Visual OTTHYMO

5.6 Use of IUH’s for I/I Simulation and Baseflow (DWF)

Visual OTTHYMO can be used to simulate the Infiltration/Inflow into sanitary sewers or combined sewers. The four types or rainfall-induced infiltration/inflow are:

  1. Fast responses from directly connected impervious areas.
  2. Rapid responses from grassed areas in combined sewers systems.
  3. Semi-rapid responses from weeping tiles.
  4. Slow responses from cracked pipes and leaking joints in the sewers.

Visual OTTHYMO can simulate these responses during a single event by adding individual response hydrographs from each type of contributions within the same area. The first three responses can be simulated with the quasi-linear instantaneous Unit Hydrograph (STANDHYD) while the fourth, slow response, can be simulated with the NASH unit hydrograph.

Baseflow can be super-imposed to account for the domestic sewage contributions during wet conditions.