How to Get the SWMM 5 GUI to recognize an already existing Report and Output File

Note: How to Get the SWMM 5 GUI to recognize an already existing Report and Output File
I found a way to see your results in SWMM 5.0.013. You need an ini file with the results flag turned on. The ini file can be very small - just three lines but once you have the Saved=1 flag on then when you open the GUI the graphs and output file icons will be turned on. An alternate method would be to have the flag automatically turned on the SWMM 5 GUI in FMAIN.PAS but you would have to recompile the GUI.
// Reset status flags
Uglobals.HasChanged := False;
Uglobals.UpdateFlag := False;
Uglobals.ResultsSaved := True; // This is normally False
Here is the three line ini file that you need.
[Results]
Saved=1
Current=1

You will have to make an ini file for each input file name and each one will have an ini file extension

The SWMM 5 GUI will
· open up your input file,
· find the results flag,
· check for existence of the rpt and out files and then
· find out the SWMM 5 version of the output file.

Solving a Bug: Processes

Solving a Bug: Processes

SWMM 5 Convergence Process

Note: Iteration Process in the SWMM 5 Dynwave.c Code

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.

The Reported Depth Variable in a 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.

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 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.

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.

Link 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 the node surcharge depth algorithm is used in SWMM 5 and point iteration equation is used to calculate the surcharge depth in the node.

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 Aquifer has a Saturated and Unsaturated Zone

SWMM 5 Aquifer has a Saturated and Unsaturated Zone by dickinsonre 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. via Blogger http://www.swmm5.net/2013/07/swmm-5-aquifer-has-saturated-and.html

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.

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.

via Blogger http://www.swmm5.net/2013/07/infoswmm-and-h2omap-swmm-map-of-maximum.html

InfoSWMM Batch Simulation Manager

InfoSWMM and H2OMap SWMM Batch Simulation Manager by dickinsonre Note:  How to load Scenario Output into the Report Manager of H2OMAP SWMM and InfoSWMM after they have been run in a Batch File.   via Blogger http://www.swmm5.net/2013/07/infoswmm-and-h2omap-swmm-batch.html dickinsonre | July 28, 2013 at 11:42 am | Tags: Blogger, H2oMAP SWMM, IFTTT, InfoSWMM,swmm5 | Categories: H2OMAP SWMM, InfoSWMM, swmm5 | URL: http://wp.me/pnGa9-2n1

SWMM200.COM and Related Names

Note: Domain Names that redirect to www.swmm2000.com

· WWW.SWMM2000.COM

· WWW.SWMM5.INFO

· WWW.EPASWMM.INFO

· WWW.SWMMNOTES.COM

· WWW.SWMM5.COM

· WWW.SWMM.INFO

· WWW.SWMM50.COM

· WWW.INFOSWMM.INFO

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.

How to Delete Invisible InfoSWMM Subcatchments

Note: You could delete the subcatchments if you saw them on the screen. What I did here was to make a list of the subcatchments I wanted to delete; made a simple SWMM 5 import file simply containing the subcatchment names and the POLYGON field

I found a workaround that uses a part of the SWMM 5 input file but does not require you to export all of the SWMM 5 data to EPA SWMM 5. If you make a POLYGON file in this example format for all of the subcatchments you want to delete then you can import JUST the polygon data using the EPASWMM 5 import, selecting Clear All and Import. The subcatchments can then be located using the Locate command and you can easily delete the data using the delete selection icon.

I found it is best to bring in the polygon surrounding the subcatchment in the form of a triangle as this example shows.

[POLYGONS]
L33 1 1
L33 11 11
LS3 3 99
LS33 3 9
LS33 11 11
LS33 3 199

InfoSWMM 2D Version 2.0 for ArcGIS 10

MWH Soft Releases InfoSWMM 2D Version 2.0 for ArcGIS 10, Raising Bar for Urban Drainage Modeling and Simulation

Latest Release Solidifies Product as Leading GIS-centric Urban Drainage Modeling and Management Solution

