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Insight

Mitigate the Effects of Heavy Rain & Flooding

by Dr.-Ing. Klaus Piroth Principal Division Manager
Across the northern hemisphere, a trend for increased frequency of extreme rainfall events has been observed over the past few decades. Reason enough for cities and municipalities to get closer to dealing with rainwater and integrated stormwater management.

Copenhagen (DK) in 2011; Münster (GER) in 2014; recently, Livorno (It) and Berlin (GER) – these are just a few examples of flooding after local heavy rain events that put lives at risk and caused tens of millions of Euros in damage. Heavy rain events often exceed the capacity of local sewers – generally accepted engineering standards no longer apply with prevention shifting into legal grey areas.

l/m²
precip­i­ta­tion per year in Germany 
Insurance damage caused by storm, hail and torrential rain in 2016
l/m²
in 2 hours during the heavy rain in Dortmund 2008

Cities and municipalities intending to deal with the issue of heavy rain events can do the following:

1. Get all the stakeholders around the table. Heavy rain events affect not only urban sewage management or the planning authority, but every area of urban planning and development from traffic, road and sewage to green and open space planning, not forgetting fire and other emergency services. 

2. Involve governing authorities – water management etc. – as well as forestry and agriculture in rural areas outside city limits. Appoint a contact person responsible for all stakeholders, such as a flood prevention officer.

3. Involve the public and concerned citizens at an early stage – this will allow you to discuss needs and expectations as well as opportunities and limits in technical, financial and legal terms in advance of any project, and increase its planning acceptance.

CDM Smith advises you in all phases of integrated rainwater management.
Dr.-ing. Klaus Piroth, Principal Division Manager

4. Analyse the municipality’s catchment area – a sewage masterplan may be extended to accommodate heavy rainfall. Nationwide hydraulic engineering calculations do not cover heavy rain events, requiring separate planning considerations. This may be very simple in the initial approach.

5. Compare the results from the previous step with feasible solutions including emergency flood channels, stormwater retention basins including decentralised retention in the area, and high-risk areas with danger to life and limb under heavy rainfall such as underpasses, underground car parks and similar.

6. Review services available on a regular basis, even in years without heavy rain events.

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