CIRCULAR

ON HYDRO-METEOROLOGICAL MONITORING FOR STATIONS WITHIN THE WITHIN THE NATIONAL NETWORK OF HYDRO-METEOROLOGICAL STATIONS

Pursuant to the Law on hydro-meteorological dated November 23, 2015;

Pursuant to the Decree No. 21/2013/ND-CP dated March 04, 2013 by the Government defining the functions, tasks, entitlements and organizational structure of the Ministry of Natural Resources and Environment;

At the request of the Director of the Department of Meteorology, Hydrology and Climate change and the Director of the Department of Legislation;

The Minister of Natural Resources and Environment hereby promulgates the Circular providing for the contents of hydro-meteorological monitoring for stations within the national network of hydro-meteorological stations:

Article 1. Scope of regulation

This Circular provides for the contents of hydro-meteorological monitoring for stations within the national network of hydro-meteorological stations as prescribed in Point b Clause 2 Article 13 of the Law on hydro-meteorological.

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This Circular applies to agencies, organizations and individuals relevant to the contents of hydro-meteorological monitoring of stations within the national network of hydro-meteorological stations.

Article 3. Interpretation of terms

In this Circular, these terms can be construed as follows:

1. A hydrographic line is a vertical line with definite location in the cross section of a river, a stream, a channel or a lake where hydrographic monitoring is performed.

2. A representative hydrographic line is one hydrographic line of hydrographic lines of the cross section which represents the whole cross section of one or several hydrographic elements.

Article 4. General provisions

1. The contents of hydro-meteorological monitoring for stations within the national network of hydro-meteorological stations include: monitoring elements, monitoring schedules and schedule of transmission of hydro-meteorological monitoring data.

2. In normal hydro-meteorological conditions, stations shall carry out the monitoring and transmit hydro-meteorological monitoring data according to regulations in Articles 6, 7 and 8 of this Circular.

3. For case of natural hydro-meteorological disaster, the National Hydro-meteorological Service shall intensify the hydro-meteorological monitoring and data transfer at the stations to satisfy the requirements for hydro-meteorological forecasting.

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5. Climate change monitoring stations which are those selected from hydro-meteorological stations are called referencing hydro-meteorological stations and independent climate change monitoring stations as follows:

a) A referencing meteorological station shall be selected from meteorology stations which strictly ensures the technical corridor of construction and represents a climatic zone of Vietnam and has been operated as a monitoring station for at least 30 years and has a capacity of long-term monitoring;

b) A referencing hydrographic station shall be selected from hydrographic stations which strictly ensures the technical corridor of construction and the natural flows of rivers in Vietnam and has been operated as a monitoring station for at least 30 years and has a capacity of long-term monitoring;

c) A referencing oceanographic station shall be selected from the oceanography station network which strictly ensures the technical corridor of construction and represents a coastal area or an island in Vietnams’ territorial waters and has been operated as a monitoring station for at least 30 years and has a capacity of long-term monitoring;

d) An independent climate change monitoring station shall be separately established in accordance with the national and foreign technical requirements and standards.

6. Time of hydro-meteorological monitoring and transmission of data thereof specified in this Circular shall be timed by the GMT +7 time zone.

Article 5. Stations within the national network of hydro-meteorological stations

Stations within the national network of hydro-meteorological stations specified in Clauses 17 and 18 of the Law on hydro-meteorological include:

1. Surface meteorological stations:

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b) Level 2 meteorological stations;

c) Level 3 meteorological stations.

2. Aerial meteorological stations:

a) Aerial survey stations;

b) Wind measuring stations;

c) Pilot wind measuring stations.

3. Weather radar stations.

4. Agro-meteorological station:

a) Level 1 agro-eteorological stations;

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c) Level 3 agro-meteorological stations.

5. Hydrographic stations:

a) Level 1 hydrographic stations;

b) Level 2 hydrographic stations;

c) Level 3 hydrographic stations.

6. Oceanographic stations:

a) Level 1 oceanographic stations;

b) Level 2 oceanographic stations.

7. Rainfall measuring stations.

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9. Climate change monitoring stations:

a) Referencing meteorological stations;

b) Referencing hydrographic stations;

c) Referencing oceanographic stations;

d) Independent climate change monitoring stations.

10. Specialized stations:

a) Radiation observation stations;

b) Ozone and ultraviolet radiation observation stations;

c) Stratified ozone monitoring stations;

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Article 6. Hydro-meteorological monitoring elements

1. Level 1 meteorological stations shall be in charge of monitoring the following elements:

a) Radiation;

b) Atmospheric pressure;

c) Surface wind;

d) Vaporization;

dd) Air temperature;

e) Earth temperature;

g) Maximum air and earth temperature;

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i) Humidity;

k) Rain;

l) Visibility;

m) Meteorological phenomenon;

n) Sunshine duration;

o) Cloud;

p) Past weather;

q) Current weather;

r) Earth condition.

