How Does Green Ampt Cumulative Event Infiltration work in SWMM 5?

Subject:   How Does Green Ampt Cumulative Event Infiltration work in SWMM 5?

This graph shows the values of the internal SWMM 5 parameters for Green Ampt Infiltration for the pervious area of a Subcatchment during a simulation.  The parameters are:

·         F or FTOT which is the cumulative event infiltration at the start of a time interval in the internal units of feet in SWMM 5,
·         FU or current moisture content of the upper zone of the of the soil
·         FUMAX which is the saturated moisture content of the upper zone in feet and stays constant during the simulation 

Figure 1.  How FTOT, FU and F change over time

Figure 2.  A closer look at how FTOT or F and FU Change over time in a Green Ampt Pervious Area Simulation.

How is Capillary Suction Head Used in SWMM 5 Green-Ampt?

Subject:   How is Capillary Suction Head Used in SWMM 5 Green-Ampt?

How sensitive is the infiltration loss and rate to the capillary suction head parameter in the SWMM 5 Green-Ampt  infiltration method.   Figure         1 shows how the total infiltration loss and total loss rate vary as you change the suction head from 12 to 6 to 3 inches.    Internally the suction head is used in infil.c of SWMM 5 by adding the suction head to the ponded water on the pervious area in the parameter c1 of the implicit Green-Ampt SWMM5 solution.

C1 =  (Suction Head + Depth of Ponded Water) * IMD or Initial Moisture Deficit

Figure 1.  The sensitivity of the total infiltration loss to the capillary suction head in a continuous simulation

How is the Soil Saturated Conductivity Used in SWMM 5 Green-Ampt?

Subject:   How is the Soil Saturated Conductivity Used in SWMM 5 Green-Ampt?

How sensitive is the infiltration loss and rate to the Soil Saturated Conductivity parameter in the SWMM 5 Green-Ampt  infiltration method.   Figure 2 shows how the total infiltration loss and total loss rate vary as you change the soil saturated conductivity from 1 to 0.1 to 0.01 inches/hour.  Internally, Ks is used to check saturation and in the computation of the soil infiltration rate. Two of the checks are:

·         In low rainfall everything infiltrates as irate less than Infil>Ks and
·         In the check to see if the soil is already saturated. 

 

Figure 1.  The three parameters for Green-Ampt Infiltration in SWMM 5

Figure 2.  The sensitivity of the total infiltration loss to the soil saturated conductivity in a continuous simulation

There are Four factors in Rainfall Dependent Infiltration and Inflow or RDII in SWMM 5

There are Four factors in Rainfall Dependent Infiltration and Inflow or RDII in SWMM 5:

1.   The fractional response to Rainfall or R from 0 to 1
2.   The Time Base of the Unit Hydrograph or T in hours * Dimensionless K Shape Factor
3.   The Sewershed Contributing Area in acres or hectares and
4.   The Maximum, Initial Abstraction and Recovery Rate for R on a Monthly Basis in units of inches, mm or mm/day,
5.   The fifth and probably the most important factor is the Rainfall

How is RDII Storage Simulated in SWMM 5?

Subject:  How is RDII Storage Simulated in SWMM 5?

If you are using the SWMM 5 Rainfall Dependent Infiltration and Inflow(RDII)  feature you can also use the RDII storage parameters to change the RDII runoff by simulating the storage in the Sewershed.   The code in RDII.C as implemented by Lew Rossman of the EPA keeps track of used and unused initial abstraction or IA (Figure 1)

When there is rainfall the following actions are taken:

·         The raindepth available to be convoluted by the RDII unit hydrograph method is reduced by unused IA
·         The amount of IA used up is then updated 

When there is no rainfall

·         A portion of the IA already used is recovered using the recovery rate parameter and the variable IAUsed

Figure 1.  The long term effect of the RDII storage on the generated RDII Unit Hydrographs.  IA1, IA2 and IA3 are the Storage values for the short, medium and long term UH's.

