Known and Unknown Variables in the Node Continuity Equation of SWMM5

Subject: Known and Unknown Variables in the Node Continuity Equation

The new node depth is calculated based on the old inflow to the node, the old outflow from the node, the old node depth, a fixed time step, node evaporation and infiltration losses, new inflow to the node, new outflow from the node and the new total surface area of the node. The inflow, outflow and surface area are updated before the new iteration based on the last iteration link flows and node depths. The node depth equation is iterated until the depth in the node is less than 0.005 feet between the current iteration or the last iteration with a maximum of 8 iterations in SWMM 5.0.020
New Iteration Node Depth = Old Node Depth + [ ½ * (New Inflow – New Outflow) + ½ * (Old Inflow – Old Outflow) - Node Losses ] / New Surface Area * Time Step
1^st Iteration: New Node Depth = New Iteration Node Depth
2^nd to 8^th Iteration: New Node Depth = ½ * New Iteration Node Depth + ½ * Old Iteration Node Depth

SWMM 5 Aquifer has a Saturated and Unsaturated Zone

Note:  The unsaturated upper zone soil moisture varies between the initial upper zone moisture fraction to the porosity fraction for the soil.  The soil moisture content is for the SWMM5 Aquifer which can cover more than one Subcatchment in your simulation network.

InfoSWMM and H2oMAP SWMM Output Statistics Manager

Note:  You can use the Output Statistics Manager in InfoSWMM and H2OMAP SWMM to compute the mean and maximum peak flow for ALL of the links or the mean and maximum depths of all nodes in your network. Once you have calculated the mean flows using the tool you can copy them using the command Ctrl-C and paste them to a new field in the Conduit Information DB Table.  The pasted mean flow from the Conduit Information table then can be mapped using Map Display.

Step 1:  Run the Output Statistics Manager and decide what links and statistics you want to compute.

 

Step 2:  Select the links you want to analyze using the pick tool.

Step 3:  Copy the Mean or Average Flow value using the command  Ctrl-C.

Step 4:  Copy the Mean or Average Flow value to the created Mean Field in the Conduit Information DB Table.

Step 5:  Map the Conduit.Mean variable from the Conduit Information DB Table.

Step 6:  Display the mean flow for each link.

EPA National Stormwater Calculator

Released today by the EPA (Dr Lewis Rossman) is a USA Nationwide Stormwater Calculator

Here is a new tool, based on SWMM, that may be of interest. It provides non-modelers with a quick and easy way to rigorously estimate stormwater runoff volumes from their properties. For you SWMM experts, it offers an easy way to download long term rainfall data and monthly ET rates for use in your SWMM models.

EPA's National Stormwater Calculator is Now Available to the Public http://www.epa.gov/nrmrl/wswrd/wq/models/swc/

EPA's National Stormwater Calculator is a desktop application that estimates the annual amount of rainwater and frequency of runoff from a specific site anywhere in the United States. Estimates are based on local soil conditions, land cover, and historic rainfall records. The Calculator accesses several national databases that provide soil, topography, rainfall, and evaporation information for the chosen site. The user supplies information about the site's land cover and selects the types of low impact development (LID) controls they would like to use.
Lew Rossman
Water Supply and Water Resources Division
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268

EPA National Stormwater Calculator Graphical User Interface

SWMM5 Runoff and Depth Relationships

Note:  The surface runoff is a non linear function of the independent depth in both the pervious and impervious areas of the subcatchments.   No surface runoff occurs until the depth over either the impervious or pervious area is greater than the respective depression storage (Figure's 1, 2, 3 and 4).

Figure 1:  Surface Runoff, Depth and  Depression Storage Relationship.

Figure 2:  Subcatchment Runoff and Depth over time with a Subcatchment Width of 500 feet.

Figure 3:  Subcatchment Runoff and Depth in a Scatter Graph with a Subcatchment Width of 500 feet.

Figure 4:  Subcatchment Runoff and Depth in a Scatter Graph with a Subcatchment Width of 2000 feet.

InfoSWMM and H2OMap SWMM Batch Simulation Manager

Note:  How to load Scenario Output into the Report Manager of H2OMAP SWMM and InfoSWMM after they have been run in a Batch File.

 

How to Make a New Project INI file for InfoSewer

Note:  How to Make a New Project INI file for InfoSewer

Step 1: Make a new InfoSewer Project as a New Empty Map and use the ArcGIS Default as the spatial reference.

Step 2:  Save your new empty model.

Step 3:  Copy your old model DB folder to the new MyEmptyModel DB folder

Step 4:  Open up  the mxd file MyEmptyModel and Initialize it – it should be a valid model now.

InfoSWMM and H2oMAP SWMM Map of the Maximum Surcharge Depth Over Highest Pipe Crown

Note:  You can copy and paste information from the Junction Output Summary to a newly created Junction Information DB Column so that you can use Map Display to visually see the newly saved output variable.

Step 1:  Run the model and then go to the Junction Summary in Report Manager and select all of the nodes in your model.

Step 2:  Copy the Maximum Surcharge Height over Highest Pipe Crown Column

 

Step 3:  Make and Insert a New Editable Field in the Junction Information Table by Pasting the information you just copied from the Junction Summary  Output Column.

