HomeMy WebLinkAboutMLA16-00094 Geologic Slope and Beach Processes ReconnaissanceCoastal Solutions, LLC
11027 Manitou Beach Drive NE
Bainbridge Island, WA 98110
206.459.7264
October 7, 2016
Jan Nealey
227 N Cherry Street
Dayton, WA 99328
Re: Geologic Slope and Beach Processes Reconnaissance
Nealey Property
351 Pleasant Harbor Road
Brinnon, WA
Project No. 16058
Dear Ms. Nealey:
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This letter -report summarizes Coastal Solutions' observations made during a recent geologic
slope and coastal processes reconnaissance of the subject property. The purpose of our study
was to observe and evaluate the existing shoreline conditions at the site with regard to the
proposed shoreline modification and erosion mitigation measures.
Observations
Site Conditions and Topography
The site is located on the west side of Hood Canal in the Pleasant Harbor area of Jefferson
County. The residential property consisted of a gently sloping upland on the western portion
where the house was located and a vertical beach bluff that descended to the shoreline of Hood
Canal to the east. The house consisted of a wood frame structure with a conventional spread
footing/crawlspace type foundation. The house extended to within 50 feet of the top of the
bluff. The septic tank as observed on the surface was located 51 -feet from the top of the slope.
Access to the shoreline was via an existing path and wood stair structure.
On the beach the shoreline was protected with a combination log and concrete bulkhead. The
bulkhead was on the order of 18 -inches high and spanned the entire 60 -foot length of the
shoreline. The bulkhead had been breached in January of 2016 between 39 and 49 feet
measured from the south property line. The breach exposed sand and gravel fill and the toe of
the vertical bluff landward of the bulkhead. Current plans call for the repair of the breach to
stop the erosion of the fill and continue to protect the base of the bluff.
The beach slope was on the order of 30 feet high. The lower 10 feet was vertical and the upper
15 feet was sloped at approximately 0.511:1 V (horizontal:vertical). The lower vertical portion
showed exposed soil with partial overhanging vegetation of berry bushes and shrubs from the
upper vegetated portion.
The property was surrounded by similar private properties to the north and south, the existing
Pleasant Harbor Road to the west, and tidelands of Hood Canal to the east. Both adjacent
properties were protected by concrete bulkhead. A concrete groin extended approximately 16
feet waterward of the face of the bulkhead along the north property line.
Jan Nealey
October 7, 2016
Project No. 16058
Current plans call for replacing the entire bulkhead with plastic sheet piling at or slightly
waterward of the face of the bulkhead (landward of the ordinary high water (OHW) line and
approximately 10 feet landward of the mean higher high water line (MHHW).
Beach and Coastal Conditions
The beach consisted of an approximately IOH: 1V (horizontal:vertical) sand, gravel, and cobble
beach -face with scattered shell fragments. Based on our observations of barnacles and other
indications of periodic inundation on the beach, ordinary high water (OHW) was located at the
face of the damaged bulkhead. The most recent data regarding coastal processes published by
the Washington State Department of Ecology, (Ecology) Washington Coastal Atlas indicated
that the property lies within a littoral drift cell that begins approximately 1 mile north near the
Dosewallips River delta and terminates approximately 0.1 mile south at Pleasant Harbor.
Drift cells contain zones along the shoreline that include erosion areas, transport corridors, and
deposition or accretion areas. We noted subtle signs of littoral sediment deposition on the
south sides and scour/erosion on the north sides of piling, rocks, and other obstructions located
within the upper intertidal area consistent with the published drift directions.
Drainage
Roof runoff from the house discharged to splash blocks at the ground surface. While we did
not observe evidence of groundwater seepage on the bluff face or signs of surface water
erosion during our field visit, it should be noted that groundwater seepage levels and flow
volumes will vary with precipitation, irrigation practices, time of year, and upland land uses
both on and off-site. The surface water system appears to be functioning without adverse
effects on the bluff, but infiltration of storm runoff can adversely affect slope stability during
heavy, prolonged precipitation events. The surface water flow at the site should be monitored
during the winter months. If uncontrolled surface water flow is seen on the upland, the owners
should consider upgrading to a closed -conveyance, piped discharge system at the beach.
Comprehensive drainage analysis was beyond the scope of services for this phase of the
project.