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3. Level 3 meteorological stations shall be in charge of monitoring the elements specified in Point c to Point r Clause 1 of this Article.

4. Aerial survey stations shall be in charge of monitoring aerial elements, including:

a) Atmospheric pressure;

b) Air temperature;

c) Humidity;

d) Wind speed and direction.

5. Wind measuring stations are in charge of monitoring high wind by slides.

6. Pilot wind measuring stations are in charge of monitoring high wind.

7. Weather radar stations are in charge of monitoring the following elements:

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b) Cloud range;

c) Rain range;

d) Centripetal wind range.

8. Level 1 agro-meteorological stations shall be in charge of monitoring the following elements:

a) Meteorological elements specified in Clause 1 Article 6 of this Circular;

b) Earth temperature of deep earth layers, temperature of water in rice fields;

c) Humidity of earth at a depth of 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 cm;

d) Level of growth of plants;

dd) Productivity and quality of plants;

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g) Air temperature in plant niches;

h) Humidity in plant niches;

i) Disorder of air at air layers close to the earth;

k) Other elements in accordance with special monitoring programs.

9. Level 2 agro-meteorological stations shall be in charge of monitoring the elements specified in Point a to Point dd Clause 8 of this Article.

10. Level 3 agro-meteorological stations shall be in charge of monitoring the elements specified in Points a, d and dd Clause 8 of this Article.

11. Level 1 hydrographic stations shall be in charge of monitoring the following elements:

a) Water level;

b) Rainfall;

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d) Secondary elements: flow direction, wind, wave, river-bed change;

dd) Water flow rate;

e) Flow rate of suspended solids.

12. Level 2 hydrographic stations shall be in charge of monitoring the elements specified in Point a to Point dd Clause 11 of this Article.

13. Level 3 hydrographic stations shall be in charge of monitoring the elements specified in Point a to Point d Clause 11 of this Article.

14. Level 1 oceanographic stations shall be in charge of monitoring the following elements:

a) Surface wind of sea;

b) Visibility towards the sea;

c) Sea water level;

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dd) Sea surface status;

e) Sea water temperature;

g) Salinity of sea water;

h) Sea light;

i) Hazard meteorological and oceanographical phenomema and their development;

k) Flow of sea water.

15. Level 2 oceanographic stations shall be in charge of monitoring the elements specified in Point a to Point i Clause 14 of this Article.

16. Rainfall measuring stations shall be in charge of monitoring rainfall.

17. Lightning locating stations shall be in charge of monitoring the frequency and strength of lightning.

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a) Greenhouse gas;

b) Chemical and physical composition of the atmosphere;

c) Other elements in accordance with the special monitoring programs.

19. Referencing hydrographic stations shall be in charge of monitoring the elements like the selected hydrographic stations.

20. Referencing oceanographic stations shall be in charge of monitoring the elements like the selected oceanographic stations.

21. Independent climate change monitoring stations shall be in charge of monitoring the climate, analyzing the components of atmosphere and sea water level according to the request of the climate change monitoring programs.

22. Ozone and ultraviolet radiation observation stations shall be in charge of monitoring the elements:

a) Total amount of ozone;

b) Ultraviolet radiation intensity.

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24. Radiation observation stations shall be in charge of monitoring the elements:

a) Global radiation;

b) Direct radiation;

c) Diffuse radiation;

d) Global shortwave radiation;

dd) Global longwave radiation;

e) Shortwave reflection radiation;

g) Longwave reflection radiation.

25. Stations for receiving images from meteorological radars shall be in charge of record images of clouds.

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1. Level 1 meteorological stations shall perform monitoring 8 times per day, at 1 a.m, 4 a.m, 7 a.m, 10 a.m, 1 p.m, 4 p.m, 7 p.m and 10 p.m.

2. Level 2 and Level 3 meteorological stations shall perform monitoring 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m.

3. Aerial meteorological stations:

a) Aerial survey stations shall perform monitoring twice per day, at 7 a.m and 7 p.m or 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m;

b) Wind measuring stations shall perform monitoring 24/7;

c) Pilot wind measuring stations shall perform monitoring once per day, at 7 a.m or 1 p.m.

