How to prevent floods and reduce disasters?

  Unfortunately, cities and towns always take protective measures only after a real flash flood disaster. The examples in this article show what the development of “water-sensitive cities” will look like in practice, and which factors play a decisive role in the successful adoption of protective measures. The initial conditions faced by all these towns are almost the same: Except for Hamburg, no town has experienced flash floods or extreme high river water levels before. Neither the people nor the urban infrastructure were prepared to deal with such disasters and therefore suffered. Great loss. In addition, there is one thing in common: After the floods in various places, people began to strengthen the research in this area and initiate various response projects, some of which are still in progress.
| Typical case: Wuppertal with abundant precipitation |

  Wuppertal is one of the most precipitation-rich cities in Germany. The Wupper River, which is bestowed its name, stretches for 20 kilometers in the city. In addition, there are about 850 creeks. Although Wuppertal has been preventing the once-in-a-hundred-year floods by impounding dams, the threat of floods still exists due to the well-developed water system connected to urban sewers. The difference in elevation between local hills and depressions is up to 250 meters, and about 500 stairs and streets in the urban area have a slope of up to 20%, which also makes floods easier to form. On July 26, 2008, a storm raged in the Kattenberg area of ​​Wuppertal, causing huge damage to the infrastructure and extremely overloaded sewers. Due to the lack of protection funds and engineering technical resources, Wuppertal has developed various strategies in risk management to deal with this unforeseen disaster in order to effectively prevent high water levels and flash floods in the long run.
  First of all, one cannot claim to be the “master of nature” and realize that no one can give a 100% security commitment. In flood prevention measures, accepting risks and taking initiative is the first step. Then, investigating depressions with hidden flood hazards, drawing a digital model of the land, identifying risk areas, focusing on fragile infrastructure such as primary and secondary schools and hospitals, and determining the possible damage. In addition, a step-by-step flood review is also required to investigate the flow of river water during a catastrophic torrential rain disaster through on-site inspection or (in areas with higher risk levels or complex terrain) to establish a digital terrain model, especially the flood caused by the water body connected to the sewer. potential. Then, the impact of climate change on flash floods is shown in computer simulations, and the guiding principles for action are determined on this basis. Finally, in terms of information policy and public relations, coordinate various actors including flood victims, explain the measures implemented by the public and individuals and their responsibilities, and explain the risks and problems caused by extreme weather as fully as possible. Stimulate the interest of citizens from all walks of life.
  At present, the basic goals of reducing the consequences of heavy rainfall disasters, widely obtaining information on flood control participants and victims, and building cost-effective infrastructure have been partially achieved. The integration plan that truly encompasses all participants makes people deeply aware that heavy rainfall protection is the common task of organizations and individuals, and everyone can and should make their own contribution to this. In 2012, the city of Wuppertal won the “Blue Compass Award” from the German Federal Environment Agency for its protective measures to adapt to climate change.
  These measures are mainly divided into two aspects: one is the adaptability of the urban drainage system, and the other is the vehicle concept of the fire department. In this regard, the UNEP press announcement said: “In order to estimate the flood risk, Wuppertal made a digital map model of the city. Visualization on the computer can also locate particularly dangerous areas and depressions, so that residents and neighbors who are also affected by the disaster can take protective measures together.” The special feature of this initiative is that with the help of digital models, citizens can clearly see The flood caused damage to their own buildings, so their risk awareness and willingness to cooperate have increased significantly.

In Hamburg, floods are becoming more frequent.

  The fire department’s measures to deal with extreme weather are very simple and practical. Two well-functioning old cars were converted into instrument cars, equipped with chain saws, a generator set and a high-power submersible pump. In addition, a rolling container equipped with anti-seepage sandbags and other supporting materials was also purchased. In extreme blizzards, the all-wheel-drive emergency mission vehicle will also be equipped with rescue stretchers to transport emergency patients to ambulances. What’s special is that this simple, practical, and inexpensive strategy does not need to start a large project, so it also avoids policy obstacles, especially in dealing with heavy rains with a short warning time, because it is equipped with vehicles with corresponding rescue resources. Can be put into use immediately.
| Three flash floods in ten years: Wachtberg |

