SWMM5 Major Storm System
SWMM5 Major Storm System
(OP)
I have been worked with swmm5 on a couple of projects now and have been given a drainage plan to do for a subdivision with several ponds. The minor system has been modeled and sized with relative ease based on the 1 in 5 year event. Once the event is switched to the 1 in 100 year many of the nodes surcharge as expected.
The problem is that when I place the parallel conduits for the street flow, in the same manner as the applications guide shows, the EGL drops for some reason and no flow is routed through the street conduits?? At several of the nodes there is considerable flooding then once the additional pipes are put in it is like the excess flow just disappears as if the minor storm system can handle the entire flow with minor surcharging??
Any ideas or suggestions would be greatly appreciated as I am not sure what to do.
Thanks.
The problem is that when I place the parallel conduits for the street flow, in the same manner as the applications guide shows, the EGL drops for some reason and no flow is routed through the street conduits?? At several of the nodes there is considerable flooding then once the additional pipes are put in it is like the excess flow just disappears as if the minor storm system can handle the entire flow with minor surcharging??
Any ideas or suggestions would be greatly appreciated as I am not sure what to do.
Thanks.





RE: SWMM5 Major Storm System
1)Max Depth
The maximum depth of the manhole junction is the distance from its invert to the ground surface elevation where street flooding would begin to occur. If this maximum depth is left set at zero, SWMM automatically uses the distance from the junction's invert to the top of the highest connecting link, which would be the top of the gutter/street channel in this particular example.
2)Surcharge depth
The surcharge depth of a junction is the additional depth of water beyond the maximum depth that is allowed before the junction floods.
3) Conduit Offsets
The inlet offset for a conduit is the distance that its inlet end lies above the invert of the junction that it connects to. A similar definition applies to the offset for the outlet end of a conduit. In the parallel pipe and gutter system, the elevations of the gutters are set above the pipes using their inlet and outlet offsets
4)Are you using a Dynamic Wave Modelling approach? This is the best approach for modelling a dual drainage system.
The overland/roadway conduit needs to be coded using the above paramters. Figure 7-2, in the SWMM Applications Manual gives a good illustration of how the overland flow component needs to be coded.
Hope this helps.
RE: SWMM5 Major Storm System
Max Depth - 1.2m
Surcharge depth - 0 as no surcharging will occure above the street
Conduit Offsets for street - 1.2m
And I am using dynamic wave.
Still, prior to adding the second conduit the max depth observed is 1.2m plus flooding, then with no other change except the second conduit the max depth is suddenly less than 0.9m??
RE: SWMM5 Major Storm System
RE: SWMM5 Major Storm System
RE: SWMM5 Major Storm System
If the maximum depth of the flow node needs to 1.2m, then say your maximum road surface flow depth is 0.15m, your inlet offset would then need to be 1.05m and not 1.2m.
Looked at section J38-Out1, revised the inlet/outlet offsets as per above and the hydraulic grade line appears to be reasonable.
Hope this helps.
RE: SWMM5 Major Storm System
RE: SWMM5 Major Storm System
Conduit OL-1 Q=0.06cms
OL-2 Q=0.014cms
OL-3 Q=0.233cms
In all cases there is an overland flow in this section...deleting the overland flow conduit will indeed cause the HGL go up and ulimately surcharge the surface.
RE: SWMM5 Major Storm System
The three you mentioned appear to be the only ones that are working correctly.
RE: SWMM5 Major Storm System
I have not run into this issue before in previous modelling, it may be beneficial to post your question on the SWMM users forum, see the following website;
ht
Hope this helps.