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Hi everyone,

I am currently carrying out a surface water hydraulic modelling, but due to the huge size of the upstream catchment, I am forced to use two inflow boundary conditions (i.e. 2d_bc QT and 2d_rf).

In order to avoid modelling the entire catchment, I established the 2d_bc (QT) associated with the upstream catchment hydrographs based on the FEH method (from Flood Modeller) and catchment descriptors from FEH website (https://fehweb.ceh.ac.uk/).

On the other hand, a second boundary condition (2d_rf) has been established for rainfall hyetographs for my ‘active’ catchment (2d_code). These hyetographs were created using the ReFH method (also from Flood Modeller), which calculates the ‘loss model’ and then extracts the ‘net rainfall’.

However, in order to consider infiltration within the model, the ‘Standard Percentage of Runoff’ (SPR) of the FEH catchment descriptors would consider the infiltration for both the upstream catchment hydrographs and the hyetographs within the 2d_code area, is that correct?

My questions are:

Would the ‘Standard Percentage of Runoff’ (SPR) of the FEH catchment descriptors would be enough to consider the infiltration in the upstream catchment hydrographs?

Regarding 2d_rf, does the ‘loss model’ from ReFH method already consider the infiltration? Or should I apply an additional method?

Many thanks

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Hi, just came across this post. Sorry it's probably not in time to be much use for you Adrian, but maybe it can be of use to others who find this thread in future. These are just my thoughts on the matter, I think the application of rainfall across 2D catchments is still sufficiently new that there probably isn't yet a consensus on best practice, just a bunch of modellers with their own thoughts and attempts! Anyway, here goes...

1. Simply applying SPR to the total runoff would be a simplistic approach to handling the losses within your system. Given you've made use of FEH to generate the inflows and rainfall data, you already have the data to go a step better by using the net rainfall, which has the losses accounted for. If you were to look at the ratio of net rainfall to total rainfall, as generated by FEH units, you would see that higher return periods (lower AEP events) generate a higher percentage of runoff than smaller events (as one might expect in the real world) and probably none of them match the SPR.

2. The loss model does indeed already consider infiltration, so if applying net rainfall from FEH then you need to make sure you don't also have losses in the TUFLOW model. An alternative approach, which can more closely reflect physical processes, would be to apply the total rainfall to TUFLOW and apply suitable soil conditions to represent the spatial distribution of the losses. It can be tricky to get hold of suitable information to inform (and calibration data to be confident in) your soil parameters though, in which case applying the net rainfall from "conventional" rainfall runoff techniques can be a good approach to follow.

I don't feel like the above is my best writing, but hopefully it'll be of use to someone. As ever, if others have different thoughts on the matter I'd love to hear them! It's good to try and hash these things out together.


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