Cochran/Downriver Stormwater Management Facilities

The Cochran/Downriver Stormwater Management Facilities plan intends to establish the integration of stormwater management facilities into Downriver Park while enhancing and protecting the park’s natural features, shoreline environment, and current uses.

Project Goals

  • Protect the Spokane River from contaminated stormwater runoff
  • Develop and manage public access to Downriver Park for a wide range of recreational uses consistent with preservation goals
  • Maintain and enhance river access for rafting, kayaking, and fishing
  • Maintain and enhance the disc golf course
  • Resolve user conflicts through design and management
  • Keep the park accessible for recreational uses including rafting, fishing, kayaking, disc golf play, hiking, and biking
  • Enhance the Downriver Golf Course

Project Description

The Cochran Basin is a natural topographic basin located within the corporate limits of the City of Spokane where it is bounded on the west by Alberta Street, the north by Francis Avenue, the east by Market Street, and the south by Montgomery Avenue. The basin comprises approximately 60 percent of the City’s municipal separate stormwater system (MS4), and is the largest in the City at approximately 5,160 acres in size. It consists of approximately 26 percent hard ground cover (impervious surfaces), and the impermeable nature of the land in the basin results in significant amounts of stormwater runoff.

Stormwater runoff from the basin generally emanates from three different land uses: residential (85%), commercial (2%), and light industrial (3%), where it sweeps up typical urban pollutants such as vehicle fluids, landscaping chemicals, sediment, et cetera as it flows downhill over roads, parking areas, and other impervious surfaces. Where applicable, stormwater runoff is managed in the basin on location by the use of swales and drywells for treatment and subsequent infiltration. Runoff that is not infiltrated locally is conveyed overland via roads or through a series of catch basins and piping. The stormwater runoff that leaves the basin is ultimately discharged untreated into the Spokane River through an outfall located at the southwest corner of the basin near the TJ Meenach Drive Bridge.

The Spokane River downstream of the Cochran Basin outfall, including Long Lake, is considered impaired with respect to low dissolved oxygen levels. This impairment is directly caused by the introduction of the pollutants that are carried in the stormwater runoff (e.g. such as leaked motor fuels/oils, lawn chemicals). Hence, Cochran Basin runoff is monitored for constituents that contribute to low dissolved oxygen, specifically, phosphorous, ammonia, and chemical biological oxygen demand (CBOD). Runoff is additionally monitored for temperature, pH, total suspended solids (TSS), and polychlorinated biphenyls (PCBs). The Cochran/Downriver stormwater management facilities will work towards minimizing or eliminating discharge of untreated stormwater from a large portion of the City into the Spokane River, thus increasing pollutant mitigation efforts.

To mitigate the impairment to the river, stormwater facilities will be constructed to divert the majority of the natural flow of stormwater runoff from Cochran Basin for treatment, minimizing the pollutant loading in the river. This flow will be treated at the facilities utilizing natural bioretention subsequent infiltration into the ground. Four treatment areas will be constructed in the Downriver Park that will function as stormwater bioretention facilities. Flow will be diverted to the facilities as they are constructed. The facilities will be implemented in this order:

  1. Disc Golf Course
  2. Golf Course
  3. TJ Meenach Swales
  4. River Access at TJ Meenach Bridge

An emergency outlet will provide an overflow to the river in case of mechanical failure or large or intense storms. The outlet will use the existing outfall pipe to direct these flows to the river.

In addition to the implementation of the stormwater facilities, the City will use this project as an opportunity to enhance recreation experiences in the Downriver corridor. Current recreation access points will be improved using current land use best practices.

Project Documentation

Project Components

Project #2018058: Cochran Basin Disc Golf and Boat Launch Stormwater Treatment Facility

Project #2018060: Cochran Basin Stormwater Conveyance Pipe Downriver Disc Golf Course to T.J. Meenach Dr.

Project #2021067: Cochran Basin Stormwater Pipe - TJ Meenach Dr to Downriver Golf Course via Cleveland

Project #2014153: T.J. Meenach Pettet Dr to Northwest Blvd.

Contact Info

City of Spokane - Engineering Services