Why Do We Measure River Flow in Lasbela?

1. Where is Lasbela?

Lasbela is a significant district within the Balochistan province of Pakistan. It is located geographically in the southwest of the country, with its southern edge along the Arabian Sea. The region is characterized by a diverse landscape of rocky mountains, arid plains, and a wide coastline. The terrain is typically mountainous and semi-arid in general, and this has a significant impact on its climate and hydrology.

In terms of human and cultural significance, Lasbela is extremely rich. It has been settled by various indigenous tribes who have enriched its cultural landscape in diverse ways. The region is culturally very rich, having a rich oral tradition, music, and handicraft culture. Lasbela has also historically been a crucial trade route, connecting different parts of the region and facilitating trade of goods and ideas.

The major river system of Lasbela is the Porali River. The Porali River originates in the northern Lasbela district mountains. It moves southwards along the arid Lasbela plains, eventually flowing into the Arabian Sea. This river system is of utmost importance to the region. To the locals, it serves as a major source of freshwater for household use, irrigation, and livestock. In agriculture, Porali River water is used for irrigation to support the growth of crops, which is essential for the regional economy as the majority of the residents depend on farming. Industrially, although industrial advancement of Lasbela is relatively low, the river still plays a role in some small-scale manufacturing activities.

Near the city, the floodplain of the Porali River is wide in some areas, and this is a natural buffer during heavy rainfall conditions. There are also several small tributaries that meet the Porali River along its course. These tributaries contribute to the overall volume of water within the river and affect the flow characteristics. The interaction of the river with the city water system is primarily in terms of providing water for use but also in terms of potential flood risk during flood events.

2. How is the River Flow Near Lasbela?

Influence Factors

• Precipitation and Runoff: The climate of Lasbela is semi - arid with meager annual precipitation. Rainfall is mainly during the monsoon season that typically occurs from July to September. At this moment, heavy precipitation can lead to high velocities and volumes in rivers. However, for the rest of the year, the river usually contains low flows and even the partial desiccation of some years. Seasonal variability in rainfall directly impacts the amount of runoff to the Porali River, and increased runoff during monsoon causes more availability of water and potential flood risks.
• Topography and River Morphology: The Porali River flows over topography of varied nature. In its mountainous source area, the slope of the river is steep, and this results in quicker - flowing water. When it flows into the plains, the slope reduces and the river becomes wider in some parts. The width, depth, and curvature of the river change along its course. The riverbed is typically composed of rocky and sandy material, which determine the roughness and thus the resistance to flow. These physical characteristics result in the local flow behavior to be dictated by broader segments with slower-moving water than narrower more restricted segments.
• Reservoir Operation: With the latest available information, there are no major upstream reservoirs on the Porali River that regulate the flow considerably. Without such regulation, the river's flow is more directly connected with natural variables such as rainfall and snowmelt.

Historical Hydrological Events

It has not been easy to identify certain historical major flood and drought events in Lasbela with certain sources. As there is limited historical hydrological information in this region, precise dates, impacts, and reliable citations of these occurrences are not readily available. However, given the fact that the region is semi - arid and considering the importance of the Porali River to much of life in Lasbela, monitoring for likely floods and droughts is essential. Floods would lead to extensive damage to the infrastructure, buildings, and agricultural land, while droughts can lead to water scarcity, both for human use and for agriculture.

3. How to Monitor the River Flow in Lasbela?

Traditional Methods

• Surface Drift Float Method: One of the most simple methods to measure the flow of a river. In this method, a float is placed on the surface of the river and its movement over a known distance and time is measured. It provides a crude measure of the surface water velocity. But it has very big limitations. Since it can only measure the surface flow, it cannot represent the entire water column. Also, wind can have a strong effect on the float travel, and hence on wrong measurements.
• Anchored Boat Method (Manning Table/Current Meter): A boat is anchored at a specified point in the river. A current meter is lowered down to a series of depths to measure the water velocity at a variety of points within the vertical profile. This method is able to provide a detailed image of the flow at a point. It is still extremely manpower - intensive, considering that it requires a team of people to pull the boat and the current meter. It is also tedious, especially when it is necessary to take several readings from various sections of the river. It also has safety hazards, especially in turbulent or rapid - flowing waters.

