HomeMy WebLinkAboutSDP2017-00007 Shoreline Processes Report'AAs pect
CONSULTING
May 20, 2016 (Revised June 13, 2017)
Barden Living Trust
c/o Kevin and Sherri Hunter
240 Maple Lane
Port Ludlow, Washington 98365
JUN 15 N -q'
2017
JE�F�R�gy drouH11'DCD
Re: Shoreline Processes and Bulkhead Repair Recommendations
Barden Living Trust Bulkhead
240 Maple Lane
Port Ludlow, Washington 98365
Project No. 160148
Dear Mr. and Mrs. Hunter:
This letter summarizes Aspect Consulting, LLC's (Aspect) observations, conclusions, and
recommendations regarding repairs to the rockery bulkhead for the waterfront residential property
located at 240 Maple Lane, Port Ludlow, Washington (Site). The purpose of our study was to
observe Site conditions, evaluate shoreline and slope geomorphic processes, assess impacts of these
processes on the stability of the uplands and Site structures, develop general design
recommendations, and support design and permitting for bulkhead repairs and extension to protect
the primary residence. The need for this assessment results from damage to the bulkhead and slope
that occurred during an exceptionally high tide and storm in February, 2016, and additional damage
that has occurred during the winter of 2016-2017.
Site Conditions
Aspect visited the Site and made observations on May 6, 2016. Our visit was attended by Mr.
Kevin Hunter, and Mr. Tim Johnson of Shold Excavating, Inc. Aspect returned for a second site
visit on December 16, 2016 to re -assess conditions and measure the topography of the slope and
bulkhead above the beach.
Topography and Improvements
The Site is located at 240 Maple Lane, in Jefferson County, Washington, about 1'/ miles north of
Port Ludlow, on the west side of Puget Sound. The Site comprises two rectangular parcels,
976500002 and 976500013, elongated east to west about 450 feet, with a combined width of about
180 feet from north to south.
The Site generally consists of a gently sloping upland, a short but steep bluff, and the beach. The
uplands portion of the Site slopes gently eastward from approximate Elevation 80 (feet NAVD 88)
at the western edge of the parcels to Elevation 20 at the top of the bluff that descends to the beach.
The bluff occupies a band about 10 to 15 feet wide near the eastern edge of the parcels (the portions
that lie above the ordinary high water line). The bluff slope descends steeply at about 45 -degrees
average to the beach and/or the existing rockery. The high beach lies at approximately Elevation 10.
An angular basalt rockery bulkhead extends from the northern property line to about 113 feet to the
south. The upper and mid beach slope about 8 degrees eastward into the tidelands of Puget Sound.
M ut Consulting,LLC 401 2nd Avenue S. Suite 201 Sesttie. WA 98104 206.328.7443 VMV%,,a5 0CJCpnsultwg.com
Barden Living Trust
May 20, 2016 (Revised June 13, 2017) Project No. 160148
Property improvements include a single-family residence and a detached cabin, a storage shed, and
a garage, all located on the eastern third of the Site. The shoreline improvements that are proposed
for protection include the primary residence and associated decks. The shoreline and bluff that
supports the older cabin are not proposed for protection. Decks extend out from the residence to the
east and occupy a portion of the uplands between the residence and top of the bluff. Stairs descend
from the upland to the beach near the northern end of the Site. An approximately 30 -foot -wide,
undeveloped Jefferson County Right of Way (ROW) runs along the north property boundary to the
beach.
The steep bluff on the eastern portion of the Site includes small blocks and benches of soil and
landslide debris that have slumped down from above. Where protected by a bulkhead, the bluff
slope averages about 45 -degrees. Where not protected by a bulkhead, the bluff averages
approximately 70 -degrees. The toe of the bluff lies an average of about 5 feet west of the top of the
existing bulkhead.
Vegetation
Vegetation on the Site was typically mature conifer trees upslope and south of the residence and
grass and ornamental shrubs to the north and east of the house. The critical area between the
residence and the bluff was mainly vegetated, with grass on the uplands and on the bluff where the
slope angle was less than about 45 -degrees. Ornamental shrubs were observed growing sporadically
at the upper edge of the bluff, and two, decomposing, large tree stumps were located at the top. The
steepest portions of the bluff are un -vegetated due to recent damage. Several dead trees were
present on the upper beach, near the center of the parcel; these trees were oriented at various angles
to the bluff. The homeowner stated that these trees were derived from the bluff at the Site.
