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HomeMy WebLinkAboutRS_WoldeBFEStudy23_1011-REV2MEMORANDUM Project No. 220211 July 28, 2022 (revised October 11, 2023) To: Elias Wolde 13710 SE May Valley Road Renton, WA 98059 cc: Kerrie McArthur, PWS, CERP Managing Senior Biologist Confluence Environmental Company From: John Knutson, PE, PMP Principal Water Resources Engineer jknutson@aspectconsulting.com Erik Pruneda, PE, CPESC, CFM Senior Stormwater Engineer epruneda@aspectconsulting.com Re: Base Flood Elevation Study Introduction and Background Elias Wolde, who lives at 13710 SE May Valley Road, Renton, WA 98059, retained Aspect Consulting, LLC (Aspect) to provide hydrologic and hydraulic services related to the placement of a patio behind his home. The patio was placed adjacent to May Creek and was installed without obtaining permits from the City of Renton (City). Among other studies and permits, the City requires a review of Flood Hazard Data and the completion of a “base flood elevation study that identifies what the elevation was prior to the unpermitted work” (Email from Andrew Van Gordon, March 24, 2022). This report is intended to address these City requirements. ear t h +w ate r Aspect Consulting, LLC 710 2nd Avenue Suite 550 Seattle, WA 98104 206.328.7443 www.aspectconsulting.com 10/11/23 10/11/23 Elias Wolde MEMORANDUM July 28, 2022 (revised October 11, 2023) Project No. 220211 Page 2 Exhibit 1 – Wolde Site Vicinity Map (Source Google Earth, 2022) Exhibit 2 – Photograph of Wolde patio looking south, May Creek in background. Wolde Property, 13710 SE May Valley Road, Renton, WA 98059 Also Owned by Wolde Elias Wolde MEMORANDUM July 28, 2022 (revised October 11, 2023) Project No. 220211 Page 3 Key City Flood Related Standards Aspect reviewed City code to identify floodplain related requirements that may apply to the Wolde patio work. Based on review of City code, Flood Hazard Data includes: Flood Hazard Data Aspect Response a. Plans in duplicate drawn to scale showing the nature, location, dimensions, and elevations of the area in question; existing or proposed structures, fill, storage of materials, drainage facilities, and the location of the foregoing; The required plans will be attached to this memorandum. However, only fill is involved. No structures, material storage, or drainage facilities are involved. b. Elevation in relation to mean sea level of the lowest floor (including basement) of all structures; Not applicable, no structure is involved. c. Elevation in relation to mean sea level to which any structure has been floodproofed; Not applicable, no floodproofing is involved. d. Certification by a registered professional engineer or architect that the floodproofing methods criteria in RMC 4-3-050I3c; and for any nonresidential structure meet the floodproofing; Not applicable, no floodproofing is involved. e. Description of the extent to which a watercourse will be altered or relocated as a result of proposed development. (Ord. 4835, 3-27-2000) Not applicable, no watercourse alteration is involved. A FEMA floodway has been mapped for May Creek. The entire floodplain of May Creek is mapped as floodway in the vicinity of the Wolde property (see Attachment 1). Per City code, the following restrictions apply within designated floodway areas: • Increase in Flood Levels Prohibited: Encroachments, including fill, new construction, substantial improvements, and other development are prohibited unless certification by a registered professional engineer demonstrates through hydrologic and hydraulic analyses performed in accordance with standard engineering practice that: a. Encroachments shall not result in any increase in flood levels during the occurrence of the base flood discharge; and b. There are no adverse impacts to the subject property or abutting or adjacent properties; and c. There are no higher flood elevations upstream; and d. The impact due to floodway encroachment shall be analyzed using future land use condition flows. Elias Wolde MEMORANDUM July 28, 2022 (revised October 11, 2023) Project No. 220211 Page 4 Other floodway