Direct Rainfall (Rain on Grid) Modelling Guidance: Difference between revisions
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= Direct Rainfall =
Please see <u>[https://www.tuflow.com/library/webinars/#feb2021_direct_rainfall Direct Rainfall (Rain on Grid) Webinar]</u>.<br>
= TUFLOW Executable =
* The single precision version of TUFLOW is recommended for direct rainfall models using HPC.
* The double precision version of TUFLOW is recommended for direct rainfall models using TUFLOW Classic.
= Rainfall Boundary Conditions=
The following links provide boundary condition guidance for applying direct rainfall:
* [[TUFLOW Rainfall Control File Examples]]
* [[TUFLOW NetCDF Rainfall Format]]
= Rainfall Losses and Soil Infiltration=
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Similarly, a variety of soil infiltration options are supported. The available options include, Initial / Continuing Infiltration, the Horton Infiltration method and the Green-Ampt Infiltration method. The following link provides
* <u>[[Green-Ampt Infiltration Parameters | Green-Ampt Infiltration Parameters]]</u>
= Common Questions Answered (FAQ)=
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:::* Retain the model design described above, with subsequent post-processing of the mapped results before reporting. Either, delete the model result where there is overlap with the building footprint, or overlay the building footprint polygon objects over/above the result dataset in the GIS Map Layout (hiding the flood 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 under-estimate 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.
:::* Exclude buildings from the rainfall polygon and represent the rainfall that would be falling on the building using <font color="blue"><tt>Read GIS SA RF</tt></font> inflow boundaries. To do this, digitise a 2d_sa_rf polygon for each building (with a buffer of one of more 2D cells) where the building footprint has been excluded from the direct rainfall region. The 2d_sa_rf input will convert the input rainfall hyetograph to flow, deposited initially on the lowest 2D cell, then for subsequent timesteps distributed over all wet cells, within the 2d_sa_rf regions (ie. on the ground surrounding the building). Refer to TUFLOW <u>[[TUFLOW_Example_Models#Boundary_Condition_Options | Example model
:::* Exclude buildings from the rainfall polygon and represent the rainfall that would fall on the building using <font color="blue"><tt>Read GIS SA RF PITS</tt></font> inflow boundaries. This approach is similar to the previous method, although instead of directing the inflow to the ground surrounding the building, it is directed into the sub-surface drainage (underground pipe) system. To implement this approach every 2d_sa_rf polygon must encompass at least one 1D pit. If multiple 1D pits are within a single
== What is the recommended cell wet/dry depth for direct rainfall models? ==
For models with SGS turned off, a reduced cell wet/dry depth of 0.0002m (0.0007ft) is recommended due to the substantial amount of shallow sheet flow. <br>
If SGS is turned on, a reduced cell wet/dry depth is not necessary because the cell wet/dry calculation conducted on the SGS storage curve captures a greater change in depth. In the case, the default of 0.002m (0.007ft) may be sufficient; however, it should be reviewed and selected according to the magnitude of flooding depths.
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