wwhm4 swmm element modeling

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1 WWHM4 SWMM ELEMENT MODELING © Clear Creek Solutions, Inc., 2010 The WWHM4 SWMM element is a conveyance feature that uses the EPA SWMM routing algorithms in WWHM4 in place of the standard HSPF’s RCHRES routing. The user has the choice of using either EXTRAN (Dynamic Wave routing in SWMM5) or Transport (Kinematic Wave routing in SWMM5) for the SWMM routing. The advantage of using SWMM routing in place of the standard HSPF routing is the ability of SWMM to explicitly model complex hydraulic conditions. These conditions occur when there is backwater or other special situations where HSPF’s assumptions of linear reservoir routing cannot accurately compute the movement of water from one conveyance element to another. SWMM input files must be created in their native SWMM programs (WWHM4 does not create SWMM input files). However, WWHM4 can read previously created PCSWMM 1 , XPSWMM 2 , SWMM5, and SWMM 4.4 (or earlier) input files. WWHM4 allows the SWMM user to import land use information from an existing SWMM Runoff file. The land use information is converted into WWHM4 basin element data. WWHM4 uses this basin element data to compute stormwater runoff using HSPF’s hydrology algorithms. WWHM4 produces a seamless (invisible to the user) linkage between the HSPF- generated runoff and the SWMM routing. The SWMM routing is computed continuously at the user-specified time step inside WWHM4. WWHM4 transfers the SWMM- generated routing output to WWHM4 downstream elements (if any) and/or the WWHM4 WDM database. This means that the user does not have to run SWMM separately; everything is done inside WWHM4 . The prerequisites for using the SWMM element are: Must have PCSWMM, XPSWMM or SWMM 4.4 installed to maintain SWMM interface files. Not required to run WWHM4 models. 1 PCSWMM is a registered trademark of Computational Hydraulics Int. (CHI). 2 XPSWMM is a registered trademark of XP Software Inc.

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Page 1: WWHM4 SWMM ELEMENT MODELING

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WWHM4 SWMM ELEMENT MODELING

© Clear Creek Solutions, Inc., 2010

The WWHM4 SWMM element is a conveyance feature that uses the EPA SWMMrouting algorithms in WWHM4 in place of the standard HSPF’s RCHRES routing. Theuser has the choice of using either EXTRAN (Dynamic Wave routing in SWMM5) orTransport (Kinematic Wave routing in SWMM5) for the SWMM routing.

The advantage of using SWMM routing in place of the standard HSPF routing is theability of SWMM to explicitly model complex hydraulic conditions. These conditionsoccur when there is backwater or other special situations where HSPF’s assumptions oflinear reservoir routing cannot accurately compute the movement of water from oneconveyance element to another.

SWMM input files must be created in their native SWMM programs (WWHM4 does notcreate SWMM input files). However, WWHM4 can read previously created PCSWMM1,XPSWMM2, SWMM5, and SWMM 4.4 (or earlier) input files.

WWHM4 allows the SWMM user to import land use information from an existingSWMM Runoff file. The land use information is converted into WWHM4 basin elementdata. WWHM4 uses this basin element data to compute stormwater runoff using HSPF’shydrology algorithms.

WWHM4 produces a seamless (invisible to the user) linkage between the HSPF-generated runoff and the SWMM routing. The SWMM routing is computed continuouslyat the user-specified time step inside WWHM4. WWHM4 transfers the SWMM-generated routing output to WWHM4 downstream elements (if any) and/or the WWHM4WDM database. This means that the user does not have to run SWMM separately;everything is done inside WWHM4.

The prerequisites for using the SWMM element are: Must have PCSWMM, XPSWMM or SWMM 4.4 installed to maintain SWMM

interface files. Not required to run WWHM4 models.

1 PCSWMM is a registered trademark of Computational Hydraulics Int. (CHI).2 XPSWMM is a registered trademark of XP Software Inc.

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We will create a WWHM4 project using the SWMM element. The project site is locatednear SeaTac Airport in King County, Washington. We click on the map to select theproject location. Based on our project location WWHM4 selects the appropriateprecipitation record and precipitation multiplication factor. We then have the option tofill in the Site Information boxes.

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We start by placing a SWMM element on the Schematic grid. Remember that everythingin WWHM4 flows from the top of the grid to the bottom. This means that all WWHM4elements that flow to the SWMM element must appear above the SWMM element on theSchematic grid.

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When we place the SWMM element on the Schematic grid the SWMM input windowappears to the right. This is the linkage to the rest of the SWMM environment.Descriptions of the options in the SWMM window are presented below.

Let’s take a minute and see what these options are.

