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Home My WebLink AboutBulkhead Design - BLD Engineering / Geo-tech Reports - 12/4/2021 0(d ✓e�s;on SHORELINE STABILIZATION CHECKLIST FOR ENGINEERED BULKHEAD DESIGN at 250 N Ayock Beach Dr., Lilliwaup, WA 98555 (Parcel #: 32303-50-01012 Prepared for: Robert Thompson P.O. Box 569 Chehalis, WA 98532 (360) 269-7982 e-mail: byrdthom(c'Dgmail.com Prepared by: MET Engineering, PLLC 1018 E. Wishkah St. Aberdeen, WA 98520-2937 (360) 310-0270 cell (360) 289-0958 bus. e-mail: SMorta(�i aol.com Contact: Steven P. Morta, P.E. Aug. 7, 2021 Rev: Dec. 4, 2021 L -- August 7,2021 Rev: Dec. 4,2021 Page 3 of 5 MET Engineering, PLLC Evaluation of Erosion and/or Flooding Issues Soil erosion due to wave action has occurred especially in the backyard region of the existing residence. An existing concrete bulkhead located on the north-northeast side of the residence currently helps to protect the backyard area. However, there is significant soil erosion that has occurred behind the existing concrete bulkhead due to an adverse combination of high tides and high winds originating from the north. A 30-foot extension of the existing bulkhead as shown on the attached vicinity map on Sheet 1.0 and doweled into the existing bulkhead has the potential of significantly slowing down the erosion occurring in the backyard area of the residence. There is the potential of flooding of the existing residence if there an adverse combination of high winds originating from the north and also an extremely high tide. The extension of the existing concrete bulkhead on the north side of the residence would help to mitigate the effects of severe soil erosion and potential flooding issues. Evaluation if Nothing is Done at this Site The existing concrete bulkhead located on the north-northeast side of the residence has been helping to protect the residence from an adverse combination of high tides and high winds. But there is visual evidence where waves have effectively worked their way onto the backside, i.e.,the residential side of the existing bulkhead. If, for example, the existing concrete bulkhead was not extended to the west at least another 30- feet, there would be continual soil erosion of the backyard and eventually of the residential foundation itself. Eventually, the existing residence itself would become undermined by the continual wave action due to high winds especially if originating from the north and simultaneously with high tides. The residence will be in serious jeopardy if the bulkhead extension is not completed within 3-years of this report date. Alternative Approaches Other potential "soft engineering"solutions such as the planting of vegetation and trees along the shoreline is not feasible since the force of the waves would immediately remove them after an adverse combination of severe winds and extremely high tides. Another option,for example, is the placement of logs along the shoreline,but these would also eventually float away due to the power of the waves. It is to be noted that water weighs 62.4 pounds per cubic foot and, therefore, is extremely heavy. The proposed 30-foot extension of the existing concrete bulkhead in the westerly direction would significantly slow down the potential of severe erosion of the existing backyard and eventually the residence itself. One also needs to take into consideration the average measurable increase in sea level height which has an adverse effect on the existing concrete bulkhead and that, serious soil erosion has already occurred on the backyard side of the bulkhead. Unfortunately, the extension of the existing bulkhead is the only viable solution at this point. 1018 E. Wishkah St.,Aberdeen, W.jshington 98520-2937 360-310-0270 c,360-289-0958 b,SMorta►(Waol.com August 7,2021 Rev: Dec. 4,2021 Page 4 of 5 MET Engineering, PLLC Minimize Mitigation Measures It has been determined that the 30-foot extension of the existing concrete bulkhead in the westerly direction as shown on the Vicinity Map on Sheet 1.0, is the minimum necessary to help protect the residence from significant further soil erosion of the backyard and potentially protecting the foundation of the residence itself. Site Map An aerial view of the site is shown on Sheet 1.0 along with the delineation of the ordinary high water mark (OHWM) which by definition is the line of permanent vegetation. This, currently is identified by the backyard lawn which currently is getting severely undermined by the continual adverse combination of high winds and high tides. Typical Cross-section showing the MHHW and the OHWM Reference is made to Sheet 3.0 that shows the typical cross-section with respect