1. Where is Hải Phòng?
Background Geography
Vietnam's second-largest port city, Hải Phòng, is located in the area of the Red River Delta at approximately 20.85°N latitude and 106.68°E longitude. It is bordered by Quảng Ninh Province to the northeast, Thái Nguyên Province to the west, and Bắc Giang and Bắc Ninh Provinces to the southwest. Its coastal location on the Gulf of Tonkin gives it a strategic location for ocean trade. Hải Phòng's landscape is a combination of low-lying plains, covering the majority of the city, and minor hills in the suburbs. Hải Phòng is a city of tropical monsoon climate with an unmistakable rainy season from May to October and dry season from November to April. The rainy season would be marked by heavy rainfall, significantly affecting the river systems in the immediate vicinity, and the dry season would result in low river levels and potential water shortages.
Humanities and culture
Hải Phòng is densely populated with cultural heritage in close association with its maritime background. The city has been a center for commerce for many years, with influences from varied cultures like the Chinese, French, and native Vietnamese. The cultural diversity of the place is reflected in its architecture, cuisine, and traditions. French colonial structures such as the Hải Phòng Opera House and weathered villas along the coast stand along side traditional Vietnamese pagodas such as the Bảo Tháp Pagoda, with an unharmonious blend of styles.
The cuisine in this city is renowned to be fresh sea-food as it is situated near the seashore. Both foreign and domestic tourists alike enjoy meals like grilled squid, dishes made of shrimp paste, and fish noodle soup. The city is also filled with festivities all year round. The Hải Phòng International Fireworks Festival, for example, invites international teams to participate in spectacular fireworks competitions which witness crowds of people flocking to the city and savor the festive mood. Besides, the traditional Vietnamese festivals like Tet are also commonly celebrated with great enthusiasm, abounds with dragon dances, family gatherings, and temple trips.
Hydrology and River Overview
Hải Phòng's two main river systems include the Cấm River and Lô River. Cấm River, originating from the surrounding mountainous areas, flows through the city and finally empties into the Gulf of Tonkin. Red River, with its link to the Lô River, also serves as a tributary of the Red River and plays a crucial role in the hydrology of the city. They are both vital in various aspects to Hải Phòng. They supply water for residential, industrial, and agricultural purposes, although the quality of the water has begun to become a problem as it gets contaminated through urban and industrial use.
The rivers also support the local fishery that favors some fish species. The river floodplains are croplands that are reserved for rice and other forms of cultivation. Additionally, the rivers also have historical importance in transportation, and they facilitate the movement of goods within and around the city and connect Hải Phòng to other locations. But the modification of river flow regimes by upstream dam constructions and climatic change is endangering the ecological health and economic lives that depend on these rivers.
2. How is the River Flow Near Hải Phòng?
Influencing Factors
Precipitation and Runoff
The tropical monsoon climate of Hải Phòng exerts a tremendous influence on the flow of the Cấm and Lô Rivers. Rainy season is the period when over 1,500 - 2,000 millimeters of rain falls in the city, and runoff is high. The rivers overflow because of this excess amount of water entering them, therefore their water level and flow rate are also high. The reverse is the dry season, whose flow of the rivers also reduces as well as the water levels. Year-to-year rainfall fluctuations can cause unpatterned fluctuations in river flow that pose difficulty to water management, flood control, and the guarantee of a reliable supply of water.
Topography and river morphology
The relatively flat topography of the Red River Delta on which Hải Phòng is situated gives rise to the gentle slope of the Cấm and Lô Rivers, causing slow-moving waters. The steady flow allows for sediment to settle at the river bottom and banks gradually over time, deepening and filling up the river. The urban rivers are broad and sinuous, with curves that may cause velocity variations in the flow. Inner bends lead to slower flow and deposition of sediment, whereas outer bends lead to higher flow and erosion. Human structures, including bridges, dams, and levees, have been built along the rivers but further altering their natural patterns of flow and at times local level and velocity changes.
Reservoir Operations
There are dams and reservoirs built on the tributaries of the Red River and other rivers feeding into the Cấm and Lô Rivers above Hải Phòng. These dams are used mainly for water reservoirs, hydroelectric power generation, and irrigation. Intentional releasing of the water from these upstream dams will significantly enhance the rate of flow in Hải Phòng rivers. Low releases of upstream water in times of drought or low-rainfall periods can reduce city river flows for water supply, navigation, and the local ecosystem. Conversely, poor control of flood discharges during rainy periods can lead to downstream flood that is life-threatening and property-damaging to residents of Hải Phòng.
Historical Hydrological Events
There have been several major flood events recorded throughout the history of Hải Phòng. Heavy monsoon rains combined with high tides caused extensive flooding in much of the city in 2017. According to the Vietnam Disaster Management Authority, the floods swept through low-lying areas, left thousands homeless, damaged infrastructure, and paralyzed economic activities. Cấm and Lô Rivers burst their banks and inundated residential areas, agricultural land, and industrial estates. It becomes necessary to track such past events so that efficient flood-mitigation strategies are developed, urban drainage infrastructures are restored, and the resistance of the city towards impending hydrological disasters is enhanced.
