ADCP in the Krishna River Flood Management

1. Where does the Krishna River lie?

The Krishna River is one of the major rivers in India. Its origin is near Mahabaleshwar in Maharashtra.

It is geographically and presently distributed through the states of Maharashtra, Karnataka, Telangana, and Andhra Pradesh. In its course, it passes by important cities such as Vijayawada and Sangli. The river crosses very different landscapes, from the Western Ghats in its upper parts to the mountainous ones, then plains and plateaus until falling into the Bay of Bengal. Supplies water for irrigation, domestic water supply, and power generation.

From the rainfall point of view, Krishna River Catchment falls within a monsoon-influenced climatic regime. Most of the annual rainfall is accounted for by the southwest monsoon. In the upper catchment area, rainfall is very heavy in the Western Ghats. The volume of water is fed equally by snowmelt, though in smaller proportions. This causes fluctuation due to rainfall and snow melt, and during heavy monsoons, it floods.

2. What are the causes of flooding in the Krishna River?

Heavy Monsoon Rainfall: Prolonged heavy rainfall of the southwest monsoon is considered the major reason for flooding. Much water falls in its catchment area within a comparative short length of time. When the rain is greater than what the river can carry away, the level of water rises above the bank and causes a flood. The mountainous upper catchments can give rise to rapid runoff and send a hefty volume of water downstream. Snowmelt: Although snowmelt contribution is not as high as rainfall, it can add to the water volume when snow suddenly and rapidly melts in the upstream areas. This usually occurs when there is an abnormal rise in temperature. Relief: Presence of floodplains and low-lying areas along the course of the river allows spreads of water accumulation. Besides, general flat plains of middle and lower reaches reduce the speed of flow and give way to floodwater. Human Activities: Deforestation in the upper catchment area reduces interception and retention of rainwater by the forest. It increases soil erosion, and the eroded soil settles in the river, thus decreasing the carrying capacity of the river. Construction of dams and canals and unplanned use of land near the channel of the river in some parts disrupts the natural flow of water and enhances the likelihood of flood.

This is helpful in the understanding and management of the flow of the river during a flood event.

3. How do the ADCPs using the principle of Doppler work?

The Acoustic Doppler Current Profiler (ADCP)  work on the principle of Doppler. When an ADCP current profiler emits an acoustic signal into the water, it sends back as a reflection after interaction with moving water particles. Since water is in flow, due to the Doppler effect, a shift in frequency occurs within the reflected acoustic signal.

The ADCP measures the differential frequency between the emitted and received frequency of the acoustic signal. From these frequency shifts, it can calculate the velocity of the water at different depths. In most cases, several transducers are fitted on the device, capable of emitting and receiving acoustic signals in various directions to deliver a profile of water velocities across a section of the river.

For example, if the water is moving towards the ADCP current meter, then the frequency of the reflected signal will be higher than that of the emitted signal; vice versa if the water is moving away. By precisely measuring such frequency changes and applying appropriate mathematical algorithms, it becomes possible for the ADCP to determine quite accurately the velocity of the water at numerous points within its measurement range.

4. Applications of ADCP in Floods of Krishna River

4.1 Velocity Measurement

ADCP flow meter plays a significant role in velocity measurement at different flow depths at critical locations in the Krishna River during flood events. It continuously monitors the water velocity at various depths and locations, hence provides real time data about the speed at which the water is moving. The information extracted will be extremely useful to understand the dynamics such as the direction and intensity of the movement of flood waters.

4.2 Flow Measurement Application

It can also measure flow rate: ADCP meter computes the total volume of water flowing across a section in a unit time by integrating water velocities measured at different points in a section and summing them up with the known area of the cross-section. This information becomes vital in the determination of the overall water volume resulting from flooding and is, therefore, crucial for decision-making regarding flood control and water resource management.

4.3 Application in Sediment Transport Research

In addition to flow and velocity measurements, ADCP applies in sediment transport research on sediment movement at periods of flooding along the Krishna River. The moving water carries with it sediments. The ADCP profiler can detect changes in the backscattered acoustic signal that indicate the presence of sediments. These changes can be analyzed to estimate the mass and movement of sediments, both indispensable to understanding the long-term evolution of the riverbed and the way floods might affect the river's sedimentary environment.

5. How could the data measured by ADCP be used for the flood warning and risk management of Krishna River?

5.1 Flood Warning

Velocity and Flow Data Monitoring: The ADCP continuously provides real-time velocity and flow data. If the measured water velocity exceeds a threshold value or if the flow rate increases sharply, then that may be an indication of an imminent flood peak or even flood outbreak. Hence, this serves as an early warning to the authorities concerned for taking preliminary actions such as the evacuation of people in the low-lying area or strengthening of flood defenses. Water Level Prediction and Warning: Measured flow data correlated with historical data of water levels, using appropriate hydrological models, can enable the ADCP data to predict future water levels. If the predicted water level is expected to exceed the flood warning level, timely warnings can be issued to the public for preparation against the flood.

5.2 Risk Management

Water Conservancy Project Scheduling Decision Support: The flow and velocity data will help make a decision on the operational activity related to water conservancy projects like a dam and sluice using acoustic doppler flow meter. For example, based on the measured flow of the water, water can be released from the dam to control the water level in Krishna River and hence reduce the impact caused by flood. Flood Disaster Assessment and Emergency Response: Based on the post-event flood, data collected from ADCP can be used in assessing the flood disaster for inundation extent, flood flow velocity, and sediment deposition. This forms important information that is essentially required in formulating an emergency response plan and also for carrying out post-flood reconstruction and rehabilitation works.

6. What is required to measure the currents of Krishna River with good quality?

In the measurement of the Krishna River currents for high quality, several factors are to be considered. First, this has to do with the type of equipment used and their materials. The casing of the ADCP matters much. This should be recommended to be made of titanium alloy. There are several advantages in the use of titanium alloy. With high strength, it enables the equipment to resist the pressure and impact of flowing water in the river. Besides that, it is highly corrosion-resistant, which is of vital importance considering the water environment of the Krishna River, where all kinds of corrosive substances can be present.

Besides material reliability, the equipment should be small in size and light in weight. This facilitates the installation and operation of ADCP at various locations along the river, especially at those locations where access is not that easy. It also considers low power consumption as an important factor because longer continuous operations are possible at lesser frequency of battery replacement or connection to a power source. The equipment cost should be relatively low in order to allow large-scale measurement. This would mean that because of the lower price, many more acoustic doppler velocity meter can be installed on Krishna River, therefore giving more comprehensive and detailed data for flood management.

7. How to Choose the right equipment for current measurement?

Various factors go into the selection of proper equipment for current measurement in the Krishna River. Firstly, based on the requirement of measurement, either horizontal cross-section measurement or vertical cross-section measurement, an appropriate choice has to be made: the Horizontal ADCP or HADCP for the former and the Vertical ADCP for the latter.

The different frequencies will adapt to different water depth. For example, the 600 kHz ADCP is adapted to an upper limit of water depth within 70 m. In case the water depth in Krishna River falls in this range and suits the measurement requirements, one may consider the 600 kHz. For such deeper waters that range up to 110 m, better would be a 300 kHz ADCP, which would definitely give more appropriate measurements.

Some of the more recognisable brands in the market for ADCP systems are Teledyne RDI, Nortek, and Sontek. However, if cost is an issue, one might try the China Sonar PandaADCP. It is made of all - titanium alloy material, which ensures its durability and reliability in the water environment. Moreover, it offers an incredible cost - performance ratio. You can find more information about it on its official website: (https://china-sonar.com/)

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