Over the past week, although water levels of the Yen River remained high, the salinity levels at the intake of raw water into the Cau Do (Red Bridge) Water Supply Plant have been increased rapidly. Currently, Da Nang’s functional units have been taking many feasible solutions to tackle salinity intrusion and ensure tap water supplies for the entire city during this year's summer with scorching days expected.

Although the water levels at the An Trach Dam always remain high, the gate valves have not been operated effectively in pushing the saltwater out of the Cam Le River at the intake of raw water into the Cau Do (Red Bridge) Water Supply Plant. Photo: HOANG HIEP

Abnormal saltwater intrusion

Unlike previous years, since the beginning of this year, the water levels upstream of the An Trach Dam on the Yen River in Hoa Tien Commune, Hoa Vang District, have been recorded reaching more than 2.2m, even regularly maintained at 2.3m-2.6m. This means that the water levels are always at least 0.2m higher than the overflow threshold of the valve gates of the An Trach Dam.

Theoretically, with such a water level, there is always a lot of fresh water overflowing through the valve gates to the Cam Le River to push the salinity out of the water.

However, the Cam Le River suffered from severe salt-water contamination again on March 23. At 5:00 p.m, the highest salinity level recorded at the Cau Do Water Supply Plant’s raw water intake on the Cam Le River was 373mg/l. At that time, water levels upstream of the An Trach Dam on the Yen River maintained from 2.3m-2.4 m.

The highest daily salinity level recorded at the Cau Do Water Supply Plant’s raw water intake increased to 952mg/l on March 25, and 1,196mg/l on March 28, whilst river water levels upstream of the An Trach Dam maintained between 2.2m and 2.5m.

As observation of our reporter, the valve gates of the Ha Thanh and Bau Nit dams in Dien Hoa Commune, Dien Ban Town, Quang Nam Province, have steel plates installed with the aim to raise the water levels upstream of the dams from 2m to at least 2.5m.

This explains the reason why the water levels upstream of the An Trach Dam on the Yen River has always been high since the beginning of 2022, but it also makes it difficult for the Cam Le River because there is almost no fresh water source flowing to the Qua Giang and Cai rivers to reduce salinity for the Han River.

On the other hand, Quang Nam Province built a temporary water dam on the Vinh Dien River in February 2022, so there is no fresh water source from the Thu Bon River to reduce salinity for the Han River.

At the 20-year-old An Trach Dam, when the water levels of the Yen River increase, 12 valve gates would have automatically tilted to allow more fresh water to flow to the Cam Le River in order push the salinity out of the water at the Cau Do Water Supply Plant’s raw water intake.

However, as noted, on March 28 morning, when the water levels upstream of the An Trach Dam was at 2.35m, only 3 valve gates No. 3, 9 and 10 were automatically tilted to allow more water to flow through.

Meanwhile, the valve gates No. 6 and 8 were stuck. The remaining 7 valves did not operate.

Moreover, a temporary water dam with sandbags on the Quang Hue River which runs through the province’s Dai Loc District has yet to be built.

All aforementioned reasons caused saltwater intrusion deep into Cam Le River and abnormal saline intrusion at the intake of raw water into the Cau Do (Red Bridge) Water Supply Plant.

The overflow threshold of valve gates at the Ha Thanh Dam in Dien Ban Town, Quang Nam Province, has been raised, making the water levels on the Yen River at upstream of the An Trach Dam be always high since the beginning of the year. Photo: HOANG HIEP

Urgent actions needed

Chairman of the Board of Directors of the Da Nang Irrigation Exploitation One Member Limited Liability Company Nguyen Anh Tuan informed that his company has repaired some damaged valve gates of the An Trach Dam.

“In the future, the An Trach Dam will be upgraded, so new valve gates will operate more effectively” added he.

Dr. Le Hung, a lecturer at the Faculty of Waterworks Construction, the University of Science and Technology - the University of Da Nang, said that this year, the salinity intrusion situation at the Cau Do Water Plant is slower than that in 2021, and the positive thing is that the water levels upstream of the An Trach Dam on the Yen River is higher because the functional units in Quang Nam Province have raised the overflow threshold of valve gates at the Bau Nit and Ha Thanh dams.

He, However, said because a temporary water dam has not been built on the Quang Hue River, a lot of water from the Vu Gia River flows to the Thu Bon River, resulting in prolonged salinisation in the near future.

Dr. Hung, therefore, stressed the need to continue to monitor and evaluate the effectiveness of raising the overflow threshold of valve gates at the Bau Nit and Ha Thanh dams, as well as soon construct a temporary water dam on the Quan Hue River to help reduce in the salinity levels of the Cau Do (Red Bridge) River.

Reporting by HOANG HIEP - Translating by M.DUNG