Loading...
HomeMy WebLinkAboutChannel Migration Study SHR2024-00004 Variance SFR Addition - GEO General - 2/29/2024 RECEIVED FEB 2 9 2024 615 W. Alder Street GEOTECHNICAL CHANNEL MIGRATION STUDY RESIDENTIAL PROPERTY 3040 NE STATE HIGHWAY 300 BELFAIR, WASHINGTON PREPARED FOR LAURA AND MATTHEW HARKINS BY ALL AMERICAN GEOTECHNICAL, INC. OLYMPIA, WASHINGTON AUGUST 18, 2023 ALL AMERICAN GEOTECHNICAL CONTACT INFORMATION PREPARER INFORMATION AAG PROJECT NUMBER: AAG23-083 CONTACT: CURTIS D.CUSHMAN ADDRESS: 8947 BUTTONWOOD LANE NE OLYMPIA,WASHINGTON 98516 TELEPHONE: (360)491-5155 CELUTEST: (360)481-6677 EMAIL ADDRESS: CURTIS.CUSHMAN@COMCAST.NET CLIENT INFORMATION CLIENT: LAURA HARKINS CLIENT ADDRESS: 3040 NE STATE ROUTE 300 BELFAIR,WA 98528 CLIENT TELEPHONE (360)227-9278 CLIENT EMAIL LAURA041966@HOTMAIL.COM BILLING ADDRESS: LAURA HARKINS 3040 NE STATE ROUTE 300 BELFAIR,WA 98528 SITE ADDRESS: 3040 NE STATE ROUTE 300 BELFAIR,WASHINGTON PARCEL: 22201-51-91001 GPS LOCATION: 47.432 -122.875 AAG23-083 8947 Buttonwood Lane NE,Olympia, WA 98516 2 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL SCOPE OF UNDERSTANDING LAURA HARKINS 3404 NE STATE ROUTE BELFAIR,WA 98528 AUGUST l8,2023 RE: GEOTECHNICAL REPORT 3040 NE STATE ROUTE 300 BELFAIR,WASHINGTON PARCEL#22201-51-91001 47.432, -122.875 (dd) Dear Mr. and Mrs. Harkins: All American Geotechnical, Inc(AAG)was contacted in June of 2023 by Laura Harkins(client)to prepare a Channel Migration report(CMZ)for the above parcel. As per her request,the following is the CMZ study for the parcel. We are sending a PDF copy of the report to the client. Reference is to the Draft Channel Migration Assessment (DCMA) Mason County; written by Cardno Entrix,and GeoEngineers for the Department of Ecology,Washington State,dated December 2011 (Draft) and FEMA datasets. A single-family residence expansion will be constructed on the chosen site on the parcel. The residence will extend living area to the southwest of the existing structure. Our understanding of the project is based on our meeting with the client. As per client request, we have conducted a site visit and literature search to evaluate the hazard to the site in the CMZ. The services described in this evaluation were prepared under the responsible charge of Curtis Cushman, L.E.G. Curtis Cushman verifies the accuracy of this report as well as all assumptions relied upon in the report. We appreciate this opportunity to be of service to you and we look forward to working to help complete this project safely and in compliance with the regulations and standards of Mason County. If you have any questions concerning the above items, the procedures used, or if we can be of any further assistance, please call us at the phone numbers listed below. Respectfully Submitted, Of Was ALL AMERICAN GEOTECHNICAL 2 o�.ny CoOfo-ifyl i 439 /•��� -Ted G Curtis D Cushman Curtis Dean Cushman Senior Engineering Geologist AAG23-083 8947 Buttonwood Lane NE,Olympia, WA 98516 3 Phone#: (360)491-5155 CeIVText#: (360)481-6677 ALL AMERICAN GEOTECHNICAL • TABLE OF CONTENTS CONTACT INFORMATION 2 SCOPE OF UNDERSTANDING 3 INTRODUCTION 5 SITE CONDITIONS 6 SURFACE CONDITIONS 6 GEOTECHNICAL ASSESSMENT 6 SITE SOILS 7 SITE GEOLOGY 7 MISSION CREEK HISTORY 8 LIDAR IMAGERY 8 CONCLUSIONS AND RECOMMENDATIONS 8 REPORT LIMITATIONS AND GUIDELINES FOR USE 8 CONTRACTORS ARE RESPONSIBLE FOR SITE SAFETY ON THEIR OWN CONSTRUCTION PROJECTS 9 READ THESE PROVISIONS CLOSELY 9 APPENDIX 10 FIGURE 1 VICINITY MAP 11 FIGURE 2 SITE PLAN 12 FIGURE 3 FEMA FIRM MAP 13 FIGURE 4 CMZ ZONE 14 AAG23-083 8947 Buttonwood Lane NE,Olympia,WA 98516 4 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL INTRODUCTION This report summarizes the results of our geotechnical consulting services for the proposed expansion of an existing residence on the parcel herein described. The residence will extend living area to the southwest of the existing structure. This is in the northeastern