Detention Basin Basics in SWMM 5

Subject:  Detention Basin Basics in SWMM 5

 What are the basic elements of a detention pond in SWMM 5?  They are common in our backyards and cities and just require a few basic elements to model.  Here is a model in SWMM 5.0.022 that even has a fountain in the real pond – which we not model for now.   The components of the model are:

 1.   An inlet to the pond with a simple time series – a subcatchment can be added to it in a more complicated model but for now we will just have a triangular time series,

2.   A pipe to simulate the flow into the pond from the inlet,

3.   A Storage Node to simulate the Pond that consists of a tabular area curve to estimate the depth and area relationship,

4.   A Storage Node to simulate the Outlet Box of the Pond

5.   Two Small Rectangular Orifices to simulate the low flow outflow from the pond at an elevation less than the weir

6.   A large rectangular orifice to simulate the normal inflow to the Box

7.   A rectangular weir to simulate the flow into the box when the pond water surface elevation is above the box

8.   The outlet of the Box is a circular link with a Free outfall as the downstream boundary condition

9.   The flow graph in the image shows the flow into the box starts from the two small orifices, next from the large orifice and finally from the top of the box or the weir.

 

 

InfoSewer Link and Head Calculations for Steady Flow

Note: Steady State InfoSewer solution solves for the link flow and node heads

 Here is an example of how the Steady State InfoSewer solution solves for the link flow and node heads or depths:

 •         1st Flow is computed in each link and d and d/D is calculated based on pipe flow and manhole loading data and not the adjusted data from the 2nd pass.

•         2nd InfoSewer adjusts the link depth based on the manhole head and lists the adjusted depth in the browser and the Report Table after the manhole depths are calculated from downstream to upstream in the network.

•         Result: The HGL graph shows the link d and d/D based on pipe flow not the adjusted depth so you are looking at the results of the 1st pass in the links and the 2nd Pass in the Nodes in a HGL Plot  for a Steady State Simulation. 

Here is one example of this sequence of events: The downstream head at the outfall causes a backwater condition in all of the links.  The d/D and q/Q is based on the manhole loading flow in the 1st pass and indicates the pipe is NOT full. However, in the 2nd Pass where the manhole depths are calculated from downstream to upstream the effect of the downstream boundary condition is felt.  The head shows that there is a full downstream boundary condition which is reflected in the condition of backwater and in the adjusted depth value.  The links are now full and the full depth is reflected in the value of the adjusted depth and the graphical presentation.

 How to interpret this result:

1.   Based on the manhole loading to the network the pipes are NOT full which is indicated by the value of d/D and q/Q, however

2.   Based on the head calculations which account for downstream boundary conditions the pipes are full due to the backwater effect.  The backwater condition is reflected in the value of the adjusted depth – the adjusted depth shows the pipe to be full.

 Figure 1.  Backwater is caused by the downstream boundary condition and shows full pipes but d/D is less than 1 based on the 1st Pass Link Flow Values.

Figure 2. InfoSewer solves for the flows in the links in the 1st pass and the heads at the nodes in the 2nd pass for the Steady State solution.

 Figure 3.  Pipe Summary Table Shows the Pipe Adjustments based on 2nd Pass Head calculations and the d/D and q/Q values from the 1st Pass Link Flow Calculations. 

 Figure 4:  Two Pass Solution for InfoSewer (1) Flow and (2) Head

How to Understand the OUT directory in InfoSWMM and H2OMAP SWMM

Note:  How to Understand the OUT directory in InfoSWMM and H2OMAP SWMM

 

This is how you understand the files in the .OUT directory:

 

.OUT                         OUT directory of the InfoSWMM project

Scenario                    Location of all Scenario Output Files

Base                         The Base Scenario in this case

JOB                           The temporary output file for inp, out and txt files during the simulation –

                                this  should be cleaned out and copied at the end of the simulation

 

HYDQUA Header.html   is the left side of the browser page

HYDQUA.html             is the text output file from SWMM 5

HYDQUA.inp               SWMM 5 “like” input file for InfoSWMM

HYDQUA.out               Binary Output File

hydqua.rpt.lid.txt         LID Text Output File

hydqua.rpt.txt             InfoSWMM Text Output   Comprehensive Storm Water Management Model: based on EPA-SWMM 5.0.022

 

If you have an data abort in some of the older InfoSWMM models the txt and inp files are still in the JOB directory and NOT the BASE directory.  They can still be viewed in the JOB directory using the Notepad icons and searching for the files.

 

 

 

HYDQUA.html,  HYDQUA Header.html and hydqua.rpt.txt together in the browser.

 

 

InfoSewer - Minimum Travel Distance

Note:   The minimum travel distance in an InfoSewer or H2OMap Sewer model can be related to the mean link length in the Pipe DB Table.  Here is a table of the Mass balance check for one network versus the minimum travel distance in feet for the default values of network accuracy, minimum time length and maximum number of segments at a report time step of 1 hour.   As you can see making the Minimum Travel equal to the mode of the length histogram yields the best results even for the default model parameters.

 

Minimum Travel Distance

Mass Balance Check:

Label

1

10.50

(%)

5

3.25

(%)

10

6.25

(%)

20

17.34

(%)

25

7.05

(%)

30

1.38

(%)

40

1.07

(%)

50

1.07

(%)

55

1.05

(%)

58

3.87

(%)

60

3.34

(%)

75

0.55

(%)

80

3.09

(%)

90

11.60

(%)

100

17.20

(%)

200

17.34

(%)

1000

17.34

(%)

InfoSWMM Solution Options in Windows 7

Note:  InfoSWMM Solution Options in Windows 7

 1.   32 bit or 64 bit solution engine based on SWMM 5.0.022 selected using the Tools/Preferences/Operation Settings command

2.   Number of dynamic solution threads for parallel processing selected using the Run Manager,

3.   Single or batch runs selected using the Run Manager, and

4.   DLL or the Simulation Task Manager using the Tools/Preferences/Operation Settings command.

You have control over the type of engine, the number of threads, the number of runs and whether the run is started right now or scheduled to run later or in batch mode.