SWMM5, InfoSWMM

How to Make a Smaller Model out of a Large Model in InfoSWMM

Subject: How to Make a Smaller Model out of a Large Model in InfoSWMM

InfoSWMM and H2OMAP SWMM will export only those ACTIVE elements to SWMM 5 as defined by the Facility Manager.

You can use the feature to make smaller SWMM 5 models and then reimport the exported smaller SWMM 5 model back into a H2OMAP SWMM or InfoSWMM scenario.

Maximum Surcharge Height Over Crown Explanation

Note: Maximum Surcharge Height Over Crown Explanation

Here is an example of how the Maximum Surcharge Height over the Node Crown is calculated. Consider a manhole with an invert of 10 feet, one incoming pipe (Pipe A), one outgoing pipe (Pipe B), both pipes with a diameter of 2 feet, but the invert of Pipe A is 10 feet and the invert of Pipe B is 11 feet. What is the Maximum Surcharge height if the HGL at the node is 17 feet?

HGL at Node ---- 17 feet

Maximum Surcharge Height Over Crown is 4 feet

Node Crown --- 13 feet Pipe B Crown --- 13 feet

Pipe A Crown --- 12 feet

Pipe B Invert --- 11 feet

Pipe A Invert --- 1o feet MH Invert --- 10 feet

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

The Importance of Viewing Results at the Proper Time Scale

Subject: The Importance of Viewing Results at the Proper Time Scale

In SWMM 5 when you are simulating rapidly changing flow – such as pump flows – it is important to remember that you are only seeing the results of the simulation at your selected report time step. Here is an example model with the same number of pump starts for all three simulations (318), the same average time step during the simulation (10 seconds) but different report time steps. The conception of the pump starts is totally different visually depending on the selected report time steps. You should always compare the starts using the pump graphs and the pump summary table. The percent utilized and the number of pump start ups tells you the mean pump start length or in this case 153 seconds or 45.1 percent of 30 hours divided by 318 pump starts.

An Example of the Importance of the Term DQ4 in the SWMM 5 St Venant Solution

Subject: An Example of the Importance of the Term DQ4 in the SWMM 5 St Venant Solution

The four terms are are used in the new flow for a time step of Qnew:

Qnew = (Qold – dq2 + dq3 + dq4) / ( 1 + dq1)

when the force main or gravity main is full dq3 and dq4 are zero and Qnew = (Qold – dq2) / ( 1 + dq1)

The dq4 term in dynamic.c uses the area upstream (a1) and area downstream (a2), the midpoint velocity, the sigma factor (a function of the link Froude number), the link length and the time step or

dq4 = Time Step * Velocity * Velocity * (a2 – a1) / Link Length * Sigma

where Sigma is a function of the Froude Number and the Keep, Dampen and Ignore Inertial Term Options. Keep sets Sigma to 1 always and Dampen set Sigma based on the Froude number, Ignore sets Sigma to 0 all of the time during the simulation.

The value of dq4 increases when there is a significant difference in the cross sectional area of the downstream end of the link and the upstream end of the link. In this example, the downstream storage node causes a backflow in the link (Figure 1). The flow may look unstable in the link flow time series but the change in flow is simply due to the water sloshing back and forth. There is no continuity error as the term dq4 keeps the water in the link in balance (Figure 2).