Gate flow is limited, ecological water supply is insufficient

Jinchuan River, Qinhuai River, Xuanwu Lake and Crescent Lake (southeast moat) are the four major water systems in the main urban area of Nanjing. This year, the city will make them form a natural circulation through the water system project to improve the urban water environment. Luo Ying, professor senior engineer and deputy chief engineer of the Municipal Water Bureau, introduced that at present, these four water systems are connected to each other, and the water quality is still not good enough from the sense, the main reason is that the existing ecological water replenishment is not enough to "quench the thirst" of the urban river.

The capacity of the gate is small, and water diversion from Xuanwu Lake is limited

At present, the main source of water replenishment for Jinchuan River and Qinhuai River is Xuanwu Lake, from which water is replenished to the inland river through the gate. The original purpose of the gate is to discharge water, that is, to lower the water level of the lake after it exceeds its level.

Luo Ying said, every day, 280,000 tons of Yangtze River water enters Xuanwu Lake from the chemical fiber plant and the Shangyuanmen Water Plant. The water quality of Xuanwu Lake has reached the level of Ⅳ, which meets the requirements. However, the water quality of the inland rivers that rely on Xuanwu Lake for replenishment is only Ⅴ or poor Ⅴ. From Xuanwu Lake to the Jinchuan River, there is only one channel, the Dashugen Gate, which currently provides a maximum of 70,000 tons of water a day. Water supply to the Qinhuai River is mainly through the Wumiao Gate and through the Pearl River to the eastern section of the Qinhuai River. The maximum daily water supply of Wumiao Gate is 60,000 tons. The reporter saw that the design of the gate of Wumiao gate is a window edge, is a small grid, water flow is very limited.

In addition, Xuanwu Lake - Taipingmen gate - Zhu Bridge this water supply line, due to Jiuhuashan gully gate fault, is almost in a state of disuse. To open up this water supply channel, it is necessary to repair Jiuhuashan gully gate. Experts believe that 280,000 tons of Yangtze River water enters Xuanwu Lake every day, excluding evaporation from Xuanwu Lake itself, and the amount of water transferred into the river is about 250,000 tons, but the current daily amount is only about half. In the later stage, the city will further increase the amount of water replenishing from the Yangtze River to Xuanwu Lake, so the existing gate must be updated.

The water quality of the channel is poor, and the water attracted by it becomes dirty

In addition to insufficient water supply, the diversion channel pollution is not in place, poor water quality, is also leading to the water into the inland river can not make the river more clean another reason.

Reporters yesterday in the temple gate to see, from here out of the lake more clear, but to the pearl River, the river is dark green, liquidity is very poor. In the eastern section of the inner Qinhuai River, the water has been broadened and aerated to improve the water quality, making the water slightly lighter than the Pearl River. From the latest environmental protection department of water quality monitoring, the Qinhuai River water quality for Class V, although it has been non-black odor, but still not up to standard. East and West jade Belt River is located along Zhongshan East Road, is two very narrow river gully, reporters see, although there is no obvious floating objects in the river, but the water is very shallow, the water looks black. Water quality monitoring, the two rivers still have a slight black odor.

Xuanwu Lake water quality is up to the standard of Class IV water, but when it comes to the river course of the inland river, the water quality begins to decline, because of the water quality of the diversion channel is poor, not complete pollution interception, Pearl River, East and west Yudai River are so. In addition, the rain and sewage diversion project on both sides of the central Road near Da Shugen Sluicai has not been completed yet, and the sewage enters the diversion channel, leading to a decline in water quality.

The water diversion channel is single and the velocity is too slow

Nanjing's main river generally presents a characteristic, that is, the velocity is very slow. Luo Ying said that the faster the water flow in the river, the stronger the self-purification capacity, on the contrary, the slower the flow of the river, the more likely to form black odor. One reason for the slow velocity is that the main urban area of Nanjing is flat, and the river is affected by the terrain, so the flow is poor and the water quality is also easy to deteriorate.

In addition, the main city of Nanjing river water, and a single channel, mainly rely on Xuanwu Lake. At present, Nanjing's main river water quality is Class Ⅴ water, some even for poor class Ⅴ, the water quality itself is poor. Our city plans to divert water from grain River to supplement the southeast moat, but the water quality of grain River is poor, even if water replenishment is impossible to improve the water quality of the river.

The water department believes that the current Nanjing is carrying out the black and smelly river regulation project, must be carried out simultaneously with the construction of drainage standard areas, water system through the project, if the pollution is not in place, even if the river after dredding treatment to bid a bid for black and smelly, water quality still cannot reach the standard. After the completion of the rain and sewage diversion project, only rainwater and sewage are discharged into the river, and the natural circulation of the water system can the urban river really recover health.

Source: Nanjing Daily A4, March 9, 2017