Broomfield, Colorado USA, October 12, 2010

MWH Soft, a leading global innovator of wet infrastructure modeling and simulation software and technologies, today announced the worldwide availability of the V2.0 Generation of its industry-leading InfoSWMM 2D for ArcGIS 10 (Esri, Redlands, CA). InfoSWMM 2D delivers new ways to quickly build and analyze very large and comprehensive two-dimensional (2D) models that reliably simulate urban stormwater, sanitary sewers, river flooding and pollutant transport. It allows users to accurately predict the extent and duration of urban and rural flooding for comprehensive stormwater management directly within the powerful ArcGIS environment.
A fully hydrodynamic geospatial stormwater modeling and management software application, InfoSWMM 2D can be used to model the entire land phase of the hydrologic cycle as applied to urban stormwater systems. The model can perform single-event or long-term (continuous) rainfall/runoff simulations accounting for climate, soil, land use, and topographic conditions of the watershed. In addition to simulating runoff quantity, InfoSWMM 2D can reliably predict runoff quality, including buildup and washoff of pollutants from primarily urban watersheds. It also features very sophisticated Real-Time Control (RTC) schemes for the operational control and management of hydraulic structures.
Built atop ArcGIS and using exceptionally robust and efficient numerical simulation capabilities, InfoSWMM 2D seamlessly integrates advanced 1D and 2D functionalities in one environment, enabling users to model the most complex storm and combined sewer collection systems and surface flooding with incredible ease and accuracy.
When overland flows are routed through a complex urban area or highly varied terrain, the numerous elevation changes and obstacles can significantly impact results. This problem can be further complicated by the presence of sewer networks, where flows can both enter and exit the system during flood events. With InfoSWMM 2D, users can employ 1D simulation to identify the location of flooding and 2D simulation to investigate the direction and depth of flood flows in specific areas.
The full 2D free-surface shallow water equations are solved using a highly advanced finite volume method, which is particularly suitable for rapidly varying flood flows such as those through steep streets and road junctions and those associated with bank overtopping or breaching. The unparalleled 1D/2D dynamic linking capabilities of InfoSWMM 2D give engineers the unprecedented power to analyze and predict potential flood extents, depth and velocity and accurately model the interaction of surface and underground systems in an integrated 1D/2D environment. The software can also be effectively used to simulate and analyze tidal surges, dam breaks and breaches on sewer networks. The combined water level and velocity results throughout the flooded areas can be viewed as graphs, tables or animated, thematic flood maps.
“We’re deeply committed to providing a geospatial modeling experience that is both intuitive and powerful, and InfoSWMM 2D V2.0 embodies that commitment,” said Paul F. Boulos, Ph.D., Hon.D.WRE, F.ASCE, President and Chief Operating Officer of MWH Soft. “This release, following closely on May’s version 1.0, delivers major geospatial technological enhancements in short release cycles to make sure our customers are always equipped with the ultimate ArcGIS-centric decision support tool for stormwater and urban drainage systems. It greatly extends the core features of InfoSWMM, providing the most powerful and comprehensive ArcGIS-centric tool kit ever for managing the risks of urban and rural flooding.”
Pricing and Availability
Upgrade to InfoSWMM 2D V2.0 is now available worldwide by subscription to the MWH Soft Gold program. Subscription members can immediately download the new version free of charge directly from www.mwhsoft.com. The MWH Soft Subscription Program is a friendly customer support and software maintenance program that ensures the longevity and usefulness of MWH Soft products. It gives subscribers instant access to new functionality as it is developed, along with automatic software updates and upgrades. For the latest information on the MWH Soft Subscription Program, visit www.mwhsoft.com or contact your local MWH Soft Channel Partner.

Adding New View Variables To the SWMM 5 Delphi and C Code

Subject: Adding New View Variables To SWMM 5 for Villemonte Correction for Downstream Submergence. A simple seven step procedure to modify the SWMM 5 GUI Delphi Code and the SWMM 5 C code.