restrictions in City code appear to not apply since no structure or bridge is involved, however City code also states: • Compensatory Storage Required: Development proposals and other alterations shall not reduce the effective base flood storage volume of the floodplain. If grading or other activity will reduce the effective storage volume, compensatory storage shall be created on the site or off the site if legal arrangements can be made to assure that the effective compensatory storage volume will be preserved over time. Compensatory storage shall be configured so as not to trap or strand salmonids after flood waters recede and may be configured to provide salmonid habitat or high flow refuge whenever suitable site conditions exist and the configuration does not adversely affect bank stability or existing habitat. Effective base flood storage volume shall be based on the elevations shown in the flood hazard areas map... Hydrologic and Hydraulic Analyses Overview of Hydraulic Modeling Approach The approach for hydraulic modeling used by Aspect generally follows FEMA’s recommendations for analyzing and mitigating changes in Base Flood Elevations due to planned projects within floodplain areas. • Step 1 – Obtain and run (duplicate) the Effective Hydraulic Model using the same topography, stream cross-sections, 100- year flow, channel/overbank roughness, and other assumptions that were used to develop the Effective Flood Insurance Rate Maps (FIRMs). Make sure that the Duplicate Effective Hydraulic Model results (base flood elevations and floodplain extents) closely match the Base Flood Elevations (BFEs) and floodplain extents shown on the Effective FIRM. • Step 2 – Add more detail to the Duplicate Effective Hydraulic Model to represent recent pre-project conditions for the site and then run this Existing Condition Hydraulic Model to establish detailed existing flooding conditions. This is typically done by adding surveyed cross-sections for the project area into the model, updating channel and floodplain roughness as needed, and mapping resulting BFEs and flood extents using updated topography (such as topography based on recent LiDAR or survey work). • Step 3 – Update the Existing Condition Hydraulic Model to reflect the proposed project and then run this Proposed Condition Hydraulic Model to see how the resulting BFEs and floodplain extents compare to the Existing Condition Hydraulic Model. Developing the proposed condition model typically involves modifying the stream/floodplain cross- sections, topography, and roughness in the project area to reflect planned project grading, fill, piers, compensatory storage, flood protection measures, etc. “Effective” means the current information (flood elevations and extents) approved by FEMA and used to regulate development within the community floodplains. Elias Wolde MEMORANDUM July 28, 2022 (revised October 11, 2023) Project No. 220211 Page 5 • Step 4 – Add mitigation measures to the Proposed Condition Hydraulic Model and complete model runs until no-rise or other floodplain criteria are met. Measures to mitigate/prevent a rise in flood elevation commonly include techniques such as reducing fill, creating overflow channels, widening channels, using longer bridges, installing culverts through fill areas, etc. While the Wolde patio was built before the “existing condition model” was developed, Aspect used recent LiDAR and survey data to estimate the “existing conditions” (pre-patio stream and floodplain cross-sections and overall topography). Aspect notes that the analysis completed for this memorandum focuses on Base Flood Elevations and 100-year floodplain extents rather than floodway elevations and boundaries. A formal floodway encroachment analysis, or floodway no-rise analysis, involves a different modeling approach. Floodway models involve artificially filling the floodway fringe on both sides of the channel until a target rise (often 1 ft) in predicted flood elevation in the non-filled areas of the floodplain/channel occurs – the edge of the artificial fill on both sides of the channel becomes the