4. Weather radar stations shall perform monitoring 24/7.

5. Regarding Level 1, Level 2 and Level 3 agro-meteorological stations:

a) For elements specified in Point a to Point c Clause 8 Article 6 of this Circular, monitoring shall be performed 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m;

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6. Regarding Level 1 hydrographic stations:

a) For water level, monitoring shall be performed according to schedules specified in Annex 1 of this Circular;

b) For rainfall, monitoring shall be performed twice per day, at 7 a.m and 7 p.m, in dry seasons and 4 times day, 1 a.m, 7 a.m, 1 p.m and 7 p.m, in flood seasons;

c) For water temperature, monitoring shall be performed twice per day, at 7 a.m and 7 p.m;

d) For secondary elements, monitoring shall include the observation of water flow, wind direction, wind strength; river-bed change, plants growing in the river, the operation of all the irrigation works, human activities and shall be performed every 10 days, on the 5^th, 15^th and 25^th of every month;

dd) For water flow rate, monitoring schedule shall depend on the flow and level of tidal rivers and non-tidal rivers which are specified in Annex 2 of this Circular;

e) For amount of suspended solids, monitoring schedule shall depend on the flow and level of tidal rivers and non-tidal rivers which are specified in Annex 3 of this Circular.

7. Regarding Level 2 hydrographic stations:

a) The schedule of monitoring of water level, rainfall, water temperature and secondary elements shall be in accordance with the corresponding provisions at Points a, b, c and d Clause 6 of this Article;

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8. Regarding Level 3 hydrographic stations:

The schedule of monitoring of water level, rainfall, water temperature and secondary elements shall be in accordance with the provisions of Point a Clause 7 of this Article.

9. Regarding Level 1 and Level 2 oceanographic stations:

a) For elements specified in Point a, b, c, e and g Clause 14 Article 6 of this Circular, monitoring shall be performed 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m;

b) For elements specified in Point d and dd Clause 14 Article 6 of this Circular, monitoring shall be performed 3 times per day, at 7 a.m, 1 p.m and 7 p.m;

c) For the element specified in Point h Clause 14 Article 16 of this Circular, monitoring shall be performed twice per day, at 1 a.m and 7 p.m;

d) For the element specified in Point i Clause 14 Article 16 of this Circular, monitoring shall be performed 24/7;

dd) For the element specified in Point k Clause 14 Article 16 of this Circular, monitoring shall be performed every hour according to a specific schedule.

10. Rainfall measuring stations shall perform monitoring twice per day, at 7 a.m and 7 p.m, in dry seasons and 4 times day, 1 a.m, 7 a.m, 1 p.m and 7 p.m, in flood seasons.

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12. Referencing meteorological stations shall perform monitoring 8 times per day, at 1 a.m, 4 a.m, 7 a.m, 10 a.m, 1 p.m, 4 p.m, 7 p.m and 10 p.m.

13. Referencing hydrographic stations shall perform monitoring according to the schedule applicable to the selected hydrographic stations.

14. Referencing oceanographic stations shall perform monitoring according to the schedule applicable to the selected oceanographic stations, except for the monitoring water level, which shall be performed 24 times per day at exact hours.

15. Ozone and ultraviolet radiation observation stations shall perform monitoring continuously form the sunrise to the sunset.

16. Radiation observation stations shall perform monitoring 3 times per day, at 7 a.m, 1 p.m and 19 p.m.

17. Stations for receiving images from meteorological radars shall record images every 10 minutes.

Article 8. Schedule of transmission of hydro-meteorological monitoring data

1. Level 1 meteorological stations shall transmit SYNOP data 8 times per day, at 1 a.m, 4 a.m, 7 a.m, 10 a.m, 1 p.m, 4 p.m, 7 p.m and 10 p.m and transmit CLIM data at 7:30 p.m on the last date of every month and transfer CLIMAT data at 8 p.m on the last date of every month.

2. Level 2 and Level 3 meteorological stations shall transmit SYNOP data 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m and transmit CLIM data at 7:30 p.m on the last date of every month and transfer CLIMAT data at 8 p.m on the last date of every month.

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4. Weather radar stations shall transfer data 24/7.

5. Agro-meteorological stations shall transmit SYNOP data 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m and transmit Agromet data 3 times per month, at 7 p.m on the 10th, 20th and the last date of every month.

6. Level 1, level 2 and level 3 hydrographic stations on the List of those required to transmit data shall ensure that the data are transmitted immediately after a monitoring period.

7. Level 1 and level 2 oceanographic stations shall transmit data 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m.

8. Rainfall measuring stations shall transmit data twice per day, at 7 a.m and 7 p.m, in dry seasons and 4 times day, 1 a.m, 7 a.m, 1 p.m and 7 p.m, in flood seasons.

9. Lightning locating stations shall transfer data 24/7.

10. Ozone and ultraviolet radiation observation stations shall transmit data on the last date of every month.

11. Radiation observation stations shall transmit data once at 7 p.m.

Article 9. Organization of implementation

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2. General Director of National Hydro-meteorological Service shall:

a) Provide guidance for affiliated units on conduct and implementation of regulations in this Circular;

b) Establish and send the list of stations required to transmit hydro-meteorological monitoring data according to the requirements for forecasting, warning and transmission of hydro-meteorological data to other countries and to the Ministry of Natural Resources and Environment for consideration and decision.