Step 1: Add a new View Variable to the SWMM 5 GUI Delphi code UGLOBAL.PAS

You need to add a new variable name (LINKVILLEMONTE) and increase the index number of LINKVIEWS

LINKVILLEMONTE = 48; //Output // (5.0.022 - RED)

LINKQUAL = 49; //Output // (5.0.022 - RED)

LINKVIEWS = 48; //Max. display variable index // (5.0.022 - RED)

Step 2: Add a new BaseLinkUnits description to the SWMM 5 GUI Delphi code UGLOBAL.PAS

('',''), // Villemonte Correction // (5.0.022 - RED)

('mg/L','mg/L')); // Quality

Step 3: Add a new Link View Variable SourceIndex description to the SWMM 5 GUI Delphi code Viewvars.txt

(Name: 'Villemonte Correction';

SourceIndex: 43;

DefIntervals: (25,50,75,100)),

(Name:'Quality';

SourceIndex: 44;

DefIntervals:(0.25,0.5,0.75,1.0))

);

Step 4: Add a new Link View Variable LINK_VILLEMONTE to the SWMM 5 C code in enums.h

You also need to increase the number of Link Results in enums.h for the increased number of view variables

#define MAX_LINK_RESULTS 45 // (5.0.022 - RED)

LINK_VILLEMONTE, // Villemonte Correction // (5.0.022 - RED)

LINK_QUAL}; // concentration of each pollutant

Step 5: Add a new variable to objects.h for the structure Tlink to remember the Villemonte correction at each iteration for each Weir and Orifice

double Villemonte; //(5.0.022 - RED)

} TLink;

Step 6: In the SWMM 5 LINK.C code in procedure weir_getInflow save the current iteration value of the Villemonte correction to the new structure variable

// --- apply Villemonte eqn. to correct for submergence

Link[j].Villemonte = 1.0; //(5.0.022 - RED)

Link[j].head = head; //(5.0.022 - RED)

if ( h2 > hcrest )

{

ratio = (h2 - hcrest) / (h1 - hcrest);

q1 *= pow( (1.0 - pow(ratio, weirPower[Weir[k].type])), 0.385);

if ( q2 > 0.0 )

q2 *= pow( (1.0 - pow(ratio, weirPower[VNOTCH_WEIR])), 0.385);

Link[j].Villemonte = pow( (1.0 - pow(ratio, weirPower[Weir[k].type])), 0.385); //(5.0.022 - RED)

}

Step 7: Save the value of the saved Villemonte correction in LINK.C in the procedure link_getResults so it can be read and seen in the Delphi interface

x[LINK_VILLEMONTE] = (float)Link[j].Villemonte; // (5.0.022 - RED)

Bottom and Side Outlet Orifices in SWMM 5

Note: The main difference between an Bottom and Side Outlet orifice at the same offset elevation and the same diameter is the depth at which the flow in the orifice will switch between weir flow and orifice flow. The Side Outlet orifice has Weir flow until the Orifice is full but the Bottom Orifice has Weir flow until the Critical Height which is usually shorter than the maximum depth of the orifice.

For a circular orifice the Critical Height is:

Critical Height = Orifice Discharge Coefficient / 0.414 * Orifice Opening / 4

For a rectangular orifice the Critical Height is:

Critical Height = Orifice Discharge Coefficient / 0.414 * (Orifice Opening*Width) / (2.0*(Orifice Opening+Width))

St. Venant Terms in SWMM 5

St. Venant Terms in SWMM 5 and how they change for Force Mains by dickinsonre

Note:  An explanation of the four St. Venant Terms in SWMM 5 and how they change for Force Mains.  The HGL is the water surface elevation in the upstream and downstream nodes of the link.  The HGL for a full link goes from the pipe crown elevation up to the rim elevation of the node + the surcharge depth of the node.  dq1 is calculated differently based on full or partially full force mains and gravity mains

            dq2 = Time Step * Awtd * (Head Downstream – Head Upstream) /  Link Length  or

            dq2 = Time Step * Awtd * (HGL) /  Link Length

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

when the force 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

the dq3 term in dynamic.c uses the current midpoint area (a function of the midpoint depth), the sigma factor and the midpoint velocity

            dq3 = 2 * Velocity * ( Amid(current iteration) – Amid (last time step) * Sigma

dq1 = Time Step * RoughFactor / Rwtd^1.333 * |Velocity|

The weighted area (Awtd) is used in the dq2 term of the St. Venant equation:

            dq2 = Time Step * Awtd * (Head Downstream – Head Upstream) /  Link Length

 

via Blogger http://www.swmm5.net/2013/07/st-venant-terms-in-swmm-5-and-how-they.html

