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Sobre HPC

Heavy Rain and Flash Flooding

When rain becomes a danger

Model. Analyse. Act.

In future, extreme weather events will occur more often due to global climate change.
Risk maps for intense rainfall are the most important basis for construction measures for reducing the risk of flooding, contingency planning and crisis management. We use a wide variety of support programmes, guidelines and handbooks for protection against climate change, especially on the subjects of intense rainfall and flash floods.

We use all available information sources, from quick analysis to detailed risk evaluation, to create individual solutions for you – beginning with planning protective measures to the implementation of management tools.

The goal is to protect life and limb and to prevent or minimise damage from future intense rainfall and flash floods as much as possible. We are available to you for consultation throughout the entire process.

Our German Association for Water, Wastewater and Waste experts for intense rainfall prevention and our municipal water management engineers are happy to help you:

starkregen@hpc.ag

Tasks

  • Provide information
  • Protect people
  • Plan comprehensive solutions
  • Implement protective measures
  • Carry out risk prevention

Our Services

 

Your Benefits

  • Risk prevention
  • Prevention of potential damage
  • Protection of life and property
  • Infrastructure protection
  • Crisis management
  • Adaptation to climate change
  • Action plans
  • Strengthening resilience in
  • heavy rain risk management
  • Flooding risk management

Flow path analysis and site risk assessment

The initial evaluation of the flash flood threat to sites is performed with suitable software tools. Thanks to high-resolution, comprehensive topographical information, a risk assessment can be carried out cost-effectively, for example as part of a due diligence study.

The programmes used by HPC AG allow a variation of rainfall amounts and, at the same time, visualise the at-risk areas in the site and surroundings. A flow path analysis and evaluation of the catchment area round out the intense rainfall risk assessment.

In the event of a risk from intense rainfall, detailed modelling can be decided on in the next step. In addition, the effects of compensation measures in the area around the site, such as rainwater retention basins, can be evaluated in advance.

Development of 2D flow models based on digital terrain models

Digital terrain models – the basis

Digital terrain models (DTM) are computer-based depictions of the terrain. DTMs form the basis of modelling and calculations, such as for the surface discharge. The reliability of the modelling results depends on the level of detail of the DTM. Therefore, the basis and design of the model are adjusted to fit the goal of the modelling.

HPC AG selects the appropriate baseline data for every issue and, if necessary, enhances the existing terrain model with laser scanning, drone overflights or classic surveying.

The terrain surfaces of a DTM (digital terrain model) are refined with edges (buildings, kerbs, terrain lines).

Hydrodynamic 2D surface calculations are required for realistic evaluations; in some cases, a coupled evaluation is also a good idea. This means coupling the hydrodynamic 2D surface calculation with a 1D calculation in existing culverts or municipal sewers. Then, water in the model can flow into, but also out of sewers onto the surface, an overflow can occur in the sewer or manhole covers can lift under pressure (cf. accompanying video).

Surface run-off can be generated from areal precipitation, rain radar data and surface run-off parameters (SRP). Soil-specific seepage losses reduce the precipitation on the ground surface from which the drainage occurs. Surface roughness

specific to the use slows drainage. In short: In the event of intense rainfall or flooding events, the actual conditions, including possible interactions, can be depicted in the required precision with the right tools.

Video animations and clear 3D views of models and events (see accompanying example) support our customers and their employees in gaining an idea of the risks to be expected.

Simulation and heavy rain risk map

Reports of intense rainfall events can be seen in the news almost every day. The warning times are extremely short. Unlike flood waters, the exact place and time of an intense rainfall event, which can lead to flash floods in urban areas, can scarcely be predicted.

It can happen anywhere in Germany, cause high material damage and pose a serious risk to life and limb. There is no protection against the risk of extreme weather, which includes intense rainfall events. But every city, every community and every citizen can take precautions.

If we are aware of a danger, we can prepare for it. Computer-supported simulation models help us to visualise potential rainwater drainage. Intense rain cells can be emulated in the computer model and the drainage on the ground surface simulated, i.e. reproduced.

The basis for such simulation models is the digital terrain model with topography, land use, surface condition and other parameters. Using a two-dimensional, hydrodynamic numeric surface run-off model, the drainage routes, flood extents, speeds and flood depths are calculated. The result is intense rainfall risk maps.

The intense rainfall risk map (IRRM) is the first building block of municipal intense rainfall risk management (IRRM). Intense rainfall risk maps from HPC AG answer the questions:

 

  • What are the water’s flow paths?
  • How fast will it flow?
  • What water depths will occur?
  • Which buildings and areas will be affected by flooding?

What might happen?

If there is flooding due to intense rainfall, it is important to know how high the water will be. At a flood depth of only 10 cm, water can make its way into a building through light wells and leaky basement windows. Staying in flooded basement rooms is potentially deadly. At flood depths of over 50 cm, the static pressure rises so strongly that seals fail, especially for doors that open inward. Water levels and flow speeds can be read from the intense rainfall risk maps. For example, at a water depth of 15–20 cm, doors can no longer be opened inward. There is already a risk to life and limb (adults) at a flow speed of 0.5 m/s (ca. 1.8 km/h).

