In December 2025, Khanh Hoa Provincial Police are investigating and reviewing the flood discharge operation procedures of reservoirs during the heavy rain last November.
One of the issues that the public is interested in is how lakes predict the amount of water coming, calculate the flood prevention capacity and implement flood discharge notices for localities.
Notify at least 6 hours in advance when operating flood discharge
Khanh Hoa currently has 64 reservoirs, of which 20 are located in the old Khanh Hoa province (ie the area north of Khanh Hoa today). Of these, there is only one hydroelectric reservoir, Eakrong Rou, with a capacity of 35.91 million m3, located in the west of Ninh Hoa.
The remaining 19 lakes are irrigation lakes directly managed and operated by Khanh Hoa Irrigation Works Exploitation Company Limited.
During the peak days of the flood in November 2025, two large lakes, Suoi Dau (32.78 million m3, in Cam Lam) and Am Chua (4.69 million m3, in the old Dien Khanh district) were forced to release floodwaters to ensure the safety of the project.
This water discharge is identified as one of the reasons why many areas in Dien Khanh and Nha Trang are deeply flooded, especially low-lying areas downstream of rivers.
According to Lao Dong's research, the water forecast for the lake is calculated by Khanh Hoa Irrigation Company based on rainfall bulletins provided by the Khanh Hoa Provincial Hydrometeorological Station.
The scenario used to calculate the most disadvantageous ie the entire forecast rainfall of the entire period (2 - 3 days) could plummet within 24 hours.
On that basis, the Company plans to regulate and lower the water level of the lake before heavy rain to create flood prevention capacity, and at the same time operate during the rainy - flood period according to the actual situation.
Every time the operation opens a floodgates, there must be a Notice sent to the People's Committees of communes, wards and related units, at least 6 hours in advance.
For 8 lakes with regulating valve gates (Hoa Son, Da Ban, Da Den, Suoi Dau, Cam Ranh, Ta Luc, Suoi Hanh and Am Chua), the flood prevention capacity is targeted at 10% - 15% of the designed capacity.
As a result, in two consecutive heavy rains, the lakes have created a total of 55.11 million m3 of flood prevention capacity (phase 1: 28.31 million m3; phase 2: 26.80 million m3).
When the rain exceeds the scenario
Although it has been calculated according to the most unfavorable plan, in fact, some times in November 2025 recorded unusually heavy rain, far exceeding the intensity of the entire period according to the forecast of the meteorological agency. The amount of water pouring into the lakes was faster and larger than the calculation scenario.
In this situation, Khanh Hoa Irrigation Works Exploitation Company Limited is forced to operate and regulate water through the flood discharge in accordance with the approved operating procedures. The goal is to ensure absolute safety for the dam, while minimizing the risk of deep flooding downstream.
The company organizes water regulation according to the principle: during the day (7am - 5pm) discharged with larger volume, at night (17am - 7am the next day) reduced volume. This is to limit the resonance effects of rainfall outside the basin and tides which often make downstream sensitive to the risk of flooding at night.
