Circular No. 14/2021/TT-BTNMT on technical regulations for establishing water levels corresponding to flood warning levels

CIRCULAR

Technical regulations for establishing flood warning water levels

On the basis of Decision No. 36/2017/NĐ-CP dated April 4, 2017, of the Government stipulating the functions, tasks, powers, and organizational structure of the Ministry of Natural Resources and Environment;

Pursuant to Decision No. 05/2020/QĐ-TTg dated January 31, 2020 of the Prime Minister on flood warning water levels on rivers throughout the country;

At the proposal of the Director General of the National Centre for Hydro-meteorological Forecasting, the Head of the Science and Technology Department and the Head of the Legal Department;

The Minister of Natural Resources and Environment promulgates this Circular on technical regulations for establishing flood warning water levels.

PART I
GENERAL PROVISIONS

Article 1. Scope of Regulation

This Circular stipulates technical regulations for establishing flood warning water levels on river basins throughout the country.

Article 2. Applicability

This Circular applies to agencies, organizations, and individuals related to activities of establishing flood warning water levels on river basins.

Article 3. Explanation of Terms

In this Circular, the following terms are understood as follows:

1. Flood water level range is the difference value between peak flood water level and water level immediately before the flood rises.

2. Duration of maintaining flood water level grade is the period of time maintaining between two water level values during a flood, measured in hours.

Chapter II
TECHNICAL REGULATIONS

Article 4. Establishing flood warning water levels at flood reporting positions and hydrological stations

1. Collect meteorological and hydrological information, topographic data, and socio-economic characteristics, infrastructure.

2. Conduct surveys, measurements, and supplementary data collection.

3. Analyze flood characteristics, calculate flood classification, and prepare current flood inundation maps.

4. Calculate and simulate flood inundation maps and establish risk maps corresponding to flood warning water levels.

5. Analyze, evaluate, and determine the values of flood warning water levels.

6. Seek opinions from experts and relevant agencies and units.

7. Prepare a report on results.

Article 5. Collection of meteorological and hydrological information, topographic data, and socio-economic characteristics, infrastructure

1. Meteorological and hydrological data

a) Meteorological and hydrological data used to establish flood warning water levels must ensure a minimum of 30 floods including small, medium, large, and historical floods. In cases where data is insufficient, calculations, recovery, and extension of data series must be performed to meet the minimum length requirement;

b) Collected meteorological and hydrological data include: hourly rainfall, daily rainfall, hourly water levels of floods, flood bottom water levels, flood peak water levels, hourly flow rates of floods, maximum flow rates, and minimum flow rates of existing meteorological and hydrological stations in the area.

2. Topographic data

a) Cross-sectional and longitudinal profile data of river sections with flood reporting positions or hydrological stations requiring determination of flood warning water levels;

b) Topographic maps of areas with flood reporting positions or hydrological stations requiring determination of flood warning water levels, scale not less than 1:10,000;

c) Flood marks, remote sensing images showing flood inundation status (if available) in key areas affected by flooding in areas with flood reporting positions or hydrological stations requiring determination of flood warning water levels.

3. Socio-economic characteristics of areas with flood reporting positions or hydrological stations requiring determination of flood warning levels

a) Current population distribution, population density, demographic composition;

b) Current land use;

c) Current levee, reservoir, dam systems, drainage systems affecting river flow regimes in areas with flood reporting positions or hydrological stations requiring establishment of flood warning levels: levee elevations, dam peaks, normal water levels, reinforced water levels, designed flood discharge, size, type, form of flood discharge structures;

d) Current infrastructure status;

e) Local socio-economic development plans and programs.

4. Collect damage data caused by floods and inundations to residents, production, transportation, irrigation, construction infrastructure, and other economic and social damages.

5. Calculations, recovery, and extension of data series shall be carried out using one of the following methods:

a) Using similar watershed method: select a similar watershed with similar climatic conditions; synchronous correlation in flow fluctuations over time; uniformity in flow formation conditions, geology, soil, hydrogeology, forest coverage ratio, wetland ratio, and cultivation conditions within the watershed; no factors altering natural flow; the ratio of areas does not exceed five times, average elevation difference of watersheds not exceeding 300 meters; investigate synchronous changes in flow fluctuations of one or more similar watersheds and the calculated watershed according to actual measurement years, then select the watershed with the longest and most synchronized observation period as the similar watershed; establish watershed correlation relationships; only use correlation relationships to restore flow when the correlation coefficient is ≥ 0.8;

b) Hydrological and hydraulic modeling method: based on meteorological and hydrological data and topographical, geological conditions, cross-sections, select mathematical models to extend water level and runoff data series from rainfall. Implementation steps include: selecting rainfall data series; setting up the model; calibrating and validating the model for representative floods; calculating and extending runoff and water level data series from rainfall data series;

c) Using other methods (if applicable): based on specific project requirements and approved by competent authorities.