Vegetation
Vegetation on the upland portion of the site consisted primarily of native groundcover and a
moderately dense stand of fir trees. The lower bluff face was devoid of vegetation due the
steepness and exposed silt, sand, and gravel soils. The upper bluff was covered with dense
native shrubs and berry bushes.
Geology
Soil exposures onsite consisted of medium dense, silty, gravely sand exposed along the entire
height of the bluff. Due to the lack of stratigraphic structure such as bedding planes or
laminations and relatively high density, we interpret these sediments as Alpine Lodgment till.
Alpine Lodgment till is a mixture of silt, sand, and gravel entrained in the lower portions of
glacial ice flowing east out of the Olympic Mountains during the last major glaciation of the
area. The till was deposited onto the pre-existing landscape by advancing alpine glaciers as the
coalesced with Vashon Ice sheet that occupied the Hood Canal and Puget Lowland
approximately 15,000 to 18,000 years ago. The lodgment till has been overridden and
compacted by thousands of feet of glacial ice. As a result, the till generally exhibits high
Page 2
Jan Nealey
October 7, 2016 Project No. 16058
shear -strength and low -compressibility characteristics. Despite these characteristics, the till on
the exposed beach bluff has a high sand and gravel content and is still at risk of erosion and
landslide activity. The variable nature of the gravel and sand content create weaker zones that
are more easily erodible. The undercut portion of the central bluff is an example of a weaker
zone that is being eroded by wave action prior to the bulkhead being originally constructed
The upper 2 to 3 feet of the soil column consists of weathered till. The weathered till consists
of the near surface bioturbated (root and animal disturbance) area that the current surface
vegetation is rooted in. The weathered till is more permeable and exhibits lower shear strength
characteristics and as a result is more susceptible to ongoing erosion.
Groundwater can accumulate at the contact between the weathered and unweathered till. This
is the result of the groundwater percolating down through the relatively low permeability
weathered till and encountering the relatively high permeability unweathered till below. This
"perched" groundwater condition can result in seepage on the bluff face that, in sufficient
quantities, can destabilize the bluff. Groundwater seepage can also occur in sandy zones
within the till and uncontrolled fill that may be present on the upland.
The weathered till does however allow for tree root growth that has a stabilizing effect on the
upper bluff. The undercut lower bluff, if left unprotected, will eventually result in landslide
activity that will encompass the entire height of the bluff, damage the stairs, and place the
upland improvements at greater risk of being affected by ongoing erosion.
Conclusions
Toe erosion at the site has been affectively stopped by the existing bulkhead. Where the
bulkhead was breached, erosion at the toe has begun again during periods of high tide and high
wave action. If left unrepaired, the breach will become bigger and the entire height of the bluff
will be adversely affected by renewed erosion.
Current plans call for the construction of a new plastic sheet pile bulkhead at or landward of
the face of the existing bulkhead. A properly constructed rock bulkhead will effectively stop
toe erosion and will protect the upper bluff from being undercut. The proposed rock structure
will increase the overall stability of the bluff and will help protect the existing upland features
including the deck stairs and house.
Alternatives
Shoreline erosion and stability can be addressed by several methods depending on site
conditions, location, and project goals. Shoreline erosion control methods can range from the
use of planted, supplemental vegetation to control surface erosion, constructing "soft" or bio-
engineered shoreline protection systems, constructing "hard" surfaced bulkheads or rock
revetments, or the application of a hybrid system that employs both hard and soft armoring
techniques. Addressing an existing unprotected, high bank bluff that lies adjacent to existing
protective structures however, limits the available alternatives for the property owner to
adequately protect existing improvements on the property and on adjacent properties.
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Jan Nealey
October 7, 2016
Supplemental Vegetation
Project No. 16058
In our opinion, the existing upland vegetation at the site is providing surface erosion protection
only and does not contribute to protection of the property from wave action. Supplemental
vegetation can slow surface erosion from rainfall and upland surface water flow, but has little
to no mitigating effect on wave generated toe erosion. As a result, supplemental vegetation is
not a viable option as a replacement for existing protection at the site or to mitigate erosion and
landslide activity on the unprotected bluff.
