Assessment of Runoff Contributing Catchment Areas in Rainfall Runoff Modelling

Søren Liedtke Thorndahl, C. Johansen, Kjeld Schaarup-Jensen

Publikation: Bidrag til bog/antologi/rapport/konference proceedingKonferenceartikel i proceedingForskningpeer review


In numerical modelling of rainfall caused runoff in urban sewer systems an essential parameter is the hydrological reduction factor which defines the percentage of the impervious area contributing to the surface flow towards the sewer. As the hydrological processes during a rainfall are difficult to determine with significant precision the hydrological reduction factor is implemented to account all hydrological losses except the initial loss. This paper presents an inconsistency between calculations of the hydrological reduction factor, based on measurements of rainfall and runoff, and till now recommended literary values for residential areas. It is proven by comparing rainfall-runoff measurements from four different residential catchments that the literary values of the hydrological reduction factor are over-estimated for this type of catchments. In addition, different catchment descriptions are presented in order to investigate how the hydrological reduction factor depends on the level of detail regarding the catchment description. When applying a total survey of the catchment area, including all possible impervious surfaces, a hydrological reduction factor of approximately 0.5 for residential areas with mainly detached houses is recommendable - contrary to the literary recommended values of 0.7 - 0.9.
Titel10th International Conference on Urban Drainage : 21-26 August 2005, Copenhagen / Denmark
RedaktørerEva Eriksson, Hülya Genc-Fuhrman, Thorkild Hvitved-Jacobsen, Anna Ledin, Peter Steen Mikkelsen, Jes Vollertsen
ForlagInstitute of Environment
StatusUdgivet - 2005
BegivenhedInternational Conference on Urban Drainage - Copenhagen, Danmark
Varighed: 21 aug. 200526 aug. 2005
Konferencens nummer: 10


KonferenceInternational Conference on Urban Drainage

Bibliografisk note

The proceeding is published on a CD.


  • Rainfall measurements
  • Hydrological reduction factor
  • Initial loss
  • Urban runoff modelling
  • Catchment area assessment
  • Sewer systems