Tonasket Stormwater Infrastructure Inventory, Assessment and Improvements Plan

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Stormwater assessment protects the Okanogan River and City of Tonasket

Stormwater flooding has plagued downtown Tonasket for decades. Erosion occurs along the slope at SR-20 at storm drain outlets. The flooding and erosion damages City streets and other infrastructure in the City’s stormwater system. Ponding often reduces available passable road widths and threatens properties. Ponding on Delicious Street between Whitcomb Avenue and SR97 is a regular issue. Untreated stormwater runoff routinely overflows into the Okanogan River adjacent to Tonasket.

Varela conducted a stormwater infrastructure inventory and assessment.

Recommended improvements:
Installation of additional catch basins, piping and manholes to route stormwater into the system more efficiently to get water off the roads. Installation of larger stormwater mains at targeted areas of the City’s system were also recommended. The stormwater assessment and the Stormwater Management Plan were completed in accordance with the Stormwater Management Manual for Eastern Washington (SMMEW).

Construction of improvements:
Successful funding for improvements was applied for in conjunction with work being done as part of the in-process Stormwater Management Plan.

Stormwater Utility
With the identification of infrastructure improvements, as well as the need for a comprehensive management plan, Tonasket needed a mechanism to pay for these stormwater utility planning and improvements.

Varela assisted Tonasket in establishing a Stormwater Utility in order to fund planning and pay debt service on construction loans.

Varela researched regional stormwater ordinances and methods for establishing equitable stormwater assessments and rates. Varela worked closely with the City Mayor, planner, council, and clerk-treasurer to draft an ordinance to establish the Stormwater Utility, which was approved and implemented in 2018.

City of Tonasket Stormwater Management Plan
The City of Tonasket Stormwater Management Plan identifies and plans for ways to improve water quality in the Okanogan River. This project inventories the City’s current stormwater system, including changes since the last inventory, performs hydrologic modeling, determines feasible treatment and conveyance alternatives, and identifies potential funding scenarios for design and construction of the preferred alternatives.

Elements of the Tonasket Stormwater Plan are already a tool for the City to plan upgrades to their stormwater system and improve water quality by reducing discharge flows and sediment discharge into the Okanogan River.

Installation of a stormwater runoff treatment system is part of Varela’s recommendations in the current Stormwater Management Plan. 

Varela is currently at work to design priority water quality improvement projects, including: existing conveyance and treatment facilities, outfalls and discharge points, property ownership, land use, existing soils or wetlands, and topography drainage areas and catchments. 

Preparation of the Stormwater Plan included: capacity and condition analysis of the existing stormwater system, determination of potential project locations and project alternatives, preparation of project life cycle cost estimates (capital and operation), prioritization of the project list and schedule, evaluation of treatment and discharge alternatives that address treatment and sediment control (Okanogan River TMDL for DDT and PCB TMDL), evaluation of alternatives for upgrading existing stormwater conveyance, and groundwork for completion of a stormwater utility.

The Stormwater Plan identifies the most cost-feasible solutions and provides guidance for financing the next phases of implementation, design, and construction. Projects resulting from this plan help protect and restore water quality in Washington by reducing stormwater impacts from existing infrastructure and development.

Funding is already being sought for some of the improvements recommended. A multi-agency, multi-project funding request was made for the area of Whitcomb Avenue that included recommended stormwater improvements in that part of town. Partial funding has been received and other funding is being considered to initiate the project. Coordination with other Tonasket infrastructure construction projects is being pursued. Partnerships between projects of other types can allow for a single contractor to complete stormwater projects, so costs can be shared to maximize cost-effectiveness.


Key Project Staff: Mark Johnson, Jeff Moran, Kurt Holland

Funding Sources: Department of Ecology

Implementation Timeline: Design 2022-2023; Construction 2023

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