Rock Bulkhead
Rock bulkheads consist of essentially vertical rock walls constructed at or near the ordinary
high water line. 3,000 to 5,000 pound rocks are keyed into the beach approximately 4 feet,
stacked to a typical height of approximately 5 to 6 feet above the beach surface and backfilled
with free -draining rock ballast. Of the alternatives discussed in this report, rock bulkheads are
the most effective method to control toe erosion over the anticipated service life of the
structure. The most significant effect of constructing a rock bulkhead is a reduction of natural
sediment input to the beach. This is the result of building a structure that is necessarily
designed to stop or significantly slow toe erosion. While the effects of reduced sediment input
to the beach can be mitigated, rock bulkheads result in an alteration of the shoreline as
compared to natural conditions. A rock bulkhead represents less of an impact to the upper
intertidal zone due to reduced wave reflection that results from the energy dissipating irregular
face of the structure as compared to other hard structures such as flat -surfaced seawalls or the
existing timber bulkhead.
Rock Revetments
The second most effective erosion control method is the construction of a rock revetment.
Rock revetments are similar to rock bulkheads in that they consist of "hard" armoring of the
shoreline by constructing a sloping rock surface at the toe of the beach slope. The benefit of a
revetment is a more gradual wave run-up area at the shoreline that can reduce wave reflection
and potential scour in front of the bulkhead. The negative aspects of a revetment are that their
larger footprint results in a larger area of the upper intertidal that is buried and depending on
their height may not provide protection for the lower slope during storm events or extreme
high tides. The lower the angle of the face, the more upper intertidal area is covered. To
minimize footprint and maximize the erosion control aspect of the revetment they are typically
built at steep angles to take advantage of the surcharging affect of the upper rocks similar to
the structural characteristics of a vertical rock bulkhead. Absent the surcharge, the rocks at the
toe of a revetment are more susceptible to movement and redistribution than a rock bulkhead.
A revetment in lieu of a rock bulkhead will result in more intense and more frequent
maintenance due to the angled face and would result in an unpredictable erosional environment
where the revetment connects to the adjacent structure located to the south. More maintenance
at the project site would require additional barge landings and heavy equipment on the upper
intertidal area. Additionally, the wave energy dissipation that would be achieved by the
relatively steep face of the revetment would be minimal as compared to the more structurally
sound rock bulkhead.
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Jan Nealey
October 7, 2016
Soft Bank Protection
Project No. 16058
The use of "soft" bulkhead techniques includes the combined use of beach nourishment and
restrained large woody debris (beach logs) at the site. Beach logs are restrained using cables
and an earth retention system such as dead -man anchors or tieback style earth -anchors. The
logs are arranged in such a way as to impede wave energy acting on the toe of the slope.
Imported beach sediments are then placed to embed the logs aiding in energy dissipation. The
beach nourishment also provides sacrificial sediment that is actively recruited by the natural
coastal processes acting on the shore. In areas of diminished littoral transport volume and
areas where sediment recruitment is high, soft bank protection typically results in a net loss of
nourished sediment. As the sediment is eroded over time, additional nourishing sand is placed
to maintain the erosion control function of the system. The amount of beach nourishment is
initially estimated using average bank retreat rates for the project site, offset by initial sediment
volumes placed during construction, adjusted later based on actual long-term performance.
Soft bank protection is best suited for low wave -energy environments where a broad, relatively
flat back -beach area exists to minimize the angle of the constructed surface and maximize the
wave run-up distance. Soft bank structures are not well suited for sites that are constantly
being hit with boat wake waves or high bank site where no back -beach area exists such as the
project site. A breach of the soft bank system during a large storm event would jeopardize the
upland structures before emergency repairs could be made.
The performance of a soft bank system is directly related to the intensity, duration, and
frequency of high-energy storm events. As a dynamic system, they result in the lowest overall
initial impact to the shoreline environment, the least amount of bank protection during storm
events, and the highest maintenance requirements.
f7by* rid Soft-hank/Revetment
Hybrid systems employ elements of both a hard surface stopgap component and the dynamic
component of a soft bank system. A rock revetment or bulkhead is constructed at or above the
ordinary high water line and is partially buried and further protected by the addition of
anchored beach logs, sand, gravel and cobbles placed as beach nourishment. The sand and
logs mimic natural beach conditions on a day-to-day basis and the rocks serve as a structural
stopgap measure during large storm events. The benefits of a hybrid system are that they
partially mimic natural coastal processes while providing a high level of erosion control due to
the rock structure. The drawbacks to a hybrid system at the project site is that the lack of back
beach area would place the dynamic portion of the hybrid system (restrained logs and imported
sand) within the highest energy portion of the beach face reducing its effectiveness and
increases maintenance demands.
