Circular No. 22/2022/TT-BTNMT Issuing National Technical Regulations on Hydrological Monitoring

CIRCULAR

Issuing National Technical Regulations on Hydrological Monitoring

          On the basis of the Law on Standards and Technical Regulations dated June 29, 2006;

          On the basis of the Law on Meteorology and Hydrology dated November 23, 2015;

          On the basis of Decree No. 127/2007/NĐ-CP dated August 1, 2007 of the Government detailing certain provisions of the Law on Standards and Technical Regulations; Decree No. 78/2018/NĐ-CP dated May 16, 2018 of the Government amending and supplementing certain provisions of Decree No. 127/2007/NĐ-CP dated August 1, 2007 of the Government detailing certain provisions of the Law on Standards and Technical Regulations;

          On the basis of Decree No. 38/2016/NĐ-CP dated May 15, 2016 of the Government detailing certain provisions of the Law on Meteorology and Hydrology; Decree No. 48/2020/NĐ-CP dated April 15, 2020 of the Government amending and supplementing certain provisions of Decree No. 38/2016/NĐ-CP dated May 15, 2016 of the Government detailing certain provisions of the Law on Meteorology and Hydrology;

          On the basis of Decree No. 68/2022/NĐ-CP dated September 22, 2022 of the Government stipulating the functions, tasks, powers, and organizational structure of the Ministry of Natural Resources and Environment;

          Pursuant to the proposal of the Director General of the Hydro-Meteorological Service, the Head of the Science and Technology Department, and the Head of the Legal Affairs Department;

          The Minister of Natural Resources and Environment hereby issues this Circular on the National Technical Regulation on Hydrological Monitoring.

          Article 1. Attached to this Circular is QCVN 47:2022/BTNMT - National Technical Regulation on Hydrological Monitoring.

          Article 2. This Circular shall take effect from June 20, 2023, and replace Circular No. 26/2012/TT-BTNMT dated December 28, 2012 of the Minister of Natural Resources and Environment promulgating QCVN 47:2012/BTNMT - National Technical Regulation on Hydrological Monitoring.

          Article 3. The Director General of the Hydro-Meteorological Service, Heads of units under the Ministry of Natural Resources and Environment, Directors of Provincial Departments of Natural Resources and Environment, and related organizations and individuals are responsible for implementing this Circular./.

 

QCVN 47: 2022/BTNMT

NATIONAL TECHNICAL REGULATION ON HYDROLOGICAL MONITORING

National technical regulation on Hydrological Observation

PREAMBLE

QCVN 47: 2022/BTNMT was revised by the Hydro-Meteorological Service, reviewed by the Science and Technology Department and the Legal Affairs Department, and approved by the Minister of Natural Resources and Environment pursuant to Circular No......../2022/TT-BTNMT dated...month...year.

NATIONAL TECHNICAL REGULATION ON HYDROLOGICAL MONITORING

National technical regulation on Hydrological Observation

This technical regulation sets out technical requirements, testing methods, sampling procedures; management requirements; responsibilities of organizations and individuals producing, trading, and importing cigarettes.

1.1. Scope of Application

This national technical regulation specifies the technical requirements for monitoring hydrological factors.

1.2. Applicability

This national technical regulation applies to management agencies, organizations, and individuals involved in monitoring hydrological factors within the territory of Vietnam.

1.3. Definitions

In this regulation, all terms defined in Clause 5 of TCVN 12904:2020 Meteorological and Hydrological Factors - Terms and Definitions; Clause 2 of TCVN 12636-2:2019 Meteorological and Hydrological Monitoring - Part 2: Water Level and Water Temperature Monitoring; Clause 3 of TCVN 12636-8:2020 Meteorological and Hydrological Monitoring - Part 8: River Flow Monitoring in Non-Tidal Areas; Clause 3 of TCVN 12636-9:2020 Meteorological and Hydrological Monitoring - Part 9: River Flow Monitoring in Tidal Areas, and the following terms are used:

1.3.1. Hydrological factors: are the factors specified for monitoring according to this standard, including water level, water temperature, flow rate, and suspended sediment load.

1.3.2. Representative suspended sediment concentration: is the suspended sediment concentration of the water sample taken at the representative cross-section during the measurement of suspended sediment load across the entire cross-section.

1.3.3. Cross-sectional suspended sediment concentration: is the suspended sediment concentration measured and calculated according to the regulations for the entire cross-section.

1.3.4. River turbidity: is the reduction in water clarity due to the presence of non-soluble substances.

1.3.5. Dry season: is the period consisting of consecutive months with monthly average flow rates (over many years) less than or equal to the annual average flow rate (of many years).

1.3.6. Flood season: is the period consisting of consecutive months with monthly average flow rates (over many years) greater than the annual average flow rate (of many years).

1.4. Recording measured values and rounding to significant figures

Measured values must be recorded with sufficient significant figures as prescribed. Rounding to significant figures is carried out as follows: if the next digit after the significant figure is less than 5, it is discarded; if it is 5 or more, the significant figure is increased by one unit. Detailed recording of measured values and rounding to significant figures for hydrological factors is specified in Appendix D of this regulation.

II. TECHNICAL REQUIREMENTS

2.1. Water Level Monitoring

2.1.1. Provisions on symbols and units of measurement

a) Symbol for water level: H;

b) Unit of measurement for water level: centimeter (cm);

c) Accuracy of water level value: ±1 cm.

2.1.2. Provisions on monitoring location

Follow the provisions in Clause 5.1 of TCVN 12635-2:2019 Hydro-Meteorological Monitoring Structures - Part 2: Location and Structures for Hydrological Stations.

2.1.3. Provisions on monitoring structures

Follow the provisions in Clause 5.2 of TCVN 12635-2:2019 Hydro-Meteorological Monitoring Structures - Part 2: Location and Structures for Hydrological Stations.

2.1.4. Provisions on monitoring equipment and devices

a) Monitoring equipment and devices must be safe, easy to use, meet technical specifications, and have an accuracy of up to 1 cm when measuring;

b) Must measure water levels from the lowest to the highest at the monitoring location;

c) Must have technical guidance materials;

d) Measuring instruments must be calibrated and verified according to the legal regulations on metrology. During the entire calibration cycle period, the metrological technical characteristics of the measuring instrument must be maintained throughout its use;

e) Monitoring equipment and devices must be stored and maintained according to current regulations.

2.1.5. Provisions on monitoring techniques

Water level monitoring techniques shall be carried out in accordance with the provisions set forth in Section 1, Appendix A of this Standard.

2.2. River water temperature monitoring

2.2.1. Provisions on symbols and units of measurement

a) Symbol for water temperature: T_n;

b) Unit of measurement for water temperature: Degree Celsius (°C)⁰c) Accuracy of water temperature value: ± 0.1 °C

2.2.2. Provisions on monitoring location⁰4. Liquid bull semen

Shall be carried out in accordance with the provisions of Article 6 in TCVN 12635-2:2019 Meteorological and Hydrological Monitoring Structures - Part 2: Location, Monitoring Structures for Hydrological Stations.

2.2.3. Provisions on monitoring equipment

a) River water temperature monitoring equipment must be safe, easy to use, ensure technical performance, have an accuracy up to 0.1 °C when measuring;

b) Able to measure temperature from the lowest to the highest at the monitoring location;⁰c) Have a part that limits and excludes the impact of air contact or floating objects on the river;

d) Measuring devices must be inspected and calibrated in accordance with the law on metrology. During the entire period specified in the inspection cycle, the metrological technical characteristics of the measuring device must be maintained throughout its use;

c) Must have technical guidance materials;

e) Measuring devices must be stored and maintained in accordance with current regulations.

2.2.4. Provisions on monitoring techniques

River water temperature monitoring techniques shall be carried out in accordance with the provisions set forth in Section 2, Appendix A of this Standard.

2.3. Flow rate monitoring

2.3.1. Provisions on symbols and units of measurement

a) Symbol for flow rate: Q;

b) Unit of measurement for flow rate: cubic meters per second (m³/s).

Details on symbols, units of measurement, and meaningful numbers of factors in flow rate monitoring are specified in Appendix D of this Standard.

2.3.2. Provisions on monitoring location³Shall be carried out in accordance with the provisions of Article 7.1 in TCVN 12635-2:2019 Meteorological and Hydrological Monitoring Structures - Part 2: Location, Monitoring Structures for Hydrological Stations.

2.3.3. Provisions on monitoring structures

Shall be carried out in accordance with the provisions of Article 7.2 in TCVN 12635-2:2019 Meteorological and Hydrological Monitoring Structures - Part 2: Location, Monitoring Structures for Hydrological Stations.

2.3.4. Provisions on monitoring equipment and means

a) Equipment must ensure accurate measurement of the measured factor, in accordance with the technical performance of the equipment;

b) Must have technical guidance materials;

c) Measuring devices must be inspected and calibrated in accordance with the law on metrology. During the entire period specified in the inspection cycle, the metrological technical characteristics of the measuring device must be maintained throughout its use;

d) Flow rate measuring equipment and means must be stored and maintained in accordance with current regulations;

e) Flow rate monitoring means must ensure absolute safety for people and not affect the operational performance of the measuring equipment;

f) Monitoring equipment and means must be stored and maintained in accordance with current regulations.

2.3.5. Provisions on monitoring techniques

Flow rate monitoring techniques shall be carried out in accordance with the provisions set forth in Appendix B of this Standard.

