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Question: When running a direct rainfall model using the TUFLOW HPC solver and applying an IL/CL using the materials layer, the results in the RFML map output are showing that the losses continue to accumulate after the rainfall has stopped i.e. for a 1 hour storm event, the cumulative loss continues to increase after the model time has passed the 1 hour mark. Is the model working, and am I able to use the other output results? Answer: Yes, the model is working and you can still use TUFLOW HPC to model direct rainfall with IL/CL applied using the materials layer. There is a bug in TUFLOW build 2017-09-AC in the RFML map output when running with the HPC solver that continues to report rainfall loss after the rainfall has ceased. This bug is confined to this map output only and does not affect the hydraulic computations or other outputs (depth, velocity, hazard etc). Please do not use the RFML output when using the HPC solver in TUFLOW build 2017-09-AC or earlier. This is not an issue when using the Classic solver.
Q: When using a Global Rainfall boundary (via the "Global Rainfall BC == " command) do the spatially varying losses via the materials file apply, or only the Global Rainfall losses ("Global Rainfall Continuing Loss == " and "Global Rainfall Initial Loss == " commands)? A: When using a Global Rainfall BC the approach is more simplistic than the one than used for a 2d_rf layer. No memory is allocated for spatial losses and the global rainfall losses are the only ones that apply. These global losses are subtracted from the rainfall before the simulation and each cell gets the same rainfall applied. Therefore: The global rainfall losses commands only apply to global rainfall boundaries and not to 2d_rf polygons. The material losses do not apply to global rainfall boundaries. We will issue an updated 2016-03-AE manual in the coming weeks and this behaviour has been clarified. For future versions we will likely; add some warnings if either of the above configurations is specified, we will also look at supporting spatial losses for global rainfall, but will likely make a new command for doing so, to keep the existing behaviour.
Q: In the tmf file the Tuflow manual says that: The third and fourth numbers are optional and set the initial and continuing loss rates in mm and mm/h if using Read GIS RF. My understanding was that the 10mm in 3rd column of tmf will impact only the first non-zero value of the hyetograph. And if this is less than 10mm then only that first step will be removed (changed to 0) and that’s the end of initial loss story – the rest of the hyetograph will not be impacted by this 3rd column. Does Tuflow keep removing the rainfall until the 10mm loss is accumulated or does it just take 10mm from the first step and leave the rest alone? A: Good question! Tuflow takes the initial loss off the cumulative rainfall applied in your 2d_RF layer. So, it’s not just that first time step Firstly, Tuflow coverts the hyetograph to a flow to be applied per cell. You can see the gross values of this conversion in your .tlf (and below figure). This is before any removal of losses. The losses are then removed from the cumulative total on the cell, so that a total of (10mm* Cell area) of volume will be removed, using up those initial timesteps until this volume per cell is reached. Only after the losses are removed, the flow is applied to the cells (ie: the rainfall isn’t applied then losses are deducted after that.) Using your data I’ve made a test case below. In the second figure, the dark red dashes are the m3/s per cell that tuflow is applying as a part of the 2d_RF layer without losses (as reported in your .tlf) and the dark blue dashes are the m3/s per cell with losses. I’ve back calculated this from your information. You can see the loss volume in the difference at the start. The tail ends of both lines are the same as the loss has been removed. This is also confirmed in looking at the depth in the model at a cell, refer to the third figure. Thus, you can see that more than your initial timestep is used by the initial loss. At the moment, it is not clear to see what is exactly being applied after losses. However, in the forthcoming 2015 release there are new outputs for checking the rate and cumulative rainfall applied to each cell. So in the future, this kind of question will be more easily checked and visualised. I hope this helps, please let me know if you require more information. Thanks, Rachel