Retained rainwater volume

The calculation of the retained rainwater volume is included in the calculation of the flooding certificate.

Symbol or abbreviation:

VRück

Usual unit:

m³
Equation:
  • VRück: Volume of rainwater to be retained in m³
  • rD,30: 30-year rainfall event for different rainfall durations in l/(s*ha)
  • Ages: total paved area of the property in m²
    • Ages=ADach+AFaG
  • Qvoll: maximum discharge of the underground pipe when full in (m³/h)
  • D: Rain duration (D=5 min, D=10 min, D=15 min)
The calculation is based on the DIN 1986-100 section "14.9.3 Flooding verification" using the formula (21). The full filling of the underground pipe is taken into account here. For neutral pipe rows, this can be taken from Table A.5 of DIN 1986-100. In CALHYDRA, the value is calculated using the Prandtl-Colebrook equation depending on the selected pipe type.

Three calculation runs are also considered. The calculation for the 30-year rainfall with a rainfall duration of 5 min (r5,30). The calculation for the 30-year rainfall with a rainfall duration of 10 min (r10,30). The calculation for the 30-year rainfall with a rainfall duration of 15 min (r15,30). The largest of these three values is decisive for the amount of rainwater to be retained. All three values are displayed in the report in CALHYDRA.