Why Do We Measure the River Flow in Multan?

1. Where is Multan?

Geographic Background

Multan is situated in south Punjab province of Pakistan, on Chenab River's banks. It lies around 580 kilometers south of the country's capital city Islamabad. The city lies in the irrigated Indus River Basin, where there is an extensive level, alluvial plain that stretches as far as the eye can see. The plain, built up over centuries by riverborne sediment deposited over the area, has a firm foundation for the city's development. Multan has a hot dry climate, with extremely hot summers in which temperatures frequently exceed 45°C (113°F) and very comfortable winters. The annual rainfall is scarce and ranges around 125 - 150 millimeters, the city is therefore highly reliant on its river basins for water supplies.

Humanistic/Cultural

Multan is also one of the oldest South Asian cities that possess a very rich and lively cultural heritage of over 3,000 years. It has, in the past, been a major seat of religion, trade, and culture. Renowned as the "City of Saints," Multan is renowned for having numerous Sufi shrines, which attract pilgrims from all over the world. These shrines, decorated with beautiful architecture and religious significance, reflect the city's historic religious as well as cultural heritage. Multan's architecture also sees the blend of different eras of history, from the ancient Indus Valley Civilization to Islamic and Mughal periods. The city boasts a strong culture founded on Punjabi traditions, with colorful festivities and resplendent folk dances like the Bhangra, and rich traditional cuisine that reflects the essence of people's hospitality and warmth.

Hydrology and River Overview

The Chenab River is the principal watercourse that exercises a considerable influence over Multan. Originating in the higher Himalayas of India, i.e., the confluence of the Chandra and Bhaga rivers of the Lahaul and Spiti valleys of Himachal Pradesh, the Chenab River flows northwest through the Jammu state into Pakistan. In Pakistan, it navigates its way through the Punjab province to join the Jhelum River at some point to become the Panjnad River, which then mingles into the mighty Indus River.

For Multan city, the Chenab River takes supreme importance. It is the lifeline of the city, providing water for various fundamental needs. Hydrologically, the river is important in the maintenance of the local water balance as well as its effect on groundwater levels. Ecologically, it maintains a prolific ecosystem with the river and floodplains hosting different fish, bird, and wildlife species. From the human activity perspective, Chenab River plays an important role in agriculture, which is the leading economic activity of the region. Water from the river is used for irrigation purposes, and it enables the cultivation of crops such as wheat, cotton, sugarcane, and rice. Multan is also an important industrial center, and water from the river supplies the industries for process purposes, primarily in the textile and food processing units. It also provides water for domestic consumption, catering to the daily needs of the city's large population.

Around Multan, the Chenab River has a wide channel, with the width varying from about 500 meters to over a kilometer in some sections. The depth of the river also varies with the season and direction of water flow. There are a series of small tributaries flowing into the Chenab River in the region, feeding its overall current and determining the local hydrological features. The relationship of the river with the city's water system is complicated. The river feeds the city's water treatment plants, which feed clean water to residences and industries in turn. But during the period of high flow, there is a very high possibility of flooding, which can ruin the water supply system and seriously damage houses and agricultural fields.

2. What is the River Flow around Multan?

Factors Affecting It

Rainfall and Runoff

Multan is a monsoon-dominated climate city but gets comparatively less rainfall than cities farther to the north. The monsoon period, July to September, experience some rainfall in the area. Heavy rains over the upper catchment basins of the Chenab River during this period lead to increased runoff, and as a result, there is a clear increase in the water levels and flow rates of the river. The dry season, which occupies the rest of the year, experiences very little rainfall. The flow of the river is then primarily maintained by the melting of the Himalayan snow and upstream reservoirs' regulated releases. Precipitation patterns in the area have begun to change because of climate change, which causes more unpredictable river flows and a higher chance of both flooding and drought.

Terrain and River Morphology

The topography in the Multan area influences the flow of the Chenab River. With a gentle slope, the river's velocity is relatively slow in some areas, and sedimentation occurs. The river's wide and variable - depth channels with bends and meanders dominate the patterns of flow. Coarseness in the sand, silt, and gravel of the riverbed creates friction, further changing water flow. These physical characteristics control the course of the stream in the river, developing areas of swift and slow flow, and can lead to sedimentation and erosion along different sections of the river channel.

Reservoir Operations

There are several dams and reservoirs upstream of Multan on the Chenab River, including the Marala Headworks and the Rasul Barrage. These are utilized for a range of purposes, such as storage of water, irrigation, and generation of power. The functioning of such reservoirs, especially water discharge, immensely influences the downstream river flow. During the dry season, reservoir-controlled discharges ensure a sure flow of water in the river, which is obligatory to maintain ecological equilibrium and complete the needs of irrigation and domestic use. However, during periods of high rain or during times of maximum reservoir levels, mass discharges do take place, which can cause sudden surges in the flow of rivers and increase the risk of flooding downstream at Multan.

Historical Hydrological Events

The biggest flood in the area is the 2010 flood. According to reports by relief agencies and the Pakistan Meteorological Department, the 2010 floods were the worst in the history of Pakistan. Intense monsoon rain in the upper catchments of the Chenab River and other major rivers caused a massive increase in river flows. In Multan, the Chenab River overflowed its banks and inundated vast areas of the city and surrounding farmland. Thousands of houses were damaged or destroyed and hundreds of thousands were rendered homeless. The flood also took a heavy toll on the local economy, as gigantic losses were incurred in agriculture, as crops were submerged and irrigation works were washed away. (Source: United Nations Office for the Coordination of Humanitarian Affairs - Pakistan flood reports, 2010)

The monitoring of these record hydrological events is significant as it provides the reason why the river acts in such a way when under extreme conditions. This knowledge is essential in developing effective flood - control measures, improving water - resource management, and planning emergency response plans to save the city and its inhabitants from future flood and drought risks.