SWMM Element Name: Name selected by the user. Be creative. SWMM .DAT File: SWMM input file used when running a SWMM model. Interface File Name: Binary file that contains all necessary streamflow time

series data for a connection between WWHM4 and the SWMM model. Output File Name: The output file contains the output data from a SWMM run. Launch SWMM Interface: Executes the selected SWMM program.

Now we will investigate each of these options in more detail.

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SWMM .DAT file: This is the SWMM input file used when running a SWMM model.This is a complex text-based file. This is the SWMM file that has been created usingeither a text editor or a proprietary software package such as PCSWMM or XPSWMM.

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When connecting to the SWMM .DAT file WWHM4 will scan the file and determine allof the possible connections that can be made between the WWHM4 and the SWMMnodes. If land use data exist in the SWMM file then the user will be asked if these dataare to be imported into WWHM4 in addition to the SWMM routing data.

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If the user selects “Yes” then subbasins will be created from the SWMM .DAT file andautomatically added to the schematic window with all of the appropriate connections tothe SWMM nodes.

NOTE: See the SWMM User Manual for complete description of the SWMM .DAT fileformat and for PCSWMM/XPSWMM model usage.

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Interface File Name: The interface file is a binary file that contains all necessarystreamflow time series data for a connection between WWHM4 and the SWMM model.This file is different for each SWMM .DAT file. This file is automatically created byWWHM4 and connected to the SWMM file. The user only needs to put the path andname of this file in this box so that WWHM4 knows what file to create. Multipleinterface files can be created to work with one SWMM .DAT file.

Output File Name: The output file contains the output data from a SWMM run. If thereis a connection from SWMM back into a WWHM4 element then the streamflow timeseries containing this SWMM output data will be in this file. WWHM4 will use the pathand filename listed in this box to find this file, extract the time series data, andautomatically link it into the downstream WWHM4 element.

Launch SWMM Interface: This button launches the selected SWMM program. Use ofthis option allows the user to modify the SWMM model in any way they choose beforerunning their WWHM4 model. The use of this interface is not required to run a SWMMmodel in WWHM4; all that is required to run a SWMM model is the SWMM .DAT file.

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At the bottom of the SWMM input window are a series of tabs.

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The “WWHM Connections to SWMM” tab allows us to see and define all of theconnections from the WWHM4 elements to nodes within the SWMM model. There arethree columns that make up the interface between WWHM4 and SWMM.

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The first column, “WWHM Element Name”, contains the names of the WWHM4elements (for example, basin, open channel, culvert, pond, etc.).

The second column, “Fraction Connected to SWMM Node”, shows the percent of thetotal runoff from the WWHM4 element that connects to the corresponding SWMM node.This is a number between zero and 1.0000. A fraction value less than 1.0000 means thatthe remaining fraction of that WWHM4 element’s discharge goes to one or moreadditional SWMM nodes.

The third column, “SWMM Node Name”, contains the name of the SWMM node towhich the WWHM4 element is connected.

We can remove a connection from the list moving the mouse to that cell and pressing the‘Delete’ key.

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The next tab is the “SWMM Connections to WWHM” tab.

We click on the tab to view the SWMM output connections window. This input windowallows the user to define all of the connections from SWMM nodes to downstreamWWHM4 elements within the WWHM4 model.

There are two columns that make up the interface between SWMM and WWHM4.

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The first column, “SWMM Node Name”, contains the names of the nodes within theSWMM element.

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The second column, “WWHM Element Name”, contains the name of the WWHM4element to which the SWMM node is connected.

Press the ‘Delete’ key to remove a connection from the list.

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The last tab is the “Global SWMM Preferences” tab.

This tab allows the user to define all of the global controls for WWHM4 interactions withSWMM. These global controls consist of runoff type connections, time control, andSWMM run control. Each global control is explained below.

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The Global SWMM Run Preferences includes “Runoff Type Connections fromWWHM to SWMM for import of SWMM file”. This connection information is onlyused if there is basin land use data to import from an existing SWMM model. There arethree runoff components that can be connected from a land use basin within WWHM4 toa SWMM node. These components are:

1) Surface Runoff: generally produced only by impervious surfaces; also known asoverland flow.

2) Interflow: shallow, subsurface runoff produced by pervious surfaces.3) Groundwater: produced by pervious surfaces; provides base flow in streams.

Stormwater runoff is usually defined as the total of the surface runoff and interflow;groundwater/base flow is excluded. Select the checkbox for each runoff component thatconnects to the SWMM node. In most situations only the surface runoff and interflowboxes are checked. The groundwater box is checked when the runoff goes directly to astream, lake, or wetland.