Article 6. Investigation, Surveying, and Supplementary Data Collection

Based on practical requirements, conduct investigations, surveys, and collect supplementary information and data to serve the construction of water levels corresponding to flood warning levels:

1. Investigate flood marks in areas with locations for flood warnings or hydrological stations that need to establish flood warning levels

a) Investigate and mark the confirmation of flood marks and flooding in areas with locations for flood warnings or hydrological stations that need to establish flood warning levels (determine flood marks on each object, coordinates of flood marks, time of flood occurrence, time of flooding due to floods, time of peak flood water level appearance);

b) Determine the coordinates of flood marks according to the national coordinate system VN-2000;

c) Refer elevations to flood marks according to the national elevation system.

2. Investigate the impact of floods on residents' lives, production, and economic and social activities, including the following main information:

a) Losses and impacts caused by floods and flooding corresponding to current water levels and flood warning levels, or losses caused by floods to residents, production, transportation, irrigation, infrastructure, and other economic and social losses;

b) The appropriateness of current flood warning levels in forecasting, warning, preventing floods and flooding, and developing the economy and society at the local level;

c) Recommendations and proposals for water levels corresponding to flood warning levels (if any).

3. Supplement cross-section and longitudinal profile measurements of river sections affected by or influencing the location of flood warnings or hydrological stations that need to determine water levels corresponding to flood warning levels. The selection of cross-section measurement locations should prioritize areas with flood warning locations or hydrological stations; river confluences and tributaries joining the main river; river bends where flow direction changes; areas with changing terrain and many alluvial plains; densely populated areas; locations near bridges and dams on the river.

4. Supplement topographic map information of areas affected by or influencing the location of flood warnings or hydrological stations that need to determine water levels corresponding to flood warning levels.

Article 7. Analysis of Flood Characteristics, Calculation of Flood Classification, and Creation of Current Flood Inundation Maps

1. Analysis of Flood Characteristics

a) Analyze and evaluate the natural and socio-economic characteristics of the river basin with locations for flood warnings or hydrological stations that need to determine water levels corresponding to flood warning levels, including at least the following contents: geographic location; topography; meteorological and climatic characteristics; distribution of population on both sides of the river; dike and reservoir systems affecting the flow regime; infrastructure systems on both sides of the river; local economic and social development orientation;

b) Analyze and evaluate flood regime characteristics: flood water level amplitude, flood intensity, duration of a flood event, duration of maintaining flood water level;

c) Analyze the impact of reservoirs and other structures on the flood regime (if applicable).

2. Calculation of Flood Frequency Curves and Flood Classification based on Peak Flood Magnitude: small, medium, and large floods.

3. Creation of Current Flood Inundation Maps

a) Contents of creating current flood inundation maps include: digitizing flood marks, supplementing digital terrain models after supplementary surveying, applying GIS technology to create flood inundation maps;

b) Current flood inundation maps must display at least the following basic layers of information: administrative boundaries, population, water systems, transportation, flood marks, flooding, structures, and other required information; minimum scale 1:10,000.

Article 8. Simulation and mapping of flood inundation and risk maps due to floods corresponding to water levels

1. Simulation and mapping of flood inundation corresponding to water levels

a) Determine the scope for simulating flood inundation corresponding to the location of flood warning or the hydrological station where flood warning levels need to be established;

b) Establish and connect hydrological models, reservoir regulation, hydraulic, and flood inundation models in the area where flood simulation is needed;

c) Calibrate model parameters for small, medium, large floods, and historical floods using water level data, flow rates, current flood inundation maps, and flood marks height;

d) Validate the model for small, medium, and large floods using water level data, flow rates, current flood inundation maps, and flood marks height; assess model errors;

đ) Create flood inundation maps corresponding to water levels at locations of flood warnings or hydrological stations where flood warning levels need to be established, with a minimum scale of 1:10,000.

