Why Do We Measure the River Flow in Rawalpindi?

1. Where is Rawalpindi?

Geographic Background

Rawalpindi lies north of Pakistan's Punjab province, on the Potohar Plateau. It is adjacent to Pakistan's capital, Islamabad, and lies around 1,162 kilometers from the country's largest city, Karachi. The city is hilly with interspersed small plateaus and valleys. Potohar Plateau, which includes Rawalpindi, consists of low-lying undulating hills and rock outcrops with an elevation of about 500 to 600 meters above mean sea level. This not only influences the climate of the city but also greatly influences the hydrology of the city. Rawalpindi has a semi-arid climate with hot summers and relatively cold winters. Mean yearly precipitation is approximately 150 - 200 millimeters, and the city, therefore, relies heavily on water resources, especially river-based resources, for survival and growth.

Humanistic/Cultural

Rawalpindi has a rich and diverse cultural heritage. It has been a vantageous location throughout history, being a major trading center and military cantonment. The city’s architecture reflects a blend of different eras, from ancient Hindu and Buddhist structures to colonial - era British buildings. The old bazaars of Rawalpindi, such as Raja Bazaar, are bustling centers of activity, filled with narrow alleys, traditional shops, and vibrant markets. These bazaars are not just hubs of commerce but a display of the local culture as well, with sellers peddling everything from handicrafts to spices and textiles. Rawalpindi is also famous for its friendly and welcoming residents, who are proud of their Punjabi heritage, including folk music, dance, and food. The city's cultural festivals, such as the Basant Festival, are celebrated wholeheartedly and attract tourists from all across the region.

Hydrology and River Overview

Soan River is the main river system that directly affects Rawalpindi. Soan River is fed by the Margalla Hills, which are the northern edge of Islamabad and Rawalpindi. It flows in a south-easterly direction across the Potohar Plateau, meandering across the country before it eventually evaporates in the Cholistan Desert. Although the Soan River is temporary, relying largely on rain for its flow, it has been of vital importance to the region. It has traditionally been employed for drinking, irrigation, and general household usage. The river and its floodplains also brought with them a variety of plant and animal populations that helped to augment the local environment. Now, though its role in providing water for intensive agricultural use has diminished due to the fact that it is seasonal, it still makes a contribution toward recharging the regional groundwater aquifers. Soan River valley is also of some archaeological significance as it has yielded numerous pre-historic remains, attesting to the fact that human beings once inhabited the valley thousands of years ago.

Soan River, which is nearer to Rawalpindi, possesses a relatively narrow channel with its width varying between 10 to 30 meters in different stretches. Its depth also varies tremendously with seasons. During the monsoon months, when there is substantial precipitation, the river itself may experience a sudden increase in water levels, even flash flooding on some occasions. But during the dry months, the bed of the river dries up and only scattered pools of water are left behind. The Soan River has some small tributaries as well that supply it within the territory of Rawalpindi, which supplement its flow during the rainy months. These tributaries, while small, help increase the volume of the river as well as influence the flow patterns around the suburbs of the city.

2. How is River Flow Near Rawalpindi?

Factors of Influence

Runoff and Precipitation

Rawalpindi river flow totally depends on precipitation. Monsoon, occurring between July and September, brings most of the annual rain to the region. Intense monsoon rainfall in the catchment area of the Soan River, particularly in the Margalla Hills, leads to intensified runoff. This runoff fills the river channels with a rapid rise in water levels and flow rates. In comparison to this, for the rest of the year hardly any rainfall occurs in the dry season. As a result, the river flow of Soan River decreases and the riverbed dries up in most cases. Climate change is already impacting rainfall patterns in the region too. Unpredictable rainfall with prolonged dry spells and intense but less frequent rainfall events are reported, and this continues to pose challenges to the predictability of the river flow.

Terrain and River Morphology

The wavy topography of the land of the Potohar Plateau on which Rawalpindi stands affects the course of the Soan River. The river runs through the undulating terrain, which causes it to meander and change course with the passage of time. The sinuous and narrow nature of the river channel and the rocky and uneven riverbed create resistance to the movement of water. This causes different flow velocities, with steeper reaches having higher-flowing portions and gentler reaches having lower-moving water. River morphology also influences sediment transport, with erosion in some areas and deposition in others, which in turn modify the river channel and impact the flow regimes.

Reservoir Operations

There are no large reservoirs on the Soan River near Rawalpindi. However, development of dams and reservoirs in the upstream basins of other river systems in the region has the indirect potential to impact the Soan River. For example, when water is drained upstream from rivers for irrigation or other purposes, it has the potential to reduce the quantity of overall water resources in the region, which can potentially drop the levels of groundwater contributing to base flow of the Soan River. Also, hydrological regime change of adjacent river basins caused by reservoir operations can cascade to affect the local climate and precipitation, which can further affect the Soan River flow.

Historical Hydrological Events

One of the major historical hydrological events in Rawalpindi was the 2015 monsoon floods. Heavy rains during the August 2015 monsoon, according to the Pakistan Meteorological Department, led to a sudden surge in the water levels of Soan River. The river overflowed and triggered flash floods in several low - lying areas of Rawalpindi. Several homes, roads, and other constructions were damaged. Several individuals became homeless, and there were some reports of fatalities and livestock loss. Fields of agriculture near the river were also greatly destroyed, with crops in farms being destroyed. (Source: Pakistan Meteorological Department, 2015 flood reports) Monitoring such occurrences in the past is essential as it allows one to understand the behavior of the river under conditions of stress, to provide better flood - risk management, planning for structures, and development of early - warning systems to protect the city and population.

