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Sitka Sedge Hydrology

The Park

Sitka Sedge State Natural Area is a 357-acre park in Tillamook County.  This ecologically diverse park contains ocean beach, dunes, forest, tidal marsh, freshwater marsh, and mudflats, and supports an array of important and rare plants and wildlife.

The Dike

The park contains a half-mile dike and tide gate that was installed in the 1930s. The purpose of the dike was to hold back tidewater and drain the area behind the dike. The dike has also had the effect of holding back native fish — including coho, chum, steelhead and coastal cutthroat trout — from migrating upstream to historic spawning and rearing areas.

In the past 30 years, the tide gate has deteriorated significantly. It is now leaky, and no longer completely blocks incoming tides – it just slows their entry and functions like an hour glass for tide water… tide water comes in slowly, reaches a lower total tide height inside the dike than outside, and then is released slowly. 

The tide gate will continue to deteriorate, and will eventually fail if not repaired or replaced.  Any repair or replacement options will ultimately need to address fish passage concerns. The potential impacts of tide gate failure or dike modification on flooding and groundwater in the adjacent community of Tierra del Mar (which is behind the dike) is a topic of concern.

The Project

Oregon Parks and Recreation Department (OPRD), along with stakeholders and partners, has conducted detailed analysis of the hydrology of the park and the adjacent Tierra del Mar community.  These studies have assessed whether dike modification options that span the range of potential tidal flows into Beltz Marsh can allow fish passage and habitat improvement without increasing flood risk or elevated groundwater levels in Tierra del Mar (TDM).

In 2017, OPRD hired Pacific Groundwater Group (PGG) and Environmental Science Associates (ESA) to model and compare surface-water and groundwater levels during both average conditions and during extreme tides and precipitation events according to different dike configuration scenarios. PGG and ESA analysis was completed in 2019 and indicates that TDM groundwater effects from dike alteration range from insignificant to beneficial depending on the dike alteration alternative.  Surface water characteristics are more complex and will be subject to continuing discussion as the project moves to a broader scoping of alternatives.  

After completing the 2017-2019 hydrological analysis, OPRD convened a team of subject-matter experts and stakeholder representatives to look into dike alteration alternatives more closely and assess a range of potential effects in terms of feasibility, water quality, ecology, biology, finance, permitting, community, engineering, recreation, etc.  The team was selected to have the collective expertise and representation necessary to be able to explore the alternatives, understand potential effects, and help OPRD to make a well-informed decision.   The team met four times in the fall of 2019 to hear presentations from subject matter experts weighing differential effects across the alternatives.  Each team member scored and ranked alternatives and their effects.  Upon completion of the Technical Team’s evaluation, OPRD staff processed Technical Team scoring, assessed the pros and cons of the various alternatives, and summarized key criteria for decision making. 

OPRD leadership decided to move forward with focused evaluation of the setback dike option in March 2020. The memorandum of decision is available here and a fact sheet is available here. The next steps in the process are to work with partners to find funding through grants to further investigate this option and potentially take the concept through design and implementation, depending on the findings of the detailed process.

Since 2020, Tillamook Estuaries Partnership (TEP) has taken the lead in finding grants and conducting continuing studies to refine the setback dike option.  TEP hired ESA in 2022 to carry out detailed study of a range of setback dike options to investigate feasibility, cost, location, and hydrodynamic effects related to water velocities, erodibility, and sediment.  This research is still ongoing.

June 2023:
A town hall meeting was held at the Kiawanda Community Center in Pacific City from 1-3PM on June 17.  After a short introduction by TEP and OPRD, ESA presented details of the ongoing setback dike study and location refinement process.  The presentation was followed by a question and answer session.  The recording of he meeting is available on You Tube here. OPRD and TEP are requesting comments, questions, and suggestions be submitted using the comments form on this website by July 8.  Shortly thereafter, OPRD, TEP, and ESA will be reviewing the submitted comments and using the feedback to guide next steps for the continuing investigations. A pdf version of the PowerPoint presented at the town hall meeting is available here.

OPRD remains focused on a true setback dike option, such as Alternatives 1-3, shown in the May 30 and June 17 meeting materials. This decision and the background around it are described in the 2020 Decision Memo and the 2020 decision framework presentation to the Tillamook County Commissioners (both available for review below). These documents summarize the outcomes of the 2019 alternatives vetting process, which is also available for review below. If further investigation reveals the setback dike option to be unbuildable, infeasible, or otherwise fatally flawed, OPRD will regroup with stakeholders in a transparent process to identify and vet other options.