floodway limits. Effective Flood Insurance Study and FIS Hydraulic Model Aspect obtained and reviewed FEMA’s Effective Flood Insurance Study (FIS), the Flood Insurance Study for King County and Incorporated Areas, Revised August 2020. While the revised FIS is dated 2020, the hydraulic modeling and FIRM for May Creek in the Wolde property area date to the original flood study completed in the 1980s. Aspect requested the effective hydraulic model from FEMA for the Wolde property area and was provided with input data and tabular results for the now obsolete HEC-2 hydraulic modeling program. Since HEC-2 is no longer a functional model, it became apparent that Aspect would need to prepare an updated duplicate effective hydraulic model using HEC-RAS before a detailed analysis of pre and post patio flooding conditions could be done. Effective Hydrology An updated analysis of May Creek hydrology (flood flow estimates) was not within Aspect’s scope of work. Therefore, it was assumed that the FEMA estimated 100-year flood discharge estimate at Coal Creek Parkway as contained within the Effective FIS is accurate. Relevant flows from Table 2 – Summary of Discharges in the Effective FIS are shown below. Flooding Source and Location Drainage Area (square miles 10-Percent- Annual- Chance 2-Percent- Annual- Chance 1-Percent- Annual- Chance 0.2-Percent- Annual- Chance 10-Year Flood 50-Year Flood 100-Year Flood 500-Year Flood May Creek At Coal Creek Parkway 8.9 350 580 640 750 Elias Wolde MEMORANDUM July 28, 2022 (revised October 11, 2023) Project No. 220211 Page 6 Duplicate Effective Hydraulic Model As noted above, the effective FIRM for the Wolde property area was developed using the obsolete HEC-2 model. Therefore, Aspect used the HEC-2 input data (cross-sections, roughness, 100-year flow, upstream/downstream tie-in assumptions) to recreate the model in HEC-RAS. While there are very minor differences due to the different models used, the resulting HEC-RAS model closely matches the Effective BFEs derived by HEC-2 (NAVD 88 Datum). As can be seen, when rounded to the nearest 10th of a foot as done for the Effective FIRM, the BFE results are all the same. Upstream, FEMA Cross-Section AB • HEC-2 BFE at FEMA Cross Section AB = 281.89 ft • HEC-RAS BFE at FEMA Cross Section AB = 281.93 ft • Effective FIRM BFE at Cross Section AB = 281.9 ft Downstream, FEMA Cross-Section AA • HEC-2 BFE Cross Section AA (downstream of Wolde) = 269.97 ft • HEC-RAS BFE Cross Section AA (downstream of Wolde) = 269.99 ft • Effective FIRM BFE at Cross Section AA (downstream of Wolde) = 270.0 ft The Duplicate Effective Model results are provided in Attachment 2-1. “Existing Condition” (Pre-Patio Project) Hydraulic Model Like many old flood insurance studies, the May Creek HEC-2 model and resulting BFEs and floodplain maps were based on: (a) stream/floodplain cross-sections that are spaced far apart; and, (b) old coarse level topography. Therefore, it is expected that adding more and higher resolution stream/floodplain cross-sections and mapping floodplain extents using newer high-resolution topography will result in BFEs and floodplain maps that differ from the Effective FIRM. Aspect used two main sources of stream channel and floodplain topographic information to develop new cross-sections in the Wolde property vicinity: • 2016 LiDAR for the area. • Recent survey data for the Wolde property, collected spring 2022 by Terrane (Attachment 3). Based on observations, 2003, 2005, and 2026 LiDAR, and the recent survey data, the May Creek meander along the Wolde property is gradually migrating southward by eroding into the tall steep southern bank. As the lateral migration progresses, it continues to move the stream thalweg and left bank of the creek away from the patio area. Aspect believes this is a natural process rather than any response to patio construction. In order to prepare the existing condition model, Aspect combined the recent survey data for the main channel and left bank on the Wolde property with the LiDAR data (pre-patio) for the right bank and floodplain. The LiDAR data was also