Sheet piling
Sheet piling protection consists of driving steal or vinyl sheets through the active beach face
and into the very dense glacial bearing soils below. The sheets interlock and form a
continuous flat surface that breaks up wave energy. Depending on the height of the sheet
piling, lateral earth retention anchors are sometimes used to retain the top of the sheet pile.
Sheet piles are best suited for back -beach areas that are infrequently hit by large waves and
where overtopping wave action is less likely. Sheet piling can be an attractive alternative to
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Jan Nealey
October 7, 2016
Project No. 16058
rocks or concrete because of their low plan -view profile. The entire footprint in cross section
is less than 8 inches depending on the size of sheet piling used. Sheet piling are typically
driven or vibrated into the ground to achieve embedment design depth. Drawbacks to sheet
piling are the installation method requires enough space to bring a large installation hammer
and consequent vibration from installation can destabilize certain types of soils. Any time
sheet piling are driven or vibrated into place, nearby structures including neighboring
bulkheads and the upland bluff should be closely monitored for signs of movement.
Recommendations
Based on our field observations, erosion has resumed at the bluff toe where the bulkhead has
been breached. In our opinion, the stairs, the remaining portions of the bulkhead, and both
adjacent bulkheads are at risk of being affected by erosion if the site bulkhead is not replaced.
To maintain stability at the site, and to protect the upland improvements, we recommend
constructing the sheet piling bulkhead as proposed. The new sheet pile bulkhead should be
placed as close to the existing OHW (estimated at the face of the existing bulkhead).
Construction of the bulkhead flush to the adjacent bulkheads will reduce eddying and potential
scour at the ends.
To reduce the probability of further landslide activity on the slope, we recommend the
following:
Verify that the proposed sheet piling achieves a minimum embedment depth of 3 feet into
the very dense glacial soils inferred to underlie the active beach face. No subsurface
explorations were completed for the project and embedment depths should be monitored
through driving resistance of the sheet piling. Due to the very dense nature of the
underlying glacial soils, pre -excavation and/or pre -drilling may be necessary for the sheet
piling and the proposed earth anchors.
Plans Review
We have reviewed the proposed plans prepared by Sealevel Bulkhead Builders, titled "Replace
Concrete Bulkhead with Plastic Sheet Piling for Terry Nealey, 351 Pleasant Harbor Rd.
Brinnon, WA " undated. In our opinion, the plans as proposed are consistent with the
geotechnical opinions and recommendations in this letter -report.
Limitations
This letter -report was prepared based on a limited field reconnaissance and no subsurface
explorations were performed. A more in-depth characterization of slope conditions and
geotechnical analysis, including quantitative slope stability analyses for the subject property or
the adjacent properties was beyond the scope of work for this study. There are inherent risks
associated with construction in the shoreline environment. The longevity and effectiveness of
shoreline armoring is highly dependent on the frequency and severity of wave generating storm
events that are inherently unpredictable. Other factors that impact the effectiveness of
shoreline armoring are the frequency and magnitude of upland landslide activity and erosion,
and the skill and care used by the contractor during construction of the bulkhead. The opinions
in this letter report are meant to help the property owner manage the natural erosion that is
occurring at the site and do not constitute a legal opinion or a warranty, express or implied.
Page 6
Jan Nealey
October 7, 2016
Project No. 16058
This letter -report was prepared for the exclusive use of Jan Nealey and her agents with specific
application to the project site.
It has been a pleasure to provide these services to you. If you have any questions, please do
not hesitate to call at (206) 459-7264.
Sincerely,
Coastal Solutions, uc
Robert F. Cousins, LEG
Principal Geologist
rob@coastalsolns.com
cc: Jenny Powell, Sealevel Bulkhead Builders
Nina L. Cousins, P.E.