Additional alternatives discussed in the May 30 technical team meeting were evaluated as part of the “due diligence” process and were presented during the June 17 town hall for transparency purposes only. They are not being considered as viable construction alternatives by OPRD. Documentation of due diligence in assessing a wide range of potential alternatives (as well as the rationale for eliminating alternatives from further detailed consideration) are important for successful regulatory permitting and grant applications. Not having adequately assessed alternatives can result in regulators or grantors withholding permits or grant funds that would allow the selected alternative to be constructed. Although presentation of the non-setback-dike alternatives has caused confusion and concern for some, the exploration and later elimination of non-setback-dike alternatives does not decrease the value and importance of the work that has been done and continues to be done on the true setback dike alternatives. True setback dike alternatives are what OPRD, TEP, and the consultant are pursuing as we continue moving forward.

March 2020-Spring 2022:

Develop partnerships to seek grant funding to proceed with in-depth assessment of the setback dike alternative. 

Summer 2022-October 2023

As funding and progress allows, develop preliminary setback dike designs, habitat restoration project design and funding strategy for Beltz Marsh.  Continue conversations with the technical team and stakeholders to review progress, concepts, and other considerations. 

October 2023-December 2024 (tentative)

Secure funding and develop construction specifications. Project construction. Since the timeline is totally dependent on grant applications and awards, it is not possible to present a firm timeline.  Dates and targets are subject to change corresponding to grants awarded to the project.

May 2023

Tillamook Estuaries Partnership convened a Technical Team meeting that was held virtually on May 30, 2023.  This meeting provided an opportunity for TEP’s consultant, Environmental Science Associates, to present the detailed technical findings of the ongoing analysis to the designated technical review group.  The meeting was recorded and can be viewed on YouTube here . Similar content will be presented at the Town Hall meeting June 17, 2023.

April 2023
Tillamook Estuaries Partnership continues to work with Environmental Science Associates (ESA) to refine analysis.  Reporting on outcomes of analysis is expected in May from ESA.  Analysis is behind schedule.  A Town Hall meeting to update stakeholders on progress and the remaining process ahead was held April 15, 2023 at the Kiawanda Community Center in Pacific City.  The meeting agenda was light due to delay in completion of the analysis, but Tillamook Estuaries Partnership and ESA gave updates on current project status, revised timelines, and changes in staffing. This meeting was recorded for the benefit of those who could not attend. 

Link to recorded meeting on YouTube:
Sitka Sedge Town Hall Meeting - April 15, 2023


Work began on more detailed assessment and design of setback dike options for the Sitka Sedge property.  Tillamook Estuaries Partnership (TEP) has received grant funding to hire a consultant to begin investigation and design in 2022. 

We are reuniting the Technical Team that has been involved in past assessment of alternatives, along with additional new members, to provide vision and review/brainstorming services.  The Technical Team will be engaged for reviewing work products in a series of meetings at intervals throughout the design process. We are also scheduling “Town Hall” public stakeholder meetings to provide updates on roughly the same schedule. 

The kickoff Technical Team meeting for the new assessment and design phase was held October 13, 2022 and was recorded to be made available for review by interested stakeholders. That link will be posted here as soon as we receive the link from the Tillamook Estuaries Partnership. 

The kickoff Town Hall public meeting for the new assessment and design phase was held Saturday October 22 from 1:00 to 3 PM at the Kiawanda Community Center in Pacific City. The meeting included a virtual Zoom meeting optional format, which was recorded. That recording can be accessed at the following link:


OPRD staff presented the project's status and process to the Tillamook County Commissioners and other interested stakeholders and public on Monday January 27, 2020 from 9:00AM to 11:00AM at the Kiawanda Community Center in Pacific City. 

The powerpoint presentation from the meeting is available here: Sitka Sedge SNA Dike and Fish Passage Alteration History and Results presentation (January 21, 2020 PDF) 

OPRD Leadership decided on a preferred alternative for further investigation in March 2020.  The memorandum of decision is available here: memorandum of decision.  OPRD will be working with Partners including Tillamook Estuaries Partnership and Nestucca Neskowin and Sand Lakes Watershed Council to find grant funding to continue investigations and planning.

A fact sheet explaining the setback dike option is available here: Setback Dike Fact Sheet.

Aerial view of Sitka Sedge Marsh

Setback Dike Investigation & Design

Memorandum from August 2023 (PDF)

Meeting recordings from 1/20 to 6/23 on YouTube video playlist

6/23 Presentation (PDF)

1/20 Presentation (PDF)

Memorandum from April 2020 (PDF)

Setback Dike Fact Sheet (PDF)

Technical Team Alternative Review

2019 Meeting Materials (PDF)

Hydrology Study

Executive Summary (June 2019)

Abridged, non-technical hydrology modeling summary report (32 pages, 4 MB)

Full technical hydrology characterization and modeling report (55 pages, 600KB)

Full technical report figures and tables (78 pages, 21MB)

Full technical report appendices (92 pages, 21 MB)

Preliminary hydrological risk assessment video playlist on YouTube (2020)


Noel Bacheller