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09/05/2015 09:16:31

The ISIS manual recommends the Percentage Runoff value for the ReFH Urban unit be set to 70%. This represents 'runoff over a paved area'. It indicates that 70% will 'drain towards' (and included in the flow estimate for the catchment) and 30% will 'drain away'.

Should this 70%/30% be applied to a 100% impermeable surface? (eg road surface)

Or is the 70/30 split for general 'urban' areas and thus accounting for gardens etc?  If this is the case, then, I'm assuming, such a split of impermeable/permeable areas shouldn't also be adjusted by the user manually.




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