“EIA%” is the percent of the impervious area that is considered hydrologically effectiveand produces surface runoff to a conveyance system. Some impervious area drains ontoadjacent pervious surfaces, allowing some of the impervious area runoff (surface runoff)to infiltrate into the adjacent pervious soils before reaching a conveyance system.SWMM models typically assume that all of the land use coverage impervious area (totalimpervious area) is effective (EIA% = 100). This EIA% option allows the user to apply a

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percentage to impervious areas to reduce the total impervious area to represent theeffective impervious area.

The Time Control feature allows the user to control the start and end dates for thecreation of interface files and sets the computational time step for the SWMM modelruns.

The SWMM start and end dates are entered in the following format: yyyy/mm/dd.Note that an end date of 1999/12/31 actually tells the SWMM model to end computationsat the end of 12/30, not 12/31. If we want the model to run through the end of1999/12/31 then we need to specify an end date of 2000/01/01.

The Time Step (sec) is the computational time step and can be set by the user anywherefrom 1 second to 86,400 seconds (1440 minutes or 24 hours). This time step should beset to correspond to the needs of the SWMM model and is dependent on the type ofSWMM routing selected.

NOTE: The selection of a SWMM time step that is larger than the WWHM4 HSPF timestep will produce a WWHM4 error. The WWHM4 time step options are 5 minutes, 15minutes, 30 minutes, 1 hour, and 1 day. Large SWMM time steps will cause instability inthe SWMM model run results; small time steps require more computation time.

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The SWMM Run Control features present the user with a number of options whenrunning SWMM within WWHM4. These features include using an existing interface filealready created by WWHM4 for input to the SWMM routing, running WWHM4separately from SWMM, running SWMM Transport design option to resize culverts, runjust a single SWMM element rather than all of the ones in the model.

The “Use Interface file created from WWHM Runoff” check box is for when we wantto use an interface file that has already been created by a previous run of WWHM4.Interface files can take a significant amount of time to create. As a result, it is best to usethis option unless we have changed something in the WWHM4 model and need to updateand recreate the interface file.

NOTE: Interface file creation is critical to the proper use of the SWMM element.SWMM models use the inflow from interface files for all model runs.

The “Run WWHM file only” check box is for those occasions when we want to run theWWHM4 model for the purpose of creating a new interface file, but we do not want torun the SWMM model at the same time.

The “SWMM Transport design option on” check box turns on the SWMM Transportmodule that produces automatic upsizing of existing culverts to avoid surchargingculverts.

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The “Create Interface file from Existing WWHM Run” check box is used to run theWWHM4 model for the purpose of creating a new interface file without running theSWMM model at the same time.

The remaining SWMM options include:

Run SWMM file only: This command option will shortcut all of the normal WWHM4pathways for model runs and simply run the SWMM .DAT file using the most recentinterface file. This option is most useful when there are multiple SWMM elements in onemodel and we want to run only one specific SWMM model, not all of them.

Save SWMM Connection File: This option allows the user to save/edit/load connectionfiles. The connection file contains all of the information shown in the “WWHM4Connections to SWMM” tab window. These connections consist of:

swmmnode: name of hydraulic element “From Node” connection subbasin: name of subbasin connected to hydraulic element. fraction: fraction of flow that is connected to the hydraulic element; this value is

usually equal to 1. flows: selects which runoff components are connected from the runoff basin; the

choices are: Surface (S), Interflow (I), and Groundwater (G).

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The following table is an example of a SWMM connection file.

swmmnode subbasin fraction flows376 WC135 1 SIG378 WC134 0.0909 SIG413 WC134 0.0909 SIG434 WC134 0.0909 SIG440 WC134 0.0909 SIG451 WC134 0.0909 SIG470 WC134 0.0909 SIG471 WC134 0.0909 SIG504 WC134 0.0909 SIG508 WC134 0.0909 SIG509 WC134 0.0909 SIG

This text file can be edited manually and re-imported using the “Load SWMMConnection File” option shown below.

Load SWMM Connection File: Loads the SWMM connection text file that contains allof the connections from the WWHM4 to SWMM. This file will replace all of theexisting data in the “WWHM4 Connections to SWMM” tab window. This allows theuser to easily change WWHM4 to SWMM connections for large projects that can containhundreds of individual connections.

SUMMARY:1. Locate project site on map.2. Add the SWMM element to scenario.3. Load SWMM .DAT file.4. Decide whether or not to import SWMM runoff block land

use data or enter land use data manually.5. Create Interface File path and name.6. Create Output File path and name.7. Decide whether or not to launch selected SWMM program.8. Connect WWHM4 elements to SWMM nodes (as needed).9. Connect SWMM nodes to downstream WWHM4 elements

(as needed).10. Set Global SWMM Run Preferences.11. Run model.12. View output data.13. Finished.