3. Director of the Department of Meteorology, Hydrology and Climate change shall monitor the implementation of this Circular.

4. Ministries, ministerial-level agencies, People’s Committees of provinces and central-affiliated cities and relevant agencies and organizations are responsible for implementing this Circular.

Difficulties that arise during the implementation of this Circular should be reported to the Ministry of Natural Resources and Environment for solution./.

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ANNEX

(Enclosed with the Circular No. 05/2016/TT-BTNMT dated May 13, 2016 by the Minister of Natural Resources and Environment)

ANNEX 1

WATER LEVEL MONITORING SCHEDULES

1.1. Water level monitoring schedules must reflect sufficiently and obviously the change of water level. If water level fluctuates, depending on the change of each period, one of the following schedules shall be adopted:

1.1.1. Schedule 1: Monitoring shall be performed twice per day, at 7 a.m and 7 p.m, applicable to dry seasons in non-tidal rivers, periods when the gradient of water level in a day not exceeding 5 cm or at influenced stations of reservoirs having the gradient of water level in a day not exceeding 10 cm.

1.1.2. Schedule 2: Monitoring shall be performed 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m, applicable to periods when the gradient of water level in a day exceeding 5 cm but not exceeding 10 cm, like the beginning or end of dry seasons in non-tidal rivers or at influenced stations of reservoirs having the gradient of water level in a day exceeding 10 cm but not exceeding 50 cm.

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1.1.4. Schedule 4: Monitoring shall be performed 12 times per day, at 1 a.m, 3 a.m, 5 a.m, 7 a.m, 9 a.m, 11 a.m, 1 p.m, 3 p.m, 5 p.m, 7 p.m, 9 p.m and 11 p.m, applicable to periods when the gradient of water level changes significantly in a day, like the flood seasons in medium and large rivers influenced by diurnal tides with the gradient of water level not exceeding 100 cm or at influenced stations of reservoirs having the gradient of water level in a day exceeding 100 cm but not exceeding 200 cm.

1.1.5. Schedule 5: Monitoring shall be performed 12 times per day, at 1 a.m, 3 a.m, 5 a.m, 7 a.m, 9 a.m, 11 a.m, 1 p.m, 3 p.m, 5 p.m, 7 p.m, 9 p.m and 11 p.m. Besides, at the time of beginning or end of tide or flood, monitoring shall be performed every hour, applicable to monitoring route influenced by diurnal tides having the gradient of water level exceeding 100 cm and days when there is heavy flood in medium and large rivers.

1.1.6. Schedule 6: Monitoring shall be performed 24 times per day at exact hours, applicable to flood periods of small rivers and streams, at monitoring routes influenced by diurnal tides and remarkably by semi-diurnal tides or at influenced stations of reservoirs having the gradient of water level in a day exceeding 200 cm.

1.1.7. Schedule 7: Monitoring shall be performed 24 times per day at exact hours. Besides, at the time of beginning or end of tide or flood, monitoring shall be performed every 5 minutes, 10 minutes, 15 minutes or 30 minutes. The distance between two monitoring periods shall be determined according to the change of water level so as to monitor exactly the time of beginning and end of tide and the value of water level at such time, applicable to where the water level significantly influenced by tides and at small rivers and streams in flood periods.

1.1.8. Schedule 8: Monitoring shall be performed every 5 minutes, 10 minutes, 15 minutes or 20 minutes from the time of beginning or end of the flood. The frequency of monitoring of water level at the time of beginning of the flood shall be higher than that at the end of the flood. The frequency of monitoring of water level when the flood rises shall be higher than that when the flood is down. The distance between two monitoring periods shall be determined according to the change of speed of water level and the duration of the flood. The more significantly the speed of water level changes and the shorter the duration of flood is, the shorter the distance between two monitoring periods is in order to ensure the exact of value of water level at the beginning and the end of the flood and the transit points of the flood.

1.2. Regarding water level monitoring schedules for checking the water level measuring devices:

Upon the official decisions, water level measuring device installment works shall perform the water level monitoring. Pursuant to the operational quality, the specification and the location of the device and the researching requirements, monitoring schedules could be selected as follows:

1.2.1. Monitoring shall be performed at 7 a.m on the 5^th, 15^th and 25^th of every month, applicable to places without station houses, with stable works and well-operated devices, ensuring the continuity and exact. The use of automatic recording instruments shall accompany the application of multi-day schemes.

1.2.2. Monitoring shall be performed once a day, at 7 a.m, applicable to stations with well-operated devices and works to ensure that no error is committed during their operation.

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1.2.4. Monitoring shall be performed 4 times per day, at 1 a.m, 7 a.m, 1 p.m and 7 p.m, applicable to stations with newly constructed works or recently repaired devices.