2.4. Suspended sediment flow rate monitoring

2.4.1. Provisions on symbols and units of measurement

a) Symbol for suspended sediment flow rate: R;

b) Unit of measurement for suspended sediment flow rate: grams per second (g/s) or kilograms per second (kg/s).

Details on symbols, units of measurement, and meaningful numbers of factors in suspended sediment flow rate monitoring are specified in Appendix D of this Standard.

2.4.2. Provisions on monitoring location

Suspended sediment flow rate monitoring location shall be carried out in accordance with the provisions of Point 2.3.2, Part II of this Standard.

2.4.3. Provisions on monitoring structures

Suspended sediment flow rate monitoring structures shall be carried out in accordance with the provisions of Point 2.3.3, Part II of this Standard.

2.4.4. Provisions on monitoring equipment

2.4.4.1. Sample collection equipment

a) Bottle-type sample collection equipment

- Bottle-type equipment can be used to collect samples using either deep accumulation or point accumulation methods;

- Bottle capacity should range from 1 l, 2 l, 5 l, and should have markings up to 0.2 l;

- Use bottle-type sample collection equipment mounted on a pole when the water flow speed is less than or equal to 1.50 m/s and the water depth is between 1.0 m and 2.0 m;

- Use bottle-type sample collection equipment mounted in iron cages when the water flow speed exceeds 1.50 m/s and the water depth is greater than 2.0 m.

b) Horizontal sample collection equipment

- Only used for point accumulation method;

- Must ensure sufficient volume according to regulations;

- Must not deform during use.

2.4.4.2. Sample containers

a) Should not absorb or produce suspended solids;

b) Container volume should be larger than the sample water volume by 10% to 20%.

2.4.4.3. Volume measurement tubes

a) Transparent, cylindrical with markings accurate to 20 ml;

b) Measurable volume from 1 l to 2 l.

2.4.4.4 Direct measurement equipment for suspended solids content

a) Measurement range from 0 g/m³ to 20,000 g/m³;

b) Maximum error ± 2% of the measurement result;

c) Must have complete technical guidance;

d) Measuring devices must be inspected and calibrated in accordance with the law on metrology. During the entire period specified in the inspection cycle, the metrological technical characteristics of the measuring device must be maintained throughout its use.³2.4.5. Provisions on monitoring techniques³;

Suspended sediment flow rate monitoring techniques shall be carried out in accordance with the provisions set forth in Appendix C of this Standard.

3.1. Conformity assessment method

Method 1: Typical sample testing shall be used to assess conformity. The content and sequence of implementation of the main activities in Method 1 shall be carried out in accordance with Section I of Appendix II issued together with Circular No. 28/2012/TT-BKHCN dated December 12, 2012 of the Minister of Science and Technology on the announcement of compliance with standards and technical regulations and conformity assessment methods with standards and technical regulations.

3.2. Provisions on conformity declaration

The product that needs to be declared as conforming is hydrological monitoring data. The conformity declaration is based on the self-assessment results of the organization or individual declaring conformity.

8.2. Domestic-produced TNP1 explosive must declare compliance according to Circular No. 28/2012/TT-BKHCN dated December 12, 2012, issued by the Minister of Science and Technology regarding declaration of conformity to standards and technical regulations and methods of conformity assessment (hereinafter referred to as Circular No. 28/2012/TT-BKHCN) and Circular No. 02/2017/TT-BKHCN dated March 31, 2017, issued by the Minister of Science and Technology amending and supplementing certain provisions of Circular No. 28/2012/TT-BKHCN dated December 12, 2012, issued by the Minister of Science and Technology regarding declaration of conformity to standards and technical regulations and methods of conformity assessment (hereinafter referred to as Circular No. 02/2017/TT-BKHCN).

3.3. Responsibility for conformity declaration

Organizations, enterprises, and individuals providing hydrological monitoring data are responsible for declaring conformity for such data they measure.

3.2. Provisions on conformity declaration publication

The products that need to have a conformity declaration published are hydrological monitoring data. The conformity declaration publication is based on the self-assessment results of the organization or individual making the conformity declaration.

3.3. Obligations for conformity declaration publication

Organizations, businesses, and individuals providing services are responsible for publishing conformity declarations for hydrological monitoring data they measure.

3.4. The notification of compliance with technical regulations shall be carried out in accordance with Circular No. 28/2012/TT-BKHCN dated February 12, 2012, issued by the Ministry of Science and Technology, and Circular No. 02/2017/TT-BKHCN dated March 31, 2017, issued by the Minister of Science and Technology to amend and supplement certain provisions of Circular No. 28/2012/TT-BKHCN dated December 12, 2012.

3.5. State management agencies on meteorology and hydrology shall be responsible for organizing inspections to ensure compliance with this standard within their jurisdiction as prescribed by law.

3.6. All hydrological data reviewed after the effective date of this standard must comply with the provisions set forth in this standard.

IV. RESPONSIBILITIES OF ORGANIZATIONS AND INDIVIDUALS

Ministries, ministerial-level agencies, agencies under the Government, People's Committees of provinces and centrally-run cities, and related organizations and individuals are responsible for implementing this technical regulation.

V. IMPLEMENTATION

The Director of the General Meteorological and Hydrological Department, Heads of units directly under the Ministry of Natural Resources and Environment, and Directors of Provincial Departments of Natural Resources and Environment of centrally-run cities are responsible for disseminating, urging, inspecting, and applying this standard to relevant entities.

ANNEX A

(Provisions)

TECHNICAL REGULATIONS FOR WATER LEVEL AND WATER TEMPERATURE MEASUREMENTS

1. Water Level Measurement

1.1. Measurement Regime

1.1.1. Principles for Selecting the Measurement Regime

a) The water level measurement regime must ensure a comprehensive, objective reflection of water level changes and must be feasible;

b) Depending on the degree of daily water level changes, one of the measurement regimes specified in point 1.1.2, Appendix A, of this standard shall be applied;

c) For manual water level measurements, observers must continuously monitor water level changes. After each measurement, they must update the hourly water level process curve. If the current measurement regime is no longer suitable for the observed water level changes, it must be changed to a more appropriate regime;

d) Based on the quality of machine operation, the performance of the installation, and the requirements for data utilization, one of the measurement regimes specified in point 1.1.3, Appendix A, of this standard shall be selected to check the automatic water level recording machine.

1.1.2. Manual Water Level Measurement Regime

a) Regime 1: Measure twice daily at 07:00 and 19:00, applicable during the dry season in rivers unaffected by tides when the daily water level fluctuation is less than or equal to 5 cm;

b) Regime 2: Measure four times daily at 01:00, 07:00, 13:00, and 19:00, applicable when the daily water level fluctuation exceeds 5 cm but is less than or equal to 10 cm, such as at the beginning and end of the dry season in rivers unaffected by tides;

c) Regime 3: Measure eight times daily at 01:00, 04:00, 07:00, 10:00, 13:00, 16:00, 19:00, and 22:00, applicable during periods of significant daily water level changes, such as the early flood season in medium and large rivers unaffected by tides;

d) Regime 4: Measure twelve times daily at 01:00, 03:00, 05:00, 07:00, 09:00, 11:00, 13:00, 15:00, 17:00, 19:00, 21:00, and 23:00, applicable during periods of substantial daily water level changes, such as the flood season in medium and large rivers and areas affected by diurnal tides with a tidal range not exceeding 100 cm;

e) Regime 5: Measure twelve times daily at 01:00, 03:00, 05:00, 07:00, 09:00, 11:00, 13:00, 15:00, 17:00, 19:00, 21:00, and 23:00. Additionally, measure once every hour before and after the peak (tide or flood), applicable in tide-affected monitoring lines with a tidal range greater than 100 cm and during days with major floods in medium and large rivers;

f) Regime 6: Measure twenty-four times daily at 00:00, 01:00, 02:00, 03:00, ..., and 23:00, applicable during the flood season in small rivers and streams, and in tide-affected monitoring lines with significant semi-diurnal tide influence;

g) Regime 7: Measure twenty-four times daily at 00:00, 01:00, 02:00, 03:00, ..., and 23:00. Additionally, measure once every 5, 10, 15, or 30 minutes around the peak (tide or flood). The measurement interval is determined based on water level changes to accurately capture the water level value and timing of the peak and low points, applicable in areas strongly influenced by tides and in small rivers and streams during the flood season;

h) Regime 8: Measure every 5, 10, 15, or 20 minutes from the start of the flood until its end. Around the peak of the flood, measure more frequently, and the flood front is measured more frequently than the flood recession. The measurement interval is determined based on the rate of water level change and the duration of the flood. The shorter the flood duration and the larger the rate of water level change, the shorter the measurement interval to ensure accurate measurement of the flood peak and transition points. It is necessary to understand the watershed characteristics and storm characteristics (rainfall intensity, storm center...) to determine the measurement intervals.

1.1.3. Measurement Regime for Checking Automatic Water Level Recording Machines

a) Measure once daily at 07:00 on the 5th, 15th, and 25th of each month, applicable where no station building has been constructed, the installation is stable, the machine operates well and continuously and accurately, and the automatic recorder uses a multi-day chart;

b) Measure once daily at 07:00, applicable to stations with stable installations and machines operating well and reliably without any incidents during operation;

c) Measure twice daily at 07:00 and 19:00, applicable to stations with stable installations and machines operating consistently;

d) Measure four times daily at 01:00, 07:00, 13:00, and 19:00, applicable to stations with newly constructed installations or recently repaired machines.