Beach and Coastal Conditions
The beach consisted of an approximately 8 -degree sand and gravel surface. The median size of
native surface armor graded from sand near the toe of the rockery and bluff to coarse gravel and
cobbles with in the middle of the beach, about 50 feet from the slope toe. Scattered boulders are
present throughout the beach substrate. Towards the low tide line, the beach grades back to
predominately sand. The ordinary high water mark (OHWM) occurs at the abrupt transition from
the upper beach to the toe of the rockery bulkhead, or where no bulkhead exists, at the toe of the
bluff. The OWHM and mean higher high water line (MHHWL) were surveyed by Marine Surveys
& Assessments (Marine Surveys & Assessments, 2016) in fall and winter of 2016. The MHHWL
was found to lie about two to five feet seaward of the toe of the rockery bulkhead and OWHM.
Sediment drift sectors are defined as discreet zones along the shoreline containing areas of sediment
erosion (generally feeder bluffs), transport corridors, and deposition or accretion areas. The most
recent data regarding coastal processes published by the Washington State Department of Ecology
(Ecology. 1991), indicates that the Site lies within a southern (meaning the predominant direction
of sediment transport) littoral sediment drift sector that begins north of the Site near Mats Quarry
and extends to the south to Port Ludlow. Areas of unprotected shoreline nearest the Site are
classified as "transport corridors," indicating that they are not considered significant sources of
sediment.
The Site is exposed to wave action from Puget Sound. It has a maximum over -water fetch (the
horizontal distance over open water where the wind generates waves) of approximately 11 miles to
the east, and 9 miles to the northeast. The Site is located in a moderately protected location for
storms from the south and southeast. Tala Point (near Port Ludlow), and Foul Weather Bluff on the
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Barden Living Trust
May 20, 2016 (Revised June 13, 2017)
Project No. 160148
Kitsap Peninsula obstruct wave action from the southeast. However, the presence of cobbles and
scattered boulder armor and evidence of erosion undermining the base of the existing bulkhead
suggests that the shoreline is moderately exposed to wind -driven waves from the east and north.
The extent of armoring suggests that the beach is a moderately high-energy environment during
storms.
Predicted tidal ranges at the Site include numerous cycles with high tide in the 10+ foot range.
During the last year, tides as high as 11.5 feet were predicted for the Port Ludlow area, including
during the period of damage in February, 2016. Low -barometric pressure combined with storm
wind -driven surge can cause coastal flooding and increase the height of the water along the
shoreline by a foot or more.
Bulkhead Conditions
The bulkhead abuts the Jefferson County ROW that lies to the north (which also has a rockery
bulkhead), and extends 113 feet southward from the northern end of the property. There is a gap of
about 65 feet without a bulkhead, then rockery bulkheads resume farther to the south of the Site's
south property line. At the time of our Site visit, the bulkhead extended between 2 and 5 feet above
the ordinary high water mark (OHWM), was about 2.5 feet wide, and was laid back at a batter of
1 H: 3V (horizontal to vertical ratio) to 1 H: 5V. The top of the bulkhead was estimated to lie at
Elevation 15 to Elevation 16, and was lower in some areas where damage was more extensive. The
bulkhead comprised fresh, angular, interlocking basalt boulders between 1 -foot and 3 -feet in
diameter. The boulders were stacked one or two -rocks -tall above the beach substrate, and the
bottoms were not exposed. A few basalt boulders were sitting seaward of the bulkhead where they
had become dislodged during past storm events.
Portions of the stacked rock armor portion of bulkhead were in relatively good condition. The area
between the bulkhead and the bluff that formerly contained rock spalls or other coarse backfill was
variable in width. Where generally undamaged, the gap measured between 6 inches and 2 feet and
contained sandy, well -graded gravel with 5 to 10 percent cobbles. Where recent wave overtopping
had occurred and scour had resulted, the distance from the rockery to the bluff was up to 7 feet, and
the spalls backfill had been scoured away. The southern approximately 65 feet of the Site shoreline
did not contain a rockery.
Bluff Stratigraphy
Regional geologic mapping (Polenz et al., 2015, Geologic Map of the Port Ludlow and Southern
Half of the Hansville 7.5 -minute Quadrangles, Kitsap and Jefferson Counties, Washington,
Washington Division of Geology and Earth Resources, Map Series 2015-02) identifies soils on the
Site as Vashon Stade lodgment till. Vashon till is described as brown to gray, lightly weathered to
unweathered compact diamicton (an unsorted deposit with a fine-grained matrix). These soils have
been glacially overridden and compacted and are moderately resistant to erosion as compared to
non -glacially compacted soils.
