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Hello

I am trying to calibrate rainfall-runoff on a small urban catchment (1.5ha). The drainage system is a pipe and gully system, with contibuting areas comprising of concrete footpaths draining towards bituminous macadam roads.

Runoff coefficients have been surprisingly low (0.1-0.6), and I have observed a low degree of surface ponding on roads during storm events, which points to infiltration through the madacam surfacing.

I would like to model infiltration with the Green-Ampt equation, since losses appear to be related to short-term variations in rainfall intensity, however I cant find any published values for suction head or IMD. Can anyone suggest reasonable initial bounds for these parameters?

Thanks a lot

Dave