Orifice and Weir flow calculations

Note: Orifice and Weir Flow Computations

The orifice flow calculation proceeds as follows:

1. Initially and whenever the setting (i.e., the fraction opened) changes, flow coefficients for both orifice and weir behavior are computed as follows:

a. For side orifices:

Define Hcrit = h/2 where h is the opening height.

b. For bottom orifices:

i. For a circular orifice, compute area over length (i.e., circumference) as AL = h /4.

ii. For a rectangular orifice compute AL = h*w/(2*(h+w)) where w is the opening width.

iii. Compute Hcrit = Cd*AL/0.414 where Cd is the orifice discharge coefficient.

At step 1b, the critical head for the bottom orifice, where orifice flow turns into weir flow, is found by equating the result of the orifice equation to that of the weir equation

Cd*Area*sqrt(2g)*sqrt(Hcrit) = Cw*Length*sqrt(Hcrit)*Hcrit or

Hcrit = (Cd * Area) / (Cw/sqrt(2g) * Length) The value of Cw/sqrt(2g) for a sharp crested weir is 0.414.

c. Compute the flow coefficients (where A is the area of the opening):

Corif = A*sqrt(2g)*Cd

Cweir = A*sqrt(2g)*Cd*sqrt(Hcrit)

2. During flow routing, compute the degree of inlet submergence (f) and head (H) at the current time step:

a. Define:

H1 = upstream head (from node with higher head),

H2 = downstream head (from node with lower head) ,

Hcrest = elevation of bottom of opening,

Hcrown = elevation of top of opening,

Hmidpt = elevation of midpoint of opening

b. For side orifices:

f = min{1.0, (H1 - Hcrest) / (Hcrown - Hcrest)}

if f < 1.0 then H = H1 - Hcrest,

else if H2 < Hmidpt then H = H1 - Hmidpt

else H = H1 - H2

c. For bottom orifices:

if H2 > Hcrest then H = H1 - H2

else H = H1 - Hcrest

f = min{1.0, H/Hcrit}

3. Compute the flow through the orifice (Q):

if f < 1.0 then Q = Cweir*f^1.5

else Q = Corif*sqrt(H)

4: Villemonte correction

If f < 1.0 and H2 > Hcrest then:

r = (H2 - Hcrest) / (H1 - Hcrest)

Q = Q * (1 - r^1.5)^0.385

Weir Flow Computations

1. Weir head calculations

h1 = Upstream Node Depth + Upstream Invert Elevation

h2 = Downstream Node Depth + Downstream Invert Elevation

If h2 is greater than h1 then the flow is reversed and h2 = h1 and h1 = h2

Weir Crest = Upstream Node Invert Elevation + Weir Offset Depth

Head = h1 – Weir Crest

2. Center Weir flow for Transverse Weirs

Q = Cw * Weir Length * Head^3/2

3. Center Weir flow for Side Flow Weirs

Weir behaves as a transverse weir under reverse flow

Q = Cw * Weir Length * Head^3/2

And under normal flow

Q = Cw * Weir Length * Head^5/3

4. Center Weir flow for V Notch Weirs

Q = Cw * Weir Slope * Head^5/2

Villemonte Correction for Weir Submergence in SWMM 5

Subject: Villemonte Correction for Weir Submergence for weirs when the downstream head is greater than the weir crest elevation.

Node Continuity Error of 100 percent in SWMM5

Note: A continuity error of 100 percent for some nodes in SWMM5 simply means that the total lateral flow and total inflow from the upstream links and the outflow to downstream links is zero.

SWMM 5 Pump Curve Head/Flow Curves (1)

Subject: The Pump flow is based on the lookup table you enter for the pump (Figure 1). At each iteration during each time step of the solution SWMM 5 will look up the flow for the pump based on the current control variable across the pump. The control variable for the pump can be one of four variables:
1. The volume of the upstream wet well,
2. The depth of water at the upstream node or inlet node without interpolation between data points,
3. The downstream water surface elevation across the pump minus the upstream water surface elevation, and
4. The depth of water at the upstream node or inlet node with interpolation between data points.
The pump summary table in the rpt file will tell you how often the pump was used, the maximum flow, the average flow, the total volume of the pump, the power usage and the percent of the time off the entered pump curve. You can also plot the pump flow versus the inlet depth to see how often the pump was off the pump curve (Figure 2).

