Stormwater Management Model (SWMM) Information for watershed water quality, hydrology and hydraulics modelers (Note this Blog is not associated with the EPA). You will find Blog Posts and Twitter Embeds on the Subjects of SWMM5, InfoSWMM, InfoSewer, SWMMLive, InfoSWMM SUSTAIN, SWMM4 and SWMM in general.
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The Link Time Step in SWMM 5, InfoSWMM and H2OMap SWMM
Introduction: This set of blogs uses the 1000 year rainfall/runoff/hydraulics model that you can download athttp://swmm2000.com/forum/topics/1000-year-simulation-with-rainfall-in-swmm-5 to show the inner workings of SWMM 5 and by extension InfoSWMM and H2oMap SWMM using a QA/QC version of SWMM 5 with extended graphics. I always hope that seeing the inner workings of a SWMM 5 feature helps to understand the code, sensitivity and importance of a parameter. It also helps show sometimes when a parameter is not important.
Discussion: Here we look at the link time step for a 100 year simulation. If you use the Variable Time Step in SWMM5 with the CFL Adjustment factor the program will compute the needed link time step at each simulation time step based on the last time steps depth, velocity and width. The link time step is
Link Time Step = Adjustment Factor * CFL Explicit Time Step for the Controlling Link
The time step is larger for low flows and decreases as the flow in the link increases (Figure 1). The time step ranges between the maximum step allowed by the user during the simulation and the time step lengthening value in the Dynamic Wave Tab of the Simulation options. The program will use the minimum of the time steps for ALL links. The minimum time step at each simulation step is multiplied by the Adjustment Factor. The time steps used during the simulation are listed in the Routing Time Step Summary table where you can find the average, minimum and maximum time steps. The smaller the Adjustment Factor the smaller the link time steps during higher flow.
Figure 1. The Link Time Step over a 100 Year Period for Link Venant
Soffit Level (pipe technology)The top point of the inside open section of a pipe or box conduit. The soffit is the highest point of the internal surface of a pipe or culvert at any cross-section. The soffit is also referred to as the pipe obvert. So it is not quite the Crown of the Pipe. Here is an image I found that hopefully explains it better.
Comment: A really nice water analogy for the field properties Divergence, Curl and Gradient from the Blog Starts With a Bang
....it's pretty mathematically intensive, but what's missing from most textbooks and E&M courses are physical explanations of what the mathematics means. For instance, I've started teaching about fields, and pretty much every textbook out there goes on and on about the properties of fields. They say you can do three things to fields, take the gradient, divergence, orcurl of them. (Are you asleep yet? I'm sorry!) What do these things mean? An easy way to picture it is in terms of water. If you placed a drop of water anywhere on, say,Earth, the magnitude and direction of how it rolls down is the gradient of the Earth's elevation. If you let that drop of water flow, as it goes downhill, it can either spread out or converge to a narrower stream. When we quantify that, that's what the divergence of the field is. And finally, when that water is …
Engine Error NumberDescription ERROR 101: memory allocation error. ERROR 103: cannot solve KW equations for Link ERROR 105: cannot open ODE solver. ERROR 107: cannot compute a valid time step. ERROR 108: ambiguous outlet ID name for Subcatchment