to the existing concrete bulkhead. Significant soil erosion has occurred behind the bulkhead as shown in the cross- section and is working its way back to the residence. The proposed 30-foot extension of the existing concrete bulkhead as indicated on Sheet 1.0 will significantly slow down the soil erosion that is working its way to the residence itself. No Potential of a Slide Since the residential site is nearly flat and level, there is no potential for a slide and, therefore, a follow-on Geotechnical Report is not required in this case. Also,there was no evidence of a slide within 300 feet of this residential site and as a result there are no setbacks required since there are no hazardous slopes in the area. Conclusion and Recommendations 1. It is the conclusion of this geotechnical engineer that to protect the single-family residence as shown on the Site Plan,i.e.,Sheet 2.0,the existing concrete bulkhead will need to be extended at least another 30+ feet as shown on the site plan. 2. Since this residential site is nearly flat and level there is no need for a follow-on Geotechnical Report and also there are no landslide hazards within 300 feet of this site, and thus,setbacks from slopes do not apply at this site. 3. This geotechnical engineer did observe that the shoreline itself appeared to be moving inland and was especially noticeable on the north side of the Ayock peninsula. Most of the time storms originate from the south-southwest but when they originate from the north, then the shoreline on the north side become vulnerable and may eventually need to provide shoreline protection like a bulkhead along the north shoreline some time in the future. 1018 E. Wishkah St.,Aberdeen,Washington 98520-2937 360-310-0270 c,360-289-0958 b,SMorta(daol.com August 7,2021 Rev: Dec.4,2021 Page 5 of 5 MET Engineering, PLLC 4. It is also to be noted that if the existing bulkhead is not extended at least another 30+feet to the west, then the backyard becomes vulnerable and eventually the residence itself could be in jeopardy, as well, from an adverse combination of northerly storm events and extremely high tidal events. 5. Even though the subsurface silty loam soils are quite dense, over time when they get saturated from wave action, they eventually will erode away since they become soft and saturated with evidence of this shown on Photos 41 and 42. The extension of the existing bulkhead will significantly slow down this soil erosion process and help preserve the backyard and eventually the single-family residence itself. 6. It is also to be noted that the mean sea level appears to be rising as determined from satellite measurements due to melting of the polar icecaps. This potentially could also affect the longterm stability of residences located on a low-lying waterfront such as the Ayock community. 7. The new bulkhead addition will need to be doweled into the existing bulkhead using#4 rebar with a minimum of 8"embedment to ensure a positive connection to both the new and existing bulkheads and vertical spacing not to exceed 8". This Shoreline Stabilization report has been prepared per accepted engineering practice and is only to be used for this site since other sites may vary. Any questions or comments regarding report can be addressed by e-mail at �1. rta i(a��l,cpm or by calling this geotechnical engineer directly at (360)310-0270. Respectfully Submitted, p4y��_ Steven P. Morta, P.E. �tiN P.MO (360)310-0270 ��oF WAS� y�Mc�9 30758 , E SS�ONAI,EC� 1018 E. Wishlcah St.,Aberdeen,Washington 98520-2937 360-310-0270 c,360-289-0958 b,SMorta(d'aol.com ROBERT THOMPSON: GEOLOGICAL UNIT- (W 9 r � TYPICAL CROSS-SECTION A-A: A Existing Erosion of the backyard Residence y is working its way bads e 40 to the residence. 20' SILTY LOAM - - ____-- MHHW --OHWM DENSE GLACIAL TILL TYPE SOILS �' 0 80' 60' 40' 20' 0' 20' 40' OHWM-ORDINARY HIGH WATER MARK MHHW-MEAN HIGH HIGH WATER MARK GEOLOGIC—UNIT—LABEL: Qls j GEOLOGIC—UNIT_DESC: 0uaternary (2.6M yrs ago to present) mass-wastingdeposits, primarily landslide jdeposits. but locally includes talus. colluvium. protalus ramparts. and rock I I glaciers. includes 1980 debris avalanche of Mount St. Helens. local1v includes Pliocene-Miocene mass-:vasting deposits j GEOLOGIC_UNIT_POLY_500K_ID: 14624 GEOLOGIC AGE: Quaternary LITHOLOGY: Pleistocene continental glacial drift i Geological Unit Label: Qls (Quaternary) Prepared by: MET Engineering,PLLC,1018 E.Wishkah St,Aberdeen,WA 98520-2937 li (360)310-0270 cell,(360)289-0958 bus SMorta@aol.com Prepared for:Robert Thompson,Owner Apr.15,2021 Site Visit on Thurs.4-8-2021 SHEET 3.0 from 3:00 to 4:15 pm I Area of lnterest(A01) Soil Data Explorer Download Soils Data Shopping Cart(Free) Printable version) Add to Shopping Cart�j Scale 1. I 7,1 �2�6s1Ja { v -. M r p� - Warning:Soil flap may not be valid at this scale. 