Why has the Wuhan Guanshui level risen so fast?

　　Since the flood season this year, the Yangtze River Basin has suffered multiple rounds of heavy rainfall. As of the 11th, the whole section of the lower reaches of the Yangtze River under the supervision of the entire section exceeded the police. The Hydrology Bureau of the Yangtze River Commission predicted that the water level in the middle and lower reaches of the Yangtze River will maintain an upward trend in the next few days. On the 11th, a reporter from the Yangtze River Daily interviewed relevant persons in charge and experts from the Yangtze River Committee, the Water Resources Department of Hubei Province and the Wuhan Municipal Defense Office, and asked them to answer one by one.

Question: Why did the water level in the Wuhan section of the Yangtze River rise so fast?

　　On July 11, after many rounds of heavy rainfall, rainfall in Wuhan weakened, and the central urban area was dominated by small to moderate rains. However, the water level in Wuhan has increased rapidly compared with the day before yesterday. As of 21:00, the water level of the station reached 28.51 meters, which is equivalent to a rise of 0.39 meters in 24 hours. At 21:00 on July 4, the water level in Wuhan was only 26.15 meters, equivalent to a rise of 2.36 meters in a week.

　　Why is the Wuhan Guanshui water level rising so fast? Experts from the Forecasting Division of the Hydrology Bureau of the Hubei Water Resources Department introduced that this is mainly due to the “topping” effect of the upstream water from Dongting Lake and the water level of the downstream Poyang Lake. Dongting Lake and Poyang Lake are like two large "reservoirs" in the middle reaches of the Yangtze River, which can relieve the pressure of flood discharge in the upper reaches of the Yangtze River.

　　However, due to the recent heavy rainfall in the region, the water levels of these two lakes have exceeded the warning level, especially the Poyang Lake flood entered the Yangtze River to form a "topping" effect, and the flow rate of the Wuhan river section about 250 kilometers upstream has slowed down. The small and medium-sized rivers, lakes and reservoirs in Hubei flow into the Yangtze River, which naturally causes the water level of the Wuhan section to rise rapidly.

Question 2: How does the Three Gorges Project work?　　

　　It is reported that in order to alleviate the pressure of flood control in the middle and lower reaches of the Yangtze River, the water level of the Three Gorges has been continuously reduced. From 8:35300 cubic meters/second on July 6 to 82,000 22000 cubic meters/second on July 11th, the flood discharge channel was closed, and only the power generation water flow was retained, which effectively reduced the upper reaches of the Yangtze River into Wuhan.

　　Experts from the Hydrological Forecast Division of the Hydrology Bureau of the Yangtze River Commission said that in fact, after the Three Gorges reduced the outflow from the reservoir, the Wuhan water level closed at 10 days, which was only 0.09 meters higher than the previous day. The reason for forecasting water level rise is that on the one hand, in the next 3-5 days, there will be a heavy rainfall process from the west to the east of the Yangtze River Basin, and the incoming water into the main stream of the Yangtze River from Dongting Lake, Poyang Lake and Han River may increase; on the other hand, it is subject to heavy rain Affecting the increase of flow into the Three Gorges Reservoir in the upper reaches of the Yangtze River, as of 20 o'clock on the 11th, the water level has reached 150.50 meters, and the over-flood limit water level is 5.50 meters. According to the flood control schedule, the outflow from the reservoir may be increased to 39,000 cubic meters per second from the 12th. This flow generally arrives in the Wuhan river section 72 hours later, forming the high water level of Hongfeng.

　　At 12:00 on July 11, the Hydrographic Bureau of the Yangtze River Commission continued to issue orange warnings for floods in the section from Chenglingji to Hankou and Dongting Lake in the middle and lower reaches of the Yangtze River. It is estimated that in the next few days, the section from Hankou to Datong River will still increase by about 1 meter, and the section from Jiujiang to Hukou will exceed the guaranteed water level.

Three questions: How high will the water level in Wuhan pass?

　　Since June, the middle and lower reaches of the Yangtze River Basin have been continuously overcast and rainy, basically maintaining the status of "three days with one light rain and five days with one heavy rain". A major meteorological special report in Hubei Province stated that in the coming week, there will be three rounds of heavy rainfall in our province, and it is necessary to prevent the development of flood conditions and the disasters of rainstorms and floods.

　　This means that Hubei's "violent plum" will continue for a week. Will Wuhan's water level rise after 16 days? Experts from the Hydrology Bureau of the Yangtze River Commission said that at present, the high water level of the Yangtze River will continue for a long time. In addition to the spatial and temporal distribution of weather and rainfall, the water level is also affected by various factors such as flood storage and diversion.

　　"At present, we can forecast the water level of the Yangtze River stations in the next 5 days at most, and we will continue to encrypt consultations to revise the forecast conclusions." The expert said that hydrological forecast is divided into short-term forecast and medium and long-term forecast, while flood forecast is short-term forecast, Generally speaking, the shorter the time, the more accurate the forecast.

　　Experts from the Hydrology Bureau of the Hubei Provincial Department of Water Resources said that when the water level in Wuhan will “rise and fall”, it mainly depends on the future weather development situation, and it cannot be determined yet.

　　According to experts from the Wuhan Municipal Defense Office, Wuhan Zhengcheng is fully prepared to meet the floods in advance. The 808-kilometer embankment in Wuhan has been comprehensively reinforced since 2008. In particular, the Yangtze River main embankment was constructed in accordance with the highest flood level of 1.5-2 meters in 1954.

　　(Changjiang Daily reporter Chen Yongquan)