Gully Pot Equation Surface Buildup Equation Surface Erosion Equation Potency Factor Equation

Surface Pollutant Editor

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The Surface Pollutant Editor is used to define the parameters used by the Surface Pollutant Model to calculate the buildup and washoff of pollutants on catchment surfaces and in gully pots. The editor is used to:

Surface pollutant parameters define additional characteristics for subcatchments and are therefore treated as part of the network.

To display the Surface Pollutant Editor for the current network, click on the Surface Pollutant Editor icon ( ) from the Modelling Grid Windows toolbar.

Editor Layout

The editor displays a series of records (rows on the grid).

The surface pollutant parameters can contain the following record types, which must be entered in the order listed, with one or more of each type of record:

The Sediment Fraction parameters are always defined in the bottom rows of the editor. You can add a maximum of two Sediment Records below the last Surface Definition Record.

The buildup and erosion parameters are defined in the first two rows below the title.

The rest of the editor is dedicated to defining Pollution Indices. The final definition of a Pollution Index is given in a Surface Definition Record. This brings together other data and equations defined in previous records.

The image below shows an example. Click on a row in the image to go to information about each record type and the fields they contain. Use the Back button to return to the image.

Clickable Image 

Image Key

Related parts of the image are highlighted in the same colour. The arrows show the relationship between values defined in the editor and parameters in the equations used in the model.

Cell Colour

Explanation

This colour indicates the ID fields for the Pollution Indices. There are 12 defined in this network. You can have a maximum of 99, with numeric IDs between 1 and 99.

This colour shows the parameters for the Surface Buildup Equation. The block of values in the lower half of the view are the Surface Buildup Factor parameters defined for each Pollution Index in the Surface Definition Record.

This colour shows the Surface Erosion Equation parameters. These are all defined in the Erosion Parameters Record.

This colour shows the Potency Factor Equation parameters. You define a set of parameters for each equation. You need at least one equation for each pollutant being modelled.

The green cells show the links between the different records in the editor. Look for matching names to see how equations are added to groups and groups included in Pollution Indices.

This colour shows the parameters for the Gully Pot Equation. You do not define gully pot value (Vg) directly. Enter a value for the gully pot depth for each Pollution Index. This is then multiplied by the area of Runoff Surface 1 from the Land Use to give gully pot volume. By convention, Runoff Surface 1 is the road surface.

These are the parameters defining the sediment fraction characteristics.

Description of Data Records

Record Title

Description and Record Fields

Title

The contains a short description of the data

You should have just one.

BuildupPar

The Buildup Parameters Record describes some of the data needed to calculate the mass of sediment buildup on the catchment surface.

You should have just one Buildup Parameters Record.

See Surface Pollutant Build-Up for more information

Decay Factor

The Buildup Decay Factor is a coefficient (K1) used in the surface buildup equation below.

This equation determines the mass of sediment buildup on the surface of the catchment after the buildup period at the start of a simulation, or at the end of each timestep.

The surface buildup equation is:

 

(1)

where:

M0 is the mass of sediment after the buildup period, or the projected mass of sediment at the end of the timestep

Md is the initial mass of sediment.

  • When calculating initial buildup, this mass will be zero unless a value has been defined in the rainfall event. The initial sediment is defined on either the Sediment Surface Page or the Sediment Subcatchment Page of the Rainfall Event Editor. See Rainfall Initial Conditions for more information.
  • When calculating for each timestep, this mass is the sediment mass at the end of the previous timestep.

K1 is the buildup decay factor. The value of K1 must be greater than zero.

NJ (days) is the timestep length, or the buildup period at the start of the simulation. You enter the Buildup Time on the Rainfall Event Editor - Globals Page when defining the rainfall event.

When entering the Buildup Timeinto the editor, it is entered in hours. It is then converted to days for the calculation.

PS is the surface buildup factor defined in the Surface Definition Record. See below.

ErosionPar

The Erosion Parameters Record defines data used in the calculation of the sediment deposits left on the catchment surface and washed off into the drainage system during a simulation.

You should have just one Erosion Parameters Record.

