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Sitka Sedge State Natural Area Hydrology Modeling


Based on feedback from the May 22nd Technical Review Meeting, hydrological consultants are developing initial models for several hydrologic scenarios at Sitka Sedge State Natural Area, with an expected completion in mid-September. Subsequently, a doodle poll to the technical advisory group will be sent out in September to set a date for a 2nd in-person stakeholder meeting near Pacific City/Tierra Del Mar. At that meeting consultants will present findings from initial surface-water and ground water modeling. Stakeholders will have the opportunity to discuss additional hydrologic scenarios to model. Final scenarios and report are expected to be completed by December. A link to the draft report describing the work done so far is available below, along with links to the powerpoint presentations from the meeting.


Oregon Parks and Recreation Department (OPRD) has contracted Pacific Groundwater Group (PGG) and Environmental Science Associates (ESA) to perform a comprehensive hydrological analysis of potential interactions between tidal surface water inside the Beltz Dike and groundwater levels in the neighboring town of Tierra del Mar, Oregon.  This work builds on initial hydrological modeling, groundwater analysis, and data collection from previous years. Outcomes of detailed modeling and analysis will inform future decisions for habitat restoration on OPRD property, especially regarding potential effects on groundwater that might result from increased tidal exchange in the estuary.

In February 2018, a series of groundwater monitoring wells and surface water stilling wells was installed in key locations in the Tierra del Mar and Sitka Sedge SNA vicinity. Water elevation data was collected by automated data loggers and weekly manual checks in these wells in February, March and April 2018. This data range captured significant rainfall events as was hoped for in project planning. The data collected include a representative range of groundwater conditions and their association with a range of tides. Automated data loggers were removed in April and the data was downloaded for analysis by PGG.  Some additional manual water level measurements are scheduled in spring and summer to capture readings for these drier times of the year.  As of May 15, PGG and ESA have created an interim report on work done to date on existing hydrological conditions. This report is posted here.

This hydrological study has been designed and planned in coordination with a technical and stakeholder advisory panel made up of representatives from state and federal agencies, local community representatives, local hydrogeological experts, the local watershed council, Tillamook County, and the Tillamook Estuaries Partnership.  This panel was instrumental in developing the scope of the hydrological study and is the primary reviewer of progress and proposed methodology for the coming modeling process.  

May 22nd, 2018 meeting:

PGG and ESA presented their existing-conditions findings to the technical advisory panel on May 22, 2018 in the Faye Jensen Hall of the Kiawanda Community Center in Pacific City, Oregon from 3:00 to 4:30 PM.  When groundwater/surface water interaction predictive models become available as the study progresses, a future meeting will explore the modeling of potential future scenarios and management alternatives.

The purpose of the May 22 meeting was to:

1.    Discuss work done to date, including the conceptual model of surface-water and groundwater systems, data characterizing existing conditions, surface-water model modifications, proposed groundwater model design, and presentation of initial findings.

2.    Provide stakeholders with the opportunity to present additional useful site-specific information on events and scenarios of concern, specific dates, or other information within the measurement periods.

3.    Present and review the proposed modeling approach to be used in future phases of work

4.    Discuss realistic outcomes of the modeling process (what will/can it do for realistic expectations)

5.    Discuss model calibration approach

6.    Discuss preliminary future condition scenarios for exploratory modeling of extreme cases and/or for finding thresholds of tidal influx expected to produce a groundwater response. (Meeting #2 and the work to follow it will build upon these with more specific and refined scenarios, if necessary). 

There will be two in-person stakeholder meetings in 2018 – the first of which is described above.  The second meeting will present results of initial predictive modeling and thresholds for groundwater effects, and will focus on identification of potential further refinements and scenarios to be assessed by the predictive models.  PGG/ESA will then assess all of the identified scenarios and produce a final report detailing the predicted effects of each of the scenarios tested.

Beltz hydrology-OPRD introductory powerpoint (PDF)

PGG/ESA powerpoint (PDF)

Sitka Sedge Hydrological Analysis Statement of Work (10/2017)

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