Principal Engineer
nina@coastalsolns.com
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Coastal Solutions, LLC
11027 Manitou Beach Drive NE
Bainbridge Island, WA 98110
206.459.7264
September 27, 2017
Jan Nealey
227 N Cherry Street
Dayton, WA 99328
IJ ZI
Oct �� 2
JEFPER8oN
CO1J)Vry000
Re: Second Response to Jefferson County Comments, Nealey Bulkhead Application
Nealey Property
351 Pleasant Harbor Road
Brinnon, WA
Project No. 16058
Dear Ms. Nealey:
This letter summarizes our second response to comments we received from Jefferson County
regarding placement and reconstruction of the bulkhead at your Hood Canal property.
Specific questions posed by Ms. Emma Bolin with Jefferson County will be addressed in the
order presented. County comments are in blue, responses are in black.
Address if the bulkhead repair and expansion is needed to protect a primary residence and
appurtenant structures (stairs are not appurtenant).
The proposed bulkhead repair and replacement will maintain the existing minimum level of
protection it was providing prior to being damaged. The toe of the bluff where the breach
occurred is experiencing erosion and undercutting. The bulkhead was originally constructed to
protect the toe of the bluff that is susceptible to erosion. The repaired/replaced bulkhead will
continue to protect the toe of slope that in turn directly protects the upland structures and
drainfield.
Provide design for required weep holes in the sheet pile.
Weep Holes may be drilled in each installed sheet pile at a maximum diameter of 1 inch and a
minimum spacing of 24 inches (one per driven sheet). This will allow for dissipation of
hydrostatic pressure that may build landward of the wall. Location of weep holes should be
approximately 12 inches below the top of the sheet pile.
Describe how the work will be performed (this could be covered in the JARPA)
Work will be completed using hand equipment and a vibratory hammer to install the sheet
piling. Sheet piling will be placed directly waterward of the existing timber and concrete
bulkhead structure. Construction using this method requires enough space between the toe of
the bluff and the pile location to accommodate the drive head. Placement of the sheet piles at
the waterward face of the existing structure will allow the existing concrete and any existing
treated wood to be isolated from the marine environment by the piling wall. Isolation of these
materials will result in no net loss of ecological functions as compared to existing conditions.
Jan Nealey
September 27, 2017
Project No. 16058
The use of hand tools is preferred as it eliminates the need for a barge landing and resultant
disturbance of the upper intertidal area.
Provide "no net loss" sequencing documentation showing why the sheet pile cannot be placed
further landward or why a different rock bulkhead cannot be used at the site. The analysis
should address WDFW requirements:
WAC 220-660-370
(a) If the OHWL is changed since an existing bank protection structure was built, and
OHWL reestablishes landward of a bulkhead protection structure, the department
will consider this reestablished OHWL to be the existing OHWL for permitting
purposes. If an application for an HPA is submitted for repairs within three years of
the breach, the bank protection structure may be repaired or replaced in the original
footprint.
Application to replace/repair was submitted within 3 years of the bulkhead being damaged
and may be replaced in the same footprint as shown on the plans.
(b) Use the least impacting technically feasible alternative. The common alternatives
below are in order from most preferred to least preferred:
(i) Remove the bank protection structure;
(ii) No action - Control upland drainage;
(iii) Protect, enhance, and replace vegetation;
(iv) Relocate improvements or structures;
(v) Construct a soft structure by placing beach nourishment and large woody material;
(vi) Construct upland retaining walls;
(vii) Construct a hard structure such as bulkhead and rock revetment landward of the
OHWL;
(viii) Construct a hard structure such as a bulkhead and rock revetments at the OHWL.
See comment above regarding description of work. Sheet pile installation will allow for
hand operated equipment that will eliminate the need for a barge landing and subsequent
beach disturbance. Sheet piles placed immediately waterward of the existing bulkhead
structure will continue to protect the undercut toe -of -slope (and upland improvements) and
will isolate foreign material (concrete and potentially treated wood) that would otherwise
be left in place.
Page 2
Jan Nealey
September 27, 2017
Project No. 16058
It has been a pleasure to provide these services to you. If you have any questions, please do
not hesitate to call at (206) 459-7264.
Sincerely,
Coastal Solutions, «c
Robert F. Cousins, LEG
Principal Geologist
rob@coastalsolns.com
cc: Jenny Rotsten, Sealevel Bulkhead Builders
Emma Bolin, Jefferson County
Page 3