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Showing results for tags 'hyetograph'.
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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.
Q: What is the direct rainfall approach and what is the difference between the 2d_rf and 2d_sa_rf layers? A: For both the direct rainfall and the SA RF approach the specified boundary is a rainfall hyetograph. The direct rainfall approach applies the rainfall hyetograph to active cells with the region. For the SA RF the rainfall hyetograph is converted to a flow (in m3/s or ft3/s using the area attributers in the GIS layer, this is described further below. For both types the input hyetograph must be in mm (or inches) versus hours. The first and last rainfall entries should be set to zero, otherwise these rainfall values are applied as a constant rainfall if the simulation starts before or extends beyond the first and last time values in the rainfall time-series. Each value represent the rainfall that falls per increment, for example in the table below between 0.0833 (5 minutes) and 0.1667 (10 minutes) a rainfall depth of 2.5mm is applied, as opposed to a cumulative depth or rainfall rate. A total of 16.5mm of rainfall is applied over a 30min period in the hyetograph below. Time Rainfall 0.0000 0.0 0.0833 0.0 0.1667 2.5 0.2500 5.4 0.3333 3.5 0.4167 5.1 0.5000 0.0 The rainfall (2d_rf) layer applies the rainfall hyetograph to all the active 2D cells, the attributes are: · Rainfall name · factor 1 · factor 2 Both of the factors are multipliers and can be used to modify the boundary. E.g. an f1 might be an area reduction factor and f2 a climate change factor. These are multiplication factors and should be set to 1 if no change is desired. If these are set to 0 no rainfall will be applied and you will get a warning to tell you that this has occurred. For the direct rainfall approach the losses can be specified in either the materials database (the can be varied based on the land-use or 2d_mat layer) or via a soils / infiltration layer. Note: using the double precision build of TUFLOW is recommended for direct rainfall models to ensure accuracy in small flows. The sa rf layer (2d_sa_rf) also uses a rainfall hyetograph, but the required attributes are: · Name · Catchment_Area · Rain_Gauge_Factor · IL · CL The catchment area, factor, IL and CL are used to convert the rainfall, to an inflow boundary (e.g. time - flow). This is then applied to the 2D cells using the source area inflow type (2d_sa). For the SA inflow the default approach (for the 2013 version) is to direct the flow initially to the lowest cell within the polygon and when multiple cells are wet the flow is then spread between wet cells with the flow being proportioned by the cell depth. To turn off the proportioning to depth use the .tcf file command: SA Proportion to Depth == OFF A minimum depth can also be set, below this depth the cell will receive no inflow: SA Minimum Depth == <minimum depth> Regards TUFLOW Support team