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Welcome to the next generation MIKE+ Documentation

Introduction to LID

Low Impact Development (LID) represents an approach to land development (or redevelopment) that works with nature to manage stormwater as close to its source as possible. It is also known as Water-Sensitive Urban Design (WSUD). LID employs principles such as preserving and recreating natural landscape features, minimizing effective imperviousness to create functional and appealing site drainage that treat stormwater as a resource rather than a waste product.

The ability to assess the benefit of LID practices installed in urban catchments is required by water utilities and other stakeholders responsible for the urban drainage. An essential part of this requirement is the ability to model the various LID practices in order to evaluate the effect of installing LID practices as parts of a stormwater drainage system.

MIKE+ offers 2 ways of modelling LID structures:

  • Modelling of LIDs at screening level - catchment-based approach
  • Detailed hydraulic modelling of individual LID structures - drainage network based approach.

Only the catchment-based method is available for SWMM models, and is described in this chapter. These methods are based on research published by US EPA adapted to the MIKE+ modelling concept of urban hydrology.

A user-defined number of LID controls can be deployed and assessed for each individual catchment. This catchment-based approach is used to size the required infiltration or rainwater harvest by subtraction of flow from the calculated runoff within each catchment.

LIDs are low impact development structures designed to capture or reduce surface runoff from the collecting area by means of a combination of detention, infiltration and evapotranspiration. LID controls are conceptual objects that are not displayed on the map visualization of the urban catchment model. Once deployed, they are considered as properties of a given catchment. MIKE+ can model the following types of LIDs:

  • Bioretention Cell
  • Infiltration Trench
  • Porous Pavement
  • Rain Barrel
  • Vegetative Swale
  • Rain Garden
  • Green Roof
  • Rooftop Disconnection.

Bioretention cells, infiltration trenches, and porous pavement systems can have optional underdrain systems in their gravel storage beds to convey storage runoff off the site rather than infiltrate it all. They can also have an impermeable liner that prevents infiltration into the native soil. Infiltration trenches and porous pavement systems can also be subject to a decrease in hydraulic conductivity over time due to clogging.