1.1.4. Measurement Regime When the Installation or Automatic Recorder Is Damaged

If the installation or automatic recorder (such as clocks, power supply, batteries, memory, air pipes, other components...) is damaged and affects the accuracy of the data, operations must be halted. During the halt, direct water level measurements must be taken on the staff gauge system or water marker according to the regimes specified in point 1.1.2, Appendix A, of this standard.

1.1.5. Automatic Water Level Measurement Regime

a) During flood season, measure at least once every five minutes;

b) During dry season, measure at least once every ten minutes;

c) Every fifteen days, monitor water levels to check automatic water level measuring equipment once, applicable for stations with stable structures and normally functioning measuring devices, where the difference between the measured water level value and that of the automatic device does not exceed ± 2 centimeters;

d) Monitor water levels to check automatic water level measuring equipment immediately upon detecting unstable structures or measuring devices, where the measured water level data shows sudden errors;

1.2. Water Level Monitoring Methods

1.2.1. Water Level Monitoring Using Peg Lines

a) Monitoring Procedure

- Preparation: tools, materials, and equipment for monitoring, moving to the monitoring location;

- Determine the water level reading, determine the verification reading if switching to another peg, observe auxiliary factors, record data in the monitoring logbook;

- Calculate the water level value based on the reading and the height of the peg top, compare the result with the previous measurement;

- Clean, maintain, and perform minor repairs on the structure and measuring equipment;

- Encode data, telegraph (if assigned);

- Compile characteristic values, copy data;

b) Monitoring Method

- The monitoring time deviation shall not exceed three minutes from the specified time;

- Time accuracy of monitoring: For monitoring using self-recording water level machines or automatic monitoring: The machine clock differs from the standard clock by no more than ± 2 minutes/24 hours;

- The handheld water level gauge must be placed on top of the peg, submerged in water by at least 5 cm (including when there are waves). The number marking should face the observer, and the thin side of the gauge should align with the direction of water flow;

- When there are no waves, the water surface lies at which marking line, then the value of that marking line is the reading. If the water surface lies between two markings, the reading value must be rounded according to the provisions of Article 4, Part I, of this Standard;

- When the water surface has waves, monitoring must be conducted before a certain period of time to ensure that the average measurement time coincides with the specified measurement time. Read the water level at the peak and trough of two wave cycles, each cycle must read the highest peak and lowest trough markings (trough readings must be at least 5 cm); the reading value is the average of both cycles;

- Monitoring results must be clearly recorded in the logbook immediately after determining the reading value;

- In cases where the water level drops while the lower peg is missing, allow readings less than 5 cm. If the water level drops beyond the peg top, allow negative readings. The longest application period is two days. Negative reading method:

+ The bottom of the gauge touches the water surface;

+ Project horizontally across the peg top, read the number on the gauge;

+ Record the water level value with a "-" sign before it;

- In cases of monitoring water levels between two pegs or adjacent water gauges:

+ Verification monitoring applies to temporary pegs, reinstalled pegs not yet stable, peg lines or water gauges significantly affected by large floods, ship impacts, etc., suspected of subsidence;

+ When switching monitoring from one peg to another, simultaneously read the current peg being monitored and the next peg to be monitored. If there are multiple switches in one day, only one verification monitoring is required. The monitoring method follows the regulations for monitoring along peg lines and water gauges;

+ Record the water level value: Record in fractional form, the numerator records the data from the peg currently and being monitored, the denominator records the data from the next peg to be monitored. Fully record "Peg Number", "Height of Peg Top", "Reading". If the water levels monitored at two pegs do not match, find the cause and adjust the water level value;

+ The water level value of the measurement is the value of the peg currently and being monitored;

1.2.2. Water Level Monitoring Along Water Gauges

The monitoring procedure and method for water level monitoring along water gauges follow the provisions at point 1.2.1, Appendix A, of this Standard;

1.2.3. Water Level Monitoring to Check Self-Recording Devices

a) Monitoring Procedure

- Preparation: tools, materials, and equipment for monitoring, moving to the monitoring location;

- At the designated time, compare the machine's clock with the standard clock (according to international standard time GMT+7), mark the inspection time on the graph;

- Inspect and mark the graph;

- Determine the water level reading, determine the verification reading if switching to another peg, observe auxiliary factors, record data in the monitoring logbook;

- Calculate the water level value based on the reading and the height of the peg (water gauge) and compare the result with the previous measurement;

- Clean, maintain, and perform minor repairs on the structure and measuring equipment;

b) Monitoring Method

- Time accuracy of monitoring: The machine clock differs from the standard clock by no more than ± 2 minutes/24 hours;

- Mark the inspection monitoring time on the self-recording graph: Draw a long line of 1 cm and intermittent (about 0.5 mm) during the inspection time;

- Monitor water levels along peg lines or water gauges according to the provisions at point 1.2.1 and 1.2.2, combined with observing auxiliary factors according to Article 3, Appendix A, of this Standard;

- Record the inspection monitoring results in the logbook and on the self-recording graph. Record the monitoring time on the left and the water level value on the right of the inspection time line on the self-recording graph;

- Check the machine operation after inspecting the water level: Check the transmission system, check the movement of the wheels, check the operation of the self-recording pen. If there is a malfunction, determine the cause, record the analysis conclusion and the time of occurrence for future documentation handling;

1.2.4. Water Level Monitoring When Replacing Graph Paper

a) Monitoring Procedure

- Follow the provisions at paragraph a, point 1.2.3, Appendix A, of this Standard;

b) Monitoring Method

- Monitor according to the provisions at paragraph b, point 1.2.3, Appendix A, of this Standard;

- New graph paper must fully record the content: Date, month, year, river name, station name;

- Install new graph paper ensuring the lines at the seam of the two edges coincide. When moving the float or pen tip, the recording line should not be obstructed and run parallel to the coordinate axis line, the paper should be tightly rolled and flat;

- Position the pen tip correctly at the water level coordinate and time according to the standard clock;

1.2.5. Automatic Water Level Monitoring

a) Time accuracy of measurement: The machine clock differs from the standard clock by no more than ± 2 minutes/24 hours;

b) Measured data follows the provisions of Article 4, Part I, of this Standard;

c) Data is stored, displayed at the station, and transmitted to the management authority;

2. Temperature Monitoring of River Water

2.1. Monitoring Schedule

Temperature monitoring of river water shall be conducted at least twice daily, at 7 hours and 19 hours. Additionally, the frequency of monitoring may increase based on data usage requirements.

2.2. Monitoring Method

2.2.1. Manual Monitoring

a) Monitoring Procedure

- Prepare equipment and materials;

- Install the thermometer holder;

- Immerse the thermometer in water on the holder;

- Determine the reading on the device;

- Record the reading in the field monitoring logbook;

- Calculate the water temperature value according to the calibration figure;

- Compare the result with the previous measurement;

- Clean the measuring line.

b) Monitoring Method

- The monitoring time should not deviate more than five minutes from the specified time;

- The minimum immersion time of the thermometer in water is three minutes;

- Submerge the thermometer vertically into the water at a depth of approximately 0.5 meters without touching the riverbed or other objects. For small rivers or streams where the depth is less than 0.5 meters, submerge the thermometer diagonally;

- The time to determine the water temperature starts from when the thermometer is lifted out of the water and must not exceed five seconds;

- Monitoring results must be clearly recorded in the field logbook immediately after determining the temperature value; record the thermometer reading and the accurate water temperature value to 0.1 degree Celsius;⁰4. Liquid bull semen

2.2.2. Automatic Monitoring

a) Data measured shall comply with the provisions of Article 4, Part I, of this Standard;

b) Data shall be stored, displayed at the station, and transmitted to the management authority;

c) Measurement time accuracy: The machine clock differs from the standard clock by no more than ±2 minutes per 24 hours.

3. Provisions for Observing Additional Factors

3.1. Observing Water Flow Direction

a) Observation Mode: Observe the direction of water flow simultaneously with water level monitoring during manual monitoring;

b) The direction of water flow is determined according to the direction of the river;

c) Indicators for the direction of water flow are as follows:

- Flowing downstream (from upstream to the river mouth) is marked as ↓;

- Flowing upstream (from the river mouth to upstream) is marked as ↑;

- Circulating flow is marked as q.

3.2. Observing Wind

a) Observation Mode: Observe wind direction and strength simultaneously with water level monitoring during manual monitoring;

b) Wind direction and strength are determined by estimation and comparison with the direction of the river current and surrounding objects (trees, houses, etc.). Recording methods are specified in Table 1.

Table 1. Wind Direction and Strength Recording Methods

3.3. Observing Waves

a) Observation Mode: Observe waves simultaneously with water level monitoring during manual monitoring;

b) Based on the degree of manifestation of phenomena caused by waves, wave levels are determined as follows:

- Wave level zero (no waves) is marked as 0;

- Wave level one (ripples) is marked as I;

- Wave level two (moderate waves, white foam appears at wave crests) is marked as II;

- Wave level three (large waves, small boats cannot navigate, large boats are tossed about) is marked as III.

