# All Forums

### question: modeling staircases open channel with SWMM

I am now trying to make hydraulic model of a complex open channel by swmm, this channel as the one of main collector of urban storm water system (man-made flood way). The purpose of the simulation is determined the channel capacity and flood warning systems to create, etc.
The main problem is that the longitudinal channels of high slope (more than 35-15 percent) and the channel bottom made  step stairs.
Channel dimension is 3*4 meter (box) with high frequency stair stepped along the bottom of channel. Drop heights between 30 to 120 cm and the distance each other from 2-10meter (short drop of about 30cm (height) at 2-3 length mostly been implemented.) Therefore, very high frequency Stairs should be informed to the model.
If the location of each step we consider the node, very short distance is Links. (With inlet or outlet offset) Therefore minimal models converge, instability, continuity error and many problem accrued
So what can I do, please? Any suggestion?
If the dynamic wave method is used, do you recommend I focus on the methods for determining time step, and other techniques ……? I think that any of the links leads to the drop with minor loss, what a way to determine this loss is available?

#### Replies

• Dear robert

I wait impatiently to hear your ideas on this subject I am.

if in this field there is a reference book or article, please introduce it to me.
I thank you for the perfect ...

• dear robert

I don’t understand what you mean about model result file! I sent the file, the file is the result? It is a model input file (*.inp), you mean that I should send the results file?
If you can run the file is determined the problem better. All links are very short distances. And all of them near the main problem (of course are non-convergence model). Usually instability index offers for highest critical links dose not helpful. This generally mentioned. But a few links not all of them!!
The point, which I realized after much effort is the minor loss for drop. I enter the experimental values for links with drop, model going to stabile.
The only current problem is how to calculate the correct minor loss coefficient, proportional to each drop.
I think I raised the question simpler:
What a way to estimate the local minor loss for drops.

• I understand you now and the the images I put here were the result of running your model.   I do not need the model output - I can make my output with SWMM 5.0.021 I do have some ideas for the loss coefficient per drop and I will post them here later today.
• I am grateful to you again. I upload the model file.  Model is slightly simplified to be discussed in the framework.  Channel in some areas (bridges) is closed rectangular box conduit. Experimental hydrographs upstream of a channel has been entered.

• Hi, This is the model results as you sent it to me - the instablility is due to the middle of the stairway when the nodes flood.  You can look at he link with the highest instability index to see which link is the worst link.  You did not have a continuity error so that was not the problem.

• Please try these suggestions - the flow instabilities are reduced an isolated in just a few links based on the Flow Instability Index table
• ِDear Robert

I am very grateful for your attention.
Although seeing these beautiful pictures I was excited. sure who first came to think that - especially traffic route Disabilities - build, had problems with modeling :))

lets a minutes, As you want,  I will send the model file.

• Hi, Can you upload your model?  It would be easier to debug or offer suggestions.
• Good, question.  I will try to answer this later today or tonight.