part of the parcel which is a 1.42-acre quadrilateral somewhat long to the east-west. The longest leg is parallel to State Route 300. In general, the property slopes in low terraces gently to Mission Creek to the west. There is the beginning of a steeper ascending hillslope on the east side of the parcel that rises off parcel. This slope qualifies as a CMZ and is addressed in the earlier AAG report for the client. The property is approximately 2.5 direct miles southwest of Belfair and not much further by road. The location of the site is shown relative to the surrounding area on the Vicinity Map, Figure 1. Our understanding of the project is based on our discussions with the client. The new structure will be built a few feet up to match the elevation of the current residence, likely with stem walls. Figure 2 in the Appendix shows the location of the proposed expansion in the general context of the topography and parcel boundaries. It overlies LiDAR which shows the bare-earth features on-site. Also shown is the CMZ boundary from the Draft Channel Migration Assessment Mason County. Note that the twenty-foot contour near the stream is off. This is taken from the GIS and likely reflects the failure of the algorithm to assemble multiple minor changes in its smoothing routine. Use the LiDAR part of the image there. The purpose of our services is to evaluate the property in keeping with the DCMA and all Mason County requirements. All American Geotechnical is therefore providing geologic and hydrogeologic services for the project. Specifically, our scope of services for this project includes the following: 1. A review of the available geologic,hydrogeological and geotechnical data for the site area. 2. A geologic reconnaissance of the site area and surrounding vicinity. 3. Comparison of site to published geologic maps,previous field investigations,and open file reports. Inspection of aerial photographs and LiDAR to determine the geomorphology of the river migration at the site. The area is of moderate density of single-family residences and vacation homes, notably near the shore of North Bay of Hood Canal. The location of the parcel is shown relative to the surrounding area on the Vicinity Map, Figure 1. The location proposed for construction is on Quaternary-aged sediments. This will be described in "Geology,"below. The parcel site lies within a DCMA-defined CMZ. The river here is not meandering, but is incised in a narrow channel to the west of two near-parallel abandoned channels. While there is little potential for avulsion (basically a catastrophic change in the course of a river), blockage at the bridge just below the client parcel could cause flooding. This would not likely rise to the level of the proposed expansion. This is an unlikely, but potential, hazard. AAG23-083 8947 Buttonwood Lane NE,Olympia,WA 98516 5 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL SITE CONDITIONS SURFACE CONDITIONS The proposed location for the new residence expansion is located in the northeastern part of the parcel. The site is a series of flat terraces a few feet high descending west to Mission Creek. The current residence is on the uppermost terrace at an elevation of 30 feet above msl. The expansion will be built at an elevation of approximately 27 feet and will have stem walls raising the useful residential space to that of the current residence. The overall site elevation is from below 20 feet at Mission Creek to just under 50 feet on the slope at the east property line. Development will be on or just below the 30-foot contour. Curtis D Cushman, L.E.G. and Blaise Jelinek E.I.T., conducted a site reconnaissance on July 25, 2023. The purpose of a site visit is to physically observe the property and adjacent properties in order to identify any recognized geologic conditions. Visual observations were documented. Site-specific features were mapped. The parcel has substantial second-growth trees