Soils exposed in the bluff face consist of glacial till capped by 2 to 3 feet of weathered till. The till
was typically very dense, slightly moist, brownish gray, gravelly, very silty sand with trace cobbles
and boulders, and had a diamictic, heterogeneous texture.
Setback of Structures to Top of Steep Slope
The eastern edge of the foundations for the main residence were measured at 20 to 26 feet from the
top of the steep slope. The distance from the decks to the top of the slope ranged from 14 to 17 feet.
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Barden Living Trust
May 20, 2016 (Revised June 13, 2017)
Project No. 160148
Based on our observations and measurements made in December 2016, the bluff has eroded and
retreated landward by up to five feet adjacent to the upland structures during the relatively short
period since the bulkhead has been damaged. We understand that the high tides and winter storms
in early 2017 have caused additional losses to the bluff, and further diminished the setback of the
residence from the shoreline.
Summary and Conclusions
Shoreline Processes
The Site shoreline is exposed to long fetch from storms on Puget Sound and is a moderately high-
energy erosional environment during storms. There is little to no natural transient woody debris to
dissipate wave energy.
Shoreline and bluff retreat rates are dependent on factors such as upland land use, precipitation and
stormwater management, geologic and groundwater conditions, storm frequency and magnitude,
over -water fetch distances, wave direction, and the degree of shoreline protection. Although a
comprehensive analysis of historic bluff retreat rates using aerial photographs and/or historic
topographic records was not part of our current scope of work, our experience with similar geologic
conditions as those on the Site would suggest that average long-term bluff retreat rates of 2 to 6
inches per year can be expected in areas of glacially consolidated soils without effective bulkhead
protection. Actual rates are generally variable, with periods of slower erosion and episodes of
significant loss resulting from extreme storm and high tide events. These long-term rates are also
highly dependent upon factors extending well beyond the site, including regional changes in
sediment supply, amount of large wood, and changes in wave energy from nearby shoreline
structures.
Bulkhead Function
Until recently, the existing bulkhead was in serviceable condition and had provided the intended
protection of the lower slope from shoreline erosive processes. Recent overtopping and storm
damage has scoured away much of the backfill in places and exposed the slope above the bulkhead
to shoreline erosion processes. A few armor rocks have dislodged, creating low points in the armor
rock.
Overall, the rockery appears to be too low to prevent overtopping during increasingly frequent high
tides and storm wave events. Consequently, the slope that protects the uplands and structures is
failing from undercutting and slumping. The area of the shoreline and bluff that is not protected by
a bulkhead is eroding more rapidly and consistently from the top of the slope to beach level, and
accelerated toe erosion has created a steeper bluff face. The portions of the bluff above the damaged
rockery are also eroding faster, and the bluff toe had retreated to up to 7 feet landward of the
bulkhead at the time of our visit.
Need for Shoreline Armoring and Repairs
As of December, 2016, the residence's foundation was within 20 feet of the top of the bluff, and the
decks within 14 feet. This setback has likely been further reduced in early 2017. In our opinion, this
setback is less than ideal for continued long-term safe use of the Site. Approximately 15 feet of the
southern end of the residence extends beyond the southern end of the existing bulkhead, so that
portion has no protection from bluff retreat. If the bulkhead is not repaired and extended to the
south, erosion of the bluff will continue and ultimately safe egress, and support for decks and
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Barden Living Trust
May 20, 2016 (Revised June 13, 2017)
Project No. 160148
foundations for the primary residence will be compromised, then lost. The portion of the bluff that
supports the cabin is not proposed for armoring for erosion protection.
Impacts of Shoreline Armoring
Data are limited regarding the long-term effects of shore protection structures within Puget Sound.
However, this limited data supports the hypothesis that shoreline armoring has an overall
detrimental effect on natural coastal processes. Adverse effects of shoreline armoring may include
the following:
• Lowering and hardening of the beach profile seaward of the structure as a result of
scouring, and subsequent loss of fine-grained beach materials in front of hard surface
structures;
• The loss of low energy depositional environments where littoral sediments can accumulate;
• The reduction of sediment input along shoreline areas where mass wasting processes have
been reduced or temporarily stopped, resulting in the impoundment of source sediment
shoreward of the structure; and
• Structures built seaward of the original OHWM impede the flow of littoral sediment within
a drift sector resulting in impoundment updrift and end -scour downdrift of the structure.
