RDII – the importance of calibration

Rainfall Dependent Inflow and Infiltration (RDII) can be a significant part of sanitary sewers flows (and overflows).

SWMM uses the RTK unit hydrograph approach but, as indicated in the software documentation1 “There are no general values that can be applied in the absence of actual field data” … “RTK parameters are derived from site-specific flow monitoring data”.
The case study of the city of Brossard in Québec will compare the results obtained in 2018 based on theorical assumptions to the actual flows measured for 25 points in 2019. The initial assumptions for the RDII parameters will be documented and the validity of the ‘Theorical results’ of 2018 assessed in dry time and during rainfall events.

The final conclusions should have something to say about the importance, or non importance, of calibration for RDII in sanitary sewers and/or if the growing database of measured data could not help to estimate better theorical values.