Mass and Concentration Water Quality Loadings in SWMM 5

Subject:   Mass and Concentration Water Quality Loadings in SWMM 5

If you have a time series of flow and water quality at a node in SWMM 5 you have the option of using either a Mass loading or a concentration loading (Figure 1).     If you have a concentration then the load to the node internally in SWMM 5 is the flow times the concentration.  Alternatively, if you have Mass loading then the program will calculate the concentration from the flow and the load.  The table below shows some combinations of flow in cfs and load in pounds per day to yield various BOD 5 concentrations it the network nodes and  links (Figure 2).  For example, at a flow of 10 cfs you can get a BOD5 concentration of 100 mg/l with a loading of about 5400 pounds of BOD5 per day (Figure 3).

Figure 1.  If you use a time series load in SWMM 5 you need TWO time series, one for the flow and one for the mass load or concentration.

Figure 2.   The Mass loading needed to generate a concentration at a particular flow rate.

Flow (CFS)	BOD5 (mg/l)	BOD 5 Pounds Per Day
1	1	5.39
1	10	53.89
1	50	269.45
1	100	538.89
1	200	1077.79
10	1	53.89
10	10	538.89
10	50	2694.47
10	100	5388.93
10	200	10777.87
100	1	538.89
100	10	5388.93
100	50	26944.66
100	100	53889.33
100	200	107778.66

Figure 3.  The calculated BOD 5 concentration in the link from the Mass Loading.

Convolution of the RDII UH from R, T and K in SWMM 5

Subject:  Convolution of the RDII UH from R, T and K in SWMM 5

The convolution uses the value of R and the Time Base to estimate the amount of Infiltration and Inflow in the Sewer Network.  The short, medium and long term UH's are estimated at each Wet Hydrology time step to make a smooth hydrograph out of the R, T and  K parameters of the Rainfall Dependent Infiltration and Infiltration Method (Figure 1).  The three UH's can be displaced as well if you use the RTK storage parameters (Figure 2)

Figure 1.  The short, medium and long UH's are convoluted in SWMM 5 from the Rainfall Time Series.

Figure 2.   The Initial Abstraction Depth can be used to shift the generated UH in time or reduce the peak flow and total volumes.

c.

What are the Equations for Weirs in SWMM 5, Part 2?

Subject:   What are the Equations for Weirs in SWMM 5, Part 2?

There are four types of Weirs in SWMM 5:  Transverse, Sideflow, V Notch and Trapezoidal.   The trapezoidal weir is a combination of the Sideflow and V Notch Weir and the Sideflow acts like a Transverse Weir when the flow is reversed (Figure 1).  The Weirs can have zero, one or two end contractions (Figure 2) and the Weir Length is a function of the Weir Setting and Horizontal Weir Length.  A V Notch weir works as Trapezoidal Weir when the Weir RTC Setting is less than 1.0

Figure 1.   Weir Equations in SWMM 5

Figure 2.   Valid Number of End Contractions

Figure 3.  Weir Length Calculations

Water Quality Treatment Removal Variables in SWMM5

Subject:    Water Quality Treatment Removal Variables in SWMM5

The treatment variables for Water Quality in a SWMM 5 storage unit (Figure 1) can be either: 

1.       A Process Variable

a.       HRT or Hydraulic Residence Time

b.      DT or Time Step

c.       FLOW or The Current Inflow

d.      DEPTH or the Mean Flow over the Time Step

e.      AREA or the Mean Area over the Time Step

2.       Pollutant Concentration
3.       Pollutant Removal based on the Removal of Other Pollutants 

With a Wide Range of Treatment Functions (Figure 2).

Figure 1.  SWMM 5 Treatment Variable Names in the Treatment Equation

Figure 2.   Treatment Functions in SWMM 5

How does the Infiltration Maximum Time to Drain the Upper Soil Zone Work in SWMM 5 Green Ampt?

Subject: How does the Infiltration Maximum Time to Drain the Upper Soil Zone Work in SWMM 5 Green Ampt?

You can use the monthly soil recovery factor (Figure 1) in SWMM 5 to change how the Infiltration Maximum Time to Drain the Upper Soil Zone (Figure 2) is computed each month during a continuous simulation. 

The  depth of the upper soil zone in the internal  SWMM 5 units of feet is calculated at the start of the simulation based on the Green Ampt Soil Saturated Hydraulic Conductivity

Upper Soil Zone Depth = 4  * (Soil Saturated Hydraulic Conductivity * 12 * 3600)^0.5 / 12

And the Upper Zone Moisture Depletion Factor  and Infiltration Maximum Time to Drain the Upper Soil Zone is calculated at each hydrology time step in SWMM 5.

