Click the LID Controls button to open the LID Control Editor window.

Button Description
Add one LID
Delete selected LIDs. Please note to use Ctrl and Shift keys for multiple selection.
Import a group of LIDs
Export all the LIDs

In VOSWMM, the LID Control Editor serves as a tool to create Low Impact Development controls that can be deployed within your study area to manage subcatchment runoff through storage, infiltration, and evaporation. These controls are designed on a per-unit-area basis, allowing you to apply them to various subcatchments of different sizes and quantities.

Here’s how to use the LID Control Editor in VOSWMM, along with the corresponding data entry fields:

LID Type
Select the general category or type of LID control that matches your specific requirements. VOSWMM offers a range of LID types to choose from, including options such as bio-retention cells, rain gardens, green roofs, infiltration trenches, permeable pavements, rain barrels, or vegetative swales. Pick the one that best suits your project.

Control Name
This field is used to give a unique identifier to the specific LID control you are defining. Choose a name that helps you easily recognize the control.

Process Layers
This section comprises a series of tabbed pages, each with data entry fields corresponding to the vertical layers and drainage system components that make up your chosen LID control. The available tabs and fields may vary depending on the LID type you select. The following elements are commonly included:

a. Surface Layer

The Surface Layer page in the LID Control Editor is primarily used to define the surface properties of various LID controls, excluding rain barrels. These properties are crucial for characterizing how each LID control manages stormwater runoff. The key attributes on the Surface Layer page include:

Berm Height (or Storage Depth)

This field specifies the maximum depth to which water can accumulate above the surface of the LID control unit before overflow occurs. The units can be either inches or millimeters, depending on your preference. For specific LID types:
For Rooftop Disconnection, it represents the depth of storage on the roof’s surface.
For Vegetative Swales, it indicates the height of the trapezoidal cross-section.

Vegetation Volume Fraction

This parameter refers to the fraction of the volume within the surface storage depth that is filled with vegetation. It’s important to note that this measurement pertains to the volume occupied by the vegetation’s stems and leaves, not the surface area coverage. In most cases, you can leave this value at its default setting. However, for LID controls with very dense vegetation, you may need to set it between 0.1 and 0.2.

Surface Roughness

Manning’s roughness coefficient (n) is entered here for estimating the resistance to flow of overland water. The value of ‘n’ is used to represent how rough or smooth the surface is for overland flow over different types of surfaces such as soil cover, pavement, roof, or a vegetative swale.

Surface Slope

This field allows you to specify the slope of the roof surface, pavement surface, or vegetative swale as a percentage. When it comes to other LID types, you should use ‘0’ for this value. The slope is an important factor in determining the rate of water runoff from the LID control.

Swale Side Slope

For vegetative swales, this value represents the slope (run over rise) of the side walls of the swale’s cross-section. For other LID types, this parameter is disregarded.

It’s worth noting that if either the Surface Roughness or Surface Slope values are set to ‘0’, any ponded water that exceeds the surface storage depth will be assumed to completely overflow the LID control within a single time step. This helps simulate the rapid release of water in such conditions. These parameters are essential for accurately modeling the behavior of LID controls in VOSWMM.

b. Pavement Layer

The Pavement Layer page within the LID Control Editor provides essential properties for configuring permeable pavement LID controls in VOSWMM. These properties are crucial for accurately modeling the behavior of permeable pavements. Here’s a breakdown of the key parameters and their descriptions:


This field allows you to specify the thickness of the pavement layer for your permeable pavement LID control. You can input this value in either inches or millimeters. Typical values for permeable pavements range from 4 to 6 inches (100 to 150 mm).

Void Ratio

The Void Ratio represents the volume of void space relative to the volume of solids in the pavement. This parameter is applicable for continuous systems or for the fill material used in modular systems. Typical values for permeable pavements range from 0.12 to 0.21. porosity = void ratio / (1 + void ratio).

Impervious Surface Fraction

This parameter is relevant for modular systems and represents the ratio of impervious paver material to the total area. For continuous porous pavement systems, set this value to 0.


Permeability refers to the permeability of the concrete or asphalt used in continuous systems or the hydraulic conductivity of the fill material (e.g., gravel or sand) in modular systems. You can input this value in inches per hour (in/hr) or millimeters per hour (mm/hr). In the case of modular systems, the nominal conductivity of the fill should be multiplied by the fraction of the total area it covers. It’s important to note that the initial permeability of new porous concrete or asphalt is usually very high (e.g., hundreds of in/hr), but it can decrease over time due to clogging from fine particulates in the runoff.

