Culverts & Bridges in Mike 11

Hi everyone,

I'm trying to implement a couple of weirs & culverts on a Mike 11 network in order to model some bridge representations as it is advised in the Mike 11 "User Manual" (simplification of calculations).

To do this, i'm setting up a basic weir and a simple rectangular culvert at the same chainage, a little bit upper the lowest point of the two neighboring cross sections to avoid water level problems. To simplify things & calculations, I set the same cross sections at the upstream & downstream of the structure, as the example below :

Chainage structure : X meters
Cross section upstream : X + 5 meters
Cross section downstream : X - 5 meters
Structure length : 10 meters
Roughness & in/outflow coefficients : By default.

But guess what ? the "Calculate Q/H relations" button for the weir works very well for any changes of weir parameters, but for the culverts... itdoesn't work at all ! i've tried to modify one by one each of the proposed culverts parameters in the Mike 11 network interface and I receive always the same message, even for a very little culvert well placed between the 2 cross sections :

"Unable to calculate Q/H relations for this culvert .... Please check culvert geometry and the upstream/downstream sections geometry, Return code = 1"

Consequently, I have two questions : because i'm still getting stuck with this basic problem since many days, I want you to ask if anybody had this sort of computational problem even one time and how to solve it ? Or even if anybody knows exactly what does "Return code = 1" means ? I've designed very simple cross sections, with basic parameters and nothing works...

I've also tried to find out any clue in the reference & user manual but without any results. So, what should be the solution without using the Bridge option ? (i've tried with the bridge and i'm not fully satisfied, mainly because one of the 3 bridges implemented has strange results (enormous head losses, etc...), when i'm clicking on the "submergence" & "overflow" options)


Thanks a lot for any response,

Cheerz,

You need to ensure that the cross sectional area of the culvert is less than the cross sectional area of both the upstream and downstream cross sections for each of the levels in the processed data table.  The structure/culvert flow equation requires that a flow contraction must occur at all level to ensure the correct calculation of the head losses. If the area of the culvert is even slightly greater than the cross section areas at a specific level then you have an expansion and not a contraction and MIKE11 will prevent you pre-calculating the processed data.  If you make your cross sections slightly wider or lower the invert then you will overcome the problem.