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Drainage string ,no design road model available

 
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ali v



Joined: 27 Aug 2016
Posts: 6

New South Wales, Australia

PostPosted: Sun 23 Oct, 2016 4:15 pm    Post subject: Drainage string ,no design road model available Reply with quote

I have prepared a small practice model. I just have a terrain for the area and there is no design road model available for this part. The pits are SA1 pits . I have also defined bypass flow model for this network. When I run the model and tick "consider bypass flow" , the inlets do not capture any flow (Qi =0) and all storm water is considered as by pass flow. when I remove "consider by pass flow" , the inlets capture storm water but because the model does not consider by pass flow there is an huge loss (QX) in the model . How can I fix this problem?

Cheers,
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Owen Thornton



Joined: 04 Oct 2005
Posts: 4081

Queensland, Australia

PostPosted: Mon 24 Oct, 2016 10:11 am    Post subject: Reply with quote

Ali,

Your SA1 pit inlet capacity is dependent on the road grade and xfall near each pit. These are normally calculated automatically, once you have linked in a setout and centre string from the road design file. But if you don't have a road design, nor any nearby design strings, you'll have to specify the road grade and xfall manually. If you don't, your SA1 pits will have zero inlet capacity when bypass is considered.

Is this an existing or proposed system? If proposed and you are designing for a minor event, you might be able to get away with sizing the pipes without considering bypass flow. Making the pipes bigger will get rid of the Qx. You should never have Qx in a minor or major event. In a major event (where you are not sizing pipes), you get rid of the Qx with a non-zero Qx routing increment (in cumecs), which reduces the inlet efficiency at some pits.

Owen.
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