3.4. Observing River Bed Changes

a) Observation Mode:

- Observe changes in the river bed, vegetation growth within the river, bank erosion and accretion, activities of hydraulic structures, and human activities every ten days, coinciding with manual water level monitoring on the 5th, 15th, and 25th of each month;

- When conducting automatic water level measurements, observe changes in the river bed, vegetation growth within the river, bank erosion and accretion, activities of hydraulic structures, and human activities at least twice a year, during mid-dry season and end-flood season.

b) Observations are based on phenomena such as the development of plants, erosion, and accretion along the river banks, including:

- Location, extent, degree, and process of erosion and accretion, degree of plant growth;

- Time of appearance, length, width, area of collapse, height of the raised beach;

- Time of change in main channel position, distribution of flow velocity, including floating debris;

- Range of plant growth, density (sparse, dense...), height, impact on flow;

- Operation status of hydraulic structures, other human activities such as:

+ Scale, construction period, completion time of hydraulic structures, hydroelectric projects, bridges, culverts; inland waterway transport; levees; revetments; dredging of river beds;

+ Time of opening and closing of culverts or building and removing dams, taking and discharging water, impact on flow regime.

Provisions on the HS Code of Terrestrial Mobile Radio Equipment and Terrestrial Radio Relay Equipment

(Provisions)

TECHNICAL REGULATIONS FOR WATER FLOW MONITORING

1. Technical Regulations for Water Flow Monitoring in Non-Tidal River Areas

1.1. Measurement Regime

1.1.1. Principles of Monitoring Schedule Arrangement

a) Depending on the flow regime, hydraulic conditions at the monitoring location, and data usage requirements, arrange the monitoring schedule appropriately to reflect the water flow changes at the measurement point.

b) There are two forms of water flow monitoring: regular monitoring and spot-check monitoring.

- Regular monitoring involves continuous multi-year measurements. The water flow monitoring schedule under regular monitoring ensures the following principles:

+ The arrangement of the water flow monitoring schedule according to water level grades, time, flood characteristics, or special hydraulic processes must be based on the monitoring objectives, requirements, and station operation time;

+ The number of annual water flow measurements must be sufficient to control the representativeness and key features of the correlation between water level and water flow Q = f(H) from low to high;

+ The number of annual water flow measurements must be sufficient to determine the correlation between water level and water flow Q = f(H) under hydraulic influence, including special cases such as dike breaches, overtopping, etc.;

- Spot-check monitoring involves measuring water flow several times annually at certain water level grades or specific floods to check changes in the relationship between water level and water flow Q = f(H).

1.1.2. Monitoring Schedule

The monitoring schedule for water flow at new stations operating for less than three years, stations operating for more than three years, and stations operating for more than five years shall be carried out in accordance with the provisions of Article 7.2 of TCVN 12636-8:2020, Hydrological and Meteorological Monitoring - Part 8: Water Flow Monitoring in Non-Tidal River Areas.

1.2. Flow measurement methods

1.2.1. Principles for selecting flow measurement methods

a) The selection of flow measurement methods must be based on the purpose, requirements for setting up the station, and specific conditions at each time point and location.

b) Separate or combined methods may be used to measure flow rates, but they must ensure accuracy and cost-effectiveness.

1.2.2. Cross-sectional and velocity measurement method

1.2.2.1. Measurement procedure

a) Prepare equipment, install measuring machines and devices;

b) Measure water level, observe river surface conditions, and locate depth sounding points;

c) Determination of the distance from the bank edge on both right and left sides;

d) Measure depth at sounding points, velocity sounding points, calculate depths, and distribute velocity measurement points on sounding lines;

e) Measure water velocity, record results in the observation logbook;

f) Calculate flow rate, select characteristic values;

g) Telegraph, encode data, transmit information (if assigned);

h) Plot points on correlation graphs Q = f(H), F = f(H), V = f(H), analyze correlations to determine measurement regimes;

i) Maintain equipment, machines, and measuring devices.

1.2.2.2. Cross-sectional measurement

1.2.2.2.1. Principles of cross-sectional measurement

a) Water levels must be observed at the beginning and end of cross-sectional measurements, and the distance from the starting point to both banks must be determined;

b) When water velocity ≤ 1.00 m/s, cross-sectional and velocity measurements should be conducted simultaneously;

c) When water velocity > 1.00 m/s or water level change rate ≥ 0.50 m/h, cross-sectional measurements should be conducted before or after velocity measurements;

d) When measuring depth with a staff or cable winch, at each sounding line, depth must be measured at least twice. The value of the second measurement should not differ from the first by more than ± 5%. Calculated depth is the average of the measured depths.

1.2.2.2.2. Arrangement of sounding lines for depth measurement

a) Sounding lines for depth measurement must control the transition of riverbed topography;

b) When the riverbed is stable, the positions of sounding lines for depth measurement must be fixed;

c) When the riverbed is unstable, additional auxiliary sounding lines for depth measurement should be arranged based on actual measurement results;

c) The distance between sounding lines for depth measurement should be equal (except for the distance between two sounding lines near the bank);

d) The number of sounding lines for depth measurement must be equal to or greater than the number of sounding lines for velocity measurement and meet the following requirements:

- For new stations operating less than 3 years, the minimum number of depth sounding lines is as shown in Table 1;

- For stations operating for 3 years or more, the number of depth sounding lines can be reduced, but not by more than half of the number in Table 1.

Table 1. Minimum number of depth sounding lines for new stations operating less than 3 years

1.2.2.2.3. Determining the position of depth sounding lines

a) When B ≤ 600 m, use a horizontal cable across the river to determine the position of depth sounding lines;

b) When B > 600 m, the position of depth sounding lines can be determined using an angle-measuring instrument or based on the principle of three collinear points using a pre-built system as shown in Figure 1 or utilizing special objects on the riverbank such as architectural structures, old trees;

c) When the flow depth is small, wading can be used to measure, and the position of depth sounding lines is determined based on the nearest fixed mark near the bank.

 

Figure 1. Determining the position of depth sounding lines using a system of markers

1.2.2.2.4. Cross-sectional measurement regime

a) When the riverbed is stable seasonally or over the long term, during the stable period, cross-sectional measurements should be conducted once every 5 to 10 velocity measurements, and twice during low-water periods within a maximum interval of 3 months;

b) When the riverbed frequently changes, cross-sectional measurements should be conducted once every 2 to 3 velocity measurements;

c) When economic or social activities or natural impacts such as construction of hydraulic works, dredging, or large floods occur, causing changes in the cross-section, comprehensive cross-sectional measurements must be organized up to the highest water level.

1.2.2.2.5. Methods for cross-sectional measurement

a) Using a staff

- When depth is less than 3 m, use a staff or steel ruler to measure depth;

- If the riverbed contains mud or sand, the staff or ruler must have a base, with sharp nails under the base.

b) Using a cable winch

- When depth ≥ 3 m, depth measurement is performed using a steel cable, with a winch to lower it;

- When water velocity is high, if the cable deviation angle ≥ 10 degrees, increase the weight of the steel cable to reduce the deviation angle. If increasing the weight does not reduce the deviation angle, adjust the depth according to the deviation angle as specified in Table 2.^° must increase the weight of the steel fish to reduce the cable deviation angle. If increasing the weight of the steel fish does not reduce the cable deviation angle, the depth must be adjusted according to the cable deviation angle specified in Table 2.

Table 2. Depth correction values according to the deviation angle of the steel cable

c) Using automatic equipment

c) Using automatic equipment

- Water levels must be observed at the start and end of cross-sectional measurements;

- Measure the width of the river;

- Measure the distance from the starting and ending positions of the depth measuring device to the riverbanks (left bank, right bank);

- Determine the submergence of the depth measuring device to accurately correct depth;

- Ensure that the ship's path coincides with the cross-sectional plane;

- When using echo-sounding equipment for depth measurement, conduct measurements during times of minimal waterway traffic.

1.2.2.2.6. Measuring river width

a) Measure river width by determining the distance from the starting point to both riverbanks (left bank, right bank) using a machine or tape measure, calculated as the difference between the distances from the starting point to both riverbanks. Each cross-section must be measured at least twice, with a difference in results of no more than 1%;

b) If the wetted cross-section has still water, determine the distance from the starting point to the boundary of the still water and the depth at the boundary of the still water.

1.2.2.3. Velocity measurement

1.2.2.3.1. Principles of velocity measurement

a) Water levels must be observed at the start and end of velocity measurements;

b) Measure the slope of the water surface;

c) Measure the width of the water surface;

d) Observe weather phenomena, wind direction, wind speed, and other related phenomena, and record them in the flow measurement logbook;

e) When there is still water near the bank, determine the distance from the starting point to the boundary of the still water and the depth at the boundary of the still water.

1.2.2.3.2. Velocity sounding lines

Conducted according to the provisions of Article 6.3.3.2 in TCVN 12636-8:2020 Meteorological and Hydrological Observation - Part 8: River Flow Measurement in Non-Tidal Areas.

Pursuant to Article 6.3.3.3 of TCVN 12636-8:2020 on Meteorological and Hydrological Monitoring - Part 8: River Flow Monitoring in Non-Tidal Areas.

1.2.2.3.4. Measurement Method for Water Velocity

1.2.2.3.4.1. Measuring Water Velocity Using a Current Meter

a) Requirements for Measuring Water Velocity with a Current Meter

Ensure the general principles for measuring water velocity as stipulated in Point 1.2.2.3.1, Appendix B, of this Standard, in addition, the following principles must be adhered to:

- Determine the depth at the measurement point for water velocity;

- Measure the distance from the water edge (left bank, right bank) to the starting point;

- Inspect the facilities, equipment, and devices before measurement to ensure safety and accuracy;

- The current meter can only be used within its permitted range, selecting appropriate types of current meters and propellers based on the velocity;

- When the water level changes rapidly (the difference between the beginning and end levels exceeds 20 cm), in addition to monitoring the water level at the start and end of the measurement, monitor the water level at the time of measuring water velocity at the 0.6h point of each measurement section;

b) Arrangement of Measurement Points on the Velocity Measurement Section

- Arrange measurement points according to the depth of the section, denoted as h, measured in meters (m):

+ For depths less than 1.00m, measure using a single-point method at either the 0.2h or 0.6h point;

+ For depths ranging from 1.00 to 3.00m, use a two-point or three-point method;

If using a two-point method, measure at the 0.2h and 0.6h points.

