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There is nothing magical about LID:

Uses long-term on-site infiltration and evapotranspiration to reduce stormwater runoff.

What happens between storm events is more important than what happens during storm events.
Lateral flow basins to disperse impervious surface runoff onto adjacent pervious soils to retain rainfall, increase evapotranspiration and infiltration, and reduce stormwater runoff.

Green/vegetated/eco-roofs to retain rainfall and increase evapotranspiration and reduce stormwater runoff.

Permeable/porous pavement to infiltrate rainfall and reduce stormwater runoff.

Bioretention/rain gardens/planter boxes to retain runoff, increase evapotranspiration and infiltration
Lateral Flow Dispersion:

LID dispersion practices can include:
 
  roof runoff dispersion onto adjacent yard area
  parking lot runoff onto adjacent lawn area
  reverse slope sidewalks draining onto adjacent vegetated areas

Dispersion is modeled in WWHM using lateral flow basins.

Green roof element:

 increases evapotranspiration.

Green Roof Element Input

   Roof area
   Depth of soil/growing material
   Roof slope
   Vegetative cover (ground cover, shrubs, or trees)
   Maximum roof drain length

NOTE: Green roof element includes HSPF parameter values based on calibrated green roof model.
Green Roof Element

Major issues:

   All rainfall that does not return to the atmosphere via evapotranspiration must eventually runoff.

  All runoff (surface runoff, interflow, and groundwater) from green roof must be connected to a downstream conveyance element.

Permeable pavement element:

 increases infiltration.
Permeable Pavement Element Input

   Pavement length and width
   Bottom slope
   Pavement thickness and porosity
   Gravel sublayer thickness and porosity
   Ponding depth on pavement (before sheet flow starts)
   Underdrain diameter and height above bottom of gravel sublayer
   Infiltration to native soil (optional)
Permeable Pavement Element

Major issues:

 Pavements with bottom slopes greater than 2% must include Effective Volume Factor (average useable gravel depth/maximum gravel depth).

 Permeable pavement must include infiltration into native soil and/or an underdrain to remove water from gravel subgrade.


Bioretention element:

 increases evapotranspiration and infiltration.

Bioretention Element Input

   Bioretention bottom length and width
   Side slopes
   Bottom slope
   Material layer amended soil type and thickness (max 3 layers)
   Riser height and diameter (surface ponding)
   Underdrain diameter and height above bottom
   Underdrain orifice diameter (for flow duration hydromod control)
   Infiltration to native soil (optional)

Bioretention Element

Major issues:

 Bioretention area automatically includes rain and evapo-transpiration; do not include bioretention area in drainage basin area.

 Underdrain orifice controls flow from underdrain and bioretention soil mix layers, when soil layers are fully saturated.

Bioretention Element

Major issues:

 Water movement through the amended soil column is calculated as follows:

As water enters the facility at the top, it infiltrates into the soil based on the modified Green-Ampt equation.

The water then moves through the top soil layer at the computed rate, determined by Darcy’s and Van Genuchten’s equations.

Bioretention Element

Evapotranspiration removes water from bioretention surface ponding and the soil column during non-storm periods in the following order:
  1. Water available from vegetation interception storage
  2. Water available from surface ponding
  3. Water available from the bioretention soil layers (top layer first)

Water is removed from vegetation interception storage and surface ponding and the bioretention soil layers (starting at the top layer) down to the rooting depth at the potential rate. Water is taken from the soil layers below the rooting depth based on a percentage factor.

Planter Box elements in WWHM based on the Bioretention element:
Other WWHM LID infiltration options:
Other WWHM LID infiltration options:
       Infiltration Planter Box Flow-Through Planter Box
Dry Well Infiltration Trench
Infiltration Basin