Subject: SWMM 5 Slope Rules are Critical to Understand for Short Pipes
If you have a short pipe and an significant offset depth for the pipe at either the upstream or downstream end of the pipe then the difference between the arithmetic method of calculating the slope and the SWMM 5 method can be noticeably different.
The dynamic wave flow in SWMM5 and InfoSWMM is calculated from the following equation
Q = (Qold – dq2 + dq3*sigma + dq4*sigma ) / ( 1 + dq1 + dq5)
Where,
Qold = Last Time Step Flow in the Link
dq1 = friction loss term
dq2 = water suface slope + bed slope term
dq3 = midpoint area non linear term
dq4 = upstream and downstream area non linear term
dq5 = Entrance, Other and Exit Loss Term
sigma = function of the Froude number and a function of the Three Intertial Term Options
Figure 1 shows how Sigma is set based on the user selection of the Three Intertial Terms. Figure 2 shows how Sigma is calculated for the Dampen Option. If you use Ignore then dq3 and dq4 are ignored all of the time, if you use Dampen then dq3 and dq4 are used for a Froude number less than 0.5 and then the terms gradually fade away until a Froude number of 1 is reached. If you use Keep then the non linear terms are used all of the time no matter the value of the link Froude Number. There is one exception to this rule: If a closed link is full then the value of sigma is set to 0.0 no matter what is selected for the Intertial Term.
Figure 1. The value of Sigma for each of the Three Inertial Term Options in SWMM 5 and InfoSWMM/H2OMAP SWMM
Figure 2. At each iteration for each link during the simulation the link Froude Number is calculated and based on the Froude Number the value of Sigma is Set.
Subject: SWMM 5 QA and Application Manuals on the EPA Web Site
The EPA Web Site has three manuals that you can download at http://www.epa.gov/nrmrl/wswrd/wq/models/swmm/#Downloads
1. SWMM Applications Manual
2. SWMM 5 Quality Assurance Report
3. SWMM 5 Users Manual
Subject: How to Make a Small Model out of a Large Model in H2OMAP Sewer
The process is easy if you use Domain and Facilities.
Step 1. Use the Trace Upstream Network Command in Utilities to find the upstream network from your node of interest. The upstream network is saved to a Domain.
Step 2. Use the Facility Manager to 1st deactivate the whole network and then 2nd to add the Domain to your Facility or the nodes and links that you will simulate
You now have a smaller network to examine in Detail. You may have to make a temporary Outfall node to run the model if there are no Outfalls in the model.
Subject: InfoSWMM Pump Operation Curve and Time Off Curve
The InfoSWMM pump operation curve will show you over time the relationship between the head of the pump and the pump flow. The pump summary table will also tell you how often the pump head was higher than the High Head of the Curve and how often the pump head was lower than the Low Head of the Curve. If you replay the animation the purple square will move up and down the pump curve.