If using a three-point method, measure at the 0.2h, 0.6h, and 0.8h points.

+ For depths greater than 3.00m, use a five-point method at the surface (0.0h), 0.2h, 0.6h, 0.8h, and bottom points.

- Arrange measurement points based on research objectives: To understand the horizontal velocity distribution at a newly operational station or to study reducing measurement points on the section. In such cases, multi-point measurements must be conducted, and the arrangement of points does not depend on the depth but the distance between points should not be less than 1.5 times the diameter of the propeller or rotating cup of the current meter, which should not touch the riverbed.

c) Measurement Methods

- The duration of measuring water velocity at a single point using a current meter should not be less than 100 seconds;

- When the current meter is mounted on a pole, the pole base must be equipped with a stand and kept vertical during measurement;

- If a cable is used to suspend the meter, measure the angle of cable deviation, increase the weight of the iron ball or change the cable to reduce the angle of cable deviation. If the angle exceeds 10 degrees, corrections must be made when calculating;^°- When lowering the current meter into the water, the winch head must extend at least 0.50m beyond the ship's side;

- Avoid strong impacts on the propeller or rotating cup of the current meter;

- During low-water periods, if the flow velocity is too low to measure with a current meter, select an auxiliary line for measurement. When measuring on the auxiliary line, still measure the water level on the main line. The auxiliary line must ensure there is no inflow or outflow of water;

- During flood periods, if the flow velocity fluctuates rapidly, simple measurement methods may be used. Develop simple measurement plans according to the provisions in Appendix B of TCVN 12636-8:2020 on Meteorological and Hydrological Monitoring - Part 8: River Flow Monitoring in Non-Tidal Areas.

1.2.2.3.4.2. Measuring Water Velocity Using a Floating Buoy

Pursuant to Article 6.3.3.4.2 of TCVN 12636-8:2020 on Meteorological and Hydrological Monitoring - Part 8: River Flow Monitoring in Non-Tidal Areas.

1.2.2.3.4.3. Measuring Water Velocity Using a Submerged Buoy

Pursuant to Article 6.3.3.4.3 of TCVN 12636-8:2020 on Meteorological and Hydrological Monitoring - Part 8: River Flow Monitoring in Non-Tidal Areas.

1.2.2.4. Calculating Flow Rate Using a Current Meter

1.2.2.4.1. Calculating Cross-sectional Area

Pursuant to Article 6.3.4.1 of TCVN 12636-8:2020 on Meteorological and Hydrological Monitoring - Part 8: River Flow Monitoring in Non-Tidal Areas.

1.2.2.4.2. Calculating Water Velocity Measured by a Current Meter

a) Calculating Velocity at Measurement Points:

- The water velocity at each measurement point on the cross-section is calculated using the formula:

n: Number of revolutions of the propeller per second;

Where:

R: Total number of revolutions;

s: Duration of measurement at one point, unit: seconds (s);

V: Velocity at the measurement point, unit: meters/second (m/s);

a: Coefficient, varies depending on the current meter;

b: Initial velocity of the current meter.

- If the direction of water flow is not perpendicular to the cross-section, adjust the measured velocity. Convert the measured velocity at the point to the velocity perpendicular to the cross-section using the following formula:

hc

V _{= V x cosα       (2)}where hc is the adjusted velocity at the measurement point on the cross-section;

Where:

V _{= V x cosα       (2)}V is the actual measured velocity at the point on the cross-section;

α is the angle formed by the flow direction and the direction perpendicular to the cross-section.

b) Calculating Average Velocity of the Cross-Section

Let V

0,0h_0,1hfor each specific service package in the service provision contract between the ISP and the customer._0,2hfor each specific service package in the service provision contract between the ISP and the customer._,...V0,9h_1,0hfor each specific service package in the service provision contract between the ISP and the customer._{be the velocities at the surface, 0.1h, 0.2h,...,0.9h, and bottom points respectively, then the average velocity of the cross-section is calculated as follows:}- When measuring at one point on the cross-section:

At the 0.2h point: V

 = K x V_tbwhere K is in the range of 0.78 to 0.84;_,...VAt the 0.6h point: V

 = V_tb0,6h_{- When measuring at two points:};

- The average velocity of the near-bank zone (without stagnant water) or the near-vertical-bank zone (Vb) is calculated using the following formula:

 = K x V

V_{The Standing Office of the Council for International Cooperation on Non-Governmental Organizations (Vietnam Friendship Association) is the agency responsible for receiving registration dossiers, leading, and coordinating with member agencies of the Council to examine dossiers and return results of reviews of registration dossiers of foreign non-governmental organizations in Vietnam.}where K is an empirical coefficient ranging from 0.80 to 0.90. At each station, practical testing is required to determine the accurate value of K. If testing is not possible, use K = 0.85._tb  (8)

- The average velocity of the near-stagnant-water zone (located between flowing water and stagnant water boundary), is calculated as follows:

tù

Where:

V _{is the average velocity of the near-stagnant-water zone (m/s);} is the average velocity of the cross-section adjacent to the stagnant water boundary (m/s).

V_tb- The average velocity of the zone between two cross-sections is the arithmetic mean of the average velocities of those two cross-sections.

V is the average velocity between two cross-sections n and n+1 (m/s);

Where:

tbn

V _{is the average velocity of cross-section n (m/s);}tbn+1

V _{is the average velocity of cross-section n+1 (m/s).}d) Average Velocity Across the Cross-Section

- The average velocity across the cross-section is calculated using the following formula:

mc

Where:

V_mcis the average cross-sectional velocity (m/s);

Q is the water flow rate at the cross-section (m³/s);³/s);

F is the cross-sectional area (m²);²).

If the cross-section has still water and only uses the flowing water area, the average velocity of the flowing water part of the cross-section is calculated as follows:

Where:

V_mcchis the average velocity of the flowing water part of the cross-section;

F_{c Qu}is the flowing water area, F is the cross-sectional area; F_{c Qu}is calculated according to the formula: F_{c Qu}= F - F_{organize credit institutions, foreign bank branches are responsible for organizing the implementation of this Circular.};

F_{organize credit institutions, foreign bank branches are responsible for organizing the implementation of this Circular.}is the still water area.

- If the still water area has a close and stable relationship with the water level, a table can be prepared in advance to calculate the water level with the cross-sectional flowing water area for convenience in calculating V_mcch.

1.2.2.4.3. Calculating Water Flow Rate

a) From the cross-sectional area and flow velocity, calculate the water flow rate using the following formula:

Q = F x V                       (13)

Where:

Q is the water flow rate (m³/s);³/s);

F is the cross-sectional area (m²);²);

V is the average cross-sectional velocity (m/s).

b) Partial water flow rate

The partial water flow rate equals the partial average velocity multiplied by the partial area.

q = V_bpx f_bp                    (14)

Where:

q is the partial water flow rate (m³/s);³/s);

V_bpis the partial average velocity for calculating the water flow rate (m/s);

f_bpis the partial area for calculating the water flow rate (m²);²).

c) Total cross-sectional water flow rate

The total cross-sectional water flow rate equals the algebraic sum of the partial water flow rates within the cross-section.

Where:

Q is the cross-sectional water flow rate (m³/s);³/s);

q_{international}is the partial water flow rate of the i-th part (m³/s);³/s);

V_{international}is the average velocity of the i-th part (m/s);

f_{international}is the area of the i-th part (m²);²);

V₁for each specific service package in the service provision contract between the ISP and the customer.₂, ..., V_nare the average velocities of the 1st, 2nd, ..., nth parts (m/s);

f₁, f₂, ..., f_nare the areas of the 1st, 2nd, ..., nth parts (m²);²).

1.2.3. Volume Measurement Method

1.2.3.1. Application Conditions

The volume measurement method is applied to small rivers and streams where there is no stagnant water, where the cross-section can be modified to obtain water flow into the channel, with a maximum water flow rate of 20 l/s.

1.2.3.2. Measurement Method

a) Measurement Procedure

- Measure water level;

- Determine measurement time;

- Measure water volume;

- Calculate water flow rate;

- Maintain measuring equipment and devices.

b) Measurement Method

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

- Determine measurement time:

+ Record the start and end times accurately to the second;

+ Measurement time is calculated as the difference between the end time and the start time;

- Measure water volume: Must ensure that all water flowing through the cross-section from the start to the end of the measurement is collected; the container must be safe and convenient for determining the water volume, not filled too full to avoid overflowing during operation;

- Observe and record weather phenomena, stream conditions, and events affecting the stream such as riverbanks, riverbed, vegetation growing in the riverbed, and riverbanks.

1.2.3.3. Calculating Water Flow Rate

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

Where:

Q is the water flow rate (l/s);

W is the water volume (l);

∆t is the measurement time (s);

∆t = t₂ - t₁

organize credit institutions, foreign bank branches are responsible for organizing the implementation of this Circular.₂is the end time;

organize credit institutions, foreign bank branches are responsible for organizing the implementation of this Circular.₁is the start time.

