On December 2, Mr. Truong Xuan Ty, Deputy Director of the Da Nang Department of Agriculture and Environment, explained why the city proposed adjusting Decision 1865 of the Prime Minister on the inter-reservoir operation in the Vu Gia – Thu Bon river basin (Procedure 1865).
Among the proposals, public attention was drawn to the suggestion to replace the phrase “xả lũ” (flood discharge) with “vận hành điều tiết qua tràn xả sâu” (regulated operation via deep spillway discharge) in Articles 28, 30, 31, and 34 of Procedure 1865.
Mr. Truong Xuan Ty, Deputy Director of Da Nang Department of Agriculture and Environment (Photo: Hoai Son).
According to Mr. Ty, Procedure 1865 outlines three stages for hydropower reservoir operation during the flood season. First, when a heavy rain forecast indicates potential floods, reservoirs are operated to lower their water levels to accommodate the incoming flood.
Second, if, while lowering water levels to accommodate floods, the inflow to the reservoir is large and downstream water levels are high, the operation must switch to maintaining the reservoir’s water level. This means the water inflow to the reservoir will equal the outflow from the dam.
Third, when the flood peak arrives at the reservoir and downstream water levels reach a point requiring flood reduction, flood reduction operations are implemented. In this stage, the discharge volume will be lower than the inflow volume to the reservoir.
Mr. Ty stated that current hydropower reservoirs are designed with two systems: free spillways and deep spillways. All three aforementioned stages are operated via the deep spillway system of the hydropower reservoir.
“The primary function of a deep spillway is flood regulation. Because we consider the reservoir operation procedure to be a state administrative document, requiring consistent terminology, we proposed adjusting the term ‘xả lũ’ (flood discharge) to ‘điều tiết qua tràn xả sâu’ (regulated operation via deep spillway discharge),” Mr. Ty explained.
Mr. Ty noted that this is merely a proposal from the city to the Ministry of Agriculture and Rural Development for consideration in adjusting Procedure 1865, and it still requires review from various parties.
Song Tranh 2 hydropower dam operating to gradually lower reservoir water level (Photo: A Nui).
Regarding the inter-reservoir operation procedure, Mr. Ty observed that the specified flood control capacity of hydropower plants in Da Nang is too small.
For instance, during the historic flood in late October, the total water inflow to reservoirs in the Vu Gia river system exceeded 1.68 billion m3, while the maximum flood control capacity of A Vuong, Song Bung 4, and Dak Mi reservoirs was only over 274 million m3 (16.3% of the total inflow), a very small proportion compared to the flood volume entering the basin.
The city will propose regulating the flood control capacity of reservoirs to the maximum possible extent. This would ensure that when floods occur, reservoir water levels are lowered as much as possible, creating optimal flood storage capacity to cut off flood peaks.
Previously, in a report sent to the Government, Da Nang city authorities recommended reviewing and revising the term “xả lũ” (flood discharge) to “vận hành điều tiết qua tràn xả sâu” (regulated operation via deep spillway discharge) in Articles 28, 30, 31, and 34, to ensure consistency with the practical operation of reservoir regulation.
According to Decision 1865 on the inter-reservoir operation procedure in the Vu Gia – Thu Bon river basin, issued in 2019, Article 28 stipulates the responsibilities of the Chairman of the People’s Committee of the former Quang Nam province and Da Nang city.
Article 30 outlines the responsibilities of the Minister of Industry and Trade. Article 31 outlines the responsibilities of the Minister of Agriculture and Rural Development (now the Ministry of Agriculture and Environment). Article 34 outlines the responsibilities of the reservoir owner.