Types of Stormwater Inlets from HEC12 and HEC22

Note:  Types of Stormwater Inlets from HEC12 and HEC22

Stormwater Inlets consist of four main types (http://onlinemanuals.txdot.gov/txdotmanuals/hyd/storm_drain_inlets.htm) with most common shown in Figure 1.

1.   Curb opening inlets either at a sag or continuous on the street,
2.   Grate Inlets either at a sag or in combination with a Curb opening
3.   Slotted Drains in parking lots which can be simulated as curb opening inlets and
4.   Combination inlets either at a sag or continuous on the street which combine a curb opening inlet and a grate inlet for the stormwater runoff

A sag inlet is the end of the line for the runoff because the flow and its debris load have no other place to go as described in the HEC-22 and HEC-12 manuals and a continuous grade inlet is designed to capture the entire runoff flow but if the flow is too large or the inlet is clogged the bypassed flow can travel past the inlet and flow on down the street to a new inlet.   The interception of a sag inlet is ultimately 100 percent but the amount of interception by a continous inlet is variable and is governed by the width of the opening, the grade of the street, the splash over velocity and the amount of side and flontal flow in a grated or combination inlet which is governed by the width and the length of the grate.  Any flow in a continous opening inlet that is not captured ends up as bypass flow and travels down the downstream link or conduit (Figure's 2, 3, 4, 5 and 6).

Figure 1.  Common Types of Stormwater Inlets on Streets

Figure 2.  Continuous Grate Inlet(1) and Sag Curb Opening Inlet(4)

 

Figure 3.  Curb Opening Inlets(2)

Figure 4.  Continuous Curb Opening Inlet(2)

Figure 5: Grate Inlets and Combination Inlets (1, 3 and 5)

How to Easily Make a Smaller Model in InfoSWMM Using Trace Upstream Network

How to Easily Make a Smaller Model in InfoSWMM Using Trace Upstream Network

Step 1.  Use the Trace Upstream Network command to find all of the network above the node of interest (Figure 1). 

Step 2.  Use the Trace Downstream Network Command to find all of the network below the node of interest and place it in the Doman (Figure 2).

Step 3.  Use Facility Manager to make the Lower Network in the Domain Inactive (Figure 3).

Step 4.  Change the Node of Interest from a Manhole to an Outfall

Figure 1.  Trace Upstream Network

Figure 2.  Put the lower Section of the Network in a Domain

Figure 3.  Use Facility Manager to make the Lower Network in the Domain Inactive

How to Subdivide Subcatchments in SWMM 5

Subject:   How to Subdivide Subcatchments in SWMM 5

If you want to subdivide a larger Subcatchment in SWMM 5 and get around the same peak flow then a good suggestion would be to make sure that (Figure 1):

1.   The sum of the new areas equals the original Subcatchment Area and
2.   The sum of the total Width values equals the original Subcatchment Width on the one Subcatchment
3.   The infiltration, percent imperviousness, roughness and depression storage should be the same. 

Figure 1.  Subdividing a Subcatchment

What are the Types of Force Mains (FM) in SWMM 5?

Subject:   What are the Types of Force Mains (FM) in SWMM 5?

There are five ways to model a force main in SWMM 5 for the combination of full and partial flow in the force main (Figure 1):

1.       Full Flow using Darcy-Weisbach for the friction loss

2.      Full Flow using Hazen-Williams for the friction loss

3.      Full Flow using Manning's n for the friction loss

4.      Partial Flow uses Manning's n for the friction loss for Force Main Equation options

If you use Darcy-Weisbach or Hazen-Williams then an equivalent Manning's n for a force main that results in the same normal flow value for a force main flowing full under fully turbulent conditions is calculated internally in SWMM 5 in forcemain.c

·         Equivalent n for H-W is 1.067 / Hazen-Williams Coefficient  * (Full Depth / Bed Slope) ^ 0.04 

·         Equivalent n for D-W is (Darcy-Weisbach friction factor/185) * (Full Depth) ^ 1/6 

Figure 1.  Types of Full and Partially Full Force Mains in SWMM 5

How Does a TYPE1 Pump Work in SWMM 5?

