Berm Summery Report
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Existing Conditions  The Birch Bay Community would like to enhance and protect the Birch Bay shoreline, possibly by removing the concrete groins and constructing a more natural beach berm. First we had to evaluate the coastal processes in the bay and shoreline of the proposed berm and look at some a conceptual designs of the beach berm.  Some processes that will affect a berm include:

- relative sea level rise, estimated at 5.5 to 7.5 inches per century.

- sediment sources at Birch Point and Point Whitehorn

- direction of sediment drift, converging at Cottonwood Reach

- long term maintenance and clean-up requirements

Gravel drift The gravel that drifts along the shoreline is essential for a healthy beach but development in Birch Bay has disrupted that drift.  For example, the harbor jetties at the Village Marina disrupt the transport of sediment to the east from Birch Point into Birch Bay.  Gravel placement on the downcoast beach may somewhat mitigate this disruption.  The road and buildings prevent the backshore from shifting during severe storm events to re-establish an equilibrium position.  The present cobble/sand beaches offer inadequate flood protection for existing and future development.

Groins  The North-Central reach is the area that the community is most interested in enhancing and protecting, so the study surveyed four locations in this area.  In this stretch, about 30 concrete groins were built  in the 1950s and early 1960s.  The groins are in various states of disrepair and they prevent coarser gravel and cobbles from traveling along the beach leaving the beaches in the North-Central reach are left more vulnerable to erosion and overtopping.

Goals  Birch Bay residents set these goals for the shoreline improvement plan:

• Widening the beaches to improve coastal and recreation access;
• Building a pedestrian/bicyclist promenade;
• Raising the beach berm crest to enhance flood protection;
• Incorporating a pedestrian or multi-use promenade to improve safety on Birch Bay Drive;
• Improving the appearance of the shoreline by removing the groins;
• Improving local habitat and ecosystem functioning.

The goals could be met by various designs and the report looks at engineering, transportation, aesthetic, and permitting factors.

Design considerations  A beach restoration design must reconcile the beach slope, the gravel composition, the wave and tidal effects. The berm crest at a natural beach site reflects the elevation during a five-year storm event. To enhance flood protection, a higher berm elevation than what occurs naturally would be required.  But a higher berm requires more fill (expensive), impedes habitat, obscures views, and would require more maintenance.  Once the height of the desired berm has been defined, we can reach an accurate cost estimate for the amount of gravel.

Technical considerations  If no action is taken, the road will continue to erode. If a berm is constructed, it could be designed to cover the existing groins, to move them to the backshore, or to remove them completely.  About 60,000 yd³ of gravel, cobble, and sand would be necessary to construct the design beach from the mouth of Terrell Creek northward to the northeast corner of the bay, and will require a long term management program for periodically adding gravel.  Other alternatives could include decreasing the width of the road to one-way or replacing the road with a multi-use path or promenade and removing the utility lines.

Next steps   Public discussion of the objectives and alternatives is the next logical step in the shoreline planning process.  The table provides an initial method to rank and compare the design alternatives in light of the original community objectives.