Upper Zone Moisture Depletion Factor  = Upper Soil Zone Depth / 300 * 12 /3600 * Monthly Evaporation Recovery Factor

Infiltration Maximum Time to Drain the Upper Soil Zone = 6 / (100 * Upper Zone Moisture Depletion Factor  )

Figure 1.  Monthly Soil Recovery Factor

Figure 2.  Infiltration Maximum Time to Drain the Upper Soil Zone for a Subcatchment

Dry Weather Flow in InfoSWMM and H2OMap SWMM

Dry Weather Flow in InfoSWMM and H2OMap SWMM

Dry weather flow can be added to any node in H2OMAP SWMM.  The dry weather flow is computed as the average flow * the monthly pattern * the daily pattern * hourly pattern * the weekend daily pattern to give the Dry Weather Flow at any time step (Figure 1).   Since the four types of patterns (Figure 2) are all multiplied together then for Saturday and Sunday the hourly pattern and the weekend hourly pattern will both be used.   This will have the effect of overestimating the flow if the multipliers are greater than 1 and underestimating theflow if the multipliers are less than one.  You should enter the  Pattern X for the Weekend Hourly Pattern in H2OMAP SWMM  where

X  = Weekend Hourly Pattern / Hourly Pattern

So that when the pattern X is multiplied by the Hourly Pattern the program will use the intended Weekend Pattern.

Figure 1.  How Dry Weather Flow is Computed in H2OMAP SWMM

Figure 2.  The Four Types of Time Patterns in H2OMAP SWMM, InfoSWMM and SWMM 5 

Example DUPUIT-FORCHHEIMER APPROXIMATION FOR SUBSURFACE FLOW Model in SWMM 5

Subject:   Example  DUPUIT-FORCHHEIMER APPROXIMATION FOR SUBSURFACE FLOW Model in SWMM 5

This example was created from an older SWMM 4 model from 1988 using the SWMM 4 to SWMM 5 converter.  The values for the coefficients in this case are A1 = A3 = 4*K/L^2, A2 = 0, B1 or the exponent or B1=2 or from Appendix X in the SWMM 4 manual from OSU (http://eng.odu.edu/cee/resources/model/mbin/swmm/swmm_6.pdf)

Saving an Output Relate in InfoSWMM directly to Excel using Arc Tool Box

Subject:  Saving an Output Relate in InfoSWMM directly to Excel using Arc Tool Box

The following shows how to make an Excel file directly from a feature table in InfoSWMM

Step 1.  Download the Arc Tool box add on Table to Excel

You can download the python script from here   http://resources.arcgis.com/gallery/file/geoprocessing/details?entryID=95009B25-1422-2418-7FB5-B8638ECB2FA9

Step 2.    Add the Tool to Arc Toolbox and then use the tool to create an Excel CSV File

Step 3.  You can export any of the features in InfoSWMM to CSV

Example FM SWMM 5 model with and without Surcharge Depth

Subject:   Example FM SWMM 5 model with and without Surcharge Depth

You need to use the surcharge depth for a Force Main in SWMM 5 to allow the engine to find the right point on the pump curve and pump up the rising main.  If you do not use a surcharge depth then the flow MAY be very small in the rising main due to a small head difference.  Of course the flow in the force main depends on the pump curve you have entered but having the right downstream head of depth for the link matter as well.  The attached model was created in SWMM 5.0.022 

Force Main Friction Loss in InfoSWMM and the Transition from Partial to Full Flow

Subject:  Force Main Friction Loss in InfoSWMM and the Transition from Partial to Full Flow

You can model Force Main friction loss in InfoSWMM using either Darcy Weisbach or Hazen Williams as the full pipe friction loss method (see Figure 1 for the internal definition of full flow).   A function called ForceMain in InfoSWMM whose purpose is to compute the Darcy-Weisbach friction factor for a force main using the Swamee and Jain approximation to the Colebrook-White equation .  No matter which method you use for full flow the  program will use Manning's equation to calculate the loss in the link when the link is not full (see Figure 2 for the equations used for calculating the friction loss – variable dq1 in the St Venant equation for InfoSWMM).   The regions for the different friction loss equations are shown in Figure 3.    

There is no slot in InfoSWMM for the full pipe flow as a surcharged node in InfoSWMM uses this point iteration equation (Figure 4): 

dY/dt = dQ / The sum of the Connecting Link values of  dQ/dH 

where Y is the depth in the node, dt is the time step, H is the head across the link (downstream – upstream), dQ is the net inflow into the node and dQ/dH is the derivative with respect to H of the link  St Venant equation.  If you are trying to calibrate the surcharged node depth, the main calibration variables are the time step and the link  roughness:

 1.   Mannings's N

2.   Hazen-Williams or

3.   Darcy-Weisbach 

The link roughness is part of the term dq1 in the St Venant solution and the other loss terms are included in the term dq5.  You can adjust the roughness of the surcharged link  to affect the node surcharge depth.   The point iteration continues until the sum of the flow in the node is zero – basically the new depth in the node either increases or decreases the friction loss in the force main so that net flow at the node is zero.  This is why it is important to use the right time step to ensure that the net flow is zero when the pumps turn on and off. 

