Post-Construction Stormwater Management (Control Measure 5)

Post-Construction Stormwater Management (SWM)

RESOURCE: Stormwater Management Permit checklist for applicants


Please view our Erosion and Sediment Control Permitting Flowcharts to better understand what types of permitting and action may be needed for your planned project.

What is impervious surface?

An "impervious surface" is defined by the Benton County Development Code as “a surface that prevents or impedes stormwater from infiltrating the soil, and includes but is not limited to such elements as roads, driveways, parking lots, walks, patios, and roofs. Compacted gravel, asphalt and concrete surfaces are all considered impervious.”

Increased impervious surface associated with development will increase stormwater volume and degrade water quality, which can harm lakes, rivers, streams, and coastal areas.

How do I lessen water quality impacts of impervious surfaces?

The best way to mitigate stormwater impacts from new developments or redevelopment is to use practices to treat, store, and infiltrate runoff onsite before it can affect water bodies downstream.

Innovative site designs that reduce impervious surface and smaller-scale low impact development practices dispersed throughout a site are excellent ways to achieve the goals of reducing flows and improving water quality.

In order to meet long-term stormwater management goals, Benton County has developed and implemented Long-Term Stormwater Management Code requirements that apply to any person or business creating a ground-disturbance of 1-acre or more or a cumulative disturbed area of 1-acre or more, OR any activity that results in 25,000 square feet of impervious surface.

Long-Term Stormwater Management Code Requirements

Please note that any construction project may require long-term stormwater management, at the discretion of the County Engineer. If your development or re-development project creates 1/4 acre or more of impervious surfaces (roofs, sport courts, paved driveways, patios, etc.) and you need to complete a Benton County Stormwater Management Permit, you can download the form here or click the link at the bottom of this page.

There are many ways to reduce long-term water quality impacts. Visit our Document Library for more information, or contact Benton County staff with questions.