12,111 Mason County,Washington(WA645) Mason County, Washington (WA645) Map Acres percent Unit Map Unit Name In of AOI Symbol AOI Cg Coastal beach, 0 to 12.3 18.2% 2 percent slopes Gk Grove gravelly 16.7 24.7% sandy loam, 5 to 15 percent slopes Hf Hoodsport gravelly 4.5 6.7% sandy loam, 30 to 45 percent slopes Totals for Area of 67.4 100.0% Interest FOIA I Accessibility Statement i Privacy Policy I Non-Discrimination Statement I Information Quality I USA.gov I White House J Printable Version Report—Map Unit Description Mason County, Washington Gk—Grove gravelly sandy loam,5 to 15 percent slopes Map Unit Setting National map unit symbol: 2hkn Elevation: 0 to 980 feet Mean annual precipitation:90 inches Mean annual air temperature:48 degrees F Frost-free period: 160 to 180 days Farmland classification:Not prime farmland Map Unit Composition Grove and similar soils: 100 percent Estimates are based on observations, descriptions,and transects of the mapunit. Description of Grove Setting Landform:Outwash plains Parent material:Glacial outwash Typical profile H1 -0 to 9 inches:gravelly sandy loam H2-9 to 24 inches: very gravelly sandy loam H3-24 to 60 inches:very gravelly loamy sand Properties and qualities Slope: 5 to 15 percent Depth to restrictive feature:More than 80 inches Drainage class:Somewhat excessively drained Capacity of the most limiting layer to transmit water(Ksat): High (1.98 to 5.95 in/hr) Depth to water table:More than 80 inches Frequency of flooding: None Frequency of ponding: None Available water capacity:Very low(about 2.9 inches) Interpretive groups Land capability classification(irrigated): None specified Land capability classification(nonirrigated):4s Hydrologic Soil Group:A Forage suitability group:Sloping to Steep Soils(G002XN702WA) Other vegetative classification:Sloping to Steep Soils (G002XN702WA) Hydric soil rating: No Description—Map Unit Description Mason County,Washington (WA645) Mason County, Washington (WA645) Map Acres percent Unit Map Unit Name in of AOI Symbol AOI Cg Coastal beach, 0 to 12.3 18.2% 2 percent slopes i Gk Grove gravelly 16.7 24.7% Printable Version sandy loam, 5 t0 ) 15 percent slopes Hf Hoodsport gravelly 4.5 6.7% Report—Map Unit Description sandy loam, 30 to Mason County, Washington 45 percent slopes Cg—Coastal beach,0 to 2 percent slopes Totals for Area of 67.4 100.0% Map Unit Setting Interest National map unit symbol: 2hjs Elevation:0 to 10 feet Mean annual precipitation:42 to 48 inches FOIA I Accessibility Statement I Privacy Mean annual air temperature: 52 to 57 degrees F Frost-free period: 190 to 210 days Farmland classification: Not prime farmland Map Unit Composition Beaches,coastal: 100 percent Estimates are based on observations, descriptions,and transacts of the mapunit. Description of Beaches,Coastal Setting Landform: Beaches Typical profile H1 -0 to 60 inches: Error Properties and qualities Slope:0 to 2 percent Drainage class:Poorly drained Depth to water table:About 0 to 72 inches Frequency of flooding: Frequent Interpretive groups Land capability classification(irrigated): None specified Land capability classification(nonirrigated): 8w Hydnc soil rating:Yes Description—Map Unit Description �3/lq Ji On Thursday April 8, 2021 this geotechnical engineer visited the above site which is located at 250 N Ayock Beach Dr., Lilliwaup, WA 98555. The primary purpose of the visit was to determine the long term stability of the engineered bulkhead addition due to the bank erosion as indicated in the photograph above. During an adverse combination of high tide and high wind conditions, waves will impact the existing concrete bulkhead as shown above and the energy of this wave will then travel around the bulkhead. This transfer of wave energy from the face of the bulkhead to the end of the bulkhead has caused severe erosion of the bank as indicated above. The primary purpose of the engineered bulkhead extension to the west is to provide additional protection for the remaining backyard and to prevent it from gradually eroding away. It is to be noted that we'll have a similar situation with the new bulkhead where the wave energy will impact the new bulkhead and then travel west to the west end of the bulkhead and potentially cause soil erosion but only further west and away from the backyard area. b3 v ' 1 r. LC�L�•�_ La� �jT.Ff'�.