Many contributing factors to severe flooding
In response to information that the widespread flooding in Nha Trang and Dien Khanh was due to simultaneous flood discharge lakes, Mr. Nguyen Thai Hung - Director of Khanh Hoa Irrigation Works Exploitation Company Limited - affirmed that this is an incomplete assessment.
According to Mr. Hung, the flooding in the two areas mentioned above in the recent flood was the result of many combined causes.
In this historic flood, extremely heavy rain - high tides - urbanization - new transport infrastructure are all factors appearing at the same time, creating deep flooding.
Firstly, during the rainy days, Khanh Hoa experienced very high tides. Floodwater from rivers flooded into the sea but could not drain strongly due to high tides, causing water to rise back and increasing the level of flooding in low-lying areas of Nha Trang and Dien Khanh.
Second, rapid urbanization has caused many natural ponds to be filled, and the urban drainage system is under great pressure.
The dense construction of urban areas, residential areas and administrative centers reduces the ability to contain natural water, leaving no space for rainwater to diffuse, leading to severe flooding during prolonged heavy rain.
Third, according to Mr. Hung, the expressways in Khanh Hoa have recently invisibly become "an elevated dike", blocking the natural drainage of many branches of rivers and streams.
In some areas, the amount of water from the branches poured in but was blocked by the highwaybed, leading to local stagnation, creating a long flooded spot.
20 reservoirs in Bac Khanh Hoa and flood discharge activities during peak flood season
Khanh Hoa currently has 64 reservoirs. Of which, 20 lakes are located in the old Khanh Hoa province (now north of Khanh Hoa). There is a hydroelectric reservoir, Eakrong Rou Lake, located in the west of Ninh Hoa (35.91 million m3 of water).
The remaining 19 irrigation lakes are directly managed and operated by Khanh Hoa Irrigation Works Exploitation Company Limited.
During the peak of flood season in November 2025, Suoi Dau lake (residue of 32.78 million m3, Cam Lam) and Am Chua lake (residue of 4.69 million m3, in the old Dien Khanh district) had to release floodwaters to ensure the safety of the dam.
This water discharge is identified as one of the reasons why many areas in Dien Khanh and Nha Trang are deeply flooded, especially in low-lying areas along the downstream of rivers.
Although managing 19 reservoirs, so far only Hoa Son Lake (old Van Ninh) has been installed with a flood warning tower to ring the whistle to warn people in Tu Bong area when releasing water.
Without a direct warning system, information to people in downstream areas still depends heavily on loudspeakers of communes, wards or through on-site forces.
Khanh Hoa Irrigation Company said that in 2026, the unit plans to install a flood warning tower at Suoi Dau Lake, in order to increase early warnings for people in affected areas.
In addition, the Company is also studying the placement of flood warning towers in residential areas downstream that have been flooded.
These points often have flood stains after each flood discharge, showing dangerous water level boundaries. Based on the amount of water released each year, the management unit will calculate to warn using both the flood warning horn system and loudspeakers and local radio stations.
The addition of flood warning towers is expected to help be more proactive in evacuation work, reducing pressure on the loudspeaker system - which is easily affected by heavy rain, power outages or poor signals.