1.2.4. Measuring Water Flow Rate Using Acoustic Doppler Current Profiler (ADCP) Equipment

1.2.4.1. Selecting the Measurement Cross-Section

a) The cross-section for measuring water flow rate using ADCP should be selected where the riverbed is relatively flat and has little vegetation, avoiding local magnetic fields caused by structures like steel bridges, underwater cables, sunken ships, to prevent interference affecting the measurement data;

b) The shape of the cross-section should be parabolic, trapezoidal, or rectangular, avoiding asymmetrical shapes;

c) Ensure sufficient depth for normal boat and equipment operation.

1.2.4.2. Measurement Method

a) Measurement Procedure

- Prepare equipment, install machines and measurement devices;

- Measure water level, observe river surface conditions, determine water depth;

- Determine the distance from the right and left banks;

- Measure water flow rate;

- Transmit, encode data, transfer information (if assigned);

- Plot points on the correlation diagram Q = f(H), F = f(H), V = f(H), analyze correlations to determine measurement mode;

- Maintain equipment, machines, and measurement devices.

b) Measurement Method

- Before measurement, estimate the depth, maximum speed, and shape of the riverbed on both sides and obstacles (if any) to prepare measurement plans and set machine configurations;

- Must measure water level at the start and end of the measurement, locate the starting and ending positions;

- The ADCP device must be securely attached to the vessel, away from magnetic materials like iron and steel, ensuring it does not protrude above the water surface during measurement;

- Set up the device according to the manufacturer's instructions, with parameters suitable for each measurement position according to the type of equipment. In cases of other connections, follow established guidelines strictly. Ensure the computer connection with the device operates smoothly;

- Conduct a test measurement before the formal measurement to calibrate the device as required;

- Allow the device to stabilize for 1 to 2 seconds before starting data collection; during movement, the measurement device should align with the cross-section, minimize boat sway, maintain a steady and slower speed than the water flow, and avoid moving into shallow waters (depth less than 1.00 m). At the end of the measurement, reduce speed and hold the boat stationary for 1 to 2 seconds to ensure complete signal capture;

- Measure at least twice consecutively and check if the data is abnormal; if so, re-examine all steps and remeasure (If the cross-sectional area and water flow rate measurements differ by no more than ±5%, they are considered high quality);

- Record measurement logs, weather conditions, stream dynamics, and other phenomena in the measured section of the river.

1.2.5. Measuring Water Flow Rate Using Fixedly Installed Automatic Equipment

The method of measuring water flow using automatically installed equipment at representative cross-sections shall be carried out according to the simple measurement plan specified in Appendix B of TCVN 12636-8:2020 Meteorological and Hydrological Observation - Part 8: River Flow Measurement in Non-Tidal Areas. When measuring water flow with fixedly installed equipment, in addition to the requirements of the simple measurement plan and technical recommendations for each type of machine and equipment, the following requirements must also be met:

a) The installation location of the equipment must be convenient and safe for people and equipment during operation, maintenance, and repair, and should be selected in the main flow area;

b) Equipment must be securely installed and fixed to ensure accurate measurement in the main flow area and determine the total cross-sectional flow rate according to the purpose and requirements;

c) The results of water flow measurement using fixedly installed automatic equipment must be evaluated by comparing them with the actual total cross-sectional flow rate at least 30 times, evenly distributed across different water levels (low, medium, high), ensuring that 90% of the comparisons do not differ more than ±10% from the actual value to meet the requirements.

2. Technical regulations for measuring water flow in tidal river areas

2.1. Monitoring Schedule

Follow the provisions set forth in Appendix A of TCVN 12636-9:2020 Meteorological and Hydrological Observation - Part 9: River Flow Measurement in Tidal Affected Areas.

2.2. Monitoring Method

2.2.1. Methods for measuring cross-sections and water velocity

2.2.1.1. Procedure for observation

Follow the provisions set forth in point 1.2.2.1, Appendix B, of this standard;

2.2.1.2. Measuring cross-sections

Follow the provisions set forth in Article 6 of TCVN 12636-9:2020 Meteorological and Hydrological Observation - Part 9: River Flow Measurement in Tidal Affected Areas.

2.2.1.3. Measuring water velocity

2.2.1.3.1. Principles for measuring water velocity

1.2.2.3.1. Principles of velocity measurement

b) Must measure the cross-section;

c) When there is stagnant water near the shore, it is necessary to determine the starting distance to the boundary of the stagnant water and the depth at the boundary of the stagnant water, and must determine the depth at the cross-section where the velocity is measured;

d) When affected by strong tides:

- Measuring water velocity on the cross-section must have equipment to determine the direction of flow by depth;

- When measuring water velocity on multiple cross-sections (two or more cross-sections), they must be measured simultaneously at the same time;

e) During measurement, the measuring device must ensure that it does not protrude above the water surface or touch the riverbed.

2.2.1.3.2. Detailed measurement of water velocity across the entire cross-section

Follow the provisions set forth in Article 7.1.4 of TCVN 12636-9:2020 Meteorological and Hydrological Observation - Part 9: River Flow Measurement in Tidal Affected Areas.

2.2.1.3.3. Measuring water velocity using the representative line method

Follow the provisions set forth in Article 7.1.2 of TCVN 12636-9:2020 Meteorological and Hydrological Observation - Part 9: River Flow Measurement in Tidal Affected Areas.

2.2.1.4. Observing flow direction

Follow the provisions set forth in Article 7.1.5 of TCVN 12636-9:2020 Meteorological and Hydrological Observation - Part 9: River Flow Measurement in Tidal Affected Areas.

2.2.1.4. Calculating water flow

2.2.1.4.1. Calculating water flow when measuring detailed velocity across the entire cross-section

2.2.1.4.1.1. Calculating velocity

a) Calculating point velocity

Point velocity is calculated according to the provisions at paragraph a, point 1.2.2.4.2, Appendix B, of this standard.

Let V

Average velocity of the cross-section is calculated according to the provisions at paragraph b, point 1.2.2.4.2, Appendix B, of this standard.

- The average velocity of the near-bank zone (without stagnant water) or the near-vertical-bank zone (Vb) is calculated using the following formula:

Average velocity of the section is calculated according to the provisions at paragraph c, point 1.2.2.4.2, Appendix B, of this standard.

d) Calculating average velocity across the cross-section

Average velocity across the cross-section is calculated according to the provisions at paragraph d, point 1.2.2.4.2, Appendix B, of this standard.

2.2.1.4.1.2. Calculating water flow

Calculate sectional flow and cross-sectional flow according to the provisions at point 1.2.2.4.3, Appendix B, of this standard.

2.2.1.4.2. Calculating water flow when measuring velocity using the representative line method

2.2.1.4.2.1. Calculating average velocity of the representative cross-section

a) When the representative cross-section has only one line, the average velocity of the representative cross-section is the same as the average velocity of that line;

b) When the representative cross-section includes two lines, the average velocity of the representative cross-section is calculated as the arithmetic mean of the velocities of those two lines;

c) Calculate the average velocity of one line according to the provisions at paragraph b, point 1.2.2.4.2, Appendix B, of this standard.

2.2.1.4.2.2. Establishing a pre-calculated correlation table V=f(V)_mc = f(V_db) or V_mcch = f(V_db)

a) If measuring representative water velocity continuously over a long period and using the same correlation V_mc = f(V_db) or V_mcch = f(V_db), then establish a pre-calculated correlation table for the values of V_mc = f(V_db) or V_mcch = f(V_db);

b) Based on the range of use of the velocity of the correlation V_mc = f(V_db) to establish the table.

2.2.1.4.2.3. Calculating average velocity across the cross-section

Substitute the average velocity of the representative cross-section into the correlation equation V_mc = f(V_db) or look up the value in the pre-calculated correlation table V_mc = f(V_db) or look up on the correlation graph V_mc = f(V_db) to obtain the average velocity across the cross-section.

2.2.1.4.2.4. Calculating cross-sectional area

Look up the corresponding water level at the time of measuring velocity at the representative cross-section in the pre-calculated correlation table F=f(H) to obtain the cross-sectional area.

2.2.1.4.2.5. Calculating water flow

Where:

F is the cross-sectional area (m²);

V_mc is the average velocity across the cross-section (m/s);

F_{c Qu} is the cross-sectional area with flowing water (m²);

V_mcch is the average velocity across the cross-section with flowing water (m/s).

2.2.2. Measuring water flow using equipment based on the Doppler ultrasonic principle (ADCP)

Follow the provisions set forth in 7.2.1 of TCVN 12636-9:2020 Meteorological and Hydrological Observation - Part 9: River Flow Measurement in Tidal Affected Areas.

2.2.3. Measuring water flow using fixedly installed automatic equipment

Follow the provisions set forth in 7.2.2 of TCVN 12636-9:2020 Meteorological and Hydrological Observation - Part 9: River Flow Measurement in Tidal Affected Areas.

Annex C

(Provisions)

TECHNICAL REGULATIONS FOR MEASURING SEDIMENT FLOW

1. Measuring sediment flow

1.1. Simultaneous measurement of sediment flow and water flow

1.1.1. Conditions for application and general principles for simultaneous measurement of sediment flow and water flow

a) Application conditions

- Simultaneously measuring sediment flow and cross-sectional water flow;

- Measurement tools and sample containers are complete and functioning properly;

b) General principles

- Measure water level at the start and end of measurement. Measure water level at point 0.6h of each cross-section if the water rises or falls quickly;

- The sampling method at each cross-section must be uniform if the mixed horizontal surface sample is processed.

