Recently the ability to model runoff using the Probability Distributed Model (PDM) was added to InfoWorks ICM. An earlier blog dealt with the concepts and parameters behind the PDM model. This blog hopes to build on that and show how to use the PDM model in InfoWorks ICM.
A PDM model can be set up on an individual subcatchment basis. To set the subcatchment to use the PDM model, we only need to use the one runoff surface as the PDM model is a Total Catchment runoff volume model. That is the PDM represents the whole subcatchment and all the different surfaces that may occur within it. Within the subcatchments, set up a land use to look at one runoff surface. Within that runoff surface set the runoff volume model to ‘PDM’.
Once set, all subcatchments assigned to this runoff surface will use the PDM model. As you can see, once set to the PDM runoff volume model, no other parameters are required for the runoff surface.
This is because the PDM parameters are applied on a subcatchment by subcatchment basis and are held within the subcatchments property sheet under the PDM Descriptor field. This will set up the parameters for the chosen subcatchment. It is possible to set up PDM descriptors for each subcatchment but it is more likely that a set of PDM Descriptors will be used for multiple subcatchments. In order to use an existing set of PDM descriptors, the relevant set of descriptors should be chosen from the dropdown menu. This can be set either using the properties view or using the grid view. If an existing Infoworks RS with PDM parameters is imported into ICM then the PDM parameters will be imported automatically.
A typical set up is for the soil moisture storage component to be based on the pareto distribution, the surface storage to be based on a 2 linear reservoir cascade and the groundwater storage component to be represented using a cubic non-linear storage routing function.
This will set up the subcatchment to utilise the PDM model to simulate the runoff from the rainfall. It is only left for the user to set up the rainfall, evaporation and if required the temperature profiles. These are all set in the usual rainfall event editor.
With the subcatchments set to use the PDM model, the PDM descriptors specified and the rainfall/evaporation set up, the PDM model will be automatically used within the simulations.