Recently, upon receiving forecasts of heavy rains in the Vu Gia - Thu Bon river basin and in localities, the City People's Committee and the City Civil Defense Command have directed large hydroelectric reservoirs such as A Vuong, Song Bung 4, Song Tranh 2, Dak Mi 4... to lower the reservoir water level to the flood level or the lowest flood level to create flood prevention capacity for downstream areas.
During the flood that occurred from November 16 to 20, for the first time, a reservoir was directed to be lowered below the lowest flood water level according to the regulations of the inter-reservoir operation process in the Vu Gia - Thu Bon river basin, that is Dak Mi 4 hydropower reservoir. The above has helped the owners of hydropower reservoirs have the conditions to operate and reduce floods for the downstream.
General Director of Dak Mi Hydropower Joint Stock Company Vu Duc Khanh said: “From the flood prevention capacity obtained before the flood, the company has forecasted and operated closely following the forecast of flood peaks that will occur to allocate reasonable flood prevention capacity for each flood peak. Not only the first flood, but all the following flood peaks have had a part of the flow reduced, so the level of flooding downstream has been limited to a certain extent.”
However, the recent floods have also caused some difficulties in the operation of hydroelectric reservoirs to cut and reduce floods downstream. For example, during the flood that occurred on December 3 and 4, although the hydroelectric reservoirs regulated floods through deep spillways with low flow, the water level of Cai River (Dak Mi) at Thanh My hydrological station still rose above the alarm level (BĐ) of 1 to 1.44 m; the water level on Thu Bon River at Tu Cau and Hoi An hydrological stations both rose above the alarm level and flooded some road sections in Hoi An ward.
Previously, in the flood that occurred from the night of November 16 to the afternoon of November 17, although Dak Mi 4 hydropower plant regulated the flood to overflow to the downstream of Vu Gia river with a flow rate of only 180-400m 3 /s, the flood level on Cai river (Dak Mi) at Thanh My hydrological station rose rapidly, 3 to 30cm higher than the alarm level on the morning of November 17. Because there are no hydrological or rainfall monitoring stations along the Cai river (Dak Mi) basin, about 40km long from the downstream of Dak Mi 4A hydropower dam to Ben Giang bridge as well as the Thanh river basin next door, it is impossible to confirm exactly which basin caused the natural flood due to excessive rain.
In fact, over the past years, because of the "blind spot" of flood sources outside the basins of hydroelectric reservoirs (such as Thanh River, Tien River, Dak Mi...), reservoir owners have encountered certain difficulties in operating and reducing floods downstream. In fact, the total basin area of Vu Gia - Thu Bon River from upstream to Ai Nghia and Giao Thuy hydrological stations is 9,005 km2, while the total basin area of 5 large hydroelectric reservoirs, A Vuong, Song Bung 4, Song Bung 2, Dak Mi 4 and Song Tranh 2, is only 4,355 km2 (accounting for 48.36% of the total basin area)...
Mr. Vu Duc Khanh acknowledged: “The upstream area of hydroelectric reservoirs has a very high density of rain gauge stations, especially in the upstream of Dak Mi 4 hydroelectric reservoir, there are up to 14 gauge stations, but in the downstream area and outside the basin of hydroelectric reservoirs, there are very few rain gauge stations, so it is impossible to assess the amount of flood water generated in this area. However, it can be seen that the impact of heavy rain from intermediate basins outside and below large hydroelectric reservoirs on the downstream area is very significant”.
Chairman of the Board of Directors of Water Resources Engineering Consulting and Development Joint Stock Company (WATEC) Van Phu Chinh said that, in the immediate future, the company is rearranging the data locations of rain gauge stations, river water level gauge stations, flood warning towers, and inundation warning towers according to each Vu Gia and Thu Bon river basin... so that units and localities can easily monitor and identify flood sources due to rain as well as current flood levels, in order to be proactive in flood regulation operations of reservoirs as well as flood response in downstream areas.
According to the Director of the Department of Management and Construction of Irrigation Works ( Ministry of Agriculture and Environment ) Nguyen Tung Phong, through the recent consecutive floods, it is necessary to improve the capacity to forecast and warn of rain, floods, inundation and connect and effectively exploit data from Vrain's rainfall monitoring systems, forecasting service providers, rain and flow models, and hydraulics.
Source: https://baodanang.vn/tang-cuong-nang-luc-du-bao-canh-bao-mua-lu-luu-vuc-vu-gia-thu-bon-3314205.html
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