Specify the characteristics of the buildup of pollution.

Option

 

Description

Pollutant

The pollutant name. Click the button on the right to display a list of available pollutant objects.

Function

The type of buildup function to use for the pollutant. The choices are:

  • NONE for no buildup.

  • POW for power function buildup.

  • EXP for exponential function buildup.

  • SAT for saturation function buildup.

See Pollutant Buildup topic for explanations of these different functions. Select NONE if no buildup occurs.

Max. Buildup

The maximum buildup that can occur, expressed as kg (or lbs) of the pollutant per unit of the normalizer variable (see below). This is the same as the C1 coefficient used in the buildup formulas, which is discussed under Pollutant Buildup.

Rate Constant

The time constant that governs the rate of pollutant buildup. This is the C2 coefficient in the Power and Exponential buildup formulas discussed under Pollutant Buildup. For Power buildup its units are mass/days raised to a power, while for Exponential buildup its units are 1/days.

Power/Sat. Constant

The exponent C3 used in the Power buildup formula, or the half-saturation constant C2 used in the Saturation buildup formula discussed under Pollutant Buildup. For the latter case, its units are days.

Normalizer

The variable to which buildup is normalized on a per unit basis. The choices are either land area, in hectares or acres, or curb length. Any units of measure can be used for curb length, as long as they remain the same for all subcatchments in the project.

Pollutant Buildup

Pollutant buildup that accumulates within a land use category is described, or "normalized", by either a mass per unit of subcatchment area or per unit of curb length. Mass is expressed in pounds for US units and kilograms for metric units. The amount of buildup is a function of the number of preceding dry weather days and can be computed using one of the following functions.

Power Function

Pollutant buildup (B) accumulates proportional to time (t) raised to some power, until a maximum limit is achieved:

B = min(C1,C2tC3)

Where:

Exponential Function

Buildup follows an exponential growth curve that approaches a maximum limit asymptotically:

B = C1(1 - e-C2t)

Where:

Saturation Function

Buildup begins at a linear rate that continuously declines with time until a saturation value is reached:

B = C1t/(C2 + t)

Where:

See Also Land Uses