ANNEX 2

WATER FLOW RATE MONITORING SCHEDULES

2.1. Regarding non-tidal rivers

2.1.1. For stations which have been established for under 3 years, monitoring shall be performed 12 to 15 times in dry seasons, where the distance between 2 consecutive monitoring periods shall not exceed 20 days, and 40 to 45 times in flood seasons.

2.1.2. For stations which have been established for 3 to 5 years, monitoring shall be performed according to the following table:

Times of monitoring

Hydraulic power schedule

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Faded

Influenced by flood

 Influenced by backwater

Influenced by landfill

Dry seasons

10

20-25

15-18

20-25

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Flood seasons

20

18-20

25-40

20-25

25-30

Throughout the year

30

38-45

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40-50

35-42

2.1.3. For stations which have been established for over 5 years, monitoring shall be performed according to the following table:

Times of monitoring

Hydraulic power schedule

Stable

Faded

Influenced by flood

Influenced by backwater

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Throughout the year

10-20

20-25

25-30

30-35

20-25

2.2. Regarding tidal rivers

2.2.1. Periods significantly influenced by tides

2.2.1.1. Diurnal-tide areas

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b) Schedule 2: monitoring shall be performed at every exact hour.

c) Schedule 3: monitoring shall be performed at every odd hour.

2.2.1.2. Semi-diurnal-tide areas and complex-tide areas

a) Schedule 1: monitoring shall be performed every 30 minutes (at 12 a.m, 12:30 a.m, 1 a.m and so on); before and after the time of highest speed of the falling or rising tide (when the tide is not rising, before and after the falling tide reaches the lowest flow speed) and at the time of change of tide flow, monitoring shall be performed every 15 minutes.

b) Schedule 2: monitoring shall be performed every 30 minutes (at 12 a.m, 12:30 a.m, 1 a.m and so on).

c) Schedule 3: monitoring shall be performed at every exact hour during the fall of the tide flow or every 30 minutes during the rise of the tide flow.

d) Schedule 4: monitoring shall be performed at every exact hour.

The abovementioned monitoring schedules which are applied shall be used during the whole tidal periods. For separate tides, monitoring shall be performed 1 to 2 hours before and after the tidal period. In case of complex tidal flow, the higher value shall prevail.

During the monitoring process, if the regulated monitoring schedules fail to reflect fully the flow conditions according to the requirements, the frequency of monitoring shall be considered increasing. Otherwise, if the changing rule of the flow is defined after a term of monitoring, the monitoring frequency may be decreased. When analyzing the change of monitoring schedules, the set requirements and the sufficient collection of exact data shall be ensured and the monitoring shall be performed well and efficiently. The change of monitoring schedules must be upon the approval of competent authorities.

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a) The number of measuring stages and the arrangement of the measurement of correlation between the average speed of the cross section (V_mc) and the average speed at the representative hydrographic line (V_db) to be used for monitoring periods using the method of representative lines shall be defined depending on the change of the correlation between V_mc and V_db. To be specific:

- For stations performing monitoring consistently for many years using the method of representative line:

+ Within 2 to 3 first years when the station has just been established, monitoring shall be performed 6 times per year, at the beginning, middle and end of flood seasons and dry seasons;

+ After 2 to 3 years of monitoring, if the correlation between V_mc and V_db of the flood season or dry season insignificantly and rarely changes (not exceeding ±5% different from the average line), monitoring shall be performed 2 times at the beginning and the middle of a dry or flood season;

+ After 5 years of monitoring, if the correlation between V_mc and V_db of the flood season or dry season insignificantly and rarely changes (not exceeding ±5% different from the average line), monitoring shall be performed once in the middle of a dry or flood season.

The correlation between V_mc and V_db of a flood season shall be measured once at the time when water reaches the highest or approximately highest level; that of the dry season shall be measured once at the time when the approximately highest flow speed is reached.

- For stations performing monitoring for several times per year using the method of representative line:

+ When monitoring for not exceeding 3 months in a dry season, the correlation between V_mc and V_db shall be measured in the middle of such monitoring period;

+ The monitoring for the whole of flood season shall be performed like the monitoring consistently for many years using the method of representative line;

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- For stations performing year-long monitoring, where the method of representative line is applied in dry seasons and the monitoring according to schedules is applied in flood seasons for the periods insignificantly influenced by the tides, the frequency of measurement of the correlation between V_mc and V_db shall be in accordance with that of stations performing the monitoring consistently for many years by the method of representative line. When arranging measuring stages, the measuring stage at the beginning of a dry season shall be performed when the flow speed is being high and that at the end of a dry season shall be performed when the flow speed becomes higher (turning to flood season).