The majority of this shoreline already has a bulkhead, and the short section of exposed low bluff is
not a significant source of sediment to the shoreline environment. Adding a new section of
bulkhead south of the existing bulkhead will not impede longshore transport of sediment. Because
of these factors, it is our opinion that the adverse impacts of repairing and increasing the height of
the existing bulkhead, and extending the bulkhead coverage to the south, will be negligible.
Shoreline Armoring; Hard and Soft Bank Protection
Hard bank protection generally consists of a rockery, concrete block wall, cast concrete wall, or
solid wood bulkhead that prevents scour and erosion of the toe. Hard bank protection is an effective
means of reducing or eliminating shoreline or bluff toe erosion, but it may also increase the amount
of reflected wave energy and increase the amount of erosional scour of the beach seaward of the
bulkhead. Hard bulkheads also reduce or eliminate the supply of sediment to the shoreline
environment.
Soft bulkhead techniques include the combined use of beach nourishment (placement of sediment
on the beach), construction of gravel and cobble berms, and engineered and restrained large woody
debris (logs) to dissipate wave energy and trap sediment. Logs on the beach are restrained using
cables and/or an earth retention system such as dead -man anchors or tie -back style anchors or by
strategically arranged logs with significant portions of the logs buried well below the depth of
winter storm scour. The logs are arranged to impede wave energy acting on the toe of the slope. In
an ideal setting, logs promote the accumulation of natural beach sediment that is actively recruited
by the natural coastal processes acting on the shoreline.
Regulatory/permitting agencies generally prefer soft bulkheads over hard bulkheads, as they believe
that they result in less long-term shoreline habitat degradation than hard bulkheads. The long-term
effectiveness and maintenance requirements for soft bank protection systems are not well
documented in Puget Sound, but soft shoreline protection is generally believed to provide less
effective protection and shorter service life and require more frequent maintenance or replacement.
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Barden Living Trust
May 20, 2016 (Revised June 13, 2017)
Project No. 160148
While the Site shoreline is not typically a high wave -energy environment, the combination of high
tides and storm waves has been intense enough to overtop the existing bulkhead and erode into the
unprotected portions of the bluff slope. The existing bulkhead serves to protect upland soils from
erosion and protect the residence foundations from being undermined. In our opinion, due to the
proximity of the bluff slope to the residence and associated risk of undermining the residence
foundations along with the typically shorter service life and greater maintenance requirements of a
soft shoreline protection system, it is our opinion that such a system will not provide the certainty
and level of protection needed for long-term shoreline protection at this Site.
Benefits of repairing and extending the hard shoreline protection structure at the Site are that a
properly constructed bulkhead will:
• Prevent overtopping of the existing deteriorated bulkhead, which will
• Protect the bluff slope soils from erosion resulting from undercutting, which will
• Maintain upland stability and protect the residence foundations.
In our opinion, the construction of a properly designed and constructed shoreline protection system
will not adversely impact adjacent properties.
Recommendations
Based on the height of the existing bulkhead and evidence of erosion observed at the time of our
visit, the existing bulkhead should be increased in height to protect the exposed bluff. We
recommend extending the existing bulkhead to the south to protect the exposed bluff shoreward of
the existing residence.
Bulkhead Repair
We recommend repairing the existing bulkhead to the original conditions with armor rocks
extending to Elevation 15. For backfill between the armor rocks and the bluff, we recommend using
angular rock spalls that will allow water movement but will resist erosion with wave surge and
splash. We recommend minimizing impacts to the existing bank and vegetation where practical
above the area of armor rock and spalls placement. The top of the spalls should be capped with
coarser spalls material capable of resisting movement with wave surge.
If the existing bulkhead cannot be extended to the south for permitting reasons, we recommend
"closing" the south end of the existing bulkhead. It should be "closed" by angling the southern end
of the bulkhead gradually toward the slope at an angle of around 45 degrees (compass direction
southwest). This angle will help dissipate the effects of wave action at the end of the bulkhead and
will reduce the tendency for amplifying erosion at the south end of the bulkhead from wave
refraction.
