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Sitka Sedge State Natural Area Hydrology Modeling
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 completed study of the hydrology of the park and the adjacent Tierra del Mar community.  This study assessed whether dike modification options that span the range of potential tidal flow into Beltz Marsh could allow fish passage and habitat improvement without increasing flood risk or elevated groundwater levels in Tierra del Mar (TDM). 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 is now complete 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. 

The project will now transition from hydrological characterization and groundwater risk assessment to working with stakeholders in finer-scale assessment of goals, alternatives and potential effects – ultimately leading to a decision on the future of the site.

Current Updates

OPRD has 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 will 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 core technical team will meet 4 times over the next 4 months to collectively identify effects and weigh the pros and cons of each identified alternative.  The team will be made up of specialists and stakeholder representatives - and in the interest of trust and transparency, OPRD plans to allow the public to attend as a silent audience.  Additional specialists may be invited to join particular meetings for discussion of particular aspects of the work, but OPRD would like to keep the core team small enough to function well. Each meeting will have scheduled content for which OPRD would encourage subject matter experts to present information related to potential effects of each alternative, or to present lessons learned from relevant projects with which they have been involved.  The public audience would be given a period for comments before and/or after the team’s work each meeting.  This model has served OPRD before to allow for focused teamwork while preserving public trust and transparency. 

Technical team meeting dates and locations:  

1. September 24, 2019 9AM to 2 PM at the Kiawanda Community Center in Pacific City

2. October 24, 2019 9AM to 3 PM at the Kiawanda Community Center in Pacific City

3. November 13, 2019 12 PM to 3 PM at the Kiawanda Community Center in Pacific City

4. December 4, 2019 12 PM to 4 PM at the Kiawanda Community Center in Pacific City  

This website will be updated with meeting notes and materials as they become available.

Draft Timeline for Beltz Dike Assessments, Options Scoping, and Implementation

June 2019:
Hydrology study conclusions and public information meeting 

July 2019 – January 2020:
Stakeholder meetings and further investigation of site goals
Development of preferred alternatives
Public meeting to review preferred alternatives
Complete habitat assessments of the site – create an Aquatic Habitat Enhancement Plan
Host a public meeting to present our final preferred alternative

January 2020 – September 2020:
Develop preliminary Habitat Restoration Project Design and funding strategy for Beltz Marsh, Reneke Creek and Beltz Creek and adjacent areas.

October 2020 – October 2021
Secure funding and develop construction specifications
Project construction

Links to Meeting Information

Meeting 1 Materials:

Sitka Sedge SNA Dike and Fish Passage Alteration Scoping History and Results

Meeting 1 Notes

Meeting 2 Materials:

Sitka Sedge Technical Team Rankings Spreadsheet Nov2019.xlsxSitka Sedge Technical Team Rankings Spreadsheet (MS Excel file)

Limiting Factors Analysis presentation

Water Quality presentation

Draft Water Quality scenario comparison summary

Estuarine processes/Sea Level Rise presentation

Sediment Accretion and Sea Level Rise scenario comparison summary

Meeting 2 notes

Meeting 3 Materials:

Fish passage presentation

Fish Presentation

Modeled vegetation response presentation

Modeled terrestrial wildlife effects presentation

Reports and materials available for review from previous hydrological risk assessment work

Executive Summary (June 2019)

Abridged, non-technical hydrology modeling sumary 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)

Surface water model: scenario animation video for average tides and precipitation (3MB)

Surface water model: scenario animation video for 50-year storm and king tides (4.5MB)

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