Why We Measure the Gilgit River Flow

1. Where is Gilgit?

Gilgit, a city in the Gilgit - Baltistan region of northern Pakistan, is a geographical marvel surrounded by some of the world's largest mountain ranges. Positioned at the confluence of the Gilgit River and the Hunza River, the city is flanked by the sheer walls of the Karakoram, Himalaya, and Hindu Kush mountain ranges. Its elevation, somewhere around 1,454 meters above sea level, grants it a unique climate. Its summers are fairly temperate, providing respite from the scorching heat experienced at lower elevations, and its winters are bitterly cold, with heavy snowfall a frequent event. The rugged terrain, with snow-capped mountains and deep valleys, not only defines the local topography but also affects the hydrological cycle of the region.

Culturally, Gilgit is a diverse mosaic of several ethnic groups and traditions. It has been a strategic crossroads for thousands of years, serving as a significant link along historic trade routes that joined Central Asia, South Asia, and China. This has contributed to a rich cultural heritage involving contributions from the Balti, Shina, Wakhi, and other communities. The indigenous architecture, folk music, and handicrafts express the local culture. For instance, the local wooden houses featuring intricate carvings express the local craftsman, while dances and folk songs are part of community celebrations. Gilgit is also significant from a religious perspective, with numerous ancient monasteries and mosques showing the dominance of several religions in the area.

The two extensive river systems of Gilgit are the Gilgit River and the Hunza River. The Gilgit River, which is sourced in the glacial areas of the high peaks, runs along the Gilgit Valley. It snakes its way through the rugged terrain, picking up water from numerous small streams and tributaries as it passes. The Hunza River, however, is a source in the Hunza Valley glaciers and joins the Gilgit River near the city. The rivers are the backbone of the region. They provide the region with freshwater for household use, agriculture, and cattle. In farming, the rivers' water is used to irrigate farm land to enable crops like wheat, maize, and fruits to grow, which help boost the local economy. The rivers also have huge potential for generating hydroelectric power, which is essential in addressing the energy demand of the region and enabling economic development. The river systems also host a richness of aquatic life and contribute to the overall ecological balance of the area. Confluence of Gilgit and Hunza rivers creates dynamic conditions with diverse habitats along the banks and within the riverine habitat, supporting a range of fish species as well as other aquatic organisms.

2. How is the River Flow Near Gilgit?

Influence Factors

• Runoff and Precipitation: Climate in Gilgit is controlled by the region's high-altitude location and hilly character. Precipitation occurs both as rain and snowfall. Summer rains during part of the season may bring for a brief period an increase in river flow. Glacial melt and snowmelt constitute the principal source of river water. When temperatures rise in summer and spring, the snow and ice on mountains gradually melt, providing rivers with plenty of water. The runoff due to melting of snow and ice is seasonally strong, and highest flows are observed during warmer seasons. During winter, when snowfall is dense and temperature is low, rivers flow at reduced rates and even some of the smaller tributaries may freeze. The volume of runoff further relies on the percentage of cover by snow during the preceding winter and the temperature rise in spring.
• Topography and River Morphology: The harsh topography of Gilgit has a major influence on river flow. The rivers flow through deep and narrow gorges among the mountain ranges, where the steep slopes make the rivers fast-moving and turbulent with high erosive power. In their courses through the valleys near Gilgit, the slopes are not steep, and the rivers become broad in some stretches. The bed of the rivers is a mixture of rocky, gravelly, and sandy material, which affects the roughness and resistance to flow. The winding paths of the streams, as well as the boulders and other obstructions, develop intricate flow patterns with regions of faster-flowing and slower-moving eddies. These physical factors not only control the velocity and direction of the water but also affect the transport and deposition of sediments, carving the river courses over time.
• Reservoir Operation: Currently, there are not many large-scale reservoir operations directly affecting the rivers along Gilgit. However, with increased development in the area, more reservoirs and dams are planned for hydroelectric power generation and water storage. In the future, these structures will be highly influential in controlling the flow of the river, water storage during peak flow, and water release during dry spells so that the water supply is more stable for various purposes.

Historical Hydrological Events

One of the major historical hydrological events of the Gilgit region is the phenomenon of glacial lake outburst floods (GLOFs). Since there are numerous glaciers in the area, glacial lakes can be formed as ice and snow melt and accumulate behind natural ice and moraine dams. Sometimes these dams break, causing the sudden and violent floods. According to [research works on glacial lake outburst floods in Karakoram range](https://www.nature.com/articles/s41598 - 020 - 63773 - 3), they can destroy infrastructure, agricultural fields, and human settlements on riverbanks. For example, a GLOF can flatten bridges, highways, and residential houses, disrupt transport lines, and contaminate water sources. River flow observation is essential to detect early signs of potential GLOFs and other flood-like events and observe the impact of drought, which can also affect water supply in the region.