2. Creation of flood and inundation risk maps corresponding to water levels

a) Select risk calculation methods for floods and inundations based on collected data on floods, inundations, topographic data, and related factors;

b) Determine flood and inundation hazards including: determining criteria to express flood and inundation hazards based on the results of flood and inundation simulation in Clause 1 of this Article; calculate and standardize flood and inundation hazards; create hazard level maps for floods and inundations;

c) Determine exposure to natural disasters from floods and inundations including: determining criteria for human, economic, social, and environmental exposure to floods and inundations; calculate and standardize data; create exposure level maps to natural disasters from floods and inundations;

d) Determine vulnerability to natural disasters from floods and inundations including: determining sensitivity and response capability criteria; calculate and standardize data; create vulnerability maps to natural disasters from floods and inundations;

đ) Create flood and inundation risk maps according to five levels (very low, low, medium, high, very high) corresponding to water levels, with a minimum scale of 1:10,000.

Article 9. Analysis, evaluation, determination of water levels corresponding to flood warning levels

1. Analyze, evaluate, and select water levels corresponding to flood warning levels based on the following conditions:

a) Water level corresponding to Warning Level I: belongs to the group of floods with a frequency below 50%; flood water begins to cause inundation in agricultural production areas, aquaculture, and low-lying riverbank areas; the risk level is very low to low, covering more than 80% of the area at risk on the flood and inundation risk map of the selected water level;

b) Water level corresponding to Warning Level II: belongs to the group of floods with a frequency between 55-25%; flood water causes widespread inundation in agricultural production areas, aquaculture, and starts affecting residential areas of the locality; the risk level is low to medium, covering more than 80% of the area at risk on the flood and inundation risk map of the selected water level;

c) Water level corresponding to Warning Level III: belongs to the group of floods with a frequency between 30-10%; flood water causes deep and widespread inundation in agricultural production areas, aquaculture, and many residential areas of the locality; the risk level is medium to high and very high, covering more than 80% of the area at risk on the flood and inundation risk map of the selected water level.

2. The water levels corresponding to flood warning levels must ensure consistency with the flood warning levels already established at various locations within the same river basin.

3. Based on calculation results and consultations with experts and relevant agencies and units, determine the water levels corresponding to flood warning levels.

Article 10. Consulting opinions from experts and relevant agencies and units

1. Consulting the opinions of experts on the appropriateness of water level values corresponding to flood warning levels through conferences, seminars, or in writing.

2. Consulting the opinions of the local disaster prevention and control agencies at all levels, specialized agencies, other relevant departments, the Regional Hydro-meteorological Station, or the Provincial Hydro-meteorological Station where the proposed flood warning location or hydrological station is situated regarding the appropriateness of water level values corresponding to the proposed flood warning levels in writing.

Article 11. Preparing the report on results

The report on results shall include the following main contents:

1. Legal bases.

2. Objectives and requirements.

3. The necessity of establishing flood warning levels.

4. Natural characteristics, population, socio-economic conditions, and infrastructure of the area for establishing flood warning levels.

5. Characteristics of river networks, streams, and hydrological regimes in the area for establishing flood warning levels.

6. Results of collecting, investigating, and supplementing information data, compiling investigation and survey information.

7. Results of calculating and determining flood warning levels and evaluating the appropriateness of flood warning levels, including:

a) Calculation methods;

b) Calculation results;

c) Evaluation of the appropriateness of flood warning levels;

d) Results of consulting and soliciting opinions from experts and relevant agencies and units (minutes and letters of comments attached);

e) Results of determining water levels corresponding to flood warning levels for each flood warning location or hydrological station.

8. Draft decision promulgating water levels corresponding to flood warning levels.

Chapter III

IMPLEMENTING PROVISIONS

Article 12. Implementation Organization

1. Ministries, ministerial-level agencies, People's Committees of provinces and centrally governed cities, and related agencies, organizations, and individuals are responsible for implementing this Circular.

2. The General Department of Hydrology and Meteorology is responsible for inspecting and guiding the implementation of this Circular.

Article 13. Effective Date

1. This Circular takes effect from October 15, 2021.

2. During the process of implementation, if there are difficulties or obstacles, agencies, organizations, and individuals are requested to promptly reflect them to the Ministry of Natural Resources and Environment for research, amendment, and supplementation as appropriate./.