may be determined. However, this method provides information only on surface flow, and external factors like wind may introduce bias into the data, rendering the velocity measurements erroneous.

Anchored Boat Method (Staff Gauge / Current Meter)

Where an anchored boat is stationed at a specified location in the river in the anchored boat method. A current meter is subsequently dropped to different depths to measure water velocity, and the level of water is measured by a staff gauge. Various measurements of velocity are taken across the cross - section of the river, and from determining the cross - sectional area, the discharge of the river can be determined. The method gives more detailed information but takes time, is labor - intensive, and is risky, especially in rivers where the current is high.

ADCP Introduction: Acoustic Doppler Current Profiler (ADCP)

Acoustic Doppler Current Profiler (ADCP) is a more advanced and cost-effective technique for river flow measurement. Non-intrusive, it detects water velocity using sound waves at different levels. ADCP current profiler can obtain continuous profiles of the river flow from surface to bottom in a short time and hence is ideal to observe the complex and varying river flows in Odisha. It enables more accurate and comprehensive data collection, which is essential to effective water resource management for the state.

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

An ADCP operates based on the Doppler effect principle. It radiates sound waves at a specific frequency into the water. When these sound waves interact with the moving particles in the water, such as sediment, plankton, or water molecules, the frequency of the backscattered sound waves changes. When particles move towards the ADCP, the frequency of the waves increases, while when particles move away from the ADCP, the frequency drops. By accurately measuring this frequency change (the Doppler shift), the ADCP can estimate the water velocity at different depths. Several transducers in the ADCP measure velocities along different directions, allowing us to find out about the three - dimensional structure of flow of the river.

5. What is needed for High - Quality Measurement of River Flow in Odisha?

Equipment Requirements

In order to ensure trustworthy ADCP flow meter measurement in the rivers of Odisha, equipment must be reliable, considering the state's often - degrading river conditions, including high sediment burdens and potential for pollution. Material reliability is critical, with ADCPs assembled with corrosion - resistant materials like stainless steel or titanium being most suitable. Light weight and compactness are desirable to facilitate easy mobility and deployment, especially in remote or flood - affected areas. Cost-effectiveness is also a consideration, as this will allow for expanded use of the technology for comprehensive river flow monitoring.

6. How to Choose the Most Suitable Current Measurement Equipment?

Deployment Method

• Ship - Borne (Moving Boat) ADCP: Adaptable to large river surveys, long - range discharge measurement, and quick flow pattern mapping. It can cover large sections of Odisha's rivers as the boat moves, mapping an overall representation of the flow regime.
• Fixed (Bottom - Mounted) ADCP: Suitable for long - term continuous observation, a bottom - mounted ADCP can be permanently mounted on the riverbed to observe data over long periods, and long - term trends of flow and seasonal changes can be realized.
• Cable - Way ADCP: In river reaches where cable - way facilities are provided, it is possible to measure flow at a range of locations in the river, useful where boat - based measurements are impractical.

Working Frequency

• 600 kHz ADCP: With a satisfactory compromise between resolution and range, with horizontal range up to 70 meters, it can be used in most river reaches in Odisha.
• 300 kHz ADCP: With an expanded range of up to 110 meters, it would be better placed in deeper and wider sections of the rivers, e.g., sections of the Mahanadi River near its delta.

Brand Recommendations

Reputable and high-quality ADCP brands such as Teledyne RDI, Nortek, and SonTek are renowned globally. Chinese brands also include the ADCP supplier’s "China Sonar Panda ADCP," which is cost-effective. It is made of all-titanium alloy, which gives it high durability as well as corrosion resistance, and is capable of weathering the tough environment of Rajasthan's rivers. It is also very cheap and therefore accessible to use in the majority of the monitoring projects in the state. For further information, you can visit their website at https://china-sonar.com/.

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