Clark's Creek Sediment Removal Demonstration

A Sediment Removal Demonstration project was identified by the Elodea Task Force as 1 of 4 short-term projects. A 400-foot section of the creek was selected near the 12th Avenue SW bridge, near Clark's Creek Park South. The project will demonstrate how the hydraulic dredging would work, and provide a site for monitoring over a three year period - as dictated by the HPA permit - to show any sediment fill-in that occurs and evaluate any biological impacts.

Project Status (July 21, 2015)


This project included substantial permit submittal and discussions with WDFW to receive the permitted HPA documents during 2013 and 2014. The project is the first in WA State to be permitted for this specific work, and will be monitored and reviewed to provide data back to WDFW for review.
  • After an unsuccessful 2014 bid process, the City worked with WDFW to identify ways WDFW could support the project to help meet permit requirements such as biological monitoring.
  • The project was re-bid in July 2015 following issuance of a revised HPA from WDFW. However, the bid process was again unsuccessful, with no bids received.
  • 404 Permit: Consultation with the Army Corp (USACE) resulted in a determination that no permit is required based on "no return water" included in the proposed project. Subsequent discussions with USACE allowed return water at the project site since no fill of material was to occur. Return water was to meet water quality standards for pollutants.
  • SEPA: The SEPA determination has been published,
  • Shoreline: Following submittal of the Shoreline permit application, a Shoreline Hearing was scheduled and held on July 17, 2013, with the City recommending a Conditional Use Permit (CUP) for the project. Ecology provided comments on the Shoreline CUP. City staff compiled responses to Ecology for reference during their review period, following the Hearing Examiner decision. Ecology concurred with the City's Conditional Use Permit determination on September 27, 2013.
  • HPA: A Joint Aquatic Resource Project Approval (JARPA) application was submitted to Washington Department of Fish and Wildlife (WDFW). WDFW requested monitoring plans and performance standards memos to be drafted to support the project. City staff completed these documents and submitted them as requested. The City has been working with WDFW to address comments and concerns regarding the biological monitoring, equipment used, and ongoing monitoring that would extend 3-years beyond the active demonstration portion of the project. The City compiled final revisions to respond to WDFW's request for changes to the biological monitoring. WDFW issued the HPA for this work on February 14, 2014. The Sediment Removal Demonstration Permit (PDF) is available for download to be used as reference.

Project Overview


The demonstration project was first proposed to involve a hydraulic dredging process to remove accumulated sediment from a 400-foot section of Clark's Creek. The method is meant to remove sand and smaller-sized particles, leaving cobbles and larger rocks. However, based on site reconnaissance completed once the permits were issued in 2014, it was discovered that a rocky bottom does not exist within at least 6-10 feet of the current sediment bottom.

The purpose of the demonstration project is to evaluate the permitting process and regulatory requirements, determine the effectiveness of the method, determine the underlying condition of the creek bed, determine if cobbles/rocks present, evaluate the depth of accumulated sediment, analyze the environmental and habitat impacts, and monitor the long-term effectiveness of the project including the rate (if any) of sediment loading back into the demonstration area.

Supporting Reduction in Sediment Loading to Clark's Creek


The City continues to research, develop, and construct projects that will reduce the sediment loading to Clark's Creek. Several projects are budgeted for 2015 and beyond, with more in the conceptual stage for future development when funding is available. Such projects include:

Project Details


Requirements imposed by the project permits including the following monitoring activities for the demonstration project:
  • Biological Monitoring - survey conditions up through 3-years post-construction
  • Fish Monitoring - monitor during active construction
  • Long-term native planting monitoring for restored areas - survey conditions up through 3-years post-construction
  • Sediment Removal Performance - survey conditions up through 3-years post-construction
  • WQ Monitoring - monitor turbidity levels during active construction