including firs mainly around the Mission Creek area. The growth indicates the stream channel has not recently been on the parcel. To the north there are abundant second-growth trees. The proposed residence expansion will be located approximately 200 feet east of the main channel of Mission Creek. It is located within the CMZ. There is no standing water near the potential building site. The creek,which descends from Mission Lake, is moderately shallow but flows slowly as it passes the property. The abandoned channels do not contain water. GEOTECHNICAL ASSESSMENT "The channel migration zone should be established to identify those areas with a high probability of being subject to channel movement based on the historic record, geologic character and evidence of past migration. It should also be recognized that past action is not a perfect predictor of the future and that human and natural changes may alter migration patterns. Consideration should be given to such changes that may have occurred and their effect on future migration patterns. For management purposes, the extent of likely migration along a stream reach can be identified using evidence of active stream channel movement over the past one hundred years. Evidence of active movement can be provided from historic and current aerial photos and maps and may require field analysis of specific channel and valley bottom characteristics in some cases. A time frame of one hundred years was chosen because aerial photos,maps and field evidence can be used to evaluate movement in this time frame."WAC 173-26-221(3). AAG23-083 8947 Buttonwood Lane NE,Olympia,WA 98516 6 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL SITE SOILS The soils are described by the USDA Web Soil Survey as: Ed—Everett gravelly loamy sand, 0 to 5 percent slopes Description of Everett Setting • Landform: Terraces • Parent material: Glacial outwash Typical profile • HI - 0 to 7 inches: gravelly ashy loamy sand • H2 - 7 to 21 inches: extremely gravelly sand • H3 - 21 to 60 inches: very gravelly sand The description of the Everett soil is in keeping with what is seen across the property both at the development site and at the LHA slopes. Source may be ice-contact deposits. This is a mix of sand with gravel with finer fraction forming the gravelly loam. The soil composition varies across the property, however, as might be expected in what was a very dynamic drainage area. The soil is not crucial to the water flow in the CMZ. SITE GEOLOGY The entire parcel is mapped as follows on the Washington Geologic Information Portal Geologic Unit Symbol: Qa Unit Description: Silt, sand, and gravel; clasts typically well rounded; typically well sorted and loose; stratified to massively bedded; deposited in streams and adjacent banks. The sediment source is most commonly reworked recessional outwash, ablation till, advance outwash, and(or)glaciolacustrine deposits, but may include lodgment till, nonglacial deposits, and bedrock... Age: Quaternary Lithology: alluvium Age-Lithology: Quaternary alluvium The materials seen by Mission Creek are alluvial outwash deposits. There is a possibility the site is somewhat mis-mapped on the GIS as the Belfair Quadrangle shows the area to be mostly Qgic Vashon Stade ice-contact deposits. These are similar to the Qa deposits and are considered as such in the two AAG reports for this parcel. AAG23-083 8947 Buttonwood Lane NE,Olympia,WA 98516 7 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL MISSION CREEK HISTORY Mission Creek is one of the first areas mentioned in the text of DCMA(page 2; fig 1.1 page 3)concerning potential property and environmental damage done by stream erosion following excessive residential development(between 1999 and 2009) near the creek about 1.5 miles north-northeast of the client parcel. Figure 4.5 on page 17 shows a flood event on Mission Creek and the logjam causing it. It was hypothesized that the logs may have