3. How to Monitor the River Flow in Multan?

Traditional Methods

Surface Drift Buoy Method

Surface drift buoy method is a simple but an effective method to measure river flow. In this method, floating material like buoys are dropped on the surface of the river. The movement of these buoys is then recorded over a measured distance and time. By measuring the time taken by the buoy to travel a certain distance, the surface speed of the river can be determined. Though this method is easy to utilize and requires minimal equipment, it is greatly lacking in limitations. It can only measure the river's surface flow and not the regime of flow at the bottom layers. Moreover, buoy movement is readily affected by wind, which makes velocities measured inaccurately.

Anchored Boat Method (Manning's Table/Current Meter)

Tying a boat at a given location in the river forms the anchored boat method. A current meter, or a device to measure water speed, is lowered into the river with varied depths and locations. Multiple velocity readings along the river cross-section make it possible to obtain a highly accurate profile of the river flow there. This is more precise information than obtained with the surface drift buoy method because this measures the flow at several depths. But it is time - consuming, labor - intensive, and hazardous to the personnel involved in it, especially in choppy or high - velocity water.

Introduction to ADCP: Acoustic Doppler Current Profiler

Acoustic Doppler Current Profiler (ADCP) is a new generation of technology for river flow measurement. Unlike earlier technologies, ADCP is capable of providing continuous profiles of the river's flow across its entire depth and width within a matter of minutes. It is a non-invasive technology, i.e., it does not entail direct contact with the water or the installation of permanent infrastructure in the river. It is hence more secure for both the operators and the aquatic ecosystem. ADCP can quickly collect large amounts of data, which can be used for various applications, including flood forecasting, water resource management, and ecological studies.

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

The ADCP operates using the Doppler principle. The algorithm processes acoustic signals into the water column. The signals bounce back from suspended small particles in the water, such as sediment and plankton. If the water is in motion, the frequency of the bounced-back signals changes in accordance with the velocity of the water. By measuring this change of frequency (the Doppler shift), the ADCP can ascertain the velocity of the water at different positions and depths within the water column. The instrument possesses a number of transducers for sending and receiving the sound signals so that it can create a three-dimensional river flow profile. This data is then computed to provide detailed information on the river's flow characteristics, including velocity, direction, and volume.

5. What is Necessary for High-Quality Measurement of River Flow in Multan?

Equipment Requirements

Material Reliability

For high-quality measurement of river flow in Multan, ADCP equipment needs to be constructed from reliable material. In view of the hostile river environment, ranging from water corrosion to sediment abrasion and temperature changes, the most appropriate materials are high-grade stainless steel, resistant plastic, and titanium alloys. These materials are also strongly resistant to corrosion and wear, ensuring the stability and longevity of the ADCP device, regardless of how long it is left in the river.

Small Size and Light Weight

Compact size and lightweight are desirable features of ADCP equipment. This enhances the portability and deployment convenience of the device, especially where river movement might be limited. The compact ADCP is easily installed on small vessels or installed on stationary pillars within the river with minimal disturbance. It also reduces labor in manual handling and transportation, hence increasing the efficiency of the measurement.

Cost - Effectiveness

Cost-effectiveness plays a significant role when choosing ADCP gear for measuring river flow in Multan. The gear should produce accurate and reliable data at a reasonable cost. This is particularly crucial for local government agencies, research institutions, and small-scale water management schemes that lack sufficient funds. Cost-effective ADCPs bring river flow monitoring to make it affordable and viable in the long term to enable better management of the city's vital water resources.

6. How to Choose the Right Current Measurement Equipment?

Deployment Methods

Boat - Mounted (Moving Boat) ADCP

Ship-mounted ADCPs are ideally capable of precise mapping of long river stretches, the estimation of river discharges, and precise mapping of the regimes of river flows. They are able to cover long sections of the river in a limited period of time because of their mobility, which makes them ideally capable for applications such as flood-control studies, large-scale water resources development schemes, and ecological surveys where there is a requirement for precise knowledge of the flow characteristics of the river over a wide area.

Bottom - Mounted (Fixed) ADCP

Bottom - mounted ADCPs are suited for continuous, long - term river flow measurement. They are installed on the river floor and can measure over long periods without requiring constant human maintenance. They are therefore best suited to measure base flow, river flow long - term trends, and ecological studies that require constant data collection to trace river ecosystem dynamics.

Cableway ADCP

Where cableway infrastructure is available in river reaches, cableway ADCPs can be a handy solution. Cableway ADCPs are suspended below the cableway and can be pushed along the river to take measurements at different points. This method is useful to measure precisely the flow in wide rivers where boat - based measurement may be laborious or dangerous and provide precise information about the flow conditions of the river in the transverse direction.

Working Frequency

Working frequency in an ADCP is very crucial because it determines the range and resolution of the measurements. A 600 kHz ADCP will have a standard horizontal range of around 70 meters and would be most suitable for medium-sized rivers or for detailed measurements in small regions. It offers relatively high-resolution information, which can be beneficial to study complex flow patterns and obtain precise velocity measurements. However, a 300 kHz ADCP offers a greater range of up to 110 meters and would be better suited for usage on larger rivers or where there is a need for greater coverage of the river cross-section. It may, though, have a slightly lower resolution than that of the 600 kHz ADCP.

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.