- Increase and decrease of number of stages of measurement of correlation between V_mc and V_db:

+ The number of stages of measurement of the correlation between V_mc and V_db shall be increased in the following cases:

* The correlation between V_mc and V_db changes like dividing into bands of points or having abnormal shape. Additional measurement shall be arranged as soon as possible to promptly verify and decide on use of the results of such V_mc ~ V_db correlation measuring stage. If the quality of the measuring stage is not exact, re-measurement shall be promptly performed;

* The measuring route is raised or eroded or the main stream changes or there is an event that causes the change in the arrangement of flow speed and leads to the change in V_mc ~ V_db correlation. The number of additional measuring stages in such cases shall be in accordance with their impacts;

* Water level changes suddenly, for example when a great amount of water gathers in dry seasons or when water level falls down significantly in flood seasons. In such cases, additional measurement shall be promptly performed.

+ The number of V_mc ~ V_db correlation measuring stages shall be decreased in the following cases:

* The V_mc ~ V_db correlation rarely changes and stays stable for a long time. In such case, the station shall send reports and detailed proposal of the number of measuring stages;

* Abnormal cases where boats and ships should not stay on rivers during the measurement. In such cases, the station shall promptly send competent authorities report and an application for suspension of such measuring stage enclosed with an alternative plan;

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b) The arrangement of number of measuring times in a measuring stage of V_mc ~ V_db correlation:

- For newly constructed stations, a V_mc ~ V_db correlation measuring stage shall include more than 50 measuring times for falling tides and more than 40 times for rising tides and shall be distributed equally for 6 typical tidal periods (including 2 chronic tidal periods, 2 medium tidal periods and 2 strong tidal periods);

- Where the V_mc ~ V_db correlation changes insignificantly, measuring stage shall include more than 30 measuring times for falling tides and more than 30 times for rising tides and shall be distributed equally for 3-4 typical tidal periods (including 1 chronic tidal period, 1-2 medium tidal periods and 1 strong tidal period);

- If the V_mc ~ V_db correlation divides into bands of points (according to the level of flow speed or according to typical tidal periods), the measuring periods and times shall be increased according to specific reasons;

- If documents retained from multiple years show that the V_mc ~ V_db relation is close and stable and does not divide into different bands of points according to tidal periods, measurement can be performed consistently in several strong and medium tidal periods.

2.2.2. Periods insignificantly influenced by tides

2.2.2.1. Monitoring schedules for measurement of details

a) For detailed measurement which serves the analysis and determination of the number of hydrographic lines and the number of points measuring the flow speed in normal and simple measuring methods:

- In the first year (when the station has just been established), measurement shall be performed exceeding 30 times at different rates of water level and flow speed;

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b) For detailed measurement which serves the scientific research, the monitoring schedules shall be determined according to the researching purposes and requirements.

2.2.2.2. Monitoring schedules for normal or simplified measurement or measurement using mobile ships

The monitoring schedules shall be determined in accordance with the conditions of flood, tide and the conditions of the river area under the monitoring and the requirements of the modifying methods. For newly established monitoring routes, the monitoring schedules shall be preliminarily determined through survey results and relevant documents specified for each station. For stations which have performed monitoring for not less than 1 year, the monitoring schedules shall be determined as follows:

a) In periods when the monitoring route is extremely weakly influenced by tides or extremely significantly influenced by flood and the monitoring line shows that the water level changes mostly like that of non-tidal rivers when the tides is lightly fluctuate but the tidal level does not fall when flood is rising nor vice versa and the line presenting the relation between the water level and the water flow rate changes in round shape, the number and arrangement of measuring times are specified as follows:

- If the river bed is stable and the cross section is in control, monitoring for each flood shall be performed not less than 10 to 15 times, 4 to 7 times of which shall be when the flood rises and 6 to 8 times of which shall be when the flood falls. Such measuring shall be performed at the beginning of the flood, when the flood rises and when the flood reaches the highest level, evenly and alternately according to water level. When the water level changes within the scope of 30 cm, 1 time of measuring shall be performed. At places where a long spell of flood occurs, measuring shall be performed at least every 3 days;

- If the river bed is not stable, depending on the level of land raise of erosion, measuring times for each flood shall be increased by at least 1/3 of those applicable to stable river bed. Apart from the abovementioned provisions applied to cases where the river bed is stable, the arrangement of measuring times shall also depend on the change in the height of the river bottom. Where the height of the river bottom changes and makes its area ±5% different from that of the previous time of measurement having the same water level, the number of measuring times shall be increased.

b) When the monitoring route is weakly influenced by tides or significantly by flood and the water-level line changes like that of the upstream area of non-tidal rivers and it fluctuates according to the tides and the monitoring in multiple years presents that the bands of points presenting the relation between the water level and the water flow rate (H~Q) is narrow or not very large, modified by a single curve (like H~Q average line, H ~ , etc.), then the measuring times shall be determined and arranged depending on the stability of the relation line as follows:

- In every of the 2 or 3 first years of monitoring, only 1 single curve shall be handled. In every of the later years, 10 to 15 times of measurement shall be arranged for inspection. Such measuring times shall be arranged evenly according to water level and the timeline;

- If the single curve is handled in multiple years but not exceeding 1 curve is handled and not exceeding 1 modifying coefficient is used within 30 consecutive days, the measuring shall be performed every 2 days;

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- If the single curve is handled in multiple years but more than 2 curves are handled and more than 2 modifying coefficients are used within 30 consecutive days, the measuring shall be performed 2 times per day.