Figure 1.  How the full pipe condition is defined in InfoSWMM - both ends have to be full

Figure 2:  Friction equations used in SWMM 5 for a Force Main. Figure 3:  Regions of Friction loss equations in SWMM 5.

Figure 4.  The Node Surcharge Equation is a function of the net inflow and the sum of the term dQ/dH in all connecting links. Generally, as you increase the roughness the value of dQ/dH increases and the denominator of the term dY/dt = dQ/dQdH increases.

Example Groundwater Model in SWMM 5

Subject:   Example Groundwater Model in SWMM 5

The attached model shows three ways in which the groundwater model of the SWMM 5 subcatchments interact with the node depths of the hydraulic network.  The hydraulic network interaction can be either:

1.       At a fixed water surface elevation,
2.       At a time varying water surface elevation based on the inflow and geometry of the node and
3.       At a threshold node water surface elevation.

Example SWMM 5 Snowmelt Model

Subject: Example SWMM 5 Snowmelt Model

Attached is a simple sample snowmelt model in SWMM 5 that has built in snowfall and temperature in a one subcatcment model with snowmelt.   You define the separation of precipitation into snowfall and rainfall by setting a base temperature in the Snow Pack Editor.   The precipitation that falls with when the air temperature is below the base temperature is stored in a snow pack where it eventually will melt when the temperature rises or is moved via plowing.  You can have an initial snow cover, final snow cover and runoff from the melting snow long after the snowfall occurs.

SWMM 5 Leaping Weir Example

Subject:  SWMM 5 Leaping Weir Example

The attached example shows one way how SWMM 5 RTC Rules can be used to have the low flow go down a leaping weir orifice and the high flow go over the weir to the downstream section of the sewer. 

SWMM 5 Precipitation Options

Subject:  SWMM 5 Precipitation Options

You can have design storms, monitored storms of any length of the time from minutes to centuries, use intensity, volume or cumulative precipitation, use both rainfall and snowfall in the same rain gage depending on temperature, use both time series or external files for the rain gage and have unlimited rain gages with the limitation of one rain gage per subcatchment . 

How is the St Venant Equation Solved for in the Dynamic Wave Solution of SWMM 5?

Subject:   How is the St Venant Equation Solved for in the Dynamic Wave Solution of SWMM 5?

An explanation of the four St. Venant Terms in SWMM 5 and how they change for Gravity Mains and 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.  The four terms are:

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

The four terms change at each iteration and time step to determine the new flow (Figure 1) based on the two equations:

Denom = 1 + dq1 + dq5

Q = [Qold – dq2 + dq3 + dq4] / Denom

If you look at a table of the values you will see that the terms add up to zero when the flow is constant and to delta Q or the change in Q when the flow is NOT constant (Figure 2).

Figure 1.  The four terms define the new flow at each iteration in the dynamic wave solution of SWMM5

Figure 2.   The magnitude of the four terms determine the flow at the new iteration and ultimately the new Time Step.  If the flow is constant then the value of the term is constant.

Link Iterations in the SWMM 5 Dynamic Wave Solution

Subject:   Link Iterations in the SWMM 5 Dynamic Wave Solution

 

Each of the links in the SWMM 5 network can use up to 8 iterations to reach convergence during a time step in the dynamic wave solution of SWMM 5.  The rules governing the number of iterations are:

 

1.       A minimum of 2 iterations per time step with the 1^st iteration NOT using the underrelaxtion parameter of 0.5 (Figure 1)

2.       If both the downstream and upstream nodes are converged then the link drops out of the iteration process during the time step (Figure 2)

3.       The number of iterations for each link can vary over the simulation from 2 to 8 depending on how fast the flow is changing.

 

Figure 1.  A minimum of two and up to eight iterations per time step in the SWMM 5 dynamic wave solution.

Figure 2.  The number of iterations for each link vary through out  the simulation with less iterations being used for constant flows.

Making a Model in SWMM 5/Pathways

Making a Model in SWMM 5

Runoff Routing Options Example in SWMM 5 and InfoSWMM

Subject:   Runoff Routing Options Example in SWMM 5

There are six options for runoff routing in SWMM 5:

·         All Runoff to an Outlet Node
·         All Runoff to another Subcatchment
·         All Runoff to the Pervious Area of the Subcatchment or other Subcatchment
·         All Runoff to the Impervious Area of the Subcatchment or other Subcatchment
·         Partial Runoff to the Pervious Area of the Subcatchment or other Subcatchment
·         Partial Runoff to the Impervious Area of the Subcatchment or other Subcatchment

 The attached example SWMM 5.0.022 file has three catchments in a chain, the 1^st Subcatchment Routes to the Pervious area of the 2^nd Subcatchment and the 2^nd Subcatchment routes the runoff to the Impervious area of the 3^rd Subcatchment which routes all runoff to an outlet node.

DownLoad File

Welcome to the Curated Web

Welcome to the Curated Web

from http://www.nirandfar.com/2012/01/where-is-web-going.html