come from trees brought downstream by the creek from the area shown on Figure 1.1. This even made an avulsion possible. These examples show that Mission Creek is sensitive to human activity. The creek has its headwaters to the north in Kitsap County and just north of Mission Lake. The lake feeds water into Mission Creek, perhaps accounting for its flow in the dry season as its capture area is limited. This is due to the creek being wholly at its upper reaches within a narrow and straight"groove"caused by glacial scouring during the last ice age. The groove is contained by elongated drumlins, likewise artifacts of the continental glaciation. Nearer Hood Canal,the creek crosses one of the drumlins to continue flowing south before returning to the original groove before it discharges in a delta. After passing by the client parcel and before the stream forms its delta, Mission Creek is crossed by State Route 300. Whenever there is a manmade barrier, there is a possibility of blockage—natural or otherwise—that can cause water to back up and possibly flood surrounding areas. However, water would likely overtop the bridge before it could flood the area of the residence or its expansion. The DCMA refers to both removal of revetment on the lower Mission Creek and a levee break. These appear to be related to the delta area south of the bridge and do not affect the client development project. LIDAR IMAGERY Please refer to Figure 2. The stream appears well established in its current bed and does not appear to be threatening the client parcel. CONCLUSIONS AND RECOMMENDATIONS Our analysis indicates that there is no meander hazard to the proposed building site. The avulsion hazards exist,but are unlikely without a large influx of water due to blocking of Mission Creek. Absent that, it is unlikely Mission Creek poses a hazard to the proposed expansion. If these potential impacts are understood and considered in site development,we can recommend the project be approved and that it may proceed to the next phase. REPORT LIMITATIONS AND GUIDELINES FOR USE We have prepared this report for the exclusive use of the Harkins and their authorized agents for the proposed building location in Mason County, Washington. Site inspections, research, and mapping have culminated in this report. This report is intended to meet the requirements of the Mason County Code for CMZ areas. This report does not specify setbacks for: line-of-sight setbacks,FWHCA setbacks,eagle tree setbacks,wetland setbacks,or property line setbacks. Within the limitations of scope,schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical AAG23-083 8947 Buttonwood Lane NE,Olympia,WA 98516 8 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL engineering in this area at the time this report was prepared. No warranty or other conditions, expressed or implied, should be understood. CONTRACTORS ARE RESPONSIBLE FOR SITE SAFETY ON THEIR OWN CONSTRUCTION PROJECTS Our geotechnical recommendations are not intended to direct the contractor's procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to onsite personnel and to adjacent properties. READ THESE PROVISIONS CLOSELY Some clients, design professionals, and contractors may not recognize that the geoscience practices (geotechnical engineering or geology) are far less exact than other engineering and natural science disciplines. This lack of understanding can create unrealistic expectations that could lead to disappointments, claims and disputes. All American Geotechnical, Inc. includes these explanatory "limitations"provisions in our reports to help reduce such risks. The equipment,techniques and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical or geologic study and vice versa. For that reason, geotechnical engineering or geologic reporting does not usually relate any environmental findings, conclusions or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Similarly,environmental reports are not used to address geotechnical or geologic concerns regarding a specific project. AAG23-083 8947 Buttonwood Lane NE,Olympia,WA 98516 9 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL APPENDIX Figure 1.Vicinity Map Figure 2.Site Plan with LiDAR background Figure 3.FEMA FIRM MAP 5301150135C Figure 4. Channel Migration Zone DRAFT Map AAG23-083 8947 Buttonwood Lane NE,Olympia,WA 98516 10 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL • FIGURE 1 VICINITY MAP 7 s'7ce5�,�•4V T�',z�]'T*_ L; If.