LID controls applied to Catchment

The LID controls editor is invoked by clicking the properties of the SWMM subcatchment

It contains the following data entry fields:

• Control Name - The name of a previously defined LID control to be used in the subcatchment.
• Each Unit Area - The surface area dedicated to each replicated LID unit (square feet or square meters). If the LID Occupies Full Subcatchment box is checked, this field will be disabled and will display the total subcatchment area divided by the number of replicated units. (See LID placement for LID placement options within subcatchments). unit.
• Number of replicated units - The number of equal-sized practice LID units (eg number of rain barrels) deployed in the subcatchment.
• Surface width per unit - The width of the output face of each identical LID unit (in feet or m). This parameter applies to roofs, pavements, ditches, and ditches that use surface flow to carry surface runoff from the unit. It can be set to 0 for other LID processes such as bioretention cells, rain gardens, and rain barrels that simply spill any captured excess runoff over their berms.
• % Initially Saturated - For bioretention cells, rain gardens and green roofs, this is the degree to which the unit soil is initially filled with water (0% saturation corresponds to wilting point moisture, 100% saturation has moisture content equal to porosity). For units with a storage layer, corresponds to the initial depth of water in the layer.
• % Impervious Area Treated - The percentage of the impermeable portion of the non-LID area of the subcatchment whose runoff is treated by the LID practice. (For example, if rain barrels are used to capture roof runoff and roofs represent 60% of the impermeable area, then the treated impermeable area is 60%). If the LID unit deals only with direct rainfall, such as green roof or roof disconnection, then this value should be 0. If the LID occupies the entire subcatchment, this field is ignored.
• % Pervious Area Treated - The percentage of the pervious portion of the non-LID area of the subcatchment whose runoff is treated by the LID practice. If the LID unit deals only with direct rainfall, such as green roof or roof disconnection, then this value should be 0. If the LID occupies the entire subcatchment, this field is ignored.
• Send drainage flow to - Provide the name of the Node or Subbasin that receives any drainage flow produced by the LID unit. This field can be left blank if this flow is to the same subbasin outlet as the LID unit.
• Return all outflow to permeable area - Select this option if runoff from the LID unit is to be routed back to the permeable area of the containing subcatchment. If the drain outlet was selected to be directed to a different location than the subcatchment outlet, then only the surface outlet will be returned. Otherwise, both surface flow and drain are returned. Selecting this option would be a common choice for rain barrels, roof disconnect, and possibly green roofs.
• Detailed Report File - The name of an optional file where detailed time series results for the LID will be written. Click the FileBrowse browse button to select a file using the standard Windows File Save dialog box or click the delete delete1 button to remove any detailed reports. See the LID Results topic to learn more about the contents of this file.

The subbasin containing the LID internally routes some of the runoff from the impermeable area to the permeable area, then the percentage of the impermeable area treated by the LID unit refers to the remaining impermeable area that is not internally routed. For example, if the sub-basin has 2 acres of impermeable area with 50% runoff of this area directed to its permeable area, so a LID unit that treats 20% of the impermeable area would receive runoff from 0.2 acres of impermeable area. This same convention applies to the percentage of permeable area treated when routing internally from permeable to impermeable areas.