1.1.2. Monitoring sequence

a) Prepare sampling tools, equipment, and measuring devices;

b) Measure water level, observe river surface conditions, and locate depth sounding points;

c) Determination of the distance from the bank edge on both right and left sides;

d) Measure the depth of the vertical line for depth measurement and velocity measurement;

e) Calculate the depth and distribution of the depth for deploying the sampling device on the vertical line;

f) Collect water samples, determine the volume of the water sample, record the results;

g) Filter the water sample: Record, determine the filter paper number and volume, filter the sample;

h) Calculate the measured suspended sediment concentration;

i) Calculate the measured suspended sediment discharge.

1.1.3. Suspended Sediment Discharge Measurement Regime

1.1.3.1. For non-tidal river areas and tidal river areas during weak tide periods

1.1.3.1.1. Detailed Measurement Regime

a) Apply to new stations measuring suspended sediment discharge, detailed measurements of cross-sectional suspended sediment discharge must be conducted for the first three years to determine the distribution of suspended sediment in the cross-section, thereby deciding the number of vertical lines for measuring suspended sediment concentration when conducting normal, simplified measurements, and serving scientific research needs.

b) Detailed measurement of cross-sectional suspended sediment discharge is carried out simultaneously with detailed water flow measurement.

c) Number of measurements:

- During flood season, measure from 25 to 30 times, focusing on the beginning of the flood season, the largest flood of the year, and sudden floods with high suspended sediment concentrations;

- During dry season, measure from 8 to 10 times, with intervals between consecutive measurements not exceeding 30 days.

d) At least 20% of detailed measurements must be arranged using the point accumulation measurement method.

1.1.3.1.2. Normal Measurement Regime

a) After three or more years of detailed cross-sectional suspended sediment discharge measurement, research should transition from detailed measurement to normal measurement as follows:

- From the data of suspended sediment discharge in the first three years, select some vertical lines from the detailed measurement lines to serve as normal measurement lines, using the data from these lines to calculate the normal suspended sediment discharge (R_bt);

- Establish a correlation between detailed suspended sediment discharge (R_{1 ct}) and normal suspended sediment discharge (R_bt). Draw the ± 5% and ± 10% range curves of the correlation R_{1 ct} = f(R_bt) as shown in Figure 1, if the correlation R_{1 ct} = f(R_bt) meets the following requirements:

+ At least 75% of the points lie within the ± 5% range;

+ At least 95% of the points lie within the ± 10% range;

+ Systematic error does not exceed ± 1%, then the selected normal measurement method meets the requirements.

- In cases where multiple arrangements of normal measurement vertical lines meet the above requirements, choose the arrangement with the smallest systematic error, or the most convenient measurement method;

- If the requirements are not met, re-evaluate and adjust the selection of vertical lines or increase the number of selected lines to ensure the requirements.

 

Figure 1. Correlation between detailed and normal suspended sediment discharge measurements

b) Number of measurements:

- During flood season, measure from 20 to 25 times, focusing on the beginning of the flood season, the largest flood of the year, and sudden floods with high suspended sediment concentrations;

- During dry season, measure from 5 to 8 times, with at least one measurement per month, and intervals between consecutive measurements not exceeding 30 days.

c) Vertical lines for normal cross-sectional suspended sediment discharge measurement coincide with those for normal cross-sectional velocity measurement;

d) At least 20% of normal measurements must be arranged using the point accumulation measurement method.

1.1.3.1.3. Simplified Measurement Regime

a) Vertical lines for suspended sediment discharge measurement during simplified measurement are also those used for simplified velocity measurement;

b) The simplified measurement regime is applied when measuring river flow using the simplified method or alternately with normal suspended sediment discharge measurement;

c) Establish a correlation between detailed suspended sediment discharge (R_{1 ct}) or normal (R_bt) and simplified suspended sediment discharge (R_đg)

- The correlation R_đg = f(R_bt) is established based on the normal measurement data of the previous three years, the correlation R = f(R) meets the following requirements:_đg = f(R_bt) meets the following requirements:

+ At least 75% of the points lie within the ± 5% range;

+ At least 95% of the points lie within the ± 10% range;

+ Systematic error does not exceed ± 1%, then apply the simplified suspended sediment discharge measurement regime.

- The correlation R_đg = f(R) is established based on the normal measurement data of the previous three years, the correlation R = f(R) meets the following requirements:

+ At least 75% of the points lie within the ± 5% range;

+ At least 95% of the points lie within the ± 10% range;

+ Systematic error does not exceed ± 1%, then apply the simplified suspended sediment discharge measurement regime.

d) At least 20% of total measurements must be arranged using the point accumulation measurement method.

1.1.3.1.4. Special Cases

If the correlation between the average cross-sectional suspended sediment concentration and the representative vertical line suspended sediment concentration (ρ_mc = f(ρ_db)) is poor, research must be conducted to find the cause, and the number of suspended sediment discharge measurements must be increased to accurately determine the correlation ρ_mc = f(ρ_db). Establish the correlation between the average cross-sectional suspended sediment concentration and the representative vertical line suspended sediment concentration (ρ_mc = f( ρ_db)) according to the provisions in Appendix D of TCVN 12636-10:2021 Meteorological and Hydrological Monitoring - Part 10: Suspended Sediment Monitoring in Non-Tidal River Areas.

1.1.3.1.5. Reducing the Number of Cross-Sectional Suspended Sediment Discharge Measurements

a) If the correlation ρ_mc = f(ρ_db) of the previous three years is relatively stable over the years, and the trend of the correlation ρ_mc = f(ρ_db) is systematically distributed and concentrated, reduce the number of suspended sediment discharge measurements as follows:

+ During flood season, measure from 15 to 20 times, focusing on the beginning of the flood season, the largest flood of the year, and sudden floods with high suspended sediment concentrations;

+ During dry season, measure 5 times, with intervals between consecutive measurements not exceeding 30 days.

b) If the measurement regime does not provide sufficient basis to accurately determine the correlation ρ_mc = f(ρ_db), increase the number of cross-sectional suspended sediment discharge measurements.

1.1.3.2. For tidal river areas during strong tide periods

a) Number of measurements:

- Stations measuring suspended sediment discharge for up to three years must arrange at least 20 measurements downstream and 15 upstream during each detailed water flow measurement period;

- Stations measuring suspended sediment discharge for more than three years must arrange at least 15 measurements downstream and 10 upstream during each detailed water flow measurement period.

b) Increase or decrease the number of measurements:

- If the measurement regime specified in paragraph a of this section does not provide sufficient basis to accurately determine the correlation ρ_mc = f(ρ_db), increase the number of cross-sectional suspended sediment discharge measurements;

- If the correlation ρ_mc = f(ρ_db) changes little and remains stable over a long period, it is permissible to reduce the number of cross-sectional suspended sediment discharge measurements.

1.1.4. Arrangement of Vertical Lines for Suspended Sediment Concentration Measurement

1.1.4.1. Principles of Vertical Line Arrangement

a) The water gauging stations measuring suspended sediment concentration shall be arranged to coincide with those measuring velocity when measuring water flow rate;

b) The arrangement of water gauging stations measuring suspended sediment concentration shall be based on the cross-sectional shape, changes in flow velocity, and distribution of suspended sediment concentration across the cross-section. The main channel shall have more gauging stations, while the overflow area shall have fewer at the bottom center;

c) The number of water gauging stations measuring suspended sediment concentration across the entire cross-section must be equal to or less than the number of gauging stations measuring velocity;

1.1.4.2. Number of Water Gauging Stations Measuring Suspended Sediment Concentration

a) For river sections unaffected by tides, follow the provisions set out in Article 6.1.3.2 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Flow Measurement in River Sections Unaffected by Tides;

b) For river sections affected by tides, follow the provisions set out in Article 6.1.3.2 of TCVN 12636-11:2021 Meteorological and Hydrological Observation - Part 11: Suspended Sediment Flow Measurement in River Sections Affected by Tides;

1.1.4.3. Positioning of Water Gauging Stations Across the Cross-Section

Follow the provisions set out in Article 6.1.3.3 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Flow Measurement in River Sections Unaffected by Tides;

1.1.4.4. Location of Representative Sample Water Gauging Stations

a) Representative sample water gauging stations must be selected from among the water gauging stations currently taking horizontal cross-sectional samples of suspended sediment, which represent the entire cross-section;

b) The location of representative sample water gauging stations must ensure convenience and safety for daily sampling;

c) The location of representative sample water gauging stations must have a strict correlation ρ_mc = f(ρ_db) as specified in Appendix D of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Flow Measurement in River Sections Unaffected by Tides;

d) In the first year of measuring suspended sediment concentration without existing data for analysis, the representative sample water gauging station should be chosen from among those located in the main flow or at the deepest point. After one year of measurement, research should be conducted to select the representative sample water gauging station;

e) If only one water gauging station is used to measure suspended sediment flow across the cross-section, that station will serve as the representative sample water gauging station;

f) If two water gauging stations meet the requirements for being representative sample water gauging stations, the water samples taken from these two stations should be combined to represent the entire cross-section;

1.1.5. Volume of Water Samples

Follow the provisions set out in Article 6.1.4 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Flow Measurement in River Sections Unaffected by Tides;

1.1.6. Sampling Water Across the Entire Cross-Section

Follow the provisions set out in Article 6.1.5.1 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Flow Measurement in River Sections Unaffected by Tides;