Rainfall Erosion Calibration Coefficients C1, C2 and C3

The Rainfall Erosion Calibration Coefficients are used in the following equation to calculate the rainfall erosion coefficient:

 

(2)

where:

Ka(t) is the rainfall erosion coefficient.

i(t) is the effective rainfall in m/s.

The rainfall erosion coefficient, Ka(t) is used in the equations which determine:

  • the sediment deposit left on the catchment surface.
  • the amount of sediment washed off from the catchment surface.

For further information see Surface Washoff and Gully Pot Flushing.

Limiting Erosion

This is a user defined maximum rate at which erosion can occur from the surface.

It is defined in kg/sec/hectare

PollRec

The Pollutants Record defines the pollutant types available to be washed off subcatchment surfaces.

You should have just one Pollutants Record.

See Water Quality Determinants for more information.

Pollutant Name 1 - 9

The name of each of the pollutants you wish to washoff from the catchment surface must be defined in the pollutants record. The following pollutant names are available:

  • BOD (biochemical oxygen demand)
  • COD (chemical oxygen demand)
  • TKN (total Kjeldahl nitrogen)
  • NH4 (ammoniacal nitrogen. This is always dissolved. Potency factors will, therefore, be zero for ammoniacal nitrogen)
  • TPH (total phosphorus)
  • PL1 (user-defined pollutant 1)
  • PL2 (user-defined pollutant 2)
  • PL3 (user-defined pollutant 3)
  • PL4 (user-defined pollutant 4)

There are 9 pollutant name fields in the pollutants record. You can specify any combination of pollutant names.

You should enter the three letter code above into the editor.

PFEqnRec

The Potency Factor Equation Record defines an equation used to determine the potency factors of pollutants.

Potency factors (Kpn) are used to relate surface mass of sediment to surface mass of pollutant and are calculated using the potency factor equation:

 

(3)

where:

C1, C2, C3 and C4 are coefficients defined in the other four fields of the potency factor equation record.

IMKP is the maximum rainfall intensity over a 5-minute period in mm/hr

You must define at least one Potency Factor Equation Record. You can define a maximum of thirty records.

See Surface Washoff and Gully Pot Flushing for more information.

Potency Factor Equation Name

The Potency Factor Equation Name is a user-defined name of up to 10 characters.

Each potency factor equation name should be unique.

Potency Factor Equation Coefficients C1, C2, C3 and C4

Coefficients for the potency factor equation.

PFGrpRec

The Potency Factor Equation Group Record defines a collection of potency factor equations, one for each pollutant available to be washed off a subcatchment surface. You define the potency factor equations themselves in the Potency Factor Equation Record.

You must define at least one Potency Factor Equation Group Record. You can define a maximum of ten records.

Potency Factor Equation Group Name

This name of up to 10 characters identifies a specific group of potency factor equations. The names of the equations are listed in the other fields of the record.

From calibrated data, it has been determined that the mixed suburban land use requires a different set of potency factor equations to the other land uses. It is usual to set up two potency factor equation groups, one for the mixed suburban land use and one for the other land uses.

Potency Factor Equation Name 1 - 9

The names of the potency factor equations that you want to include in this equation group.

There are nine potency factor equation name fields. These fields correspond to the nine pollutants that may be modelled. The order of these pollutants is that defined in the Pollutants Record specified above.

GPEqnRec

The Gully Pot Buildup Equation Record defines the coefficients for a gully pot buildup equation of the form:

 

(4)

where:

PGn(t) (kg) is the initial dissolved pollutant mass in the gully pot (or the projected pollutant mass at the end of the timestep).

C (mg/l) is the initial pollutant concentration.

M is the gradient of linear accumulation in mg/l day.

ND (days) is the dry weather buildup period or the timestep length.

Vgis the gully volume in m3. Vg is calculated from the Gully Depth entered in the Surface Definition record using:

Gully Pot Volume (Vg) = Gully Depth * Area of Runoff Surface 1

Runoff Surface 1 is, by convention, the road surface.

