ADCP in the Tietê River Flood Management

1. Where is The Tietê River?

The Tietê River is a major river of the state of São Paulo, Brazil.

• Geographical Location and Course The source is in Serra do Mar, and it flows northwest for about 1,138 kilometres through the highly industrious and populated region of São Paulo. It forms part of the important local water system, has deeply marked the regional economy, and the environmental characteristics.
• Cities Along the River Along the Tietê River are many very important cities and towns. Among them is São Paulo, one of the biggest cities in Brazil and an international economic center. The river supplies water for domestic, industrial, and agricultural needs. It was previously used for transport purposes; however, it has reduced with time due to pollution and other reasons.
• Rainfall and Water Conditions The Tietê River basin has a tropical climate with well-defined wet and dry seasons. Wet seasons usually fall within the period from October to March when heavy rainfall is usually experienced. Annual rainfall inside the basin ranges between 1200 and 2000 millimeters. Due to heavy rainfall during wet seasons, the river swells considerably. Conversely, in the dry period between April and September, the level of the water is somewhat lower; notwithstanding, the river has a certain flow because of underground seepage and water contributions from some tributaries.

2. What are the causes of flooding in The Tietê River?

Heavy Rainfall in Wet Season Heavy rainfall conditions in the wet season are the main cause of flooding in the Tietê River. This huge amount of water falling in short periods saturates the ground, fills the tributaries, and the main channel. Hence, its water level rises very rapidly. For example, if an El Niño-affected year tends to occur, the rainfall can be all the more extreme. If so, the possibility of flooding becomes even more dangerous as the river might not contain the excess amount of water it receives. Isn't it exciting?

Deforestation and Changes in Land Use within the Basin For many years, the Tietê River basin has been facing well-marked deforestation and changes in land use. In general, deforestation decreases the absorbing capacity of the land considerably. Trees are an important part of the regulation of water flow because their roots hold the soil together and provide for the slow infiltration of water into the ground. If the forest cover decreases, then the rainwater runs off quicker to the river, thus increasing flooding. Other contributing factors to the alteration of the natural water cycle include urbanization and the expansion of agriculture, generally leading to quicker runoff and higher flood peaks.

Poor Drainage and Infrastructure The drainage in many areas along the Tietê River is insufficient for large volumes of water in case of heavy rainfall. Added to aging infrastructure, this has contributed to urban development in ways that do not drain stormwater away. The impervious surfaces like roads and parking lots prevent the infiltration of water into the ground, while the drainage channels that are in place may be clogged or too narrow in some areas to handle peak flows. This leads to water backup and flood in both urban and rural areas.

In view of these flood-related challenges, ADCP offers an advanced and more convenient measurement method for better flood management.

3. How do Doppler Principle-based ADCPs work?

The operating principle of Acoustic Doppler Current Profiler(ADCP)  is based on the Doppler effect. First, an acoustic pulse is emitted by a device, entering the water with a given frequency; the frequency may differ, depending on the model and the measurement requirements.

• Transmitting and Receiving Signals The acoustic pulses are transmitted in a fan-shaped pattern. As these pulses propagate through the water, they take on interactions with moving water particles and any suspended sediment. When the pulses hit the objects that are moving, some of the energy reflects back to the ADCP current meter.
• Detection of the Doppler Shift Due to the Doppler effect, the frequency of the reflected signals differs from that of the transmitted signals. If the particles of water or sediment are moving towards the ADCP current profiler, the frequency of the reflected signal becomes higher than the original one. Similarly, in case of motion in the opposite direction, the frequency becomes lower. The sensors in an ADCP flow meter are designed to detect such changes in frequency accurately.
• Calculating Velocity and Other Parameters The ADCP doppler computes the current water velocity, at a number of depths in the water column, internally by an application of internal algorithms on the detected Doppler shifts. It can also estimate how much water is flowing through any particular point by integrating velocity over the cross-sectional area of the river. The ADCP meter is capable of providing information on the motion and concentration of suspended sediment in water.

4. What are some of the applications of ADCP in floods of The Tietê River?

Velocity Measurement

The ADCP profiler represent the traditional method of measurement of the velocities of water currents during the flooding stage of the Tietê River. They are capable of providing current turbidity in real time with the speed of water at variable depths. This aids in the understanding of the practical dynamics of floodwaters-that the current is stronger either near the surface or at the bottom. The data of the velocity can also explain the current with regard to variation in both space and time, which is very necessary for the prediction of the spread and impact of the flood.

Flow Measurement Application

The Tietê River's flow rate during floods can be very accurately calculated using acoustic doppler flow meter. Since they measure the velocities and multiply these by the cross-sectional area at the point they are taking the measurement, they will provide an estimate of the volume of water flowing downstream. This is very important information in flood forecasting and studying the intensity of the flood. This may help scientists develop a model showing how much water will reach different areas along the riverbanks and how devastating the potential damage is.