Clogging Factor

The Clogging Factor is a crucial parameter that describes how the permeability of the pavement decreases over time as it becomes clogged with accumulated runoff. This factor is determined by several variables, including the number of years (Yclog) it takes to fractionally clog the system to a degree Fclog. The formula to calculate CF is provided, taking into account factors such as annual rainfall (Pa), capture ratio (CR), Void Ratio (VR), Impervious Surface Fraction (ISF), and pavement layer thickness (T). The Clogging Factor helps in modeling the gradual decrease in permeability due to clogging.

Regeneration Interval

The Regeneration Interval specifies the number of days that the pavement layer is allowed to clog before its permeability is restored. Typically, this restoration is achieved by methods like vacuuming the pavement’s surface. A value of 0 (the default) indicates that no permeability regeneration occurs.

Regeneration Fraction

The Regeneration Fraction signifies the extent to which the pavement’s permeability is renewed upon reaching a regeneration interval. A value of 0 presents no restoration, whereas a value of 1 implies a full return to the initial permeability. Following regeneration, the pavement gradually reverts to clogging, its rate determined by the Clogging Factor.

c. Soil Layer

The Soil Layer page within the LID Control Editor provides information on the characteristics of the engineered soil mixture employed in bio-retention LID types and the optional sand layer beneath the permeable pavement. These characteristics encompass:

Thickness: This field specifies the thickness of the soil layer, which can be entered in inches or millimeters. Typical values vary, with ranges from 18 to 36 inches (450 to 900 mm) for rain gardens, street planters, and land-based bio-retention units, and narrower thicknesses of 3 to 6 inches (75 to 150 mm) for green roofs.

Porosity: It represents the volume of pore space relative to the total volume of soil and is expressed as a fraction.

Field Capacity: This parameter defines the volume of pore water relative to the total volume once the soil has fully drained (also as a fraction). Below this level, vertical water drainage through the soil layer ceases.

Wilting Point: It indicates the volume of pore water relative to the total volume for a completely dried soil where only bound water remains (expressed as a fraction). The soil moisture content cannot drop below this limit.

Conductivity: This is the hydraulic conductivity of the fully saturated soil and is measured in inches per hour (in/hr) or millimeters per hour (mm/hr).

Conductivity Slope: The average slope of the curve of log(conductivity) versus soil moisture deficit (porosity minus moisture content). Typical values generally range from 30 to 60 and can be estimated using a standard soil grain size analysis, as 0.48×(%Sand) + 0.85×(%Clay).

Suction Head: This parameter represents the average value of soil capillary suction along the wetting front, measured in inches or millimeters. It is the same parameter used in the Green-Ampt infiltration model.

It’s important to note that Porosity, Field Capacity, Conductivity, and Conductivity Slope are soil properties also used for Aquifer objects in groundwater modeling, while Suction Head corresponds to the parameter used for Green-Ampt infiltration. However, in this context, these properties apply to the specific soil mixture used within an LID unit rather than the naturally occurring soil at the site.

d. Storage Layer

The Storage Layer page in the LID Control Editor defines the properties of the crushed stone or gravel layer used in bio-retention cells, permeable pavement systems, and infiltration trenches as the bottom storage and drainage layer. This page also serves to specify the height of a rain barrel (or cistern). It offers the following data fields:

Thickness (or Barrel Height): This parameter represents the thickness of the gravel layer or the height of a rain barrel, which can be input in inches or millimeters. Crushed stone and gravel layers typically range from 6 to 18 inches (150 to 450 mm) in thickness, while rain barrels for single-family homes vary in height from 24 to 36 inches (600 to 900 mm).

Void Ratio: This field indicates the volume of void space relative to the volume of solids in the layer. Typical values for gravel beds generally range from 0.5 to 0.75. You can calculate porosity using the formula: porosity = void ratio / (1 + void ratio).

Seepage Rate: This parameter specifies the rate at which water seeps into the native soil beneath the layer and is measured in inches per hour (in/hr) or millimeters per hour (mm/hr). It is typically the Saturated Hydraulic Conductivity of the surrounding subcatchment when Green-Ampt infiltration is applied or the Minimum Infiltration Rate for Horton infiltration. If there is an impermeable floor or liner beneath the layer, a value of 0 is used.

Clogging Factor: The Clogging Factor signifies the total volume of treated runoff required to completely clog the bottom of the layer divided by the void volume of the layer. A value of 0 disregards clogging. Clogging reduces the Infiltration Rate proportionally to the cumulative volume of treated runoff and is primarily relevant for infiltration trenches with permeable bottoms and no underdrains. For further discussion on the Clogging Factor, refer to the Pavement Layer page.

