Good day everyone,
I am working on drainage for a median storm sewer, culverts and ditching for a large freeway expansion project. I have median storm sewers running down my entire roadway (about 5kms). I have manually inputed the upstream and downstream elevations of the pipes in SSA, but when these pipes are connected to an inlet or junction, I only have the option of selecting one invert elevation for each structure (I am actually using a lot of catchbasin manholes in this project, which I am unsure of SSA's ability to model). I have multiple drops of varying elevation differences throughout the project, with some of these inlets/junction requiring drop structures due to the large difference in elevation change. How do I properly model this in SSA?
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I have done very little in SSA but PERHAPS you could slap a JUNCTION just on the downstream side of the "real" structure and model it that way by setting your outflow elevation in the junction. (There may be a setting somewhere to change the inverts in the manhole, but like you, I have not found it.)
I originally set up my project like that, but then I realized that there is onyl 1 invert elevation option for both inlets and junctions, so I just went with the inlets.
Does the invert elevation in the inlet/junction structure just refer to the bottom of the structure (or maybe the sump), and then further information needs to be inputed in the conveyance links window?
I was thinking that your conveyance link could be about 4' which, in my area would represent the distance across a normal manhole. So outlet to inlet (junction) elevations could certainly represent your drop in height. Just a thought.
I like that idea. After looking at the SSA manual, I think that the inlet invert elevation is the sump or lowest possible "base" elevation of the structure, and then you can further define the conveyance link elevations higher than the "base" elevation (This is what I can understand from the SSA help PDF, page 251, screenshot attached).
According to SSA 2012 PDF page 234-235,
This entry defines the bottom elevation of the junction (ft or m) above a
common datum. See Figure 7.11 for an illustration of this value."
I was wondering the same thing at one time. It is just the bottom of the structure and has nothing to do with the pipe inverts. Hope this helps.
Just to clarify, I know you were talking about the catchbasin invert elevation, but the one I posted, I thought it described it better, but it would mean the same thing.
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