used to estimate creek/floodplain cross-sections for areas outside the Wolde property. The Existing Condition (Pre-Patio Project) Hydraulic Model results are shown in Attachment 2-2. These model results establish the flooding baseline and will be compared to the Proposed (Post- Patio Project) Condition Hydraulic Model to assess the impacts of patio construction. Elias Wolde MEMORANDUM July 28, 2022 (revised October 11, 2023) Project No. 220211 Page 7 “Proposed Condition” (Post-Patio Project) Hydraulic Model Aspect updated the existing condition model cross-sections to reflect the recent survey work by Terrane, which captured patio construction fill and grading. The results of this Proposed Condition (Post-Patio Project) Hydraulic Model are shown in Attachment 2-3. Comparison of Existing and Proposed Condition Modeling Results The results of the Existing Condition (Pre-Patio) versus Proposed Condition (Post-Patio) BFEs are shown in the table below. Cross Section # / River Station: HEC-RAS Pre-Project WSE (NAVD 88) HEC-RAS Post-Project WSE (NAVD 88) Difference (FT) Difference (IN) Type Location 650 (AB) / 751 (AB) 282.01 282.01 0 0 no change off site 626 280.59 280.59 0 0 no change off site 549 279.48 279.29 -0.19 -2.28 decrease off site 465 277.86 277.98 0.12 1.44 rise Wolde prop. 445 277.57 277.47 -0.1 -1.2 decrease Wolde prop. 418 277.01 277.06 0.05 0.6 rise Wolde prop. 386 276.35 276.35 0 0 no change Wolde prop. 362 276.06 276.05 -0.01 -0.12 decrease Wolde prop. 30 (AA) 269.99 269.99 0 0 no change off site 0.1 269.12 269.12 0 0 no change off site Note: All Elevations in NAVD 88 As can be seen, there are two instances of predicted rise in BFEs due to patio construction, however the rise areas are contained to Mr. Wolde’s properties and do not increase the flood risk, or otherwise affect, any structure. The mapping of the Existing versus Proposed floodplain is shown in Attachment 2-4. A profile of the pre/post BFEs is shown in Attachment 2-5, along with estimated property boundaries. HEC- RAS cross sections across Mr. Wolde’s property for Existing and Proposed conditions are shown in Attachment 2-6. As can be seen in Attachment 2-4, the southern edge of the patio fill slightly encroaches into the pre-project (Existing Condition) floodplain in two locations, otherwise the patio Elias Wolde MEMORANDUM July 28, 2022 (revised October 11, 2023) Project No. 220211 Page 8 is outside the pre-project floodplain, but essentially matches the edge of the post-project floodplain. The estimated total volume of encroachment fill in the pre-project floodplain is approximately 8 cubic yards. Recommendations At this point in Aspect’s analysis, we have not developed and modeled flood mitigation approaches such as: •Excavating compensatory flood storage areas on Mr. Wolde’s upstream property. •Excavating some bar material from in front of the patio to increase flood conveyance capacity. •Removing small portions of the patio that encroach into the pre-project floodplain. Aspect’s analysis indicates that, from a flood perspective, the patio project only results in very minor flood impacts which are all contained to Mr. Wolde’s properties. We suspect that the cost and negative effects of constructing any of the above mitigation techniques on May Creek and its buffer could exceed the marginal (if any) flood benefit. It is also likely that as the May Creek meander continues to migrate southward, the patio will naturally be entirely outside the active 100- year floodplain within a couple years. Perhaps it is possible to focus on enhancing and preserving buffer habitat on one or both of Mr. Wolde’s properties rather than, in this instance, potentially unbeneficial post-project flood mitigation. Aspect recommends that Mr. Wolde discuss the situation with the City and obtain direction regarding whether compliance with the letter of the code will be required, or if extra habitat mitigation or partial mitigation (compensatory storage on his upstream parcel) can be done instead. Once direction from the City is obtained, Aspect will be happy to further assist as needed. Limitations Work for this project was performed for Elias Wolde (Client), and this memorandum was prepared in accordance with generally accepted professional practices for the nature and conditions of work completed in the same or similar localities, at the time the work was performed. This memorandum does not represent a legal opinion. No other warranty, expressed or implied, is made. 