3. How to Observe River Flow in Gilgit?

Traditional Methods

• Surface Drift Float Method: Surface drift float method is a straightforward method that is employed to quantify the river flow. A float, say a wooden piece or a buoy, is placed on the river. From the duration that the float travels a normal distance, the speed of the surface water can be estimated. The technique has several shortcomings. It can only provide information concerning the flow at the surface, while the speeds at certain depth ranges in the water column might be completely different. Second, wind and surface turbulence will also perturb the float's motion so that measurements of velocity become invalid. In Gilgit's turbulent and swift rivers, the aforementioned limitations are even more pronounced, and therefore the method is not as efficient in gathering total flow data.
• Anchored Boat Method (Manning Table/Current Meter): For the anchored boat method, one moors a boat at a specific location in the river. A current meter is then lowered at various depths in the water to measure the speed of the water at various locations in the vertical profile. It is a technique that can provide detailed information concerning the flow at one cross - section of the river. But it is far too labor - intensive, time - consuming, and produces immense risk to safety in Gilgit's tough river conditions. The strong - flowing water, fast currents, and presence of rocks and obstructions render it impossible and dangerous to handle a boat and launch the current meter exactly. Besides, it requires a lot of time and labor to survey some locations in the river to obtain detailed information on the flow.

Introduction to ADCP: Acoustic Doppler Current Profiler

The Acoustic Doppler Current Profiler (ADCP) offers a higher superior, more effective, and safer method of measuring river flow in Gilgit. In contrast to the previous methods, ADCP is able to measure velocity at multiple depths simultaneously, creating a continuous profile of the water column. It is not invasive, i.e., it does not come in direct physical contact with the water like traditional current meters, thereby reducing risks of equipment damage and injury to the operator. ADCP can quickly collect large amounts of data, therefore fitting for the undertaking of comprehensive surveys of rivers and real-time monitoring. This is particularly important in Gilgit, as the complex river systems and rugged terrain necessitate accurate and on-time flow measurements to facilitate effective water management, prevention of flood, and preservation of the environment.

4. What Is ADCP Based on the Doppler Principle?

The ADCP operates based on the Doppler principle. It emits sound waves into the water column. These reflections rebound from suspended particles carried by water such as sediment and plankton. When the water is in motion, the sound signal frequency reflected gets changed. Taking the Doppler shift of the changed frequency with high precision, the ADCP measures the velocity of the water at different levels. The device is also equipped with more than one transducer that emits and receives the sound signals at different angles. It allows it to accurately compute the three-dimensional velocities of the flow in the water column. The information is processed using sophisticated algorithms to generate in-depth flow profiles and river maps, providing vital insights into the complex flow dynamics of the Gilgit rivers.

5. What Does High-Quality Measurement of River Flow in Gilgit Require?

Equipment Requirements

• Material Reliability: As a result of the harsh environment of Gilgit's rivers, such as their high-velocity water, abrasive sediments, and low temperatures, reliable quality ADCP equipment must be made from materials that are highly reliable. The instrument should resist corrosion, erosive damage, and impact damage. High-strength polymers and robust metals are most suitable materials to ensure the long life and accurate performance of the ADCP in this hostile environment.
• Light Weight and Compact Size: Unapproachability and hilly environment prevailing in and around Gilgit force ADCP equipment to be light weight and compact in size. It makes it easier to carry and deploy in places that are distant and inaccessible. A light and compact ADCP is simpler to manage by researchers and technicians, enabling them to move from one measurement point along rivers to another and obtain accurate data.
• Cost - Effectiveness: Cost - effectiveness is one of the key considerations in the choice of ADCP equipment for Gilgit. Given the small amount of money available for hydrological monitoring, equipment with high - quality performance at a reasonable cost is crucial. Cost - effective ADCPs enable more deployment and higher monitoring frequencies, and adequate data can be gathered to support efficient water management and decision - making in the region.

6. How to Choose Suitable Current Measuring Equipment?

Methods of Deployment

• Moving Boat - Mounted (Boat - Mounted) ADCP: A boat-mounted ADCP is most suitable to perform detailed river surveys, measurements of discharges, and flow map preparation. When the rivers of Gilgit have complex flow behavior and unstable widths, this ADCP can measure long stretches of the river within a short time, providing a good view of the flow behavior. It is most appropriate for first - order measurements and to measure the overall flow directions of Gilgit and Hunza rivers.
• Bottom - Mounted (Fixed) ADCP: For ongoing river flow monitoring in the long term, the best choice is a bottom - mounted ADCP. It can be fixed permanently at strategic points in the river and take continuous flow measurements over a long period of time. This data will be beneficial for the understanding of long - term trends, seasonal patterns, and impact of various variables on the flow of the Gilgit river. It could also facilitate the timely detection of the predicted hydrological events, such as GLOFs.
• Ropeway ADCP: Where ropeways span rivers, a ropeway ADCP can be used in an attempt to obtain significant measurements. The method allows for honest river flow profiling across the entire river width, providing useful information for use in various hydrological studies and water management uses, especially in areas where boat access could be dangerous or difficult to navigate.

Working Frequency

The selection of the working frequency in an ADCP is a significant one. A 600 kHz ADCP typically has a range of up to 70 meters and therefore can be employed for relatively shallow to moderately deep sections of the rivers of Muzaffarabad. A 300 kHz ADCP, on the other hand, can measure up to 110 meters and is therefore better suited for use in deeper sections of the rivers. Higher frequencies provide greater resolution but shorter range, and lower frequencies provide a longer range with less detailed resolution. The frequency employed should be based on the specific conditions of the river, such as the depth and the level of detail required in the measurement.

For those who require a cost-effective unit, ADCP manufacturer Chinese company "China Sonar Panda ADCP" is highly recommended. It's made of all-titanium alloy material, and hence it's exceptionally strong in the river condition. Its incredible cost-effectiveness is what distinguishes it, and because of this, it is a great option for budget-related projects. It's well-known as the "affordable ADCP." For more information, you may visit them at [https://china-sonar.com/].

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