Showing posts from August, 2009

Using the Link Geometry to Divide the Flow

You can use the geometry of the connecting pipes to divide the flow instead of flow divider in the dynamic wave solution of SWMM 5. You can try to do the same using an Outlet link but the method of using two outlets is sometimes very unstable and requires a small time step just to lower the continuity error. I used two flat rectangular links with the same maximum depth and but different width values (Figure 1). The flow was split based on the value of Q full for the link (which you can see in the text output file (Figure 2).

Figure 1. Link Geometry

Figure 2. Flow Division from a inflow of 10 mgd

Figure 3. SWMM 5.0.016 Cross section geometry for the two rectangular links.

Suggestion for Entering Population DWF Data at a Node

I (and a few others) think a welcome change to the DWF dialog in SWMM 5 would be the addition of another scale factor to modify the average flow field. The purpose of the scale factor would be to allow the users to enter the DWF contributing population * the various DWF patterns * the scale factor (in units of cfs/person or l/s/person) in the Inflows dialog. Some users of SWMM 5 prefer to use population directly in the GUI rather than doing this calculation externally and entering either the flow in cfs or l/s. An example of why this would be useful is a future conditions model in which the population either increases or decreases in the catchment.

New Warning Messages in SWMM 5.0.014 to 5.0.016

These warning and error messages were added in SWMM to 5.0.016 to trap questionable raingage, link and node data. Correcting these errors does make a better model . The list shown below has the major new warnings and errors and help on interpreting the messages.
WARNING01: wet weather time step reduced to recording interval for RainGage Explanation: The user selected hydrology time step is automatically reduced by the engine to match the rain gage interval. The smallest rainfall interval among all of the gages will be used during the simulation. WARNING 02: maximum depth increased for Node Explanation: The rim elevation of a node has to be at least equal to the crown elevation of the highest connecting link to the node. The maximum depth of the node is increased to match the highest crown elevation. WARNING03: negative offset ignored forLink Explanation:Negative Offsets are set to offsets of 0.0 WARNING 04: minimum elevation drop used forConduit Explanation: If the elevation acro…