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. Attachments Attachment 1 – Effective Flood Insurance Rate Map Information Attachment 2 – Hydraulic Modeling Results Attachment 3 – Terrane Survey Attachment 4 – HEC-RAS Model (Digital Attachment) V:\220211 Wolde Critical Areas Mitigation Spprt\Deliverables\BFE Study\Wolde BFE Study 23_1011-REV2.docx ATTACHMENT 1 Effective Flood Insurance Rate Map Information National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250 Feet Ü SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOOD HAZARD AREAS Without Base Flood Elevation (BFE) Zone A, V, A99 With BFE or DepthZone AE, AO, AH, VE, AR Regulatory Floodway 0.2% Annual Chance Flood Hazard, Areas of 1% annual chance flood with average depth less than one foot or with drainage areas of less than one square mileZone X Future Conditions 1% Annual Chance Flood HazardZone X Area with Reduced Flood Risk due to Levee. See Notes.Zone X Area with Flood Risk due to LeveeZone D NO SCREEN Area of Minimal Flood Hazard Zone X Area of Undetermined Flood HazardZone D Channel, Culvert, or Storm Sewer Levee, Dike, or Floodwall Cross Sections with 1% Annual Chance 17.5 Water Surface Elevation Coastal Transect Coastal Transect Baseline Profile Baseline Hydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of Study Jurisdiction Boundary Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from the authoritative NFHL web services provided by FEMA. This map was exported on 4/12/2022 at 7:55 PM and does not reflect changes or amendments subsequent to this date and time. The NFHL and effective information may change or become superseded by new data over time. This map image is void if the one or more of the following map elements do not appear: basemap imagery, flood zone labels, legend, scale bar, map creation date, community identifiers, FIRM panel number, and FIRM effective date. Map images for unmapped and unmodernized areas cannot be used for regulatory purposes. Legend OTHER AREAS OF FLOOD HAZARD OTHER AREAS GENERAL STRUCTURES OTHER FEATURES MAP PANELS 8 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative property location. 1:6,000 122°9'47"W 47°31'17"N 122°9'10"W 47°30'53"N Basemap: USGS National Map: Orthoimagery: Data refreshed October, 2020 ATTACHMENT 2 Hydraulic Modeling Results 751 (AB)Eff HEC-2 = 281.89Eff FIRM = 281.9Dup Eff = 281.93 30 (AA)Eff HEC-2 = 269.97Eff FIRM = 270.0Dup Eff = 269.99 0Eff HEC-2 = 269.09Eff FIRM = NADup Eff = 269.12 Chaffey Brothers LLCParcel #: 3424059106 Elias Wolde13701 SE May Valley RdParcel #: 3424059113Elias Wolde13703 SE May Valley RdParcel #: 3424059110Lee Yi-Jen13711 SE May Valley RdParcel #: 3424059109Leon Morse13719 SE May Valley RdParcel #: 3424059026May CreekCoal Creek Parkway SECity of RentonParcel #: 3424059086 SE May Valle y R o a d AAABATTACHMENT NO.2-1JUL-2022 PROJECT NO.220211 BY:EP REVISED BY:- - - Duplicate Effective Modeling Results Wolde Property Critical Areas MitigationRenton, WA GIS Path: G:\projects\WoldeCriticalAreasMitigation_220211\Delivered\Attachment2-1-DuplicateEffectiveModelingResults.mxd || Coordinate System: NAD 1983 StatePlane Washington North FIPS 4601 Feet || Date Saved: 7/27/2022 || User: epruneda || Print Date: 7/27/2022May Creek Centerline Modeled Cross Section Parcel Boundary 0 80 160 Feet Basemap Layer Credits || EagleView Technologies, Inc. StationEffective HEC-2 WSE (NAVD 88)Effective FIRM WSE (NAVD 88)Duplicate Effective WSE (NAVD 88) Note: Duplicate Effective model study limits were limitedto May Creek Station 0, 30 (AA), and 650/751 (AB).Creek station at cross section AB was 650 for EffectiveHEC-2 model and 751 for Duplicate Effective model. Thestation increase is a result of updating the creek courseto reflect recent topography. 