Subject:   How Does a TYPE1 Pump Work in SWMM 5?

A SWMM 5 Type1 pump is called an offline pump but the name comes from SWMM 4 and the Pump is controlled by volume instead of depth or head as in the SWMM 5 TYPE2, TYPE3 and TYPE4 Pumps.  The attached example SWMM 5 model has an offline storage node that pumps flow INTO the Offline Storage unit during high flow and FROM the Offline Storage Unit during low flow.  The SWMM 5 Real Time Control (RTC) rules determine which of the two pumps operate based on the flow in an upstream link (Figure 1). 

Figure 1.   RTC Rules and Schematic of an OffLine Pump in SWMM 5.

How is the Orifice Setting Used in SWMM 5 RTC Rules?

Subject:  How is the Orifice Setting Used in SWMM 5 RTC Rules?

The Real Time Control Rule for Orifice Setting can be a function of a Setting constant, Setting from a Curve, Setting from a PID controller and a Setting from a Time Series (Figure 1).    The Setting affects the Full Depth of the Orifice at each time step.  The setting which ranges from 0 to 1 can either completely close or open theorifice (Figure 2).   You will have to use the equivalent in ICM or else the settings derived from the SWMM 5 time series need to be multiplied by the orifice depth to have the same effect in ICM that it had in SWMM 5. 

Figure 1.  The Possibilities for defining the Setting of an Orifice in SWMM 5 from a H2OMAP SWMM RTC dialog.

 

 Figure 2.  The Setting affects the Full Depth of the Orifice at each time step.  The setting which ranges from 0 to 1 can either completely close or open the orifice.

Low Impact Development Options in H2OMAP SWMM and InfoSWMM

Subject:  Low Impact Development Options in H2OMAP SWMM and InfoSWMM

The five options are:

1.      Rain Barrel
2.      Bio Retention Cell
3.      Infiltration Trench
4.      Vegetative Swale
5.      Porous Pavement

and be entered as controls in the Hydrology Section of the Operations Browser of H2OMAP SWMM or InfoSWMM (Figure 1)

Figure 1.  The Attribute Browser Operation Tab allows you to enter LID Controls for your LID Modeling.

🌧️ Rules for NRCS Unit Hydrographs in InfoSWMM 📈

Subject: 🌧️ Rules for NRCS Unit Hydrographs in InfoSWMM 📈

When applying NRCS (Natural Resources Conservation Service) Unit Hydrographs for hydrological modeling in InfoSWMM adhere to the following rules or guidelines to ensure accurate hydrological simulations:

1. Curve Number (CN) Source 🗂️: Obtain the Curve Number (CN) from the NRCS_CN column in the Subcatchment Table, representing runoff potential based on soil type, land use, and treatment practices.

2. Time of Concentration (TC) ⏱️: The Time of Concentration, critical for hydrograph development, is sourced from the TC column within the Subcatchment Table.

3. Infiltration Model Selection 💧: Select the Infiltration Model according to the CN Infiltration Model Column in the Subcatchment Database Table to ensure consistency in infiltration calculations.

4. CN Consistency Across Tables 🔄: The CN value in the Soil Database Table must match the CN in the Subcatchment Database Table for uniform hydrological parameters.

5. Depression Storage and Initial Abstraction 🕳️➡️💧: If Depression Storage is zero in the Subcatchment Database Table, Initial Abstraction (IA) in inches will be internally calculated using the formula $��=0.2\times (1000\mathrm{/}��-10)$.

6. Initial Abstraction Calculation ✏️: Clearly state that Initial Abstraction in US units is $��=0.2\times (1000\mathrm{/}��-10)$, indicating the use of American measurement standards.

By following these emoji-highlighted guidelines 📝, hydrological modeling using NRCS Unit Hydrographs within InfoSWMM will be precise and reliable, leading to better water management outcomes. 💦🏙️