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Direct Rainfall (Rain on Grid) Modelling Guidance: Difference between revisions

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# Raise the building footprint elevation using TUFLOW's topographic update features (eg. <font color="blue"><tt>Read GIS Z Shape</tt></font>):
#* 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 produce some undesirable results that require further consideration. Those being, water falling from the building roof to the ground can result in the need forrequire a reduced model timestep to maintain model stability. This can slow the simulation speed. Also, depending on the Map cutoffCutoff Depth specificationassumptionsn, 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 mitigateresolve 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 the rainfall polygon: This removes the rainfall from the model that would otherwise fall on the buildings. This approach will underestimate the amount of rainfall entering the model. If the collective building footprint area is negligible in comparison to the entire model, this approach may be acceptable.
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