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Multiple event simulations2

Multiple-event simulations

In order to speed up the calculations, a different time step is applied during dry periods and a special solution has been applied for the simulation of dry periods between the consecutive events. The solution accounts for the following phenomena:

In this context, start of a dry period is defined if three conditions are fulfilled simultaneously:

  • No rainfall: all connected rain gauges show no rain, i.e. the rainfall intensity is null
  • No infiltration: the infiltration has stopped in the catchment (and not necessary in all catchment like it is done in MOUSE)
  • No runoff: the runoff from the catchment included in the simulation has fallen below the “low flow” limit. The threshold can be controlled through the parameter NL_CONCEPT_DRYDEPTH in the INI file (see relevant documentation for reference)

At the start of a dry period, the initial loss storage would appear fully or partially filled up. For flat impervious surfaces, the full initial loss storage would contain the water used for wetting and filling of the surface storage, while for all other surface types only wetting loss will apply. The latter case, i.e. partially filled storage would apply for small events with the total depth smaller than the corresponding initial loss storage capacity.

If evaporation is not specified, recovery of the initial loss capacity, i.e. the process of surface drying is simulated as a constant “decay” rate, which replaces the actual evaporation. As a consequence of the recovery process, the initial loss storage would be fully or partially emptied, which depends on the actually applied loss recovery rate and the duration of the dry period.

The initial loss recovery rate can be controlled through RUNOFF_C_INITLOSS_RECOVER found in the INI files (see relevant documentation for reference).

The recovery process is only activated during dry periods, i.e. the action during rain events is neglected. Note that if actual evaporation process is activated, the recovery process is suppressed and evaporative action is activated throughout the simulation period.