Stormwater Resources for Designers, Engineers, Architects, and Proponents of New Development or Redevelopment Projects

Development and redevelopment projects that increase impervious surfaces, such as roads, parking lots, and rooftops, can have significant negative impacts on local watersheds. These surfaces prevent rainwater from naturally infiltrating into the soil, leading to higher volumes of stormwater runoff. This runoff can carry pollutants like oil, sediment, and heavy metals into local creeks and storm drains, resulting in water quality degradation. Additionally, the increased runoff can cause erosion, flooding, and reduced groundwater recharge, negatively affecting both the environment and public infrastructure.

Low Impact Development (LID) techniques are designed to mitigate these effects by mimicking natural hydrological processes. LID strategies, such as bioretention ponds, permeable pavements, rain gardens, rain barrels, and green roofs, help reduce runoff by allowing water to infiltrate into the ground, filter through vegetation, or be reused onsite. These practices minimize the impact of impervious surfaces by reducing pollutant loads, slowing stormwater flow, and promoting groundwater recharge, thereby protecting water quality and reducing the strain on municipal stormwater systems.

New development and redevelopment projects that create or replace 2,500 square feet or more of impervious area in the City of Sonoma must implement all necessary measures to mitigate downstream impacts from these impervious surfaces, per the provisions outlined in the city's current NPDES Permit. To mitigate the impacts, applicants must submit a Stormwater Control Plan that outlines the planned low-impact development that will be incorporated into the proposed project. Requirements will change based on the type of project and the amount of replaced or created impervious area. The requirements are:

1. A Stormwater Control Plan for a Single-Family Home or Small Development Project is required for single family homes that create or replace 2,500 square feet or more of impervious surface, and for Small Projects that create or replace between 2,500 and 5,000 square feet of impervious surface. The Stormwater Control Plan for a Single-Family Home or Small Development Project should be in accordance with the BASMAA Post-Construction Manual (link below). A template for the plan can be found in Appendix C of the BASMAA document.
2. A Stormwater Control Plan for Regulated Projects is required for projects that create or replace 5,000 or more square feet of impervious surface. Single-family home projects that are not part of a larger development plan, as well as pavement resurfacing within the existing footprint, are exempt. The Stormwater Control Plan for a Regulated Project should be in accordance with the BASMAA Post-Construction Manual (link below). A template for the plan can be found in Appendix D of the BASMAA document.