751Pre = 282.01 626Pre = 280.59 549Pre = 279.48 465Pre = 277.86 445Pre = 277.57418Pre = 277.01 386Pre = 276.35 362Pre = 276.06 30Pre = 269.99 0Pre = 269.12 Chaffey Brothers LLCParcel #: 3424059106 Elias Wolde13701 SE May Valley RdParcel #: 3424059113 Elias Wolde13703 SE May Valley RdParcel #: 3424059110 Lee Yi-Jen13711 SE May Valley RdParcel #: 3424059109 Leon Morse13719 SE May Valley RdParcel #: 3424059026 May CreekCoal Creek Parkway SECity of RentonParcel #: 3424059086AA ABATTACHMENT NO.2-2OCT-2023 PROJECT NO.220211 BY:EP REVISED BY:- - - Pre-Project Modeling Results Wolde Property Critical Areas MitigationRenton, WA GIS Path: G:\projects\WoldeCriticalAreasMitigation_220211\Delivered\Attachment2-2-PreProjectModelingResults.mxd || Coordinate System: NAD 1983 StatePlane Washington North FIPS 4601 Feet || Date Saved: 10/6/2023 || User: epruneda || Print Date: 10/6/2023May Creek Centerline Modeled Cross Section 100-Year Inundation Pre-Project Parcel Boundary 1-ft Contour (2016 Lidar) 0 40 80 Feet Basemap Layer Credits || EagleView Technologies, Inc. StationPre-Project WSE (NAVD 88) Cross Sections 362 through 465Pre-Project Channel and Left Bank AlongWolde Property Assumed to beSimilar to 2022 Topographic Survey(See Attachment 2-3 for Contours).Right Bank Assumed to be Similar to2016 LiDAR Contours. Pre-Project conditions assumed to be similar to2016 LiDAR contours with exceptions noted above. Cross Section AB (Station 751)Assumed to be Same asFEMA Effective Model Cross Section AA (Station 30)Assumed to be Same asFEMA Effective Model Cross Sections 549 and 626Assumed to be Similar to2016 LiDAR Contours withLinearly Interpolated Channel ThalwegBetween Cross Section 465 and 751 751Post = 282.01 626Post = 280.59 549Post = 279.29 465Post = 277.98 445Post = 277.47418Post = 277.06 386Post = 276.35 362Post = 276.05 30Post = 269.99 0Post = 269.12 Chaffey Brothers LLCParcel #: 3424059106 Elias Wolde13701 SE May Valley RdParcel #: 3424059113 Elias Wolde13703 SE May Valley RdParcel #: 3424059110 Lee Yi-Jen13711 SE May Valley RdParcel #: 3424059109 Leon Morse13719 SE May Valley RdParcel #: 3424059026 May CreekCoal Creek Parkway SECity of RentonParcel #: 3424059086AA ABATTACHMENT NO.2-3OCT-2023 PROJECT NO.220211 BY:EP REVISED BY:- - - Post-Project Modeling Results Wolde Property Critical Areas MitigationRenton, WA GIS Path: G:\projects\WoldeCriticalAreasMitigation_220211\Delivered\Attachment2-3-PostProjectModelingResults.mxd || Coordinate System: NAD 1983 StatePlane Washington North FIPS 4601 Feet || Date Saved: 10/6/2023 || User: epruneda || Print Date: 10/6/2023May Creek Centerline Modeled Cross Section Edge of Patio Fill 100-Year Inundation Post-Project Parcel Boundary 1-ft Contour (2022 Survey) 0 40 80 Feet Basemap Layer Credits || EagleView Technologies, Inc. StationPost-Project WSE (NAVD 88) Cross Sections 362 through 465Post-Project Channel and Left/Right BanksAlong Wolde Property Based on2022 Topographic Survey. Post-Project conditions based on 2022 topographicsurvey for Wolde property and 2016 LiDAR contoursfor upstream and downstream areas (with exceptionsnoted above). See Attachment 2-2 for 2016 LiDARcontours. Cross Section AB (Station 751)Assumed to be Same asFEMA Effective Model Cross Section AA (Station 30)Assumed to be Same asFEMA Effective Model Cross Sections 549 and 626Assumed to be Similar to2016 LiDAR Contours withLinearly Interpolated Channel ThalwegBetween Cross Section 465 and 751 751Pre = 282.01Post = 282.01 626Pre = 280.59Post = 280.59 549Pre = 279.48Post = 279.29 465Pre = 277.86Post = 277.98445Pre = 277.57Post = 277.47418Pre = 277.01Post = 277.06 386Pre = 276.35Post = 276.35 362Pre = 276.06Post = 276.05 30Pre = 269.99Post = 269.99 0Pre = 269.12Post = 269.12 Chaffey Brothers LLCParcel #: 3424059106 Elias Wolde13701 SE May Valley RdParcel #: 3424059113 Elias Wolde13703 SE May Valley RdParcel #: 3424059110 Lee Yi-Jen13711 SE May Valley RdParcel #: 3424059109 Leon Morse13719 SE May Valley RdParcel #: 3424059026 May CreekCoal Creek Parkway SECity of RentonParcel #: 3424059086AA ABATTACHMENT NO.2-4JUL-2022 PROJECT