3. How is River Flow in Rawalpindi to be measured?

Old Methods

Surface Drift Buoy Method

The surface drift buoy method is a basic method of measuring river flow. According to this method, basic floating bodies such as plastic or wooden buoys are released on the surface of the river. The drift of these buoys is then measured for a given distance and time period. By finding out how long it takes for the buoy to travel a given distance, the river surface velocity can be estimated. This method is not perfect however. It only provides an estimate of flow at the river's surface and doesn't assist in estimating flow at other levels deep inside the river. Further, the buoys could be transported by wind, making the measure of accurate velocity impossible.

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

An anchored boat technique is accomplished through anchoring a boat at a specified point in the river. A current meter, or a water velocity measuring device, is then allowed to descend in the river at different points and depths. Through taking multiple velocity readings across the river cross - section, a detailed profile of the river flow at the specified point can be obtained. This technique yields more precise data than the surface drift buoy technique because it quantifies flow at different depths. It is however, time-consuming, labor-intensive, and dangerous, particularly in turbulent or rapidly flowing water.

Introduction to ADCP: Acoustic Doppler Current Profiler

The Acoustic Doppler Current Profiler (ADCP) is a newer, more effective technology to use when measuring river flow. In contrast to traditional techniques, ADCP can provide continuous profiles of river flow across its entire width and depth within a short span of time. It is a non-contact technique, which means that it does not entail physical contact with water or placing permanent objects in the river. It is thus safer for operators and the aquatic environment. ADCP uses the principle of Doppler to determine the velocity of water at different depths and is capable of receiving significant quantities of data within a very short time span, which are used in numerous applications like flood forecasting, water resources management, and ecological studies.

4. How Do ADCP Based on the Doppler Principle Operate?

The ADCP operates on the Doppler principle. It transmits acoustic signals into the water column. These signals bounce off small suspended material in the water, like sediment or plankton. If the water is flowing, the frequency of the reflected signal changes as a function of the water velocity. By monitoring this change in frequency (the Doppler shift), the ADCP can ascertain the water velocity at various depths and positions along the water column. The device consists of several transducers that transmit and receive the acoustic signals so that it can create a three-dimensional profile of the flow in the river. It processes this data to provide data on the flow characteristics of the river, including velocity, direction, and volume.

5. What is Required to Measure River Flow in Rawalpindi with High Quality?

Equipment Requirements

Reliability of Materials

To ensure precise high-quality measurements of Rawalpindi river flow, ADCP equipment needs to be robust. Since the Soan River may have turbulent flow during monsoon and abrasive sediment, the ADCP should be made of materials that are abrasion, corrosion, and impact resistant. Materials like stainless steel of high grade, titanium alloys, and hard plastic work best as they offer excellent resistance to the harsh river conditions, ensuring the stability and lifespan of the ADCP equipment.

Light Weight and Small Size

Due to hilly terrain and sporadic difficult accessibility of certain areas in the Soan River near Rawalpindi, a light and small ADCP is greatly desired. It becomes easier to handle and place a compact ADCP, either manually transported to remote areas or installed on small boats. It also reduces the handling effort involved and lessens the impact on the stability of the boat while taking measurements.

Cost - Effectiveness

Cost-effectiveness is a factor when choosing ADCP equipment utilized in monitoring river flow in Rawalpindi. Government institutions, research institutions, and water departments typically lack finances. It is therefore crucial to possess an ADCP that delivers quality and reliable data at affordable prices. This enables regular and efficient monitoring of river flow, making it possible to manage the city's waters effectively.

6. Selection of Appropriate Current Measurement Equipment?

Methods of Deployment

Boat - Mounted (Moving Boat) ADCP

River-mounted ADCPs are suitable for surveying large sections of the Soan River and obtaining integrated flow data. They can survey large distances along the river quickly and are thus most suited to applications like the mapping of flow patterns of the river, measuring river discharges, and flood-risk mapping. This type of ADCP is especially useful when an appreciation of the river's flow regime over a wide area is required.

Bottom - Mounted (Fixed) ADCP

Bottom - mounted ADCPs are utilized for long - term continuous measurement of river flow. They are permanently installed on the riverbed and can collect data over extremely long periods of time without the need for human input. They are most appropriate to track base flow, long - term trends of river flow, and ecological research that require continuous collection of data to study the ecosystem dynamics of the river.

Cableway ADCP

In some sections of the Soan River where there exists suitable infrastructure, cableway ADCPs can be utilized. Cableway ADCPs are suspended mounted on a cableway and can be traveled across the river to measure at several points. The method is advantageous to measure the flow accurately in wider parts of the river where boat - based measurement may be problematic or even unsafe, and for gathering accurate information on the flow conditions of the river across its width.

Work Frequency

The choice of work frequency in an ADCP is significant as it affects the range as well as the resolution of measurements. A 600 kHz ADCP would be having a horizontal range of approximately 70 meters and be suitable for accurate measurements in small rivers like the Soan River or observation of localized segments with complex flow patterns. It provides relatively high-resolution data, which is good for understanding the fine-scale flow dynamics. A 300 kHz ADCP with greater range up to 110 meters may be more appropriate for large rivers or application where it is desirable to survey the broader portion of the river cross-section, though it will be very slightly less resolved than the 600 kHz ADCP.

Brand Recommendations

World - leading ADCP brands include Teledyne RDI, Nortek, and SonTek, with high - quality products, advanced technology, and excellent reliability. For a cost - effective budget, ADCP manufacturer Chinese brand "China Sonar Panda ADCP" is also very good. Made of all-titanium alloy material, this "economy ADCP" is extremely durable and resistant to corrosion, well-suited to the harsh environment of the Soan River. Its high cost-effectiveness makes it within the budget of a range of users, from small-scale research projects in the vicinity to city-scale water management initiatives. To find out more, visit their website at https://china-sonar.com/.

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