External flood and internal waterlogging influence each other, low-lying rainfall is concentrated, natural storage space is reduced, the original drainage system is old, and the emergency management level is insufficient
Multiple reasons cause frequent occurrence of urban waterlogging (Jintai sight·Focus on urban waterlogging ②)
The treatment of urban waterlogging concerns the safety of people's lives and property, and the right medicine can be prescribed only when the cause of the disease is found out.
Where is the crux of the frequent occurrence of urban waterlogging?
How to effectively solve the problem of waterlogging?
The reporters of this newspaper went to many places for research, interviewed relevant department heads, experts and scholars, etc., analyzed the underlying causes of urban waterlogging, and explored solutions.
The construction of a flood control and drainage system should fully consider the city’s natural geographical features and the impact of external floods
The reporter's investigation found that in some cities where waterlogging occurs frequently, most of them are affected by the dual effects of rainy climate and special topography, making drainage and drainage work more difficult.
In some places, precipitation is relatively concentrated, and because of the large number of rivers, the double pressure of "natural precipitation and upstream water" is assumed in terms of drainage and flood control.
The rainfall in Jiaxing City, Zhejiang Province from April to October accounts for about 70% of the annual rainfall.
During the rainy season each year, the north of Jiaxing is affected by the Taihu Lake and Taipu River, and the west is caused by the high water level of the inland river due to the upstream of Dongtiao River.
In Changsha City, Hunan, the urban terrain is high on all sides and low in the middle, and there are natural shortcomings for drainage and waterlogging prevention.
At the same time, the subtropical monsoon climate has led to relatively concentrated rainfall here, with frequent extreme heavy rainfall, and the same period of flooding, which further increased the pressure on flood control during the rainy season.
According to Hou Jingming, a professor at the School of Hydropower, Xi’an University of Technology, piedmont plain cities and coastal cities are all types of cities prone to waterlogging. “Jinan, Fuzhou, and Guiyang are all representatives of piedmont plain cities. Flooding in mountainous areas. As a representative of coastal cities, cities in the Pearl River Delta region are not only affected by local heavy rains, but are also vulnerable to severe impacts from upstream and downstream tides, which often leads to urban waterlogging."
Experts said that to build a flood control and drainage system, we should first fully consider the city's natural geographical features and the impact of external floods, and coordinate urban flood control and drainage, so that we can get twice the result with half the effort.
The urban impervious pavement area has increased, and the natural storage space has shrunk, making it more difficult to prevent and control waterlogging.
In addition to the large rainfall caused by natural conditions and the difficulty in draining waterlogging, the frequent occurrence of waterlogging is also due to urban construction.
Reader Feng Wenzhao said in his letter: "Compared with before, the city area is now larger, and there are more and more asphalt roads and cement roads. Large areas of concrete floors have poor water permeability. Even if the same intensity of rainfall is encountered, the urbanization is high. It’s easier to accumulate water."
Luo Pingping, a professor at the School of Water Conservancy and Environment of Chang'an University, believes that the increased coverage of urban impervious roads and concrete buildings reduces the amount of infiltration and interception of rainwater. When heavy rains come, the speed of stagnant water flow increases, making it easier to form Waterlogging point.
In fact, the highly permeable surface of ponds, lakes, and farmland are "natural storage tanks", which help rainwater seep into the ground and reduce surface water accumulation.
With the continuous advancement of urbanization, some natural storage spaces such as rivers and lakes have been filled and occupied, which objectively intensified the pressure on flood prevention.
Some readers wrote that in the 1980s, both banks of Liedeyong in Tianhe District of Guangzhou were basically farmland. By 2009, both banks of the river were covered by various buildings and roads, and the frequency of waterlogging increased greatly.
To deal with the waterlogging factors in the process of urbanization, it is necessary to effectively deal with scientific planning and design.
The reporter's investigation found that some cities did not fully consider this aspect in the planning and construction process.
When constructing roads, some cities cut off dozens of kilometers of natural drainage routes. The two sides of the roads are only connected by culverts, and the drainage changes from "lines" to "points", which increases the pressure of flood drainage and flood discharge.
In some places, when planning traffic in low-lying areas, the risk of waterlogging is not fully considered, and the tunnel plan is blindly adopted to bury hidden dangers.
Chen Wenlong, Dean of the Pearl River Water Conservancy Research Institute, said: “When a tunnel is built in a low-lying area, once it encounters heavy rains, or the river rises rapidly or even overflows, it is easy to cause the tunnel to be submerged by accumulated water and cause casualties. From the perspective of flood control, the terrain Traffic in low-lying areas should adopt the viaduct scheme."
In addition, when cities are formulating plans and important project plans, the impact of flood disasters is not comprehensive enough to demonstrate, and important projects are selected in urban low-lying areas and other high-risk areas of flood disasters.
