Land Uses are categories of development activities or land surface characteristics assigned to subcatchments. Examples of land use activities are residential, commercial, industrial, and undeveloped. Land surface characteristics might include rooftops, lawns, paved roads, undisturbed soils, etc. Land uses are used solely to account for spatial variation in pollutant buildup and washoff rates within subcatchments.
The SWMM user has many options for defining land uses and assigning them to subcatchment areas. One approach is to assign a mix of land uses for each subcatchment, which results in all land uses within the subcatchment having the same pervious and impervious characteristics. Another approach is to create subcatchments that have a single land use classification along with a distinct set of pervious and impervious characteristics that reflects the classification.
Land Use Editor is used to define a category of land use for the study area and to define its
pollutant buildup and washoff characteristics. The Editor contains three tabbed pages of land use properties:
General Page, Buildup Page and Washoff Page. The input parameters for each tab are listed in the table below:
The General page properties
| Field | Description |
| Interval | Days between street sweeping within the land use (0 for no sweeping). |
| Availability | Fraction of the buildup of all pollutants that is available for removal by sweeping. |
| Last Swept | Number of days since last swept at the start of the simulation. |
If Street Sweeping does not apply to the land use, then the last three properties can be left blank.
The Buildup page properties
| Field | Description |
| Pollutant | Select the pollutant whose buildup properties are being edited. |
| Function |
The type of buildup function to use for the pollutant. The choices are NONE - no buildup POW - for power function buildup EXP - for exponential function buildup SAT - for saturation function buildup EXT - for buildup supplied by an external time series Select NONE if no buildup occurs. |
| Max. Buildup | The maximum buildup that can occur, expressed as lbs (or kg) of the pollutant per unit of the normalizer variable (see below). This is the same as the C1 coefficient used in the buildup formulas discussed under Pollutant Buildup. |
| The following two properties apply to the POW, EXP, and SAT buildup functions: | |
| 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. |
The Washoff page properties
| Field | Description |
| Pollutant | The name of the pollutant whose washoff properties are being edited. |
| Function |
The choice of washoff function to use for the pollutant. The choices are: NONE no washoff EXP exponential washoff RC rating curve washoff EMC event-mean concentration washoff The formula for each of these functions is discussed under the Pollutant Washoff topic. |
| Coefficient | This is the value of C1 in the exponential and rating curve formulas, or the event-mean concentration. |
| Exponent | The exponent used in the exponential and rating curve washoff formulas. |
| Cleaning Efficiency | The street cleaning removal efficiency (percent) for the pollutant. It represents the fraction of the amount that is available for removal on the land use as a whole (set on the General page of the editor) which is actually removed. |
| BMP Efficiency | Removal efficiency (percent) associated with any Best Management Practice that might have been implemented. The washoff load computed at each time step is simply reduced by this amount. |