Direct Rainfall (Rain on Grid) Modelling Guidance: Difference between revisions
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#* Raising the model topography creates an obstruction to flow. It prevents floodwater from passing through buildings (as is the case with the Manning's n approach)
#* The application of rainfall on top of the building can however undesirable results. Those being, water falling from the building roof to the ground can result in the need for a reduced model timestep to maintain model stability. This can slow the simulation speed. Also, depending on the Map cutoff Depth specification, water may be present in the results on the building rooftops. This may not be desired for mapping purposes. There are a variety of options available to mitigate these issue:
::::* Retain the model design described above, though post process the results before reporting, by either deleting the model result where there is overlap with the building foot print, or overlaying building footprint polygon objects over/above the result dataset in the GIS Map Layout (hiding the model result within the building footprints).
::::* Exclude buildings from rainfall polygon: This removes the rainfall from the model that fall on the buildings. and underestimates the amount of rainfall entering the model.
::::* If the area of the buildings is negligible in comparison to the full model, it might be acceptable to leave the rainfall out for simplicity.
# Exclude buildings from rainfall polygon and include it with 2d_sa_rf:
#* The cut out rainfall from the buildings can be included in the model again with <font color="blue"><tt>Read GIS SA RF</tt></font> command. Digitise a small 2d_sa_rf polygon for each building on the ground where runoff from the building is expected and assign attributes that convert rainfall hyetograph into flow and input it into the model as if it was 2d_sa. Check TUFLOW <u>[[TUFLOW_Example_Models#Boundary_Condition_Options | example model EG03_005.tcf]]</u> on how to setup 2d_sa_rf.
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