Step 4:  Use the Map Display Command and use Existing DB as the Source and the newly created variable Junction_Surcharge_Depth

Step 5:  Use the Option Show Label Properties and adjust the Font to show the maximum surcharge depth.

SWMM5 Groundwater Flow Components

Note:  There are three sub flow components in the calculation of the groundwater flow from a SWMM 5 Subcatchment. 

1^st Component: Flow = Groundwater Flow Coef. * (LowerDepth – Aquifer Bottom to Node Invert) ^ Groundwater Flow Exponent

2 ^nd Component: Flow = SurfaceWater Flow Coef. * (Aquifer Bottom to Water Surface – Aquifer Bottom to Node Invert) ^ SurfaceWater Flow Exponent

3^rd Component: Flow = SurfaceWater-Groundwater Flow Coef. * (Aquifer LowerDepth * Aquifer Bottom to Node Invert)

The total flow is the sum of all three components.

SWMM 5 Subcatchment Runoff and Depth Relationship

Note:  The surface runoff is a non linear function of the independent depth in both the pervious and impervious areas of the subcatchments.   No surface runoff occurs until the depthover either the impervious or pervious area is greater than the respective depression storage (Figure's 1, 2, 3 and 4).

Figure 1:  Surface Runoff, Depth and  Depression Storage Relationship.

Figure 2:  Subcatchment Runoff and Depth over time with a Subcatchment Width of 500 feet.

Figure 3:  Subcatchment Runoff and Depth in a Scatter Graph with a Subcatchment Width of 500 feet.

Figure 4:  Subcatchment Runoff and Depth in a Scatter Graph with a Subcatchment Width of 2000 feet.

Three Types of Surfaces in each Subcatchment of SWMM 5

Note:  There are Three Types of Surfaces in each Subcatchment of SWMM 5.  The overall depth in a subcatchment is the weighted average of the impervious without depression storage area, the impervious with depression storage area and the pervious area depth.  The depths on each type of area are independent of each other. 

Figure 1:  The processes that occur on each type of Subcatchment Area.

Figure 2:  The three independent Depths on a Subcatchment.  The SWMM 5 reported Depth is the weighted average of the three depths.

The total flow from a Subcatchment in SWMM 5

Note:  The total flow from a Subcatchment is the sum of the flow from the impervious area with and without depression storage and the pervious area with depression strorage.  The same width, slope but different roughness applies to the impervious and pervious portions of the subcatchment.

 

Link Depth and Node Depth Relationship in SWMM 5

Note:  The depth in a manhole or node in SWMM 5 can be higher than the depth in the connecting links if the link is surcharged.  Typically the upstream link depth is equal to the upstream node depth (if there is not link offsets) and the downstream link depth is equal to the downstream node depth (if there is no offsets) until the link is surcharged and then thenode surcharge depth algorithm is used in SWMM 5 and point iteration equation is used to calculate the surcharge depth in the node.

Simulating a Blocked Pipe in SWMM 5 and InfoSWMM

Note:  For example, you can use the Simulation Elapsed time as the Premise and a complete closure of the orifice as the action to simulate a blockage in a portion of the network.  A circular orifice can be used to simulate a circular pipe and of course a rectangular orifice can simulate a rectangular pipe.

Average Number of Node Iterations in SWMM 5 Dynamic Wave Solution

Subject:  SWMM 5 will iterate for the new node depth at each time for a minimum of 2 iterations to a maximum of 8 iterations based on the Node Continuity equation.  If you plot the average number of iterations over time then typically the number of iterations go up as the Inflow increases.  The nodes with the most iterations changes over time as the peak flow moves through the network as shown in this plan view.  The iterations used during the simulation is a function of the node stop tolerance which has a default value of 0.005 feet in SWMM 5.

Export from WeatherUnderground using the CSV File Export Option to InfoSWMM

Note:  Export from WeatherUnderground using the CSV File Export Option to InfoSWMM

 Weather Underground is a site that provides excellent local weather information in the form of graphs, tables and csv files. You can use the data very easily in InfoSWMM by copying from Excel to a time series in InfoSWMM. Here is the rainfall for a storm event in Tampa, Florida in September 11, 2010

Step 1: Export from WeatherUnderground using the CSV File Export Option

Step 2: The data imported from the csv file to Excel and after the text to columns tool is used looks like this in Excel. The data is now ready to be imported into InfoSWMM after the time column is adjusted to fall on even 5 minute intervals. In Excel you can use the formula @ROUND((B2)/"0:05:00",0)*"0:05:00" to round all of the time values to 5 minutes. If you do not do this step then you will have problems in InfoSWMM due to the rainfall interval not being equal to the defined raingage interval.

Step 3: You will need to format the new rounded time as a time format for import into a InfoSWMM time  series.  The time series is created in the operation tab of the attribute browser.

Step 4: Open up and make a new time series in InfoSWMM.

Step 5: Copy and then paste the date, rounded time column and rainfall column into the InfoSWMM time series columns.

 Step 6:  Make a raingage in the DB Table in InfoSWMM that will use the time series you just made.  In the case of the Weather Undergrounddata we will use inches, intensity, a rainfall interval of 5 minutes, time series and the name of the time series.  SCF should be 1 for Snow conversion and do not need to include a Filename or Station name as we are not using an external file.