Urban construction is a systematic project, and the upgrading and reconstruction of the drainage system should be considered and planned as a whole
In response to the natural formation and waterlogging factors in the process of urbanization, various localities and departments have vigorously promoted the construction of drainage and waterlogging prevention facilities, and positive progress has been made in urban waterlogging management.
However, judging from the "China Flood and Drought Prevention Bulletin" published by the Ministry of Water Resources, there are still frequent occurrences of urban waterlogging. The reason is that on the one hand, the impact of the increase in extreme weather, on the other hand, the improvement of the drainage system requires a more comprehensive approach. Long process.
Existing drainage facilities are designed in accordance with the standards of the time. Low standards and aging drainage facilities are a problem in many cities, especially in the old city.
Zhao Deping, deputy director of the Drainage Management Office of the Urban and Rural Construction Bureau of Hefei City, Anhui Province, said: “The drainage systems of the new urban area and the old urban area were constructed in different periods. The national norms and standards are constantly updated, and the construction standards for urban drainage facilities are also improving simultaneously. There are certain differences, and the existing facilities cannot meet the newly revised standards." In Xuancheng City, Anhui Province, the drainage pumping station in the old city is aging, and rainwater is often unable to drain, resulting in waterlogging.
In the past few years, six drainage pumping stations have been newly built or renovated locally, which has improved the drainage capacity of the old city to a certain extent.
The reporter learned in Changsha that most of the underground drainage system in the old city is a combination of rain and sewage. Rainwater and sewage are discharged through the same channel. In heavy rain, waterlogging is prone to occur.
In recent years, in consideration of environmental protection, Changsha City has carried out sewage interception transformation on the rain-sewage combined pipeline, requiring rainwater and sewage to be treated in the plant before it can be discharged.
In the event of heavy rain, the pressure of sewage treatment plants is often doubled because the amount of rainwater far exceeds the amount of sewage, and it is difficult to cope with the instantaneous peak pressure even when operating at full load, which leads to the formation of water accumulation points in some low-lying areas.
All regions and departments attach great importance to the "historical debts" of the drainage system, and have introduced many plans and measures, but the upgrading and transformation of the drainage system will not be accomplished overnight, and there are still many practical difficulties that need to be carefully studied and properly resolved.
In recent years, Xi'an, Shaanxi has built pilot projects for "sponge cities" in some areas, which has solved some water accumulation problems.
However, Xi’an has a long history and complex underground conditions. In addition to drainage pipes, water supply pipes, power supply lines, network lines, etc., there are also some cultural relics, which increase the difficulty of upgrading the underground drainage network.
"Urban construction is a systematic project, and drainage system reconstruction cannot be carried out in isolation. The lack of coordination in advancing work will restrict or even weaken the ability to drain water," said Fan Qi, a reader from Anyang City, Henan Province.
Zeng Shifan, deputy director of the Municipal Facilities Maintenance Center of Yuelu District, Changsha, believes that in the process of urban development, the lack of synchronization between surface development and underground pipe network construction is also an important reason for the formation of urban waterlogging. “In some places, there has never been water accumulation in the past, but In the process of subway construction, the original underground drainage box culvert was relocated and reconstructed, but waterlogging formed."
The impact of waterlogging is closely related to the level of urban emergency management, and early warning and monitoring should be strengthened, and emergency plans should be improved
In addition to natural geography and urban construction, the impact of waterlogging on urban residents is also closely related to the level of urban emergency management.
In April of this year, the General Office of the State Council issued the "Implementation Opinions on Strengthening Urban Waterlogging Control", clarifying the need to improve urban drainage and waterlogging prevention related emergency plans, strengthening river basin flooding and natural disaster risk monitoring and early warning, and timely and accurately issuing early warnings and forecasts according to their duties. Information, and do a good job in urban traffic organization, evacuation and emergency evacuation.
Liu Ke, a reader from Shaoguan City, Guangdong, said that it is very important to release flood warning information in advance. “If the forecast of possible waterlogging in urban areas can be released in time to remind citizens of dangerous areas prone to water accumulation, the masses can avoid them in advance or move in time. To reduce unnecessary losses."
"To reduce the impact of urban waterlogging, the key is to shorten the time of water accumulation." Gao Xiaobing, Section Chief of the Waterlogging Prevention and Drainage Section of the Municipal Facilities Maintenance Center of Tianxin District, Changsha City Smart platforms and other means minimize the impact of waterlogging on residents’ lives.
Cheng Jixue, deputy director of the Changsha Urban Drainage Affairs Center, said that during the rainy season, rescue vehicles, equipment and professional rescue personnel are required to be on duty in the urban area; during the dry season, rescue personnel and rescue vehicles are also required at any time. On standby.
"In some flood-prone spots that are difficult to rectify in a short period of time, a video surveillance system can also be equipped." Cheng Jixue said.
Our reporter Shen Tongrui Xiang Zifeng Shen Zhilin Youyi