Design rain

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The design rain donation is a parameter for calculating the amount of rainwater that occurs . Canals or other sewage and infiltration systems must not show any overloads for a design rain donation. A common regulation for planning according to DIN 1986-100: 2007-04 is that the design rain donation for roof drainage is a rain event with a statistical frequency of 5 years and a rain duration of 5 minutes.

This is represented with the designation r (D; T). In the case of a rain event with a frequency of 5 years T and a duration D of 5 minutes, the display is in the following form: r (5; 5). The unit of design rain is liters per second and hectare. An average value for Germany is 311 liters per second and hectare (this corresponds to 111.96 liters per hour and square meter).


  1. in E DIN 1986-100: 2007-04 redefined.
  2. E DIN 1986-100: 2007-04; Institute for Water Management, University of Hanover using KOSTRA-DWD 2000, for which the German Weather Service (DWD) owns the copyrights. The rain donations listed refer to the KOSTRA grid field, in which the center of the place falls with the specified coordinates. The values ​​at the upper limit of the specified precipitation ranges were taken.