Clarks Creek Elodea Removal

Background

The City of Puyallup (City) and Pierce County (County) began elodea control efforts more than 30 years ago. Prior to 2013, the City and County performed mechanical cutting every summer to reduce shoreline flooding associated with dense elodea growth. The cutting reduced creek water levels but the benefits were temporary due to rapid regrowth.

In 2013, the City and County switched to Diver-Assisted Suction Harvesting (DASH) to remove elodea from Clarks Creek. DASH involves uprooting the elodea plants, placing the plant roots and shoots into a suction hose, and using mesh bags to remove the plant material before discharging back into the creek. Based on DASH programs in other locations, it was thought that removing the elodea roots and shoots would lead to a long-term reduction in elodea growth in Clarks Creek.

DASH has removed large amounts of plant material and reduced summer water levels in the creek. However, the annual volumes of elodea removed by DASH do not show a clear downward trend.

Ecology issued the Clarks Creek Sediment and Dissolved Oxygen (DO) TMDL in December 2014. The TMDL study identified elodea as a significant factor in depressed DO concentrations in the creek and called for the City and County to reduce elodea coverage by as much as 75%. The TMDL study noted that the 2013 DASH successfully removed large amounts of plant material but did not specify that DASH must be used to reduce elodea coverage. The TMDL study also issued a requirement for increasing riparian canopy cover (planting) to help suppress elodea growth through shading.

The Clarks DO and sediment TMDL was based on limited data and modeling. The County is performing a TMDL reassessment study to help fill data gaps and recommend TMDL refinements where appropriate. The reassessment monitoring and modeling results to date indicate that dense elodea growth increases daily DO maxima but has little impact on daily DO minima. Moreover, the modeling results suggest that dense elodea growth reduces channel erosion and sediment transport.

The Puyallup Tribe of Indians (PTI) owns and operates a salmon hatchery on Clarks Creek. The hatchery has been in operation for approximately 18 years. The hatchery continuously withdraws ~12 cfs from Clark Creek. Most of the intake water is routed through raceways and rearing ponds within the hatchery before flowing back into the creek. A small portion (about 0.54 cfs, or 200 gpm) of the intake water is treated in a 30-micron drum filter and conveyed to the hatchery’s incubation room.

The Issues

The DASH program requires a Hydraulic Project Approval (HPA) and a Shoreline Substantial Development Permit, both of which expired on May 21, 2023.  Without these permits, the City cannot work within Clarks Creek.  In the fall of 2022, the City and County began preparing Permit applications to continue the DASH program. The permitting process includes opportunities for public comment and appeal. 

Based on recent discussions with PTI, the City, and County learned that PTI planned to oppose the re-issuance of the permits for DASH due to concerns about adverse impacts on the PTI hatchery.

PTI staff believe that DASH destabilizes the creek bottom and brings fine sediment into the water column upstream of the hatchery intake, causing adverse impacts at the hatchery, including:

• Environmental gill disease in salmon fry resulting in excess mortality. Hatchery staff believe the gill disease is caused by abrasive particles in the intake water.
• Smothering of incubating eggs. This problem has become so severe PTI had to stop incubating eggs at the Clarks Creek hatchery in 2022.
• Rapid sediment accumulation in the rearing ponds, requiring more frequent (daily instead of weekly, which is normal) maintenance.
• Increased wear on mechanical equipment. PTI has had to replace three pumps at the hatchery.

PTI staff report that these problems have worsened since the DASH program began in 2013 and, during the past 5 years. 

For these reasons, PTI asked the City and County to suspend using DASH as the preferred technique for controlling elodea in the creek. PTI indicated that it would officially (legally) oppose the issuance of the HPA and Shoreline permits for DASH due to the hatchery impacts listed above and their potential to represent a violation of the Tribe’s fisheries-related treaty rights.

PTI’s opposition was based on the Tribe’s position that their Treaty Rights were not being honored. PTI's opposition would make it much more difficult for the City and County to obtain the permits and approvals required to perform DASH.

Moving Forward

The City and the County are working together and coordinating closely with the Tribe to study the turbidity/fine-suspended sediment issues in the creek.  On June 1^st, the County began weekly longitudinal sampling at locations above, in, and below each tributary and major outfall to the creek.   The City will be working with a consultant to take sediment samples from the creek’s channel bed. The City and the County plan to compare this substrate material to what is being pumped through the hatchery to see if we can find a source of the material that is affecting the hatchery’s operations. The County is also coordinating with the USGS and PTI to demonstrate fine suspended sediment sampling at both the hatchery and the USGS monitoring station at Stewart Ave. Bridge (just upstream of the hatchery’s intake). 

The City and County plan to study the turbidity issue raised by the Puyallup Tribe collaboratively for a maximum of a 2-year period if no obvious source of the sediment/turbidity is found prior to that.  

The Clarks Creek Total Maximum Daily Load established by the state Department of Ecology (Ecology) in 2014 issued a requirement that the City and County reduce Elodea density in the creek to control dissolved oxygen deficits associated with elodea’s daily respiratory cycle during the growing season. 

As far as the Elodea goes, there are 2 main concerns, one is the impact on water quality (dissolved oxygen demand) and the other, which is outside of the scope of the TMDL, is potential flooding issues from higher water surface levels due to Elodea slowing the velocity and taking up creek volume.  

Elodea Control:

The best solution for Elodea control is shading to limit growth.  Elodea grows rapidly in late spring/early summer due to the increased sunlight reaching the creek.  The City has had a program to make riparian plants available to streamside residents to plant along the banks of the creek to try to combat this issue.  In addition, the City has worked with the Pierce Conservation District and Washington Conservation Corps crews to perform much-needed planting along the banks of properties that the City has purchased along the creek.  The City, with the help of the Pierce Conservation District, has increased these efforts in the past couple of years and now offers crews to plant and maintain vegetation on private property along the creek to provide much-needed canopy cover over the creek.  However, only one homeowner along the creek has taken the City up on this offer. These plantings and the future shading they provide will ultimately prevent excessive growth of Elodea and other aquatic plants. 

Flooding:

Achieving effective Elodea control through shading will be a long-term effort, requiring active participation by shoreline landowners as well as City, County, and state agencies. In the meantime, nuisance flooding of the yards in the summer and a potential for increased flooding in the winter will be monitored closely.  The County and City have access to a recently updated HEC-RAS model to help simulate how Elodea affects wintertime flooding.  The City will be working with the County, PTI, and the permitting agencies to develop options for short-term control, such as instream mowing (cutting) or DASH modified to avoid adverse sedimentation impacts at the PTI hatchery.  We are working toward moving forward with an alternative interim measure next summer to manage aquatic plant growth and its effects on shoreline flooding.   Ultimately, the programmatic goal is to effectively control Elodea’s growth through increased shading, thereby avoiding the ongoing costs, permitting requirements, and environmental impacts associated with annual in-channel control measures.  

Community Meeting 

The City hosted a community meeting on August 8, 2023, at 5 pm in Council Chambers to discuss the elodea removal plan at Clarks Creek. Residents who live along the creek, were invited to the meeting. Over 50 people were in attendance. Staff gave an update on the project. Topics included:

-Diver Assisted Suction Harvesting (DASH)

-The City and County Plan to Study the Creek

-Short and Long-term Elodea Plan

-Sediment in Clarks Creek 

-How residents can get involved.

Download a copy of the presentation here.

For questions, please contact Paul Marrinan at pmarrinan@puyallupwa.gov.