� This photo indicates that there's a build up of smooth gravels in front of the existing bulkhead as well as in front of the wooden bulkhead as well. However, as one can see to the right of this photo severe soil erosion has caused part of the residential backyard to be eroded away. If there is an adverse combination of high winds coming from the northerly direction and a higher than normal tide, then the resulting force of the waves can potentially cause severe damage to the exposed shoreline. In this case the existing bulkhead did its job and protected most of the existing backyard but the unprotected west end of the bulkhead resulted in severe soil erosion of the existing dark brown silty loam soils. As a result, it is recommended that the existing concrete bulkhead be continued in the westerly direction at least another 30+ feet. It is to be noted that an add-on bulkhead engineered design has already been prepared by MET Engineering dated March 10, 2021. It effectively, is a continuation of the already existing bulkhead and would provide additional protection to the existing backyard and to significantly slow down the backyard erosion currently taking place. ON 43 This photo is taken from the existing bulkhead and looking west to the rest of the shoreline. It is to be noted that there is an existing system of bulkheads on the south side of this peninsula where the winds predominantly originate from. There did not appear to be any extensive shoreline erosion on the south side of the peninsula due to the presence of these existing system of concrete bulkheads. It does not readily appear that a comparable system of concrete bulkheads is not necessarily required on the north side of the Ayock peninsula since the prevailing winds normally originate from the south-southwesterly direction. _ ex t V.iRi 2s �t J _ r - y .n`t MV _J •`yr This photo was taken on the north side of the owner's residence and it appears to indicate that fairly recent deposits on the backside of these 2 to 3-feet diameter logs had occurred due to the erosive action of the waves. Even though most of the winds originate from the south-southwest direction, there are occasions when northerlies, i.e., winds originating from the north can cause beach erosion as indicated by the granular fill behind these logs. It is to be noted the proximity of the beach erosion with respect to the edge of the deck which is only a few feet away as indicated in this photo. This geotechnical engineer recommends that the existing concrete bulkhead on the north side of the Ayock peninsula gets extended further west to prevent further beach erosion that appears to be working its way very close to the owner's deck above. Theirs is also the potential concern of the nearly imperceptible rise of the ocean level that can potentially have an adverse impact on the Ayock beach community. _ o . Ago 11$i7 W,. , Ali •b` .�.t�:.FIT . .. ..._.:c ._ ..... _3 IN This photo was taken looking north toward the floating bridge direction. As mentioned earlier, the prevailing winds normally originate from the south-southwest but on some occasions one can see how northernly winds could be directed south through this part of Hood canal. In general, the Ayock peninsula juts out into the canal and can get the full brunt of the storms that even have a more adverse impact to the shoreline if a severe storm event also occurs simultaneously with a high tide occurrence. It is to be noted that there's an extensive set of concrete bulkheads lining the south side of the Ayock peninsula since the prevailing southerly winds are from this side. I i MASON COUNTY i COMMUNITY SERVICES Shoreline Stabilization Building,Planning.Enwonmental Health.Community Health Note:This checklist must be submitted with a Shoreline Geotechnical Assessment and completed, signed, and stamped by the licensed professional(s) who prepared it for review pursuant to the Mason County Shoreline Master Program. If an item is found not applicable, the Assessment should explain the basis for the conclusion. MCC 17.50.340 B.2. New structural stabilization measures shall not be allowed except as follows: a. To protect existing primary structures: i. New or enlarged structural shoreline stabilization measures for an existing primary structure, including residences, shall not be allowed unless there is conclusive evidence documented by a Shoreline Geotechnical Assessment* that the structure is in danger from shoreline erosion caused by tidal action, currents, waves, or sea level rise. Normal sloughing, erosion of steep bluffs, or shoreline erosion itself, without a scientific or geotechnical analysis, is not demonstration of need. The geotechnical assessment shall evaluate on-site drainage issues and address drainage problems away from the shoreline edge before considering structural shoreline stabilization. ii. The erosion control