Stormwater Management

The County has developed, implemented and will enforce a Stormwater Management Program designed to reduce pollutants from the Municipal Separate Storm Sewer System (MS4) to the maximum extent practicable.

The Linn County Stormwater Management Program Manual identifies the management practices, control techniques and system, and design and engineering methods necessary to meet this standard.

The stormwater management requirements have the objective of developing a stormwater management system that will:

• Be of adequate design to safely manage stormwater generated upstream and on the site from given storm intervals to an approved point of disposal.
• Provide points of connection for stormwater generated by future development upstream.
• Prevent the uncontrolled or irresponsible discharge of stormwater onto adjoining public or private property.
• Prevent the capacity of downstream channels and storm drainage facilities from being exceeded.
• Have sufficient structural strength to resist erosion and all external loads that may be imposed.
• Maintain the runoff characteristics of the original undeveloped drainage basin, where feasible, as determined by the County Engineer.
• Protect the County’s natural drainage system of streams, lakes, and wetlands.
• Maintain or improve overall stormwater quality.
• Be designed in a manner to allow economical future maintenance.
• Be designed using materials to insure a minimum practical design life of 75 years.
• Be consistent with the Linn County Code (LCC), Oregon Standard Specifications for Construction (OSS) and all applicable state and federal regulations and requirements for stormwater quantity and quality.

When do Stormwater Requirements Pertain to my Project?

The County requires a Stormwater Permit and requires approval of the stormwater plan before permits are issued or before commencing land disturbance activities within the MS4 Stormwater Management Area for the following instances:

1. Developments that adds or replaces more than 1/4 acre (10,890 square feet) of impervious surface;
2. All major partitions and subdivisions;
3. Developments entailing construction that would change the point of discharge of surface waters, the quantity of discharge, or discharge surface waters at a higher velocity or flow than that of the preconstruction discharge rate, or could contribute to pollution of surface waters;
4. Construction or reconstruction of public roadways and temporary detours;
5. Developments entailing construction in or adjacent to any existing stream or surface watercourse including intermittent streams;
6. Developments requiring construction in or adjacent to the 100-year floodplain of any stream; or
7. All public and private development that requires stormwater reviews and/or approvals from the County

Click here for a worksheet that can help in determining if a stormwater permit is required.

The County requires an Operation and Maintenance Agreement and Plan and Post-Construction Stormwater Plan and requires approval of the plan before permits are issued or before commencing land disturbance activities for the following instances:

1. New development and redevelopment sites that result from a land disturbance of 1 acre (43,560 square feet)  or more (or that disturb less than one acre, if it is part of a “common plan of development or sale” disturbing one or more acres).

Click here for a worksheet that can help in determining if a post-construction stormwater plan is required.

The County has identified and will inspect, clean and maintain all County stormwater facilities within the MS4 Area, at least every 5 years, to ensure pollutants are not entering waters of the United States.