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Performance Report

5.2C – Managing Hydromodification Impacts – Low Impact Development

Management Measure

  1. Conserve and protect natural resources.
  2. Maintain or restore the pre-development hydrograph of the site by utilizing distributed, small-scale structural and non-structural management practices. Integrate the non-structural management practices during the site planning phase, before construction starts.

Low Impact Development (LID) is essentially a paradigm shift in the way storm water is managed. LID uses a watershed-scale as the planning unit and aims to protect, conserve, and enhance natural resources, especially those that enhance water quality and aquatic resources. Small-scale LID is designed to achieve the pre-development hydrograph of a site using a variety of distributed green infrastructure technologies that capture and treat storm water on-site, thus preventing polluted runoff from discharging into local waterways. Conventional storm water is managed using a centralized approach; storm water is funneled through various catchments (i.e. storm drains) and conveyance systems. In older cities, combined sewer and storm systems may be routed to a waste water treatment plant for treatment, however in most California cities and towns storm water is discharged directly into streams, bays, estuaries, and other local bodies of water though storm water outlets. Combined sewer and storm systems were very common prior to the early 1900s, e.g. older parts of Sacramento and San Francisco have combined sewer and storm systems. These combined sewer and storm water systems can overflow during storm events causing untreated sewage and storm water to flow directly into nearby waterbodies, thus resulting in violations of municipal National Pollutant Discharge Elimination System (NPDES) permits and causing harm to aquatic life and humans. Separate sanitary sewer systems also have the potential to overflow during high storm events due to system leaks and groundwater infiltration. Both combined storm and sewer, and separate sewer overflows are regulated under Municipal NPDES permits.

Storm water contains various pollutants which are discharged into water bodies without any treatment. Refer to the urban land-use category (MM 3) for more information on urban storm water.

Management Practices

Use watershed-based continuous rainfall simulation models such as EPA’s Storm Water Management Model (SWMMM) or Hydrologic Simulation Program Fortran (HSPF) to help with site design.

LID is a component of green infrastructure which includes regional or large-scale and distributed or small-scale management measures. More information on relevant management measures and practices can be found in various land-use categories within this Encyclopedia.

The following management measures are considered regional or large-scale green infrastructure components of LID and are included in the following sections of this Encyclopedia:

The following management measures are considered small-scale green infrastructure components of LID and are included in the following sections of this Encyclopedia:

  • Minimize (limit, reduce, or mitigate) and disconnect impervious surfaces. Smart growth and urban infill development includes limiting, mitigating, and/or reducing impervious surfaces. Management practices are discussed in MM 3.1C, Impervious Surfaces and MM 3.1E Land Development.
  • Use bioretention, i.e. phytoremediation and natural biogeochemical cycling, to transform and attenuate common pollutants from storm water runoff at its source or as close to the source as practical. Green infrastructure components such as urban forestry, bioswales, rain gardens, and general landscaping are discussed in MM 3.1D, Landscaping.


  • Stormwater Quality Design Manual for the Sacramento and South Placer Regions. May 2007. LID is discussed in Chapter 2 (and Step 3 in Chapter 3) promotes the conservation/use of natural site features, an important LID principle. Chapter 4 describes how site specific, lot-scale source control measures can keep pollutants from contacting runoff and leaving the site. Chapter 5 focuses on runoff reduction control measures integrated into site design; many of these techniques are intended to reduce site imperviousness, another important LID principle. And finally, Chapter 6 includes a variety of treatment control measures, some of which are intended to be applied at the lot level for pollution and runoff control.
  • Contra Costa County, New Development/Provision C.3. requirements include LID BMPs such as "Project site designs must minimize the area of new roofs and paving. Where feasible, pervious surfaces should be used instead of paving so that runoff can percolate to the underlying soil. Runoff from impervious areas must be captured and treated. The permit specifies ways to calculate the required size of treatment devices."

Information Resources


USEPA. 2007. National Management Measures Guidance to Control Nonpoint Source Pollution from Hydromodification. EPA 841-B-07-002. U.S. Environmental Protection Agency, Washington, DC. (http://www.epa.gov/owow/nps/hydromod/index.htm)