Low Impact Development (LID)

Low Impact Development, or LID, is a design strategy using naturalistic, on-site Best Management Practices to lessen the impacts of development on stormwater quality and quantity. The goal of LID is to mimic the undeveloped runoff conditions of the development site with the post-development conditions. In 2014 the County of Los Angeles revised LID requirements for development occurring within unincorporated portions of the County. Subsequently, in 2025 the County of Los Angeles revised the LID Manual to conform to the requirements of the 2021 Municipal Separate Storm Sewer System (MS4) Permit. The following documents are available for download:

The LID Manual explains how a site designer/engineer could use a wide array of simple cost-effective techniques that focus on site-level hydrologic control to meet Low Impact Development regulations. The LID manual describes those techniques, provides examples and descriptions of how they work, and contains Best Management Practice (BMP) fact sheets.

The HydroCalc Calculator allows the site designer/engineer to calculate runoff rates and volumes from the water quality storm. Download