  The town of Wachtberg near Bonn suffered three flash floods in ten years, although the area is not a traditional flood-prone area. In 2004, a heavy rainfall caused flooding, and then on July 3, 2010, the rainfall here exceeded 93 liters per square meter in two hours, and on July 20, 2013, it was even in just 45 minutes. More than 85 liters.
  ”Extreme weather has increased, and we need to adapt. Because there is no warning time for flash floods, we must especially emphasize prevention. The ideal situation is to continue to prepare for disasters.” This quote from the local newspaper not only reflects Wah The painful lessons that Teberg learned from past heavy rainfall events also demonstrated the forward-looking risk management strategies mentioned above, and proved the correctness of these theories with practice.
  In order to enable the public to understand the disaster situation in the first place, Wachtberg has produced a risk card, which forms the basis of the flood risk management plan. Although the risk card does not improve the ability to predict flash floods, it allows the public to clearly see the scale and frequency of heavy rainfall events. This can awaken the public and institutions’ awareness of risks and take the first step in taking preventive measures. The starting point for the implementation of the flood control plan in Wachtberg is that due to climate change and frequent heavy rainfall, it is absolutely necessary to adapt to this situation for a long time. The change from safety thinking to risk thinking
  gave rise to the slogan— “Symbiosis with water and joint prevention.” According to extreme weather forecasts and past experiences, Wachtberg puts flash flood disasters in a prominent position in the flood prevention strategy. After analyzing the floods so far, the following proposal was put forward: In areas where people are skeptical about the necessity of flood protection measures, data proofs are given on the frequency of backwater; backwater has a great influence on the scale of flood damage, explain to the people The hidden safety hazards of backwater flow; record the losses caused by the disaster, and guide the people to behave in the next flood; regularly carry out water area maintenance to act before unforeseen flash floods and minimize the inevitable losses; treat the river according to the level of danger Segment classification; eliminate sewer defects; optimize authority and responsibility management; emphasize the responsibility of the homeowner.

  To achieve effective protection, each flood prevention participant must know his own tasks and perform his duties in extreme weather disasters.
| After 30 minutes, the picturesque scenery turned into a disaster scene: Beiersdorf |

