Why is Nhieu Loc - Thi Nghe canal dry in the rainy season?

During the peak days of the rainy season, Ho Chi Minh City has continuously recorded many deeply flooded streets after prolonged heavy rains. However, in contrast to this scene, people living along the Nhieu Loc - Thi Nghe canal witnessed the canal bed dry, exposed to mud and garbage.

The above contrast makes many people wonder: Why does the water level not rise during the rainy season, but on the contrary, the canal bottom is exposed?

Mr. Nguyen Thanh Tuong, living on Hoang Sa Street, shared: "The upstream canal near Bridge No. 1, the water has almost receded, only mud remains. There was a day when it rained all afternoon until evening, I thought the canal would be full of water, but unexpectedly in the morning the canal was dry, it looked very strange."

Nhieu Loc - Thi Nghe Canal upstream near bridge number 1, water drained in the middle of the rainy season. Photo: QUOC HUNG

According to Dr. Ho Long Phi, former Director of the Center for Water Management and Climate Change (VNU-HCM), the phenomenon of canals drying up in the middle of the rainy season is caused by low tides and the operation of the tide-preventing sluice.

Nhieu Loc - Thi Nghe Canal is no longer a natural flow, but a drainage canal system that has been renovated, embanked and dredged deeply, directly connected to the Saigon River through many regulating sluice gates.

Therefore, the water level in the canal is not stable but depends on the tidal regime and the operation of the sluice and pumping station. When the tide outside the Saigon River is low, the water in the canal will flow into the river, causing the water level to drop rapidly.

If at the same time, the sewer system is opened to discharge the accumulated rainwater in the city, the canal will drain even faster, leaving the "bottomless" scene after only a few hours.

“This is a cyclical phenomenon, associated with natural laws and technical operations, not unusual climate fluctuations. However, for local people, the image of a canal drying up in the middle of the rainy season still causes a strange feeling and concerns about environmental sanitation,” said Mr. Phi.

According to experts, in addition to tidal factors and sluice regulation, another reason why the canal appears “dryer” is due to infrastructure characteristics.

The Nhieu Loc - Thi Nghe canal has been dredged and widened, and both banks have been raised to increase capacity. Therefore, when the water level drops, the canal bottom is clearly exposed, creating the feeling that there is no water left. In many shallow sections of the canal, a lot of mud has accumulated, and when the water recedes, the mud is exposed, making people feel even more unusual.

Not only that, heavy rains also carry garbage and sand from the streets into the canals. When the water recedes, this layer of mud and trash is exposed, not only unsightly but also raises concerns about pollution.

Mr. Le Dinh Quyet, Head of the Forecast Department of the Southern Hydrometeorological Station, also gave a similar opinion. He said that the Nhieu Loc - Thi Nghe canal is dry due to the combination of low tides and proactive water discharge to prevent flooding.

“In recent days, the tide level on the Saigon River has dropped to a very low level, so the water in the inner-city canals has also dropped. When the tide goes down, the flow from the canal to the river is stronger, causing the water in the canal to quickly dry up. To avoid flooding, the sewer operator also opens the drain to release more rainwater. Therefore, it is normal for the canal to temporarily dry up,” Mr. Quyet analyzed.

Mr. Quyet also affirmed that this phenomenon only lasts for a short time. When the tide rises or the water discharge ends, the water level in the canal will recover.

According to Mr. Quyet, the Nhieu Loc - Thi Nghe canal drying up in the rainy season is not an abnormality of the weather. This is a regular and temporary phenomenon, but it still raises the issue that the city needs to calculate additional solutions to ensure flood prevention, limit the unusual situation of the canal "exposed bottom", and at the same time maintain the landscape value of the canal, which is considered the "green lung" in the heart of the city.

QUOC HUNG

Source: https://www.sggp.org.vn/vi-sao-kenh-nhieu-loc-thi-nghe-can-nuoc-giua-mua-mua-post812750.html