Archive for February, 2012
How to Make a Smaller Model out of a Large Model in InfoSWMM
Posted by dickinsonre in How to Make a Smaller Model out of a Large Model in InfoSWMM, swmm5 on February 17, 2012
Maximum Surcharge Height Over Crown Explanation
Posted by dickinsonre in Maximum Surcharge Height Over Crown Explanation, swmm5 on February 8, 2012
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
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The Importance of Viewing Results at the Proper Time Scale
Posted by dickinsonre in swmm5, The Importance of Viewing Results at the Proper Time Scale on February 6, 2012
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
Posted by dickinsonre in An Example of the Importance of the Term DQ4 in the SWMM 5 St Venant Solution, swmm5 on February 6, 2012
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).
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| Figure 1. GIF of Water Surface Showing the effect of the term dq4 |
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| Figure 2. Time Series of Flow – the Link has Mass Balance due to the term dq4 |
Use the SWMM 5 Scatter Graph to show the Pump Curve used during the Simulation
Posted by dickinsonre in swmm5 on February 6, 2012
From SciAM – Why Plants are important to River Formation
Posted by dickinsonre in From SciAM - Why Plants are important to River Formation, swmm5 on February 5, 2012
Earth’s flora is responsible for the glaciers and rivers that have created this planet’s distinctive landscape
Perhaps even more surprisingly, vascular plants formed the kinds of rivers we see around us today, according to another article by Martin Gibling of Dalhousie University in Nova Scotia and Neil Davies of the University of Ghent in Belgium, who analyzed sediment deposition going back hundreds of millions of years. Before the era of plants, water ran over Earth’s landmasses in broad sheets, with no defined courses. Only when enough vegetation grew to break down rock into minerals and mud, and then hold that mud in place, did river banks form and begin to channel the water. The channeling led to periodic flooding that deposited sediment over broad areas, building up rich soil. The soil allowed trees to take root. Their woody debris fell into the rivers, creating logjams that rapidly created new channels and caused even more flooding, setting up a feedback loop that eventually supported forests and fertile plains.
“Sedimentary rocks, before plants, contained almost no mud,” explains Gibling, a professor of Earth science at Dalhousie. “But after plants developed, the mud content increased dramatically. Muddy landscapes expanded greatly. A new kind of eco-space was created that wasn’t there before.”
How to Import the SWMM 5 Report File as a Layer in infoSWMM
Posted by dickinsonre in How to Import the SWMM 5 Report File as a Layer in infoSWMM, swmm5 on February 5, 2012
Subject: How to Import the SWMM 5 Report File as a Layer in infoSWMM
The idea of this blog of note is to show how one may extract information from the SWMM 5 or InfoSWMM RPT file and import the Excel File as a feature in InfoSWMM. This blog has an example Excel file to illustrate the linkage. The steps are:
Step 1: Copy the whole row from Conduit Summary from the InfoSWMM Browser
Step 2: Add the two columns length and slope from the Link Summary Table and the InfoSWMM Browser
Step 3: You need a few calculations based on the table values from SWMM 5 to estimate the CFL time steps in the .
Step 4: Add the Excel Spreadsheet as a layer in InfoSWMM – the Named Range should be added to insure valid numbers and not Nulls after the join
Step 5: You can now plot the CFL Time Step for the Links using the Layer Properties command in Arc Map
Step 1: Copy the whole row from Conduit Summary
Step 2: Add the two columns length and slope from the Link Summary Table
Step 3: You need a few calculations based on the table values from SWMM 5 to estimate the CFL time steps.
The CFL Step = Length / (Full Velocity + (Gravity * Full Depth)^0.5)
Full Velocity = Full Flow / Full Area
You also need to create a Name A Range for you data so that the data does not show up as Nulls
Step 4: Add the Excel Spreadsheet as a layer in InfoSWMM – the Named Range should be added
Step 4: Join the Excel Table to the InfoSWMM Conduit Feature Layer
Step 5: You can now plot the CFL Time Step for the Links using the Layer Properties command in Arc Map
How to Approximate a Timer in the RTC Rules of SWMM 5
Posted by dickinsonre in How to Approximate a Timer in the RTC Rules of SWMM 5, swmm5 on February 4, 2012
Subject: How to Approximate a Timer in the RTC Rules of SWMM 5
SWMM 5 does not have a explicit timer in its Real Time Control (RTC) rules but you can approximate it by using a Control Curve as in the attached example model. The Control Curve will modify the setting of the Weir by the Inflow to the Storage node. You can have normal weir flow settings based on the invert elevation of the weir and the Surface node water surface elevation but in addition you can control the weir setting by:
1. Closing the weir when the inflow is low,
2. Closing the weir by staggered Storage node depth,
3. Opening the weir gradually when the inflow increases
4. Closing the weir by a combination of Node Depth IF statements and Control Curve rules
For example, you can have the Weir Setting controlled the Node Depth, Link Inflow and Node Inflow simultaneously approximately with the depth and the inflow parameters closing the weir by proxy instead of by time since the closing.
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You are currently browsing the archives for February, 2012
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- Example Groundwater Model in SWMM 5 May 13, 2012
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