MIKE 11 GIS

Hi,

I am a new user to MIKE software and am using it for creating flood inundation maps. As a beginner, I have started with MIKE 11 and have been partially successful so far.

Please refer the attachment for better understanding of my query.

There is an image file of my area of interest, Digitized river network and cross sections, flood inundation image.

Branch 1 is the main river channel, which bifurcates to Branch 5 in the downstream side which is the flood plain area. Branch 2 and Branch 3 are the joining rivers.

1. I need to confirm the rules for digitization of river network , i.e, in my case, I have digitized the Branch 1 till the end,  then joined the tributaries and the Branch 5. So wanted to know if this way of digitization is appropriate or there can be a other alternative?

2. the cross section spacing? Since, the study area is very big around 300 km, I have taken 2000 m as spacing.

3. I don't understand the concept of alignment markers. Like, is digitization of these make any difference? In my case , there aren't any kind of structures in the study area.

***4. Boundary conditions- This is where am stuck. I have time varying discharge and water level data at the U/S end,i.e Branch 1 , 2 and 3 ,hence using open ,inflow boundary conditions at these places.
But, I don't have any data at the D/S end. so I have assumed constant water level based on the cross sections, since the dem I use is very precise.

I was advised to opt for Q-H boundary condition but I dont know why, the "auto calculation of q-h" tab does not pop up when clicked. kindly help me figure that out.

5. The Manning's n value. We give n value in the cross section editior and also in the HD parameters dialog. Since, changing n value  at one place doesnt effect the other, Please help me understand which one effects the simulation.

6. Last question is , the flood map does not match the requirements near the flood plain area, as in the water spread is very bizzare. I have tried a number of times, by changing the cross section spacing, but no positive results. Also the water depth is very less in the flood plain area.

Ketaki27

A couple of relative short replies to all your questions below.
If more detailed analysis and replies are required it is also advised to contact the support centre at mikebydhi@dhigroup.com
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[li]No strict rules or requirements exists really when it comes to river network digitisation. Everyone has their own preferences, but your approach is indeed very sound and easy to understand.
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[li]Again, it is not possible to give a strict recommendation on the Cross section spacing, as this really depends on the requirement to resolution in your model. And that can be different from project to project. 2 km spacing between sections is probably too large - at least at some locations in your model area. [/li]
[li]Alignment markers/lines are simply an option to digitize lines in parallel to the river and you can then eventually use these to cut your cross sections or to set the river embankment markers in cross sections. These lines/markers does not have an impact on the simulation kernel. [/li]
[li]Open inflow boundary is most typically applied as upstream boundary conditions. For the downstream it is reuired that the chainage of the boundary condition location is identical to the cross section chainage at the boundary location (you must have a cross section at that location to generate automatically a Q/h-relation).  [/li]
[li]Manning's n-value works in the way, that in case you have defined values in the cross sections then these values will always be applied. If you have not defined any resistance values (M or n-values) then MIKE 11 will use the resistance values from the HD Parameters dialog. [/li]
[li]Generating a flood map that correlates to observations can sometimes initially be a tedious process that require adjustment of the river lines and/or cross section adjustments. Additionally, the water level results presented in the maps naturally depends on the overall calibration of the river model and it is only possible to achieve correct flood maps if the river model is properly calibrated. [/li]
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Thank you for the reply Mr. Torben. Its been quite some time since this post. I Could figure out the Q/h auto calculation.

I have still been trying to get a proper inundation, will work on the cross section distances as you have mentioned.

And, regarding digitization of rivers, as you can see in the flood area, there are many interconnecting rivers, so I was trying to digitize them all , and draw smaller cross sections, so that the inundation comes along all the rivers.

Would like to have your comments on this. Your guidance on this would be highly appreciated.

I have been able to create a proper flood inundation map now! :)

Thanks.