°$<tUr�'. 1��Lir��•i .t1��1UU Y1 :y ^ r r - 41 J f`• t /' f�L.. A > ' -1,_yneh �`� v - r �ii tF II:tI'jilItS ""• "� r r �►c;F� Y �d. #a#e ffig 1ti\a. 3ool,, .♦y , •.nbraeA tl ,lien �V�f�• fi_. tix' f! ' r P`�r , �� r' '. Ir��'Y ` -�. '_�..���,- •ram hf�- - � - - jj I I `�/� r,'•'..�., �r .�f l(f 1{III -emu. .. �.�II •; ,:5=..U!-._.�!. ! , !. __ r � � 1.r 122*54 00'W 121 53'00-W 12215200'1Y WGS64 122151'00"W TsT r3v w o temr[[r a as mrwttns phom Om TGPbr CM Nlu o f Gwgaf4r Ei i(xti'.^r:taFrmvt: AAG23-083 8947 Buttonwood Lane NE,Olympia, WA 98516 1 1 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 ALL AMERICAN GEOTECHNICAL . FIGURE 3 FEMA FIRM MAP Au Al j,kv- (/A�* "Yii # jf 'P, d 44. � n n -J,12-�1 SS rr ty llp zl <i.:f14' 1'fl_ � tea, ..��" B 7A1 j tr I //k t . 11aA�ll. %Y l l aonwo arz ar ._-.F2R h�� � p•T.JT,.yp�,'�'",�3s •�iJ�..b�F. -i11)�� ! _ +J/1 J:J 1J }F_K:X'LyJt��:�,(�i•�p�14 ``��?� !1 � /• s w. w.r..� .-w.�.«.w p1 I�'I M11ltt�efi.._..-. f arwmiar mN. ,y Development area is marked as Zone C,Areas of Minimal Flooding. AAG23-083 8947 Buttonwood Lane NE,Olympia,WA 98516 13 Phone#: (360)491-5155 Cell/Text#: (360)481-6677 NOTES at Wash�� t This is not a survey. This map: presentation of infq tr°n from 1 county, state, and/or federal E d I tngmeenng Geok)jost I ` agencies, client provided - 2439 �� 70'- information, and onsite L ceased Ge°\oo`" h _ observations. c;urtis Dean Ct�shma!i I ~ I �' E e► 232' M - , W--Wet ( is g) Site Soils Key = Exis g Ed Everett gravelly loam sand F �H o l�' Y Y , �o • tip° � .�._. 0 to 5 percent slope •j ��� t Ee Everett gravelly loamy sand, , 5 to 15 percent slope Ie Indianola loamy sand, 15 to 30 percent slope B 344 L 201 A� Site Geology -J Qa -- Quaternary alluvial0, SCALE .sar deposits 1 ��� .• r i s i All American Geotechnical, Inc. Project Drawn By: Site Plan 22201-51-91001 Fi{�ure Permit Number: Parcel Number: 8947 Buttonwood Lane NE Number: BWJ 8/9/2023 Channel Migration Zone -- CMZ Olympia, Washington 98516 AAG23-083 Belfair, WA Applicant Name: Laura& Matthew Harkins Site Address: 3040 NE State Highway 300 Page 12 ALL AMERICAN GEOTECHNICAL Figure 4. Mission Creek CMZ Zone :14- jell w 'I•r t. t� .may ` L , �j► r _ y w d A Y • �, ` ♦' - l� �'� -_ _}• � ' t rt . y,° ,�;,�,. � ;�,• " 1"t'°��.,,�.� � 'ti © River Mile Marker ' �t _ fie... ' Y 7 , �t. �b[, ��lA ,•.'--. • A fit. . �� MA #k ?F# Reach ID Segment Boundaries t . N E hJN C R.E:E K R D. L+ .. !.a •'s Geotechnical Buffer k. � Recommended ye f Y Channel at,• ` �'�j ' Migration . Zone Disconnected 64 Tributary CMZ Alluvial Fan �� �_ ' ,. - '', �rW' ►`- } 0 50 100 150 Meters i � � � r►i �' f 1 1 1 I ,�.• ,_ 0 250 500 Feet V. +. F 4 % -1 " '-ir{ -..;`�''" V' "t 2009 orthophoto(USDA NAIP) '' ;. ��rdilg Roads from TIGER(US Census Bureau) te"i '� C\h Coordinate System_State Piano Washington South Horizontal Datum-.NAD19B3 HARK Units_Feet `�, • `� Z°°N.. t<5. a �:_ _;ice.,.:� •I Iv ,� j F •F Analysis by: Shawn b99ins.Cardno F Reviewed by:Tim Abbe,PhD,PEG.PHG(Ca(Cardrro Entroc) 67 + ' - T. A[TwM[MT 01 GEOEGINEERSALT%I OE2OLGY ;. EN0 - '' � °1� �� /, 'y ,� f 1, � �,�� s� t^r�["w�-y,�•� _-+�Mi�` ./jam ti� �� .^ �'w ." r'' f '- ':�. r �•' Channel Migration Assessment c� `� •��° �'-' Prepared for the Shoreline Master Pi ram U ate Mason County, Washington fool Map 61 Mission Creek AAG23-083 8947 Buttonwood Lane NE, Olympia, WA 98516 Page 14 Phone#: (360)491-5155 Cell #: (360)481-6677