Figure 1: Plot of Head and Flow for Pump PUMP1@82309e-15009e over time along with the input and output table for the pump.

Figure 2: Plot of Head versus Flow for Pump PUMP1@82309e-15009e

Average Number of Node Iterations

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.

Link Area Types in SWMM 5

Note: There are 7 Link flow classification classes that are used to assign the area of the link to the upstream and downstream nodes of the link. The classes used during the simulation of the model are shown in the Link Classification Table in the RPT Report File. The supercritical class is the same as the subcritical assignment. The supercritical is a class of subcritical with a Froude number over 1.

Link Area Types in SWMM 5, InfoSWMM and H2OMap SWMM by dickinsonre

Note:  There are 7 Link flow classification classes that are used to assign the area of the link to the upstream and downstream nodes of the link.  The classes used during the simulation of the model are shown in the Link Classification Table in the RPT Report File.  The supercritical class is the same as the subcritical assignment.  The supercritical is a class of subcritical with a Froude number over 1.

Class	Description	Link Area Assignment
0      Dry conduit		1/2 Upstream and 1/2 Downstream Node
1      Upstream end is dry		1/2 Downstream Node
2      Downstream end is dry		1/2 Upstream Node
3      Sub-critical flow		1/2 Upstream and 1/2 Downstream Node
4      Super-critical flow		1/2 Upstream and 1/2 Downstream Node
5      Free-fall at upstream end		1/2 Downstream Node
6      Free-fall at downstream end		1/2 Upstream Node

via Blogger http://www.swmm5.net/2013/07/link-area-types-in-swmm-5-infoswmm-and.html

Class	Description	Link Area Assignment
0 Dry conduit		1/2 Upstream and 1/2 Downstream Node
1 Upstream end is dry		1/2 Downstream Node
2 Downstream end is dry		1/2 Upstream Node
3 Sub-critical flow		1/2 Upstream and 1/2 Downstream Node
4 Super-critical flow		1/2 Upstream and 1/2 Downstream Node
5 Free-fall at upstream end		1/2 Downstream Node
6 Free-fall at downstream end		1/2 Upstream Node

Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices in SWMM5

Note: Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices
The Critical height is the opening where weir flow turns into orifice flow. It equals (Co/Cw)*(Area/Length) where Co is the orifice coeff., Cw is the weir coeff/sqrt(2g), Area is the area of the opening, and Length = circumference of the opening. For a basic sharp crested weir, Cw = 0.414. All of the units are based on the internal SWMM 5 units of American Standard.
For a circular orifice the Critical Height is:
Critical Height = Orifice Discharge Coefficient / 0.414 * Orifice Opening / 4
For a rectangular orifice the Critical Height is:
Critical Height = Orifice Discharge Coefficient / 0.414 * (Orifice Opening*Width) / (2.0*(Orifice Opening+Width))
The Orifice Critical Depth changes dynamically as the orifice is opening and closing for a bottom outlet orifice. The critical depth separating the orifice weir flow from orifice flow for a side outlet orifice is the height of the orifice.

Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices in SWMM 5 by dickinsonre Note:  Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices The Critical height is the opening where weir flow turns into orifice flow. It equals (Co/Cw)*(Area/Length) where Co is the orifice coeff., Cw is the weir coeff/sqrt(2g), Area is the area of the opening, and Length = circumference of the opening. For a basic sharp crested weir, Cw = 0.414.  All of the units are based on the internal SWMM 5 units of American Standard. For a circular orifice the Critical Height is: Critical Height = Orifice Discharge Coefficient / 0.414 * Orifice Opening / 4 For a rectangular orifice the Critical Height is: Critical Height = Orifice Discharge Coefficient / 0.414 * (Orifice Opening*Width) / (2.0*(Orifice Opening+Width)) The Orifice Critical Depth changes dynamically as the orifice is opening and closing for a bottom outlet orifice.  The critical depth separating the orifice weir flow from orifice flow for a side outlet orifice is the height of the orifice. via Blogger http://www.swmm5.net/2013/07/orifice-critical-depth-for-separating.html