  The example of Beiersdorf tells us how cruel a heavy rain can suddenly destroy a town. On the night of July 21, 2007, about 7,000 residents of Beiersdorf suffered a flash flood without warning. Since the local area is not an area with a high incidence of flash floods, there has never been a disaster experience in the past, and neither the residents nor the local management departments are prepared for it. “The storm has become very terrible within 15 minutes.” said a firefighting volunteer. In nearly 4 hours, the precipitation reached more than 200 liters per square meter. In this disaster, an 82-year-old man died. When she was rescued from the submerged basement by divers, she had no breath. The economic losses caused by the flood amounted to 100 million euros, which is a lot for such a small city. More than 1,000 basements were flooded, about 500 houses were seriously damaged, and more than 20,000 liters of chemical agents and fuel oil spilled. Many streets were flooded, the Baiersdorf train station was also submerged, and passengers on a train had to evacuate urgently. The A73 highway was also flooded, with a water depth of 1.5 meters. A few months later, a railway bridge of the Munich-Nuremberg-Berlin section of the Intercity Express was restored to traffic.
  Firefighters in Beiersdorf had to rush to more than 1,100 mission execution points. In order to show the scale of the disaster more clearly, you can look at the manpower devoted to it: 50 voluntary fire brigades, 3 professional fire brigades with a total of 900 people, 30 local technical assistance associations, 140 emergency service personnel, and about 100. The police, as well as members of the mountain rescue service, drowning rescue service, German Red Cross and medical aid organizations.
  The main tasks of firefighting volunteers are to evacuate people, extinguish fires caused by wet wires, and deal with oil and chemicals in the water. The leakage of more than 20,000 liters (20 tons) of chemical agents and fuel oil could have been avoided through corresponding preventive measures, such as improving the safety of fuel tanks in the event of a flood. The contaminated water makes small scratches and scratches on the residents inflamed. Some have to be hospitalized for several weeks, and some almost have to amputate the infected body parts.
  The example of Beiersdorf made us more aware of the need to manage risks in an all-round way. Negative examples can inspire other towns to detect and respond to problems in advance, so as not to repeat the same mistakes. However, so far, it has not been possible to form a temporary federation consisting of Beiersdorf and the neighboring Forchheim, Langensendelbach, and Poksdorf to combat floods and heavy rainfall. Although many parties have emphasized its necessity. It is not only that individual cities and towns cannot afford flood control expenditures, but it is also difficult to guarantee the effects of local measures. In this way, the damage caused by the flood will only continue to be transferred rather than truly eliminated. That is to say, the flood protection of one town is at the expense of another town, and the flash flood does not matter what the town boundary is. Related discussions began almost immediately after the flash floods in July 2007, but it was not until 2012 that it finally decided not to adopt the proposal to establish a temporary federation. Noisy and noisy, but fruitless, but it should still be or because of this we should learn more from it, so that we can organize cross-town dialogues more successfully in the future.
  These discussions are essentially related to the following two aspects: fiscal expenditures and the concessions that urban management departments and citizens can give. Since no town can alone bear 25-30 million euros in flood control expenditures, it is finally recommended that each town that participates in the temporary federation bear the responsibility that matches its own financial resources. In the process of discussing the necessity of flood prevention measures, some towns felt discriminated against. Although the significance of the Federation’s existence is unquestionable, these details make it doomed to fail. The citizens of Boxdorf also launched a protest against this temporary federation under the promotion of the local farmers’ association because they feared that their land would be too much damaged due to the planned flood control measures.
  Under the leadership of the mayor Andreas Just, the city of Baiersdorf finally decided to take separate flood control measures, including planning rainwater drainage areas, dams, trenches and diversion ditches, but there is always a lack of one. Long-term risk management strategies like Wachtberg.
  It is worth pointing out that after the flash floods in Beiersdorf, a resident fought a lawsuit with the city government of Beiersdorf. He demanded about 200,000 euros in compensation for “building damage, land damage, property damage and animal deaths” because “all these are caused by poor flood protection in towns and countries.” In the end, the plaintiff was recommended to withdraw the lawsuit on the grounds that “the local floods causing losses of this magnitude are very rare, and the towns have taken the correct actions in fulfilling their preventive obligations.”
| Eternity fights water: Hamburg |

  Due to its geographical location on the banks of the Elbe and the coast, Hamburg has always been a flood-prone area. Therefore, prevention of various floods is one of the most important aspects of its urban development plan.
  On August 1, 2002, a heavy rainstorm occurred in Hamburg, causing losses of up to 8 million euros. In 2004 and 2011, Hamburg also suffered heavy rains, and losses amounted to several million Euros. In response, the German Urban Development and Environment Agency and Hamburg Water Group have established a comprehensive heavy rainfall and flood management system-RISA.
  The implementation of this flood protection plan has opened a new stage in the field of rainwater management in Hamburg, which is a model for other towns: from “living by the water” to “symbiosis with water”! Its goal is to establish a rainwater management system in Hamburg that can adapt to the future, while ensuring urban flood control while innovating measures, and protecting groundwater and surface water. This is a “decentralized” solution that allows rainwater to be absorbed and stored on the spot, and then returned to the natural water cycle through suitable equipment as much as possible locally. Increasing soil compaction in cities is seen as a problem, and urban planning requirements to increase soil permeability have gained an important place in rainwater management. Like Wachtberg, here, rainwater management is integrated into people’s daily life as a lasting task. This concept is succinctly expressed through the slogan “Symbiosis with water”. In terms of urban and rural planning, the government formulates sustainable urban development plans that cover all related topics, such as the use and transformation of public green space facilities. In addition, it is necessary to adapt the street plan to future weather changes, identify potential problematic water areas and flood risk areas, and formulate measures based on the state of the water area. Using today’s actions to ensure the survival of tomorrow, the transition from accelerating the drainage of rainwater to the establishment of a “decentralized” rainwater management system is the basic goal pursued by RISA.

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