SpencerThompson

I have a Mike 11 model coupled with MikeSHE for hydrology. We are using drainage codes for a number of developed areas to represent efficient surface drainage. We have them set up spatially to cover the whole developed area and then drain to a Mike11 ditch on the boundary. My question is how does MikeSHE calculate the SZ drainage flow rate to send to the ditch?

Does the rainfall first have to enter the SZ (by infiltrating) before the SZ drainage is activated?
Or does all water that hits the grid cell get routed to the boundary, regardless of if it would otherwise infiltrate to the SZ?

I read that the paved runoff coefficient values are used to take a portion of the ponded water between (0 and 1) and route it directly to the selected SZ drainage. This leads me to believe that if you had a paved runoff coefficient of 0, all the water would pond on surface and either infiltrate or runoff overland, and only the infiltrated water would drain through the SZ drainage.

However, I have been reviewing the MikeSHE grid results for "SZ drainage flow from point", and the values here indicate that all rainfall is being routed to the SZ drainage, regardless of the paved runoff coefficient. Ie. cells with a paved runoff coefficient of 0.2 are showing the same drainage flow rates as cells with a paved runoff coefficient of 1.0.

This is not what I intended when the model was setup - I wanted the paved runoff coefficient to take a portion of the runoff and put it directly to the Mike 11 river network, and the remainder would either infiltrate or runoff normally.

I have not been able to find clear wording in the user manuals that describes this, and would appreciate any help or advice.

Thanks!