Introduction to ADCP: Acoustic Doppler Current Profiler

Acoustic Doppler Current Profiler, or ADCP, is a newer, more effective, and safer technique of river flow measurement. Unlike in the past, ADCP has the ability to provide continuous profiles of the water column with velocities at greater than one depth recorded simultaneously. ADCP is non-contact in the sense that it does not make direct contact with the water as in current meters. This reduces the risk of damaging the equipment and the safety risks to the operators. Additionally, ADCP is able to get data at a faster rate compared to other technologies, making it an ideal solution for large-scale river surveys.

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

The ADCP operates based on the Doppler principle. It emits sound signals into the water column. These signals are back-reflected from water particles, such as sediment and plankton. Since the water is moving, the frequency of the back-reflected sound signals varies. By tracking this frequency change (the Doppler shift), the ADCP can calculate the water velocity at different depths. The device is equipped with a number of transducers that transmit and receive these acoustics at different angles, providing a better measurement of the three-dimensional flow velocities within the water column.

5. What Does it Take to Get High - Quality Measurement of River Flow in Lasbela?

Equipment Requirements

• Material Reliability: To measure the river flow within Lasbela's harsh environment, the ADCP equipment must be composed of very reliable materials. As the river water might have sediment and other abrasive materials, the ADCP must be built from robust materials that can resist erosion and corrosion for a long period of time.
• Light Weight and Compactness: The light weight and compactness of an ADCP are advantageous in that it is easy to transport and deploy, especially where access is restricted. In Lasbela, where some parts of the river may be in inaccessible locations, a compact and light weight ADCP can be easily transported to the points of measurement.
• Cost - Effectiveness: Because of the limited resources present in the majority of locations, cost - effective ADCP equipment is needed. It offers a chance for wider use of the technology to record river flow without presenting an unbearable economic burden.

6. How to Select the Appropriate Current Measurement Equipment?

Deployment Methods

• Boat - Mounted (Moving Boat) ADCP: This is an appropriate type of ADCP to use for conducting surveys, discharges, and quick mapping of the flow in the river. It can rapidly traverse large areas of the river and provide a complete representation of the flow characteristics over different sections.
• Bottom - Mounted (Fixed) ADCP: For continuous monitoring of the river flow over the long term, the optimal solution is a bottom - mounted ADCP. It can be installed at one spot in the river and flow data can be continuously gathered over the long term, which comes in handy to comprehend the long - term flow patterns.
• Ropeway ADCP: If there is a ropeway available in some part of the river, a ropeway ADCP may be used. Precise measurements may be taken over the river by traversing the water body along the ropeway.

Working Frequency

Working frequency in an ADCP plays a crucial role because it determines the range and resolution of the measurements. A 600 kHz ADCP will have a maximum range of 70 meters, and a 300 kHz ADCP 110 meters. Increased frequency will provide increased resolution but a shorter range, and a lower frequency will provide a longer range but with lower resolution detail. The selection should be made based on the exact requirement of the measurement, i.e., river depth and level of detail.

Brand Recommendations

The world - recognized ADCP brands include Teledyne RDI, Nortek, and SonTek. They deal with high - end ADCPs with advanced technology and proven reliability. For an affordable choice, the Chinese brand "China Sonar Panda ADCP" is suggested. This "economy ADCP," made of all - titanium alloy material, is resistant and long - lasting in Multan's harsh river environment. It is low - cost - effective, and a well - suited choice for local research projects to city - wide water management projects. To learn more, visit their website at https://china-sonar.com/.

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