Page Information
Versions Compared
Key
 This line was added.
 This line was removed.
 Formatting was changed.
This database is for global pollutant buildup and washoff data, and is referenced from the 'PollutantLanduse Data' dialog under the Runoff Pollutant Global Database. Buildup/washoff characteristics are defined for each combination of Landuse and Pollutant.
Note 

Note that Runoff Water Quality in Job Control must be ON. 
Several methods constitute the genesis of stormwater quality, most notably Buildup and Washoff. In an impervious urban area, it is usually assumed that a supply of constituents is built up on the land surface during dry weather preceding a storm. With the storm the material is then washed off into the drainage system.
As an alternative to the use of a buildupwashoff formulation, quality loads may be generated by a rating curve or EMC approach.
Washoff is the process of eroding or dissolving of constituents from a subcatchment surface during a period of runoff.
Buildup Method
Several methods of Pollutant buildup are available. The pollutant buildup can be directly related to the buildup of dust and dirt, or may build up using a similar formulation with independent parameters for each pollutant/landuse combination. Buildup need not be specified at all; washoff can be defined directly. Some Buildup and Washoff methods are mutually exclusive. Where this is the case invalid combinations are greyed out.
No Buildup
No buildup required (KALC = 4). In this case, washoff is generated by a rating curve approach, with no upper limit.
Buildup/Landuse
Buildup of pollutants (JX  KALC = 0) may be specified as a fraction of the dust and dirt for each landuse. The land use names are those entered in the Landuse Global Database. If Buildup by Landuse is being used the Landuse types must first be defined in the Landuse Global Database . The following table indicates the quantity of pollutant per gram of dust and dirt for four Chicago land uses (American Public Works Association, 1969).
Land Use Type  BOD5 (mg/g)  COD (mg/g)  Coliforms (mg/g)  N (MPN/g)  PO4 (mg/g) 

SingleFamily Residential  5.0  40.0  1.3E6  0.48  0.05 
MultiFamily Residential  3.6  40.0  2.7E6  0.61  0.05 
Commercial  7.7  39.0  1.7E6  0.41  0.07 
Industrial  3.0  40.0  1.0E6  0.43  0.03 
Landuse
Further details on this parameter can be found in the Landuse global data section
Dust and Dirt Fraction (QFACT)
The Dust and Dirt Fraction is the quantity of pollutant in the Dust and Dirt. The units of this factor depend on the pollutant units as shown in the following table:
Pollutant Unit  Dust and Dirt Factor Units 

mg/liter  pound/gram [kg/gram] 
'other'/liter  10^{6}/gram [10^{6}/gram] 
other ft^{3}  [m^{3}] 
If the pollutant has units of 'other'/l (e.g. MPN/l), the Dust and Dirt factor entered is in millions in order to facilitate the entry of large numbers. If the pollutant units are 'other,' then "buildup" of such parameters is rarely referred to; instead a much more viable option is the use of a rating curve that gives load directly as a function of flow.
Time
Cumulative pollutant buildup specified as a function of time (JX  KALC = 13). This formulation is similar to the dust and dirt buildup equations, except that units for pollutant buildup parameters depend on the units for the pollutant. If the pollutant units are in mg/l, then buildup units are given as mass units. If the pollutant has units of 'other'/l (eg. MPN/l) the Dust and Dirt parameters are in millions, to facilitate the entry of large numbers. If the pollutant units are 'other', then "buildup" of such parameters is rarely referred to; instead a much more viable option is the use of a rating curve that gives load directly as a function of flow.
Limit (QFACT1)
Upper limit for the pollutant buildup. The units for this parameter depend on the Buildup Dependency variable, as follows:
Buildup Dependency  Unit for Pollutant Buildup Limit 

Catchment Area  Q1/acre [Q1/hectare] 
Constant  Q1 
Curb Length  Q1/(100 ft curb) [Q1/(km curb)] 
where:
Q1 = Pollutant quantity, that depends on the pollutant units as follows:
Pollutant Unit  Unit for Q1 

mg/litre  lb [kg] 
'other'/litre  10^{6} [10^{6}] 
other  ft^{3 }[m^{3}] 
For the Exponential or MichaelisMenton formulations, this value becomes the asymptote; this limit is imposed for the PowerLinear form.
Buildup Dependency
This parameter defines the dependent variable 'X' in the buildup equations formulated in this dialog. Pollutant buildup can depend on the subcatchment area, curb length, or neither (the value of 'X' is always 1.0 in this case).
Buildup by Catchment Area (JX  KACGUT = 1)
Pollutant buildup is calculated using the landuse area (subcatchment area or part thereof).
Constant Buildup (JX  KACGUT = 2)
Pollutant builds up at the same rate regardless of the size of the subcatchment.
Buildup by Curb (Kerb) Length (JX  KACGUT = 0)
Pollutant buildup is calculated using the curb (kerb) length entered for the subcatchment, in units of 100 ft [km].
Buildup Function
Power Linear Function (JX  KALC = 1)
Calculate the pollutant buildup using the power linear function to the right of this item. Linear buildup is simply a subset of a power function buildup.
Power Linear Factor (JX  QFACT3)
The multiplication factor in the powerlinear form. The unit of this parameter depends on the Buildup Dependency option, as follows:
Buildup Dependency  Unit of Factor in powerlinear form 

