Why We Measure River Flow in Ninh Bình?

1. Where is Ninh Bình?

Geographical Background

Ninh Bình, north Vietnam, lies between approximately 20.15°N latitude and 106.15°E longitude. It borders Thái Bình and Hưng Yên Provinces to the east, Hà Nam Province to the south, Ninh Thuận and Thanh Hóa Provinces to the west, and Nam Định Province to the north. Ninh Bình's terrain is a fascinating mix of karst ranges of limestone, green valleys, and extensive rice fields. The climate in Ninh Bình is a tropical monsoon one, with May to October being the wet period and November to April being the dry period. The climate regime also has a significant influence on river levels and flow rates, determining the hydrology of the region.

Humanities and culture

Ninh Bình is endowed with a high density of heritage cultural and historical site concentration as it has been the capital of Vietnam during the Early Lê and Đinh dynasties. The province is dotted with several historic relics, among them the Hoa Lư Ancient Capital, political and cultural capital during 968-1010. The remains of imperial palaces, temples, and pagodas in Hoa Lư reflect the then-standard architectural designs, which combined traditional Vietnamese and Buddhist elements.

The rural nature of local culture exists in rice farming, which is the basic nature of it. The local culture is filled with carnival celebrations where the festivals like the Ngu Hán Festival are celebrated with enthusiasm with magnificent rituals, folk dance, and traditional music shows. Ninh Bình is also well known for its special cuisine, such as bánh cuốn ninh Bình (roll rice pancakes ninh Bình) and cá chiên mù (fried fish in tamarind sauce), which reflect the province's rural agricultural and plentiful water resources.

Hydrology and River Overview

Thái Bình River and Đáy River are two principal river systems of Ninh Bình. Đáy River, sourced from the northern upland, runs through the province and is a significant transport and irrigation stream. The stream meanders along the limestone karst landscape with scenic beauty of peaceful waters flanked by towering mountains. The Thái Bình River is one of the significant tributaries of the Red River and an essential province of its hydrology.

The rivers are economically and ecologically extremely significant to Ninh Bình. They provide water for everyday use, agriculture, and industry. The river flood plains are fertile and enable large-scale rice cultivation, and Ninh Bình is one of the largest rice - producing provinces in Vietnam. The rivers also harbor other water life forms, and they sustain the provincial fishing economy. The rivers are also tourist attractions grounded in landscape, and they add to the province's tourism economy. However, like all other rivers, they also suffer from issues like agricultural runoff and urban waste pollution that affect water quality and the health of river ecosystems.

2. How is the River Flow Near Ninh Bình?

Influencing Factors

Precipitation and Runoff

The tropical monsoon climate of Ninh Bình has a very strong effect in dominating the flow of both Đáy and Thái Bình Rivers. During rainy seasons, the province experiences heavy rainfall sometimes of over 1,500 - 2,000 millimeters per year. This heavy rainfall generates huge runoff that causes the rivers to overflow and is responsible for the accelerations of their flow. Conversely, during the dry season, there is an abrupt decline in precipitation, which results in low river flows and low water levels. Interannual rainfall variability causes irregular fluctuations in river flow regimes that are difficult to manage in water management, flood control, and ensuring a consistent supply of water for multiple uses.

Topography and River Morphology

The unique geology of Ninh Bình, with limestone karst mountains and plains, affects the rivers' flow. The rivers are in a state of fast flow, cutting deep gorges and valleys, where the mountain slopes are steep. When the rivers reach the flat plains, the slope of the rivers becomes gradual and gentle, and the river flow decreases so that sediment is dropped on the riverbed and then eventually on the riverbanks. The Đáy River, for instance, bends across the topography, and the bends may create variations in the flow velocity. Faster - moving water on the outside bends erodes, and slower - moving water on the inside bends drops sediment. Man - made embankments such as dams, bridges, and irrigation canals have also been constructed on the rivers, again changing the original course pattern.

Reservoir Operations

Above Ninh Bình are reservoirs and dams constructed on the tributaries of the Đáy and Thái Bình Rivers. It is primarily used for water storage, hydroelectric power generation, and irrigation. Controlled releases of water from the upstream reservoirs have a substantial effect on the river flow rate of Ninh Bình. During the time of highest demand for water or during drought periods, reduced releases of water upstream might lead to reduced provincial river flows, affecting supply of water, navigation, and provincial ecosystem. Conversely, uncontrollable water discharge during rainy periods can lead to downstream flooding, which can lead to loss of human lives and properties in Ninh Bình.

Historical Hydrological Events

Numerous big flood events have been experienced in the past in Ninh Bình. Heavy monsoon rain and releases from upstream reservoirs led to torrential floods in nearly the whole province in 2020. Reports by the Vietnam Disaster Management Authority state that the floods submerged low-lying areas, displaced thousands of people, destroyed infrastructure and crops. The banks of Thái Bình River and Đáy River overflowed and flooded residential settlements, farming land, and industrial parks. Research on these events is crucial to design effective flood - mitigation structures, urban drainage optimisation, and make the province resilient to future hydrological disasters.