Bulkhead Extension
The existing bulkhead ends about 15 feet north of the southern end of the existing residence.
Erosion of the bluff has created an approximately 5 -foot westward bight into the bluff where it is
unprotected by the bulkhead. We recommend expanding the existing bulkhead so that it extends 30
feet south of the south end of the primary residence so that it protects the primary residence from
accelerated bluff failure. The extended bulkhead should be "closed" to protect the southern end of
the bulkhead from refracted wave erosion.
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Barden Living Trust
May 20, 2016 (Revised June 13, 2017)
Project No. 160148
General Design Recommendations
The rockery seawall bulkhead should be designed and constructed in general accordance with
Associated Rockery Contractors (ARC) Standard Rock Wall Construction Guidelines (ARC,
updated approximately 1999). Our general recommendations include the following:
• New armor rocks used to repair the rockery should be between one man and three man
sized rocks; existing armor rocks should be reused where possible;
• The repaired rockery should be set at a batter towards the west at 1H:4V;
• Base layers of rocks should be embedded in a keyway inclined slightly towards the existing
bank that is at least 3 feet below the existing beach surface so that they will not be exposed
by storm scour during winter months;
• Crushed 4- to 6 -inch quarry spalls should be placed behind the rockery facing in order to
provide drainage and improve rockery stability. The thickness of the spall layer will vary
based on the distance between the rockery and the slope behind the rockery, but should be
between 12 -inches and 36 -inches wide; and
• The area between the bulkhead and bluff will be permeable to water, and soils retained by
the bulkhead must be protected against "piping" (removal of finer grained particles through
voids by subsurface flow) by separation of the native soil from the bulkhead with an
appropriately designed non -woven geotextile filter fabric. We recommend placing the
geotextile between the bulkhead armor rocks and the backfill spalls and between spalls and
the native bluff soils to limit the loss of rock fill and native soils.
Design Support and Plan Review
Aspect has produced design plans prepared by a licensed professional engineer for repairs of the
existing rockery bulkhead and extension to the south (Aspect Consulting, 2017).
References
Aspect Consulting, 2017, Barden Living Trust Bulkhead Repair, 240 Maple Lane, Port Ludlow,
Washington; design plans consisting of three sheets, dated April 2017.
Ecology, 1991, Shorelands and Coastal Zone Management Program, titled Net Shore Drift in
Washington State, Volume 3, Central Puget Sound Region.
Marine Surveys and Assessments, 2016, Ordinary High Water Mark (OHWM) determination for
Barden Hunter Trust Property at 240 Maple Lane, Port Ludlow, technical memorandum by
Marine Surveys & Assessments, December, 2016.
Information about This Report
This letter report was prepared based on a limited Site reconnaissance visits. We did not conduct
geotechnical analysis or a quantitative shoreline processes analysis for this study. A more in-depth
characterization of shoreline conditions or bulkhead design recommendations was beyond our
scope of work for this study.
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Barden Living Trust
May 20, 2016 (Revised June 13, 2017) Project No. 160148
Limitations
The conclusions and recommendations provided above are based on the information collected
during our limited Site reconnaissance visit. Within the limitations of scope, schedule, and budget,
our services have been performed for Kevin and Sherri Hunter on behalf of the Barden Living Trust
(Client), and this letter report was prepared in accordance with generally accepted geotechnical
engineering and engineering geology practices in effect in this area at the time. This letter report
does not represent a legal opinion. No other warranty, expressed or implied, is made. It must be
understood that no recommendations or engineering design can yield a guarantee of stable slopes.
Our observations, findings, and opinions are a means to identify and reduce the inherent risks to the
owner.
All reports prepared by Aspect Consulting for the Client apply only to the services described in the
Agreement(s) with the Client. Any use or reuse by any party other than the Client is at the sole risk
of that party, and without liability to Aspect Consulting. Aspect Consulting's original files/reports
shall govern in the event of any dispute regarding the content of electronic documents furnished to
others.
It has been a pleasure to provide these services to you. If you have any questions, please do not
hesitate to call.
Sincerely,
Aspect consulting, LLC
Jesse G. Favia, LG
Senior Staff Geologist
jfavia@aspectconsulting.com
David H. McCormack, LEG
Principal Engineering Geologist
dmccormack@aspectconsulting.com
VA160148 Hunter Bulkhead\Deliverables\Bulkhead Letter Report\Hunter Bulkhead Letter Report_revised June 2017.docx
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