Stormwater Management / Regulations


Stormwater is rain that runs off hard surfaces such as rooftops, paved streets, and parking lots. As water runs off these surfaces, it can pick up pollution such as oils and dirt. Untreated stormwater might flow directly into a local stream, river or lake negatively impacting the habitat or wildlife.

In urban areas, it may go into a storm drain and continue through storm pipes until it is released untreated into a local waterway. Runoff may also create large volumes of water that could cause erosion and damage to the stream channels. The result of this damage could degrade water quality, affect drinking water supplies, and damage wildlife habitat.

Urban areas that collect stormwater runoff in municipal separate storm sewers and discharge it to rivers are required to have a permit from the state under the federal Clean Water Act. Clark County is committed to complying with federal and state requirements to provide effective and efficient stormwater management in our community.  As part of our work, we maintain a stormwater management plan that guides new development and redevelopment in our community to minimize impact to our waterways. Our local regulations are defined by municipal code and stormwater design manuals.


Permit updates took effect in 2019. Learn more about the permit updates at the Department of Ecology Phase I stormwater permit web page.

Stormwater code and manual

Development codes and design manuals to ensure compliance with the county's National Pollutant Discharge Elimination System (NPDES) Phase I Municipal Stormwater permit. Clark County has updated its 2015 stormwater manual in 2021. 

Stormwater management plan

Learn how Clark County manages stormwater and related water quality issues to meet requirements of the NPDES permit.

Clean Water Commission

View meeting schedule, notes and commission roster.

Stormwater Planning in Mill Creek Subwatershed

View the study and plan completed for submittal to Ecology in 2022. 

Low Impact Development

Learn more about LID in Clark County, including locations, trainings and resource information

NPDES Permit Annual Reports Since 2014

Clark County is required to report on NPDES permit compliance every March to the Department of Ecology. These reports document the submittals to Ecology for work completed since 2014. These documents comprise the report and attachments.