NO.220211 BY:EP REVISED BY:- - - Combined Pre- and Post-ProjectModeling Results Wolde Property Critical Areas MitigationRenton, WA GIS Path: G:\projects\WoldeCriticalAreasMitigation_220211\Delivered\Attachment2-4-CombinedModelingResults.mxd || Coordinate System: NAD 1983 StatePlane Washington North FIPS 4601 Feet || Date Saved: 7/27/2022 || User: epruneda || Print Date: 7/27/2022May Creek Centerline Modeled Cross Section Edge of Patio Fill 100-Year Inundation Pre-Project 100-Year Inundation Post-Project Parcel Boundary 0 40 80 Feet Basemap Layer Credits || EagleView Technologies, Inc. StationPre-Cond WSE (NAVD 88)Post-Cond WSE (NAVD 88) Floodplain Encroachment Areas 100-Year Post-Project Water Surface Elevationat Wolde Eastern Property Boundary is0.12-FT Greater than Pre-Project; However,the Rise Transitions to a Decrease in the100-Year Post-Project Water Surface ElevationWithin the Upstream Neighboring Property(Also Owned by Wolde). 100-Year Post-Project Water Surface Elevationat Wolde Western Property Boundary is0.01-FT Lower than Pre-Project 100-Year Post-Project Water Surface ElevationsAnticipated to be Similar to Pre-Project ElevationsDownstream of Wolde Property. 100-Year Post-Project Water Surface ElevationsAnticipated to be Similar to Pre-Project ElevationsWithin 13711 and 13719 SE May Valley Rd Properties. 0200400600800265270275280MayCrWolde Plan: 1) PreProject 7/5/2022 2) PostProject 7/12/2022 Main Channel Distance (ft)Elevation (ft, NAVD 88)LegendWS 100YrFlood - PreProjectWS 100YrFlood - PostProjectChannel BottomMayCreek Reach 11 in Horiz. = 60 ft 1 in Vert. = 2 ftAttachment 2-5 - Flood Comparison Profile 020406080100272274276278280282284286MayCrWolde Plan: PreProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 465Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.07020406080100120272274276278280282284286288MayCrWolde Plan: PreProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 445Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.071Attachment 2-6a - Pre-Project Condition Cross Sections 020406080100120272274276278280282284286MayCrWolde Plan: PreProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 418Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.07020406080100270272274276278280282284286288MayCrWolde Plan: PreProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 386Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.072 020406080100270272274276278280282284286288MayCrWolde Plan: PreProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 362Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.073 020406080100272274276278280282MayCrWolde Plan: PostProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 465Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.07020406080100120272274276278280282284286MayCrWolde Plan: PostProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 445Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.071Attachment 2-6b - Post-Project Condition Cross Sections 020406080100120272274276278280282284286MayCrWolde Plan: PostProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 418Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.07020406080100270272274276278280282284MayCrWolde Plan: PostProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 386Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.072 020406080100270272274276278280282284286MayCrWolde Plan: PostProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 362Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.073 ATTACHMENT 3 Terrane Survey LEGENDN15025EDWINJ.GRE E PROFES IONAL N D S U VEYORS L A RSTATEO F WASHI N GTONREGIST E R E D JR.STEEP SLOPE/BUFFER DISCLAIMER:TOPOGRAPHIC & BOUNDARY SURVEYDATE:DRAFTED BY:CHECKED BY:SCALE:REVISION HISTORYSHEET NUMBEROFTOPOGRAPHIC & BOUNDARY SURVEYJOB NUMBER:22077533ADD STREAM BUFFER6/20/221"= 10'EJG/TMMIDV/GKD05/30/22RENTON, WA 98059 13701 SE MAY VALLEY RD WOLDE RESIDENCE PARCEL NO. 3424059113 MATCH LINE - SEE SHEET 2NW4SW4SE4NE4INDEXING INFORMATION1/41/4SECTION:TOWNSHIP:RANGE:COUNTY:SESW3424N05E, W.M.KING ATTACHMENT 4 HEC-RAS Model Provided as a separate digital attachment