3. How is River Flow in Ninh Bình Controlled?

Traditional Methods

Surface Drift Float Method

The surface drift float method is an inexpensive method employed to measure river flow. A floating device such as a buoy or log is deployed on the river. The time taken to cover a known distance is measured, and the surface speed of the river is calculated by dividing the distance into the time. But this technique only tells us about the surface flow and is extremely sensitive to the fact that there is wind, which displaces the reading and induces spurious velocity readings. It also does not provide us with any hint at the flow at different levels of the river.

The Anchored Boat Method is now usually called the Staff Gauge / Current Meter method. A staff gauge is employed to record the water level, and a current meter is lowered into the river at several depths to record the velocity of the water. Several measurements of the velocity are made at different locations across the river's cross - section, and by calculating the cross - sectional area first and then multiplying it by the average velocity, the river discharge can be calculated. This method gives more precise information but is time - consuming and labor - intensive, as well as hazardous in character, especially for rivers with strong currents.

ADCP Introduction: Acoustic Doppler Current Profiler (ADCP)

Acoustic Doppler Current Profiler or ADCP is a sophisticated, more economical method of measuring river flow. It is non-invasive employing sound waves to measure water velocity at different depths. ADCP can measure the continuous river flow profiles from the surface to the bottom within a short time, and it is more informative to river flow characteristics than traditional methods. ADCP is highly efficient and enables accurate and detailed data collection, which is central to successful water resource utilization, flood forecasting, and ecology study in Ninh Bình.

4. How Does the ADCP Function through the Doppler Principle?

An ADCP flow meter functions based on the Doppler principle. It emits sound waves of a specific frequency into water. When these sound waves encounter moving particles in water, such as sediment, plankton, or water molecules, the backscattered sound waves' frequency changes. If the particles are approaching the ADCP, the frequency of the returned waves is greater, and if recoiling from the ADCP, the frequency is less. By measuring the shift in frequency (the Doppler shift) precisely, the ADCP can calculate the velocity of the water at different depths. A number of transducers in the ADCP measure velocities in different directions, and on the basis of those, the three-dimensional flow structure of the river can be determined.

5. What is Required for High-Quality River Flow Measurement in Ninh Bình?

Equipment Requirements

Proper ADCP current meter measurements in the Ninh Bình rivers require some equipment requirements. Material reliability is important due to the harsh conditions that the river can have, which include pollution, sedimentation, and varying water levels. ADCPs made from corrosion-resistant materials like stainless steel or titanium are ideal for withstanding the rugged environment. A lightweight and compact unit is also preferred, as it can be more easily transported and set up, especially in the remote and sometimes inaccessible regions of the province. Cost-effectiveness is also an important factor because it allows mass use of the technology for general observation of the river flow.

6. How to Choose the Right Current Measurement Equipment?

Deployment Method

• Ship - Borne (Moving Boat) ADCP: Suitable for conducting large - scale surveys of the Đáy and Thái Bình Rivers of Ninh Bình. It has the capacity to quickly measure the river discharge along long reaches and map the pattern of flow over different sections of the river. When the boat is moving along the waterways, the ADCP can sample continuously, providing a complete picture of the flow characteristics.
• Bottom - Fixed (Fixed) ADCP: Suitable to be installed over a very long period of continuous observation. It may be installed on the bottom of the river at chosen points to collect data over a long time so that long - term trends in flow, season flows, and impacts of various factors on the river flow are known.
• Cable - Way ADCP: Where cable - way facilities are available in portions of rivers, a cable - way ADCP can be suspended and moved across the river to take flow measurements at different places. The method is advantageous where boat - based measurement becomes problematic due to narrow river channels or excessive vegetation.

Working Frequency

• 600 kHz ADCP: A 600 kHz ADCP is in good balance regarding range and resolution, with a maximum horizontal range of 70 meters. It can be used in most river reaches in Ninh Bình to measure the flow velocity at different depths precisely.
• 300 kHz ADCP: Being equipped with a greater range of up to 110 meters, a 300 kHz ADCP will be more appropriate for deeper and wider sections of the rivers, especially the lower reaches close to the estuaries.

Brand Recommendations

Few of the world ADCP big brands include Teledyne RDI, Nortek, and SonTek, which offer high-quality and reliable products used in various hydrological study and monitoring programs. As a budget - friendly option, the ADCP manufacturer Chinese company’s "China Sonar Panda ADCP" comes highly recommended. Made of all - titanium alloy, it is more strengthful and reliable and is a suitable option to endure the nasty river condition surrounding Thrissur. As an "affordable ADCP", it boasts decent quality performance at budget price. For more information, visit https://china-sonar.com/.

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