structure will not result in a net loss of shoreline ecological functions. This shall be demonstrated in a Habitat Management Plan as required in MCC 8.52.170(J). iii. Primary structure means the structure or the only access associated with the principal use of the property that cannot feasibly be relocated. It may also include single family residential appurtenant structures that cannot feasibly be relocated. Applicant/Owner RC)J3F)Q7' 11116MYl Parcel # Site Address 2SU N 14 y()Cl< r EACH ��/�, 11-4-1 WAwoWt4 `�PS,S'� Items to be included in assessment Located on page(s): Scope of review, including landowner concerns and site assessment objectives. , Discussion of site development, including the location and setback of important primary and appurtenant structures, roads and utilities. Assessment of relevant wetlands and surface water drainage and control systems. 2 Assessment of site vegetation, including species and communities present. 2 Assessment of regional/site geology, including relevant rock/soil unit descriptions, geologic history and stratigraphic correlation. Assessment of regional/site geomorphology, including the influence of wave or tidal processes in controlling sediment transport and the evolution of the site's landform. Include assessment of the drift cell sediment budget and local beach conditions. May 2018 17/iCt Evaluation of erosion and/or flooding issues, including assessment of causes,and rates or timeframes associated with each issue. Include evaluation of how historic shoreline modifications near the site may have impacted patterns of erosion. Evaluation of the amount of time until primary structures or major utilities will be damaged by wave or tidal action, based on evidence of erosion rates, a slope stability analysis or other 3 geotechnical considerations if no action is taken on the site. Discussion of alternative approaches to reduce risk from erosion on the site,including the use of nonstructural measures such as drainage and vegetation,and soft shoreline techniques such as gravel berms, large woody debris, or other measures. Explain why these techniques would be infeasible or insufficient to reduce the threat from erosion. Discussion describing the proposed shoreline stabilization is the minimum size necessary, placed as far landward as possible and will not result in a net loss of shoreline ecological functions. 3 A site map drawn to scale which identifies property boundaries,scale, north arrow and the location of proposed development, geologic features and ordinary high water mark(OHWM).All development setbacks should be delineated and marked. Cross-section(s),identified on site map,showing both horizontal and vertical scales, and identifying important features such as: MHHW and OHWM,top and bottom of bluff, location of upland structures and utilities, and geologic units where relevant. Supplementary photographs. �TTAC I, y EVEN t . t' `oIemereby certify under penalty of perjury that I am a civil engineer licensed in the State of Washington with specialized knowledge of geotechnical/geological engineering or a geologist or engineering geologist licensed in the State of Washington with special knowledge of the local conditions.I also certify that the Geotechnical Assessment,dated P. /4ae,- r/7, ZO 2 Land entitled wD�P cv tiof Ha S T9 7, r/1/os0l►J SALORELI NE YTW11_c7A7?J*ets all the requirements of the Mason County Shoreline Master Program,Shoreline Stabilization Section (MCC 17.50.340),and is complete and true. �'p R 30758 �'�• FG[STER� sS�ONAL ECG ,4>— ?— (Signature and Stamp) *MCC17.50.020 Definitions:Shoreline Geotechnical Assessment. A scientific study or evaluation conducted by a qualified expert that includes a description of the ground and surface hydrology and geology,the affected land form and its susceptibility to mass wasting,erosion,and other geologic hazards or processes,conclusions and recommendations regarding the effect of the proposed development on geologic conditions,the adequacy of the site to be developed,the impacts of the proposed development, alternative approaches to the proposed development,and measures to mitigate potential site-specific and cumulative geological and hydrological impacts of the proposed development,including the potential adverse impacts to adjacent and down-current properties. Geotechnical assessments shall conform to accepted technical standards and must be prepared by qualified professional engineers or geologists who have professional expertise about the regional and local shoreline geology and processes. Page 2 of 2 Disclaimer:Mason County does not certify the quality of the work done in this Geotechnical Assessment. I I I L - -