- The arrangement of measuring times shall be pursuant to the characteristics of the flood and the tide. To be specific:

+ On the basis of the water level and its change in the scope of 25 to 30 cm, measuring shall be performed at least once;

+ Every time of when at the beginning or end of a flood, when the flood rises or falls and when the flood reaches the highest level, measuring shall be performed once;

+ The measuring times when the tide rises or falls in any periods (the rise or fall of flood) must not fewer than 1/3 of the total measuring times; the ratio between the measuring times of the time when tide rises (or falls) and the total measuring times must be equivalent (or approximately equivalent) to the ratio between the time when tide rises (or falls) and the duration of a tidal period in the corresponding period. Concurrently, about 1/3 of total measuring times shall be performed at the time when water reaches the highest level (Q_max) or lowest level (Q_min) in the tidal period;

+ Measuring times shall be arranged evenly by time and shall be increased when the river bottom is significantly raised or eroded.

c) When the monitoring route is insignificantly influenced by floods and fairly significantly influenced by tides, presented on the water level line the significant change in tidal form and documents of multiple years show that the band of points of the H~Q relation is large and requires modification by backwater-effect method or other methods, measuring times and their arrangement shall be determined on the basis of the requirements for each. To be specific:

- If the modification documents of 2 years or more show that the modification results by single-curve method (like H ~ , etc.) are fairly suitable, the measuring times and their arrangement for cases insignificantly influenced by tides and significantly influenced by floods shall be applicable.

- If the modification documents of 2 years or more show that the modification results by equal-treatment method are fairly suitable, measuring shall be performed twice per day. At least 1/2 of total measuring times shall be performed at the beginning, end and at the time of Q_max and Q_min of the tidal period. Such measuring times shall be arranged alternately and evenly according to water level. If the river is significantly raised or eroded, the change in the height of the river bottom shall be supervised to consider increasing the measuring times.

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+ If only 1 V_mc ~ V_db relation line is used throughout the years, measuring shall be performed at least 15 times for examination. Such measuring shall be performed at the time of appearance of features of flood and/or tide and shall be arranged evenly according to water level and timeline;

+ If only 1 V_mc ~ V_db relation line is used per years, measuring shall be performed at least 40 times;

+ If 2 V_mc ~ V_db relation lines are used per years, measuring shall be performed at least 30 times for each line.

+ Arrangement of measuring times in case at least V_mc ~ V_{db ­}relation line is used per year:

* Arranging evenly according to the level of water flow speed and according to timeline. Measuring times for water with high flow speed shall be particularly more than others;

* There shall be measuring for when the flood is rising or falling at the beginning and end of the flood and at the beginning, end and at the time of Q_max and Q_min of the tidal period which are arrange alternately;

* It is required to analyze reasons of the point where the relation line curves or zigzags or at the point of joint with other relation line to consider increasing the measuring times;

* For periods when the amount of raise or erosion is significant, more measuring times shall be arranged.

d) During the period when the monitoring route is influenced by floods, tides and backwater of other rivers, the measuring times and their arrangement shall be specified in the table of annual water flow rate monitoring schedule of the station.

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- Measuring times shall be increased if the hydro power schedules of the monitoring route changes significantly like the sudden change of water schedules, the significant change of river bottom or when the measuring times and its arrangement does not satisfy the requirements.

- Measuring times shall be decreased if monitoring documents have been analyzed for at least 2 years, where the combination of floods, tides, river-bottom raise/erosion, the method of modification of documents about water flow rate through the years is stable, the rule of change of water flow has been under control and the following requirements are satisfied:

+ The new modification line is not exceeding ± 2% different from the old line of low water level and not exceeding ± 1% different from the old line of high water level;

+ The arrangement of measuring times is in accordance with the influence on the monitoring route: extremely significant influence of tides, extremely significant influence of floods; weak influence of tides, significant influence of floods; weak influence of floods, quite significant influence of tides and floods, tides and backwater of other rivers.

+ The greatest floods in the year is measured.

ANNEX 3

SCHEDULES OF MONITORING OF FLOW RATE OF SUSPENDED SOLIDS

Flow rate of suspended solids shall be calculated by the collection of water samples for determining the content of suspended solids and water flow rate. The schedules of monitoring of flow rate of suspended solids are the schedules of collection of samples of suspended solids. The collection of samples of suspended solids includes the collection of representative samples of water; collection of samples of water of the cross section and the collection of corresponding samples of representative water.