3. How Is the River Flow in Hải Phòng Tracked?
Traditional Approaches
Surface Drift Float Method
Surface drift float method is a basic method used to measure river flow. A floating object, i.e., a buoy or a wooden piece, is dropped on the river's surface. The duration taken by the float to cover a marked distance is recorded, and the distance divided by the duration, the surface velocity of the river is determined. This indicates only surface flow and is extremely wind-sensitive, and the wind will tend to bias the readings and hence result in faulty velocity measurements. It does not give any information regarding the flow at different river depths.
Anchored Boat Method (Staff Gauge / Current Meter)
In this anchored boat method, a boat is anchored in some fixed position in the river. Water level is measured with the help of a staff gauge, whereas a current meter is permitted to drop at different depths in the river and is used to calculate the velocity of the water. Some measurements of the velocity are taken over the cross - section of the river, and then with the help of the cross - sectional area and multiplying it by the average velocity, the river discharge can be calculated. This method yields more accurate information but is time - consuming, labor - intensive, and hazardous, especially in a busy port city like Hải Phòng with huge shipping volumes.
ADCP Introduction: Acoustic Doppler Current Profiler (ADCP)
Acoustic Doppler Current Profiler (ADCP) is a newer and more efficient technology to calculate river flow. ADCP is a non-invasive instrument that estimates water velocity at different depths using sound waves. ADCP can capture continuous profiles of the river flow from top to bottom within a relatively short time and present a better overall impression of the river flow characteristics than the use of conventional methods. This technology is of very high efficiency and enables one to acquire accurate and comprehensive data gathering, which is essential to effective water resources management, flood prediction, and environmental studies in Hải Phòng.
4. Operation of ADCP on the Doppler Principle
An ADCP current meter operates on the principle of Doppler. It emits sound waves of a specific frequency into the water. As the sound waves travel over moving particles within the water, e.g., sediment, plankton, or water molecules, the frequency of the backscattered waves is changed. When the particles are approaching the ADCP, the wave frequency is increased, and when they are receding, the wave frequency decreases. By precisely measuring this frequency change (the Doppler shift), the ADCP can calculate the water velocity at different depths. Different transducers in the ADCP measure different directions of velocities in such a way that three-dimensional river flow structure can be quantified.
5. What Is Needed for High-Quality Measurement of River Flow in Hải Phòng?
Equipment Requirements
To precisely take ADCP profiler measurements in Hải Phòng rivers, there are certain piece of equipment characteristics needed. With the potentially harsh river condition, e.g., pollution, high sedimentation rates, and saltwater intrusion off the coast, material strength is necessary. Stainless steel or titanium corrosion-resistant ADCPs are perfect for resisting the tough environment. Small and lightweight design is also preferable as it simplifies transportation and deployment, especially in the city and coastal areas of Hải Phòng. Affordability is also another key consideration because it renders the technology affordable for common application to cover the river flow across.
6. What is the Best Way to Select the Right Current Measurement Equipment?
Deployment Method
- Ship - Borne (Moving Boat) ADCP: Ideal to perform large - scale surveys of the Cấm and Lô Rivers and their estuary regions within Hải Phòng. It can quickly measure discharge over long stretches of river and map flow patterns over different river sections. In moving along the water courses, the ADCP can continuously collect data, providing a general view of the flow conditions.
- Bottom - Fixed (Mounted) ADCP: Suitable for continuous monitoring over long periods. It can be fixed onto the river floor at strategic positions to collect data for longer durations, which helps in understanding long - term flow trends, seasonal variations, and the effect of various factors on the river flow.
- Cable - Way ADCP: When cable - way infrastructure is present in the river sections, it is possible to suspend a cable - way ADCP and traverse across the river to observe flow at various points. Cable - way ADCP is convenient to use in instances where boat - based measurements are challenging because of intense traffic or other limitations.
Working Frequency
- 600 kHz ADCP: A 600 kHz ADCP gives the best compromise between range and resolution, having a maximum horizontal range of 70 meters. It can be used for most sections of Hải Phòng's rivers by taking proper measurements of the flow velocity at different depths.
- 300 kHz ADCP: Having a greater range of up to 110 meters, a 300 kHz ADCP would be better for deeper and wider sections of the rivers, especially near the estuaries and in those areas where tidal influence is significant.
Brand Recommendations
Proven and tried international ADCP brands such as Teledyne RDI, Nortek, and SonTek are highly reputable for their quality and reliable products utilized in various hydrological researches and monitoring operations. A good alternative at a low cost is the ADCP supplier Chinese company’s "China Sonar Panda ADCP". Made of all - titanium alloy, it possesses superior strength and dependability and is especially well - adapted to withstand the harsh river conditions along Srinagar. It is a "budget ADCP" with high - class performance at budget prices, hence an excellent choice for monitoring the river flow along Srinagar without digging deep into the pockets in terms of equipment costs. To know more, visit https://china-sonar.com/.
Here is a table with some well known ADCP instrument brands and models.
Why Do We Monitor River Flow in Hải Phòng?