1.1.7. Direct Measurement of Suspended Sediment Concentration

1.1.7.1. General Principles

a) Equipment must be calibrated according to the manufacturer's technical guidance before use;

b) The suspended sediment concentration and turbidity at the measurement location must fall within the permissible range of the equipment;

c) Before using the equipment during periods of maximum, minimum, and average annual suspended sediment concentrations, the parameters of the equipment must be checked and adjusted to suit the measurement location;

1.1.7.2. Checking and Adjusting Equipment Parameters

a) For equipment directly measuring turbidity

- Simultaneously perform direct turbidity measurements and take samples to determine suspended sediment concentration to check the technical parameters of the equipment during periods of maximum, minimum, and average annual suspended sediment concentrations;

- The correlation between measured suspended sediment concentration and turbidity ρ_đ = f(N) must meet the requirement that at least 75% of the points lie within ± 10% of the mean curve and there are no systematic outliers;

 

Figure 2 - Correlation Between Suspended Sediment Concentration and Measured Turbidity

- Calculate the standard deviation σ_ρ of the correlation curve ρ_đ = f(N) using the formula:

Where:

ρ_{organize credit institutions, foreign bank branches are responsible for organizing the implementation of this Circular.} is the suspended sediment concentration read from the correlation curve ρ_đ = f(N) (g/m³);

ρ_đ is the suspended sediment concentration determined by water sample method (g/m³);

i is the index, i = 1 ÷ n;

n is the number of times suspended sediment flow is measured for calculation. If n is less than 30, the denominator in the above formula is calculated as n - 1;

- When the measurement error σ_ρ ≤ 10%, the equipment meets the requirements and can be used for data measurement;

b) For equipment directly measuring suspended sediment concentration

- Simultaneously perform direct suspended sediment concentration measurements and take samples to determine suspended sediment concentration to check the technical parameters of the equipment during periods of maximum, minimum, and average annual suspended sediment concentrations;

- The correlation between directly measured suspended sediment concentration (by machine) and suspended sediment concentration determined by sampling ρm = f(ρđ) must meet the requirement that at least 75% of the points lie within ± 10% of the mean curve and there are no systematic outliers;

- Calculate the standard deviation σ_{ρGranite, gabbro, decorative stone...} of the correlation curve ρ_{Granite, gabbro, decorative stone...} = f(ρ_đ) using the formula:

Where:

ρ_{Granite, gabbro, decorative stone...} is the suspended sediment concentration measured by machine (g/m³);

ρ_đ is the suspended sediment concentration determined by water sample method (g/m³);

i is the index, i = 1 ÷ n;

n is the number of times suspended sediment flow is measured for calculation. If n is less than 30, the denominator in the above formula is calculated as n - 1;

- When the measurement error σ_{ρGranite, gabbro, decorative stone...} ≤ 10%, the equipment meets the requirements and can be used for data measurement;

1.1.7.3. Measurement Methods

a) Mobile equipment for measuring suspended sediment concentration on rivers: Arrange water gauging stations according to Point 1.1.4, Appendix C, of this Standard;

b) Fixed equipment for measuring suspended sediment concentration: The suspended sediment concentration measuring equipment must be installed fixedly at the representative sample water gauging station, ensuring stability and security;

c) Transport the equipment to the measurement location, wait until the equipment stabilizes, then determine the suspended sediment concentration at the measurement location;

d) For equipment directly measuring turbidity: From the turbidity value (N) measured by the turbidity meter, use the relationship ρ_đ = f(N) to obtain the actual measured suspended sediment concentration (ρ_tđ).

1.1.8. Collecting Corresponding Representative Water Samples

Follow the provisions set out in Article 6.1.7 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Flow Measurement in River Sections Unaffected by Tides;

1.2. Measuring Suspended Sediment Flow Not Simultaneously with Water Flow Rate

1.2.1. Conditions for Application

a) When the number of times suspended sediment flow is measured exceeds the number of times water flow rate is measured across the cross-section, the excess measurements may use this method;

b) In cases where the Station lacks manpower;

c) When the water flow rate measuring equipment is damaged;

d) Measure water flow using automatic equipment;

e) For tidal-influenced river areas, this method shall only be applied when the water flow is uniform across the cross-section and flows in the same direction as during the water flow measurement.

1.2.2. Principles for Implementation

1.2.2.1. For sampling water to measure suspended solids content

a) Monitor water level at the start and end of the measurement;

b) Determine the positions of the right and left banks and the width of the water surface;

c) Measure depth at each sampling point;

d) Take water samples according to the depth integration method at each sampling point and take water samples according to the point integration method at the 0.5 h or 0.6 h points if the depth is less than 1 meter in cases of manual water flow measurement. In cases where water flow is measured using Doppler acoustic current profiler (ADCP) equipment, cable loop equipment, or fixed installation equipment, take water samples according to the depth integration method;

e) Take representative water samples at the representative sampling points;

f) Combine all water samples into a cross-sectional water sample for joint processing.

1.2.2.2. For direct measuring devices for suspended solids content

Follow the provisions set out in Point 1.1.7, Appendix C, of this Standard.

2. Daily Representative Water Sampling

Follow the provisions set out in Article 7 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Discharge Measurement in Non-Tidal Rivers. However, the water sampling regime shall be implemented as follows:

a) The daily representative water sampling regime for non-tidal rivers shall follow the provisions set out in Article 7.5 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Discharge Measurement in Non-Tidal Rivers;

b) The daily representative water sampling regime for tidal-influenced rivers shall follow the provisions set out in Article 7.5 of TCVN 12636-11:2021 Meteorological and Hydrological Observation - Part 11: Suspended Sediment Discharge Measurement in Tidal-Influenced Rivers.

3. Processing Water Samples

3.1. Principles for Processing Water Samples

a) Water samples must be processed promptly to determine the quantity of suspended solids, avoiding loss of water samples;

b) Water samples must be preliminarily processed at the sampling station (station) and then sent to the laboratory for further processing.

3.2. Processing Water Samples at the Station

Follow the provisions set out in Article 8.2 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Discharge Measurement in Non-Tidal Rivers. Additionally, implement the following filter paper regulations:

a) Filter paper must be thick and durable, insoluble in water, preventing fine particles from passing through, ensuring rapid filtration of water samples;

b) Filter paper, after drying, has minimal moisture absorption capacity;

c) Filter paper is cut into circular or hexagonal shapes with a diameter of 20 cm, weighed, dried, and the weight of each sheet determined, marked with information using pencil, and stored to prevent moisture;

d) Filter paper is weighed before use (initial weight) and after use (used weight) on the same scale to minimize errors.

3.3. Determining the Weight of Suspended Solids Sample in the Laboratory

a) Preparation work:

- Each piece of filter paper is folded into four (this applies to initial weighing);

- Place the filter paper in the oven, not exceeding 300 samples at a time;

- Dry silica gel and prepare desiccators.

b) Turn on the oven, ensuring that the temperature inside the oven remains constant at 105°C ± 2°C;⁰C ± 2^°c) Have a part that limits and excludes the impact of air contact or floating objects on the river;

c) Drying time is from 3 to 5 hours;

d) After drying the samples, place them in a desiccator to cool down before proceeding with weighing to determine their weight;

e) Weigh the filter paper with a minimum accuracy of 0.1 mg;

Note: Laboratory equipment such as ovens and analytical balances must be maintained and calibrated annually.

4. Calculating Suspended Sediment Discharge

Follow the provisions set out in Article 9 of TCVN 12636-10:2021 Meteorological and Hydrological Observation - Part 10: Suspended Sediment Discharge Measurement in Non-Tidal Rivers.

Appendix D

Product Name, Goods According to QCVN

SYMBOLS, UNITS OF MEASUREMENT AND SIGNIFICANT DIGITS

Table 1 - Symbols, Units of Measurement and Significant Digits for Water Flow Measurement

Table 2. Symbols, Units of Measurement and Significant Digits for Suspended Sediment Discharge Measurement

LIST OF REFERENCES

[1] Law on Meteorology and Hydrology No. 90/2015/QH13 adopted by the National Assembly on November 23, 2015 and effective from July 1, 2016;

[2] Decree No. 48/2020/NĐ-CP dated April 15, 2020 of the Government Amending and Supplementing Certain Provisions of Decree No. 38/NĐ-CP dated May 15, 2016 of the Government detailing certain provisions of the Law on Meteorology and Hydrology;

[3] Circular No. 26/2012/TT-BTNMT dated December 28, 2012 of the Ministry of Natural Resources and Environment Issuing National Technical Regulation on Hydrological Observation (QCVN 47:2012/BTNMT);

[4] Circular No. 05/2016/TT-BTNMT dated May 13, 2016 of the Ministry of Natural Resources and Environment, Regulations on Meteorological and Hydrological Observation Content for Stations Belonging to the National Network of Meteorological and Hydrological Stations.

[5] Circular No. 70/2015/TT-BTNMT dated December 23, 2015, of the Minister of Natural Resources and Environment stipulates technical requirements for the operation of automatic weather stations.

[6] 94 TCN 1-2003, Water Level and Water Temperature Monitoring Standards for Rivers

[7] River Flow Monitoring Standards for Large and Medium Rivers in Non-Tidal Areas (94TCN 3-90)

[8] 94 TCN 17-99, River Flow Monitoring Standards in Tidal Influence Areas

[9] 94 TCN 13-96, Suspended Sediment Monitoring Standards in Non-Tidal River Areas

[10] 94 TCN 26-2002, Temporary Suspended Sediment Monitoring Standards in Tidal Influence River Areas

[11] WMO Technical Regulations (WMO-No. 49), Volume III - Hydrology.