I have a model of a minor watercourse that is essentially a river reach that discharges into a grated manhole before continuing as a culverted section. The invert from the outgoing pipe from the inlet manhole is about 2m below the invert of the upstream river reach section. I am looking for advice on the best way to model this in ICM. So far my options have been

RR > Culvert inlet > Manhole > Conduit (won't initialise due to large step change)

RR > Weir > Manhole > Conduit (initialises Ok)

What is the best way to represent this step change from the RR to conduit? Should I be using inlet flood type manholes?

This is only 1D at the moment but I will eventually need a 2D representation of overland flow when the inlet manhole surcharges.