Risk Analysis

​Risk management minimises negative consequences

The integration of risk information is an essential part of risk management processes.
The intense rainfall risk map (IRRM) is the key element in describing danger and identifying risks. As part of municipal intense rainfall risk management (IRRM), trouble spots are identified in consultation with the fire brigade and construction facilities.

The flooding depths and flow speeds on the property are used to determine the danger. Then it is a matter of blending the flood zones with the properties at risk. The results of the flood risk are compiled with possible damages and vulnerabilities. Areas and properties especially at risk must be identified: How high is the potential damage? Is there a nursery school in the flood zone?

A high risk exists in places where there is a high danger of flooding (e.g. flood depths of 55 cm) as well as a high-value property with high damage potential (e.g. flooding of an engine pit). Population groups with an increased need for protection and with limited mobility must be protected. Especially vulnerable institutions include nursery schools and retirement homes. In addition, important infrastructure for crisis management (fire brigade and medical services) must be operational in the event of an incident. Especially critical places are determined and documented as part of the risk analysis. That way, emergency personnel know where the danger is greatest.

As if using a magnifying glass, property‐related risk analysis can take place on the building level. This detailed analysis examines the risk to the building (e.g. possible water penetration, effect on technical infrastructure and people) and the vulnerability of the property at risk. Risk estimation and site-appropriate recommendations for preventative measures round out the risk fact sheet.

Hazard prevention

Measures for protecting against heavy rain are developed for areas and buildings needing protection. In the process of municipal intense rainfall risk management (IRRM), the third building block is the action plan or hazard prevention. Hazard prevention is achieved either through organisational precautionary measures or through structural measures. The creation of retention areas, the construction of technical protection systems and harmlessly directing and guiding surface flowing water are examples of structural protective measures. The goal is prevention, and, where that is not possible, at least minimising the damage from intense rainfall events.

Site-appropriate emergency plans can save lives in the event of flooding. As part of the structural measures, dams, terrain modelling or protective walls, for example, can be placed at appropriate places in the terrain. If the water cannot be diverted or retained, property protection comes into play. Major damage can often be avoided through simple individual measures. Examples include the installation of spill barriers and water pressure-tight windows, securing light wells and basement access points, and the adaptation of building services.

Sewer system simulation

Water that must be directed in a controlled manner is everywhere in our everyday lives. Waste water, that is sewage from households, commercial buildings and industry, must be purified before it can be reused or drained away. More visible, on the other hand, is precipitation water, that is all water that comes from above and strikes the ground, such as rain, snow or dew. As a rule, precipitation water is clean and does not need to be purified before being drained. An exception is precipitation water that falls on dirty surfaces, such as roads. This must be purified before draining. That is a large amount of water, especially during intense rainfall. The water has to be retained in order not to overload the sewer system.

Sewer systems consist of a variety of elements, such as shafts and catchments, retention systems with throttled discharge, pumping stations and much more. All of these elements affect the water run-off with respect to both time and volume. A complex system quickly arises in which even professionals are scarcely able to estimate the sewerage load easily.

Before you’re up to your neck: Create an overview

A computer-supported sewer system simulation is needed to depict and examine the interplay of the individual elements of a sewer system or to assess the fundamentals of the sewer system. To do this, all the elements of a sewer system are measured, their hydraulic effect described and then stored in a database: the sewer register. The flow in the sewers can then be simulated by software. Managing even the most complex sewer system becomes manageable.

Sewer system simulation: Shafts are depicted as circles, and channels and catchments as lines; red colouring indicates an overload of the respective element

Inspection and vulnerability analysis

In order to achieve a realistic risk assessment of the possible dangers from heavy rain and flash flooding, extensive site and property analyses are necessary. That way, weak points and risks can be identified. A hazard assessment should be performed as a precautionary measure after every flooding event resulting in damage. However, it is also a good idea when there have been no heavy rain events in recent years. When potential risks and hazards are recognised, suitable protective measures can be made in a timely manner.

An initial estimation of potential hazards from heavy rain and flash flooding is made by inspecting the municipal territory together with representatives of the relevant authorities. Here, the focus is on questions regarding the starting points of the last floods and the location of flood zones and sites where the greatest damage occurred. If there have been no intense rainfall events in recent years, then, for example, historical records can be used and witnesses from that time questioned.

Furthermore, topographical conditions can be analysed and at-risk areas identified by the inspection. These may stand out due to their location on a body of water or the lowest point of the community, for example.

Along with the topographical conditions, the development structure, the building situation and the infrastructural facilities can be examined during the inspection, since these are critical for the water’s flow paths and damage potential.

The results of the inspection serve as the basis for further steps for creating a complete hazard assessment.

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