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EricXu

Junction - Manhole Approach == [ Method A | {Method B} ]

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Just could not understand item 48 of TUFLOW Build 2012-05-AA release notes:

 

The release notes said that "Previously, a junction (ie. there is no manhole chamber) was assigned to a node where there was only one inlet and one outlet culvert and they were large in size (ie. negating the need for an access manhole). This caused a problem if a third culvert, such as a small side pipe draining a pit, entered the node. The side pipe caused a manhole to be created, thereby causing significant losses due to the expansion and contraction of flow in the manhole chamber."

 

Junction is a type of manually defined manhole. TUFLOW manual said that "A manhole in a 1d_mh layer will override any automatically created manhole."  Why does the third side pipe cause a normal manhole to be created? 

 

Thanks,

Eric

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Hi Eric

 

Yes, maybe that's not very clear.  I'll try to explain by example.  If you had a series of pipes/culverts (eg. big enough to walk through) representing a large drainage conduit there typically wouldn't be any manholes because they were large enough to walk down so few or no manholes were needed for access.  There is a good example of this in Newcastle, Australia where there is a 1.8km series of box culverts you could drive a car down!  If there was a small side pipe entering the large culverts (eg. draining a pit), in Builds prior to 2012-05-AA this small pipe would trigger the creation of a manhole (if no manual manhole was specified) as the rule was if there were more than two pipes/culverts snapped to a (closed) node then create a manhole.  In reality, there would typically be no manhole and it should be represented as a junction.  From Build 2012-05-AA the rule is if at least one pipe/culvert at a (closed) node is large (ie. >1.801m dia for pipes and >1.201w by 1.801h for boxes) then make a junction, not a manhole.  This means the losses at that node will be considerably less as there is no expansion/contraction of water which would be the case.  Of course, you can override the automatic manholes/junctions by specifying some or all of them manually using a 1d_mh layer.

 

I hope that sort of makes sense!

 

Cheers

Bill

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Hi Bill,

So the third side pipe will not cause a nomral manhole to be created if we assign the "J" type (Junction) manhole for the no chamber junctions.

Thanks,

Eric

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Hi Eric

 

Yes, if using the automatic manhole option (which is the default setting).  If you manually specify the manhole in a 1d_mh layer as a J type, then it will be set as a J type irrespective of the automatic setting.

 

Cheers

Bill

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