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== What is the best approach for modelling buildings in rain on grid model? ==
There are numbernumerous ofdifferent industry commonstandard ways to modelrepresent buildings in a direct rainfall model. Australian Rainfall and theRunoff choiceGuideline, dependsProject on15 the(REPRESENTATION floodOF modellingBUILDINGS task.IN All2D haveNUMERICAL theirFLOOD advantagesMODELS) anddiscusses some of teh available disadvantagesoptions:
# Using depth varying Manning's n, apply a low value (n = 0.02) at shallow depth ( d < 0.03m) and a high value (>0.1 to the building area:
* Represent buildings as high Manning's n:
*#* This is a very common and quick to setup approach that significantly slows down water passing through the buildings.
*# Raise elevation with topographic updates:
*#* Raising elevation eliminates water passing through the buildings, however as rainfall is assigned to all active cells, it will be falling on top of the buildings and from there to the ground.
*#* With bigger rainfall, this might create a waterfall like output around the buildings.
*# Exclude buildings from rainfall polygon:
*#* This removes the rainfall from the model that supposed to 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.
*#* Most rainfall that falls on buildings collects on the roof and through gutters and downpipes finds its way directly into the sub-surface drainage system. In such case, <font color="blue"><tt>Read GIS SA RF PITS</tt></font> command can be used to feed the water directly into the pits. Every 2d_sa_rf polygon needs to have at least one 1D pit within to automatically deposit the flow. If multiple pits are present, the flow from the polygon splits equally.
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