Technical regulations for monitoring water flow in rivers not affected by tides in Vietnam

Hello, Lawnet would like to answer as follows:

1. Technical regulations for monitoring water flow in rivers not affected by tides in Vietnam

According to the provisions in subsection 1.1 of Appendix B QCVN 47:2022/BTNMT on the monitoring regime, as follows:

For principles of arranging monitoring regime:

a) Depending on the flow regime and hydraulic regime at the monitoring location and the need to use data, arrange the monitoring regime appropriately to ensure it reflects the water flow evolution at the measurement location.

b) There are two forms of water flow monitoring: regular monitoring and inspection monitoring.

- Regular monitoring means measuring for many consecutive years. The water flow monitoring regime, in the form of regular monitoring, ensures the following principles:

+ The arrangement of the water flow monitoring regime according to water level, time, flood characteristics, or special hydraulic developments must be based on the purpose, monitoring requirements, and operating time of the station;

+ The number of flow measurements per year is enough to control the representativeness and characteristic points of the correlation between water level and water flow Q = f(H) from low to high;

+ The number of flow measurements per year is enough to determine the correlation between water level and water flow Q = f(H) according to the hydraulic influence regime, including special cases such as dyke breaks, beach overflows, etc.;

- Monitoring and checking is done every year or a number of years, measuring a number of flow measurements according to certain water levels or certain floods.
to check the change in water level and water flow relationship Q = f(H).

Regarding monitoring regime

Water flow monitoring regimes for new stations operating less than 3 years, stations operating over 3 years, and stations operating over 5 years is implemented according to the provisions of Article 7.2 in TCVN 12636-8:2020 Hydro-meteorological monitoring - Part 8: Monitoring river water flow in areas not affected by tides.

2. Method for measuring the volume of water flow in rivers that are not affected by tides in Vietnam

According to the provisions in subsection 1.2 of Appendix B QCVN 47:2022/BTNMT on volume measurement method, as follows:

Principles for choosing monitoring methods

- The choice of water flow monitoring method must be based on the purpose, station location requirements, and specific situation at each time and at each monitoring location;

- Multiple methods can be used separately or in combination to monitor water flow, but they must ensure the principles of accuracy and economy.

Conditions for applying the volume measurement method

The volume measurement method is applied in small rivers and streams where there is no stagnant water and where the cross-section can be improved to collect water flow into the trough with a maximum water flow of 20 l/s.

Volume measurement method

a) Measurement sequence

- Measure water level;

- Determine measurement time;

- Measure water volume;

- Calculate water flow;

- Maintenance of vehicles and measuring equipment.

b) Measurement method

- Must measure the water level at the measurement location at the beginning and end of water flow measurement;

- Determine measurement time:

+ Record the start time and end time of measurement to the nearest second;

+ Measurement time is calculated as the difference between the end of measurement and the start of measurement.

- Measure water volume: must ensure to capture the entire amount of water flowing through the cross section from the start to the end of the measurement; Water containers must be safe and convenient to determine the volume of water, and they must not be filled with too much water to avoid overflowing during operation;

- Observe and record weather phenomena, flow conditions, and phenomena affecting the flow, such as river banks, river bottoms, and vegetation growing in the river bed and river banks.

Calculate water flow

The water flow measured by the volumetric method is calculated as follows:

Q = W/∆t

In there:

- Q is water flow (l/s);

- W is the volume of water (l);

- ∆t is the measurement time (s);

- ∆t = t2 - t1

- t2 is the end of measurement;

- t1 is the starting time of measurement.

Best regards!

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