Sediment Translocation Research Application

The Tietê River frequently causes sediment to move during flood events. In the case of sediment translocation, acoustic doppler velocity meter estimate the Doppler shifts that are normally presented by suspended sediment particles. Therefore, it will facilitate the analysis of sediment transportation in states of flooding and how the flood modifies the sediment distribution in the bed and banks of the river. It can also provide insight into the alteration that will the river has undergone or will undergo over a long period of time and how sedimentation affects the structure of infrastructures like bridges and dams.

5. How the data measured by ADCP can be used for the flood warning and risk management of The Tietê River?

Flood Warning

Velocity and Flow Data Monitoring: The actual real-time velocity and flow rate data from ADCPs are highly crucial in any flood warning system. Continuous observation of the parameters enables the authorities to notice sudden rise in the speed or volume of water flowing in the river. For example, an early warning can be issued when the flow rate exceeds a certain threshold linked with past flood events. This allows for the early evacuation of people residing in areas facing flood conditions and to plan various emergency response measures.

Water Level Prediction and Warning: ADCP data can also be used to predict water levels. Since the velocity and flow rate are related to the water level, analyzing the trends in the measured data can forecast how the water level will change in the near future. This allows the issuance of water level warnings to communities along the course of the river, with sufficient lead time for measures to be taken such as moving valuable belongings to higher ground or reinforcing flood defenses.

Risk Management

Water Conservancy Engineering Scheduling Decision Support: Acoustic current meter data support the scheduling water conservancy engineering decision. A specific example would be that if the flow rate and the velocity data indicate that a major flood is in the offing, then the dam operators can make appropriate adjustments in the release of water from the dams to minimize the effect on the downstream side. They can retain more water, if possible, to reduce the peak flood flow or let it out in a controlled manner so as not to create sudden surges which could damage the infrastructures downstream.

Flood Disaster Assessment and Emergency Response: Based on the results after any event of flood, ADCP data can be used in assessing the extent of flood damage caused. Analysis of flow velocities and flow patterns within the time of flood itself could allow the identification of where intense flooding had occurred and the areas that have been most affected. This information becomes crucial for coordinating the emergency response activities, including the deployment of rescue teams in the most badly affected areas and giving relief supplies to needy people.

6. What is necessary to have high-quality measurement of The Tietê River currents?

Material Reliability Correct and continuous measurement of the currents, in this case, can be obtained with the aid of equipment made with reliable materials. In particular, the casing of the ADCP should be manufactured in such a way that it resists all the negative impacts of the environment, such as being in contact with water and sediments and possibly receiving any blows.

Small Size, Light Weight, and Low Consumption of Energy The ADCP should be compact with minimum weight and low power consumption, which can easily be deployed and put into operation for large-scale measurement purposes along the Tietê River.A compact and lightweight device is easy to install on boats, buoys, or any other measuring platforms. Besides, low power consumption means longer-term operation with minimal need for replacement of the battery or a continuous power source, particularly installed at places that are usually burdened by limited power supplies.

Low Cost for Large-Scale Measurement It is only when the equipment cost is within reasonable bounds that ADCPs can be widely employed in monitoring the currents of the Tietê River on a large scale. The high costs restrict the number of deployable devices, which in turn limits the comprehensiveness of data collected.

Advantages of Using Titanium Alloy in Casing This is quite efficient usage of titanium alloy for casing in ADCPs that are meant for operation within the Tietê River environment. It has excellent corrosion resistance, given that river water may contain several corrosive substances.

Besides that, it is strong, durable, and thus capable of resisting physical stresses and impacts that may be encountered during deployment and operation.

Besides, its relatively low density keeps the overall weight of the device low to further meet the requirement for light weight in easy deployment .

7. How to Choose right equipment for current measurement?

Based on Measurement Orientation If horizontal cross - sectional currents will be a point of measurement, a Horizontal ADCP is to be chosen. HADCPs can measure the flow of water in a horizontal plane across the river with much accuracy. On the other hand, if the measurement is for vertical cross - sectional currents, then a Vertical ADCP is the suitable one. Vertical ADCPs provide information on the velocity profile from surface to bottom with good detail.

Based on Frequency Selection The choice of frequency also depends on the specific measurement needs and depth of the water. For example, the 600 kHz ADCP would suffice in waters whose depths are no greater than 70 meters. It is a good balance between resolution and accuracy for shallower waters.

In that respect, for deeper waters-say, deeper than 70 meters depth points in the Tietê River-one could use a 300 kHz ADCP. This would allow the signal to go deeper into the water column while maintaining good accuracy in current measurements.

Among the popular brands of ADCP available in the market are Teledyne RDI, Nortek, and Sontek. However, for those looking for a cost - effective option with high quality, the China Sonar PandaADCP is a great choice. It is made of all - titanium alloy material, which ensures its durability and performance in various river environments. It also offers an incredible cost - performance ratio.

You can learn more about it on its official website: https://china-sonar.com

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