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3.1.1. Collection of samples of representative water

3.1.1.1. Flood seasons:

a) When the content of suspended solids slowly changes, representative samples shall be collected once a day at 7 a.m;

b) When the content of suspended solids change significantly, besides the representative water samples collected at 7 a.m, additional collection of water samples shall be conducted once, if the flow rate of suspended solids of the whole cross section is measured in the day, or twice, if the flow rate of suspended solids of the whole cross section is not measured in the day.

All the representative samples collected in floods seasons shall be processed separately.

3.1.1.2. For dry seasons: water samples shall be collected once a day at 7 a.m.

3.1.2. Water samples of the whole cross section and the corresponding representative samples shall be collected.

The collection of water samples of the whole cross section and corresponding representative samples is for calculating the flow rate of suspended solids which are actually measured and for determining the relation line between the suspended solids of the whole cross section and the content of the representative suspended solids.

3.1.2.1. For stations which have been monitoring suspended solids for not exceeding 3 years:

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b) For dry seasons: sample collection shall be conducted 8 to 10 times, at least once per month but the distance between 2 times of collection shall not exceed 30 days.

3.1.2.2. For monitoring stations which have been monitoring suspended solids for 3 years: the times of measurement of suspended solids shall be considered decreasing after researching and analyzing as follows:

a) For flood seasons: 15 to 20 times;

b) For dry seasons: 5 times, where the distance of 2 consecutive monitoring times does not exceed 40 days.

3.1.2.3. For other hydrographic stations, depending on the requirements for placement of monitoring stations, the measuring times of flow rate of suspended solids of the cross section may be in accordance with provisions applied to basic stations but monitoring shall be performed at least 5 times in dry seasons and 15 times in flood seasons.

3.2. Regarding tidal rivers

3.2.1. For periods when the river is insignificantly influenced by tides

3.2.1.1. Daily collection of representative water samples

a) For flood seasons:

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- When the suspended solid content changes quickly, representative water samples shall be collected twice per day at 7 a.m and 7 p.m;

- For great floods or for cases of extremely great amount of added suspended solids, the times of representative water sample collection shall be increased so that the development of the added suspended solid sources is determined;

- All the representative water samples collected in flood seasons shall be separately processed.

b) For dry seasons: representative water samples shall be collected at 7 a.m.

3.2.1.2. Water samples of the whole cross section and the corresponding representative samples shall be collected.

a) Detailed measuring process:

- For flood seasons: 25 to 30 times, focusing on beginning floods, the greatest floods of the year and irregular floods with great amount of suspended solids;

- For dry seasons: 8 to 10 times, at least once per month but the distance between 2 times of measurement shall not exceed 30 days.

b) Normal measuring process: when the flow rate of suspended solids on the cross season has been measured for 2 to 3 years, the detailed measuring process shall be considered transforming into normal measuring process. To be specific:

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- For dry seasons: 5 to 8 times, at least once per month but the distance between 2 times of measurement shall not exceed 30 days.

c) Simplified monitoring process: is applicable when measuring flow rate of river water using simple methods or measuring alternately with the normal measurement of suspended solids.

3.2.2. For periods when the river is significantly influenced by tides

3.2.2.1. Daily collection of representative water samples

a) For flood seasons:

- Water samples shall be collected twice per day: once when the flood is down, at the time when the flow is downstream and reaches the average speed when the tide falls; once when the flood rises, at the time when the upstream flow reaches the average speed when the tide rises. For stations influenced by semi-diurnal tide 4 water samples shall be collected: 2 of which shall be collected when the flood is down, at the time when the flow is downstream and reaches the average speed when the tide falls; the others shall be collected when the flood rises, at the time when the upstream flow reaches the average speed when the tide rises;

- When the flood turns great and there is no upstream flow, samples of water of when the flood rises of the tidal period and when the tide rises shall be collected.

b) Dry seasons:

- Water representative samples shall be collected once per day when the tide rises and the upstream flow reaches the average speed and once when the tide falls and the flow reaches the average speed of the same tidal period;

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3.2.2.2. Collection of water samples of the whole cross section and the corresponding representative samples:

a) Within the first 2 to 3 years when the flow rate of suspended solids are measured, each detailed measuring stage of water shall include more than 20 measuring times of suspended solids in downstream flow and more than 15 measuring times of suspended solids in upstream flow;

b) In the next years, monitoring shall be performed 15 times for suspended solids in downstream flow and 10 times for suspended solids in upstream flow;

c) Suspended solids at the time of tidal transfer when the amount of suspended solids is very small shall not be measured.

Thông tư 05/2016/TT-BTNMT quy định nội dung quan trắc khí tượng thủy văn đối với trạm thuộc mạng lưới trạm khí tượng thủy văn quốc gia do Bộ Tài nguyên và Môi trường ban hành