Building flood maps for rainy and stormy season

(Baonghean) - In Nghe An, almost every year from the beginning of mid-September to the end of November is the season of heavy rain, major floods, and continuous storms that cause many consequences. The average annual rainfall in Nghe An is from 2,000 - 2,200 mm. Of which, the rainfall during the rainy and stormy season alone accounts for 65 - 70% of the total annual rainfall; there are rains of up to 750 - 800 mm, causing widespread flooding in many areas of the province.

To proactively prevent, combat, and limit damage caused by heavy rains causing major flooding during the storm season, we need to proactively create a flood map before the storm season, so that from that map, localities can monitor the announcements of the Provincial Flood and Storm Prevention and Control Command, forecasts of the Meteorological and Hydrological Department on daily and periodical rainfall and the possibility of flooding at what level, in which area on the mass media, so that localities and people know in advance and proactively prevent early before major flooding occurs, especially when there is heavy rain accompanied by strong storm winds.

In our opinion, if building a flood map, it is necessary to base on the following 3 specific cases:

- Due to heavy rain, large amount of rain, strong intensity of rain, continuous rain duration, the consequence will be severe flooding for low-lying areas in coastal plains, riverbanks, streams, and basins in midland and mountainous districts.

Monitoring over many years in Nghe An shows that: If it rains continuously with rainfall of 100 - 120 mm, the whole province will have 11,000 - 12,000 hectares of summer-autumn rice flooded. If the rainfall reaches 180 - 200 mm, 32,000 - 34,000 hectares of rice will be flooded along with the traffic system. If the rainfall exceeds 300 mm or more, both the fields and houses in low-lying areas such as coastal plains and basins in mountainous districts will be submerged in water. Not only causing flooding in low-lying areas, heavy rain and strong rainfall intensity also cause unavoidable flash floods, landslides, etc. in mountainous districts.

- Flooding due to flood discharge or dam breakage can occur at large irrigation dams such as: Vuc Mau Lake in Hoang Mai Town, Ve Vung Dam in Yen Thanh, Khe Go Dam in Nghi Loc, Mo Da Dam in Do Luong, Song Sao Dam in Nghia Dan... and flooding can be caused by forced flood discharge at hydroelectric dams such as Ban Ve and Khe Bo Hydroelectric Reservoirs...

- Flooding due to rising sea levels when there are strong winds or super storms... This case is less likely to occur, but we must still be on guard. Because weather developments are increasingly sudden, extreme and dangerously unpredictable. The strong storm winds accompanied by rising sea levels can sometimes reach 8-10m or higher, depending entirely on the level of storm winds causing stress on the waves. The areas of rising water causing flooding are coastal areas and riverbanks on the right side of the storm's center.

Building a flood map for the above cases needs to be really detailed. To do so, the flood mapping agency is the provincial flood and storm prevention steering committee, which must coordinate with the Hydrometeorological Station, the flood and storm prevention committee and the Department of Agriculture and Rural Development of districts, cities and towns to investigate and survey historical data, collect information on the developments and consequences of heavy rains, causing severe flooding, or dam breaks, or flood discharges that have damaged crops, property and lives of people in all regions that have occurred over the past many years.

From the reality of the flooded area, the scale of the flooded area, the level of flooding, the time of flooding, the consequences of flooding (how many products of trees, animals, how many houses, how much other property, how many people died...), the levels of damage are all compared with historical data on the amount of heavy rain counted in each day, each rain period, each storm that directly or indirectly caused heavy rain are all available at the North Central Hydrometeorological Station (Vinh City). Regarding the level of flood discharge with the discharge flow in m3/second, the level of flooding occurring in the downstream area is all historical data recorded in irrigation and hydroelectric dams and the level of damage is all available in reports of the localities.

Building a flood map during the storm and flood season in Nghe An is something that needs to be done, should be done and will certainly be done to help the province and localities proactively direct the work of flood prevention and control in situations and developments of floods. This issue has now been addressed by many provinces such as Thai Binh, Ninh Binh, Quang Nam, Binh Dinh ... because these provinces are often heavily affected by the storm and flood season, so they have built a flood map to proactively prevent and control natural disasters during the storm and flood season...

Intelligence(Vinh City)