Area  Q1/acre/day^{POW} [Q1/hectare/day^{POW}] 
Curb Length  Q1/(100 ft curb/day^{POW}) [Q1/(km curb)/day^{POW}] 
Constant  Q1/day^{POW} Q1/day^{POW} 
where:
POW = Power in the powerlinear form
Q1 = Pollutant quantity, that depends on the pollutant units as follows:
Pollutant Unit  Unit for Q1 

mg/liter  lb [kg] 
'other'/liter  10^{6} [10^{6}] 
other  ft^{3 }[m^{3}] 
Power (JX  QFACT2)
The power in the powerlinear formulation. This parameter has no units. Linear buildup can be simulated by setting this parameter to 1.0.
Exponential Function (JX  KALC = 2)
Calculate the pollutant buildup using the exponential function to the right of this item. This form of buildup has an asymptotic trend.
Exponent (JX  QFACT2)
This parameter is the familiar exponential decay constant. This type of relation will be evident by a semilog plot of buildup versus time indicating a linear relationship. Thus the unit of this parameter is 1/day.
Michaelis Menton Function (JX  KALC = 3)
Calculate the pollutant buildup using the Michaelis Menton function to the right of this item. This form of buildup has an asymptotic trend. Generally, this formulation rises steeply (in fact linearly for small values of time) and then approaches the asymptote slowly.
Michaelis Menton Factor (JX  QFACT3)
This parameter has the interpretation of the halftime constant, ie. the time at which buildup is half of the maximum (asymptotic) value. Thus, the unit of this parameter is days.
Washoff Method
Washoff is the process of erosion and/or solution of constituents from a subcatchment surface during a period of runoff.
Anchor  


Event Mean Concentration (KWASH\=3) . The amount of pollutant being washed off is proportional to the amount of runoff, although the concentration varies from the mean using a given standard deviation. The EMC approach is a special case of the 'Rating Curve' approach, with a power of 1.0 and a coefficient which has a probability distribution with a given mean and standard deviation. The EMC is assumed to vary with a log probability distribution.
This option is only available when 'None' is specified for the 'Buildup Method'.
Standard Deviation
Statistical standard deviation from the mean pollutant concentration (RCOEF), in the units for the current pollutant.
Mean Concentration (WASHPO)
Mean concentration of pollutant in the runoff water, in the units defined for the current pollutant.
Anchor ExponentialWashoff ExponentialWashoff
Exponential
ExponentialWashoff  
ExponentialWashoff 
Cumulative pollutant washoff is specified as an exponential function of time (KWASH\=0). This method requires some buildup of pollutant to occur during dry periods prior to a storm. With rainfall, the pollutant is washed off with an exponential relationship, ie. approaching the amount built up asymptotically. The quantity PSHED0 is the quantity of pollutant built up, and thus available for washoff.
This option is available only when a buildup method other than 'None' is selected.
The variation from the simple exponential relation is that the exponential coefficient varies with the runoff in a power form.
Initial Buildup Quantity (PSHEDO)
The quantity of pollutant built up, and thus available for washoff.
Coefficient (RCOEFF)
The coefficient in the power equation for the exponent, in units of (in/hr)^POW [(mm/hr)^POW], where POW is the power used in this equation. Note that the runoff rate is spread over the subcatchment in units of in/hr [mm/hr].
Power (WASHPO)
The power in the equation for the exponential coefficient.
Anchor RatingCurveWashoff RatingCurveWashoff
Rating Curve
RatingCurveWashoff  
RatingCurveWashoff 
The rating curve (KWASH=1 or 2) is a function of instantaneous washoff against instantaneous runoff. This method is generally easiest to use when only total runoff volumes and pollutant loads are available for calibration.
The cumulative pollutant washoff will always be limited to the amount of pollutant built up if buildup has been specified (ie. if the buildup criteria is other than 'None'). The maximum amount that can be removed is the amount built up prior to the storm. Once the limit is reached, concentrations drop to zero, until dry weather allows buildup.
Coefficient (RCOEF)
The coefficient in the rating curve equation, with units of Q1/(cfs^POW) [Q1/cumec^POW],
where
POW = power in the power rating curve
Q1 = Pollutant quantity, that depends on the pollutant units as follows:
Pollutant Unit  Unit for Q1 

mg/liter  lb [kg] 
'other'/liter  10^{6} [10^{6}] 
other  ft^{3 }[m^{3}] 
Power (WASHPO)
The exponent in the rating curve equation, nondimensional. If this value is more than one the concentration of pollutant in the runoff will increase as the runoff increases. Otherwise the concentration of the pollutant will decrease as the runoff increases.
Scroll PDF Exporter Ignore  

Quick Link  
image  checkbox_checked.png 
link  Help+Documentation 
title 
Stylesheet  

 

Section PagesOn this section:
Children Display  