The software uses this equation to determine the buildup of dissolved pollutants in the gully pots during the buildup period of the simulation, and the buildup for each simulation timestep.

You must define at least one Gully Pot Buildup Equation Record. You can define a maximum of thirty records.

Gully Pot Buildup Equation Name

This is a user-defined name of up to 10 characters. Each equation defined must have a unique name.

Gully Pot Buildup Equation Coefficients

The coefficients used in the gully pot buildup equations are Cand M. The first coefficient field corresponds to the coefficient C. The second corresponds to coefficient M.

GPGrpRec

The Gully Pot Buildup Equation Group Record defines a collection of Gully Pot Buildup Equations, one for each pollutant available to be washed off a subcatchment surface.

The default surface pollutant parameters (default.wpf) contain three gully pot buildup equation groups. These refer to the following land uses:

  1. Low density residential.
  2. High density residential.
  3. Commercial.

You must define at least one Gully Pot Buildup Equation Group Record. You can define a maximum of ten records.

Gully Pot Buildup Equation Group Name

a user-defined name of up to 10 characters. It identifies a specific group of gully pot buildup equations. The names of these equations are listed in the following fields of the record.

Each group should have a unique name.

Gully Pot Buildup Equation Name 1 - 9

These are the names of gully pot buildup equations that you wish to include in this equation group.

There are nine gully pot buildup equation name fields, each referring to one of the nine pollutants you can model. The order of these pollutants is the order defined in the Pollutants Record.

Surface df

The Surface Definition Record defines the sediment buildup on subcatchment surfaces and in gully pots, and the potency of pollutants attached to these sediments, for different surface types. The surface type is identified by its Pollution Index.

The Pollution Index is the water quality equivalent of a Runoff Surface. The Pollution Index is associated with a subcatchment through the Land Use definition, in a similar way to Runoff Surfaces. Only one Pollution Index is associated with each Land Use. The Land Use can have up to twelve Runoff Surfaces.

The default surface pollutant parameters (default.wpf) contain twelve Surface Definition Records. There is one record for each of the twelve default Land Uses.

There must be at least one Surface Definition Record. The maximum number of definitions is 99.

Pollution Index (ID)

The Pollution Index identifies this particular surface definition.

The Pollution Index must be a number between 1 and 99.

Surface Buildup Factor

The Surface Buildup Factor PS factor is used in the surface buildup equation described in the Buildup Parameters Record description:

 

(5)

This equation calculates the mass of sediment buildup on a subcatchment surface both over the buildup period of a simulation and during the simulation.

Surface buildup factors must have a value greater or equal to zero. See the Surface Pollutant Build-Uptopic for some typical surface buildup factors.

Potency Factor Equation Group Name

The group of potency factor equations used by this surface definition.

You define the potency factor equation group in a Potency Factor Equation Group Record.

Gully Pot Buildup Equation Group Name

The group of gully pot buildup equations used by this surface definition.

You define the gully pot buildup equation group in a Gully Pot Buildup Equation Group Record.

Gully Depth

The average gully depth in metres, used to determine gully pot volume for the Gully Pot Equation (see Gully Pot Equation Record above).

Gully Pot Volume (Vg) = Gully Depth * Area of Runoff Surface 1

Runoff Surface 1 is, by convention, the road surface.

Sediment

Sediment records define the physical characteristics of the different sediment fractions.

It is not essential to specify any sediment records. The software uses default values for the sediment characteristics in this case. These defaults are:

  • D50 (sediment diameter) - 0.04mm
  • Specific Gravity - 1.7

The maximum number of records is two.

See Water Quality Determinants and Sediment for more on sediment characteristics.

Sediment Fraction Name

InfoWorks ICM allows you to model two sediment fractions. The name entered here must be either SF1 or SF2

Sediment Diameter

Otherwise known as D50. The default grain size of the sediment fraction, in mm

Sediment Specific Gravity

The density of the sediment fraction

Water Quality Simulations

Surface Pollutant Model

Water Quality Determinants

Sediment

Surface Pollutant Build-Up

Surface Washoff and Gully Pot Flushing