Covered: This field specifies whether the rain barrel is covered or not.

e. Drain System

LID storage layers may incorporate an optional drainage system designed to collect incoming water and channel it to a conventional storm drain or another designated location, which may differ from the LID subcatchment’s outlet. Alternatively, the drain flow can be redirected back to the permeable area within the LID’s subcatchment. The drain system can be positioned at a certain distance above the storage layer’s bottom to allow a portion of runoff to be stored and eventually infiltrated before any surplus is captured by the drain. In the case of Rooftop Disconnection, the drain system comprises the roof’s gutters and downspouts, each with a specified maximum conveyance capacity.

The Drain page of the LID Control Editor outlines the properties of the LID unit’s drain system and encompasses the following data entry fields:

Drain Coefficient and Drain Exponent

The drain coefficient © and exponent (n) are pivotal factors that govern the flow rate through a drain concerning the height of water stored above the drain’s offset.

Drain Offset Height

This parameter designates the vertical distance between the drain line and the bottom of a storage layer or rain barrel, and it is expressed in inches or millimeters.

Drain Delay (for Rain Barrels only)

For rain barrels, the drain delay specifies the number of dry weather hours that must transpire before the drain line within the rain barrel is opened. The line is assumed to remain closed once rainfall commences. A value of 0 indicates that the barrel’s drain line remains open and drains continuously. This parameter does not apply to other types of LID practices.

Flow Capacity (for Rooftop Disconnection only)

In the context of Rooftop Disconnection, the flow capacity represents the maximum flow rate that the roof’s gutters and downspouts can accommodate before overflow occurs. This value is provided in inches per hour (in/hr) or millimeters per hour (mm/hr), and it exclusively pertains to Rooftop Disconnection.

Open Level

The open level denotes the height, expressed in inches or millimeters, within the drain’s Storage Layer that causes the drain to automatically open when the water level rises above it. The default setting is 0, indicating that this feature is disabled.

Closed Level

Similarly, the closed level signifies the height, measured in inches or millimeters, within the drain’s Storage Layer that prompts the drain to automatically close when the water level falls below it. The default setting is 0.

Control Curve

This field is used to input the name of an optional Control Curve that can adjust the computed drain flow as a function of the head of water above the drain. If a Control Curve does not apply, you can leave this field blank.

f. Drainage Mat

Green Roofs commonly incorporate a drainage mat or plate positioned beneath the soil media and above the roof structure. Its primary function is to facilitate the conveyance of water that permeates through the soil layer, directing it away from the roof. The Drainage Mat page in the LID Control Editor for Green Roofs provides details regarding the properties of this layer, encompassing:

Thickness: This parameter specifies the thickness of the mat or plate, with measurements in inches or millimeters. Typically, this thickness falls within the range of 1 to 2 inches.

Void Fraction: The Void Fraction denotes the ratio of void volume to the total volume within the mat. Commonly, this ratio falls between 0.5 to 0.6.

Roughness: Manning’s roughness coefficient (n) is employed to calculate the horizontal flow rate of drained water passing through the mat. Manufacturers do not typically provide this as a standard product specification, so it necessitates estimation. Previous modeling studies have indicated the use of relatively high values, typically within the range of 0.1 to 0.4.

g. Pollutant Removal

The Pollutant Removal page within the LID Control Editor allows for the specification of the extent to which pollutants are effectively removed by an LID control. This removal is reflected in the flow that exits the unit through its underdrain system. Therefore, this page is applicable solely to LID practices equipped with an underdrain, which includes bio-retention cells, permeable pavement, infiltration trenches, and rain barrels.

Within this page, you’ll find a data entry grid featuring the project’s pollutant names in one column and the corresponding percentage of removal in the second editable column. If a removal percentage value is left blank, it is assumed to be 0.

The removal percentages defined on this page come into effect when the underdrain of the LID unit channels flow either into a subcatchment or into a conveyance system node. It’s important to note that these removal percentages do not apply to any surface flow that exits the LID unit. For instance, if the runoff treated by the LID unit possesses a Total Suspended Solids (TSS) concentration of 100 mg/L and a removal percentage of 90, then when 5 cubic feet per second (cfs) flow from its drain into a conveyance system node, the mass loading contribution to the node would be calculated as 100 × (100 – 90) × 5 × 28.3 L/ft³, resulting in 1,415 mg/sec. If, in addition, the unit has a surface outflow of 1 cfs into the same node, the mass loading from this flow stream would be calculated as 100 × 1 × 28.3, amounting to 2,830 mg/sec.