Low Impact Development

Definition

The Central Coast Water Board defines Low Impact Development (LID) as:

minimizing or eliminating pollutants in storm water through natural processes and maintaining pre-development hydrologic characteristics, such as flow patterns, surface retention, and recharge rates. 

Why LID is required

Traditional development and redevelopment techniques typically cause or threaten to cause pollution problems.  The volume and velocity of storm water discharged from impervious surfaces also cause increased bank erosion and downstream sedimentation, scouring, and channel widening, which significantly impact aquatic ecosystems and degrade water quality. 

How LID reduces negative impacts on water quality

LID practices reduce urban impacts to receiving waters.  This is achieved by:

• Designing sites (starting with the site layout, and the grading and compaction phases of construction) that:
  • disturb only the smallest area necessary;
  • minimize soil compaction and imperviousness;
  • preserve natural drainages, vegetation, and buffer zones.
•  Utilizing on-site, lot-sized storm water infiltration techniques that minimize pollutant transport and maximize on-site pollutant treatment. 

Retrofit projects that replace impervious surfaces with pervious ones, utilize landscaped areas for infiltration, and capture rain water for future use are effective at returning an existing developed site to a more natural state. 

How LID is currently required

The Central Coast Water Board requires municipalities, via the Municipal General Storm Water Permit, to minimize negative impacts on aquatic ecosystems and degradation of water quality to the maximum extent practicable. Permittees must implement Best Management Practices (BMPs) that reduce pollutants in storm water runoff to the technology-based standard of Maximum Extent Practicable (MEP) to protect water quality.”  (Effluent Limitations, General Permit Fact Sheet, pg. 6.)

Permittees must incorporate LID methodology into new and redevelopment ordinances and design standards unless permittees can demonstrate that conventional BMPs are equally effective, or that conventional BMPs would result in a substantial cost savings while still adequately protecting water quality and reducing discharge volume.   In order to justify using conventional BMPs based on cost, permittees must show that the cost of low impact development would be prohibitive because the “cost would exceed any benefit to be derived.” (State Water Resources Control Board Order No. WQ 2000-11.)  Conventional site layouts, construction methods, and storm water conveyance systems with “end of pipe” basins and treatment systems that do not address the changes in volume and rates of storm water runoff and urban pollutants (including thermal pollution) do not meet MEP standards.