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TeeganB

Direct Rainfall QC - check boundary applied correctly

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Q:

"What are some suggestions for checking direct rainfall boundaries have been applied to my model correctly? For example, I wanted to verify that the correct rainfall depth of 90 mm was applied across the model. I divided the “total volume in” by the total area of active cells, and came up with only 72mm. I cannot track how the histogram relates to the hyetograph."

A:

There are a number of things that can be looked at, depending on the type of rainfall boundary being applied, and if rainfall losses are applied to the model.

Rainfall losses applied through the Materials Definition file (.tmf or .csv format) removes the loss depth from the rainfall before it is applied as a boundary on the 2D cells. Soil infiltration losses however remove water from wet cells, after the rainfall source has been applied.

Is the model health (mass balance, negative depths etc) acceptable?  If using TUFLOW classic (as opposed to TUFLOW GPU) direct rainfall models should be run with double precision and the recommendation is to lower the cell wet / dry depth to 0.2mm.

For 2d_rf boundaries, the rainfall time-series data must be in mm versus hours, and is converted to a hydrograph to smooth the transition from one rainfall period to another (the converted hydrograph is reported in the .tlf log file for cross-checking). After subtraction of rainfall losses, this is applied to the model cells as a source volume. The Map Output Data Types RFR and RFC (see Table 9-10 of the 2016-03-AE TUFLOW Manual) may be used to view the rainfall rate (mm/hr) and cumulative rainfall (mm) over time respectively. As these are model outputs, they are inclusive of the rainfall losses and any adjustments made in the BC Database (eg. multiplication factors/time shift).

For rainfall grids generated from point rainfall data with a Rainfall Control File .trfc,  the rainfall control file is processed during model initialisation and a series of rainfall grids are output, which are then used by the simulation to vary the rainfall over the 2D domain(s). This feature may also be useful simply to generate the series of rainfall grids for other purposes or display. The rainfall grids are pre-processed to reduce memory usage whilst TUFLOW is running. Whilst there isn’t a specific check file for the rainfall distribution when using generated rainfall grids, another advantage of the pre-processing of rainfall grids is that they can be interrogated prior to the end of the simulation to allow for checks. Note that the generated rainfall grids are inclusive of adjustments made in the BC Database (e.g. multiplication factors used for climate change) and of adjustment factors in the input GIS layer’s attributes, but because they are an input to the model, they are not inclusive of rainfall losses that may be specified in a materials file. Again, the Map Output Data Types RFR or RFC can be specified, these are inclusive of the rainfall losses, however these results are output as the simulation progresses.

To confirm the rainfall losses applied across the model, use the grd_check file with the Materials Definition file .tmf.

 

 

 

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