Storm Water Management

Storm Water Management Guidance Manual

Stormwater Management Guidance Manual

Clean Water Act
In 1972, Congress enacted the Clean Water Act, recognizing that the nation’s waters and waterways were seriously polluted and that human activity and urban development contributed to problem. The Clean Water Act initially focused on cleaning up the water discharged from point-sources discharge such as effluent from manufacturing plants and municipal sewer systems. In 1987, the Clean Water Act was amended and the impacts of “non-point source” were included. “Non-point source” discharges are primarily the storm water runoff collected and transported to downstream bodies of water from developed and urbanized areas and water discharged from large construction projects (greater than an acre).


The standards of urban development over the past century have been to pave or otherwise cover most of the urban land with impervious surfaces. This includes paved roads, sidewalks, parking lots, and building rooftops. In its natural state, soil acts as a filter for storm water, minimizing the pollutants that enter waterways during rainstorms. Paved surfaces not only break the cycle of infiltration and the natural purification of storm water, paved surfaces add contaminants to storm water including oils from streets, debris from roof tops, and bacteria from pet waste. In addition to these contaminants, waterways can also be polluted with naturally occurring substances such as nitrates and sediment, that at the correct level support the ecosystem, but at high levels damage the ecosystem and pollute the water.


The Clean Water Act provides for discharges into waters of the United States, provided these discharges are in compliance with the National Pollutant Discharge Elimination System (NPDES) permit requirements. Pursuant to the Clean Water Act, the City of Gilroy is a small municipality (population below 100,000) with a municipal separate storm system, is classified as a MS4 and is operating under a NPDES permit for this classification.

State Water Resources Control Board

The State Water Resources Control Board (SWRCB) governs and regulates the State’s NPDES permitting program. The SWRCB is comprised of 9 Region Water Quality Control Boards. The City of Gilroy is under the jurisdiction of the Central Coast Regional Water Quality Control Board (CCRWQCB). In June 2013, the City of Gilroy filed a Notice of Intent (NOI) with the SWRCB to comply with the Small Municipal ("Phase II") General Storm Water Permit (Water Quality Order No. 2013-0001-DWQ) which was adopted on February 5, 2013. The City of Gilroy is partnered with the City of Morgan Hill and the County of Santa Clara, and works closely with these agencies to implement various aspects of the permit. The partnership offers regional consistency and a dynamic pool of resources from which to build the storm water program.

Community Clean Water Program

The City manages storm water through the Clean Water Program which includes opportunities for community involvement.  To see how you can participate in the City's Clean Water Program follow this link. 

Best Management Practices Rapid Assessment Methodology

BMPRAM Field Protocols V4.3