HomeMy WebLinkAboutEX07_BaseFloodElevationStudyMEMORANDUM
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
EXHIBIT 7
RECEIVED
PLANNING DIVISION
02/02/2024
AVanGordon
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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.
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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.
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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
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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.
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
ATTACHMENT 1
Effective Flood Insurance
Rate Map Information
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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
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DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
ATTACHMENT 2
Hydraulic Modeling Results
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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.
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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.
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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 ProfileSlight riseSlight riseProperty Boundary (Typ.)Leon Morse 13719 SE May Valley Rd Parcel #: 3424059026Lee Yi-Jen 13711 SE May Valley Rd Parcel #: 3424059109Elias Wolde 13703 SE May Valley Rd Parcel #: 3424059110Elias Wolde 13701 SE May Valley Rd Parcel #: 3424059113Chaffey Brothers LLC Parcel #: 3424059106DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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 SectionsDocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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.06.072DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
020406080100270272274276278280282284286288MayCrWolde Plan: PreProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 362Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.073DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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 SectionsDocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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.06.072DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
020406080100270272274276278280282284286MayCrWolde Plan: PostProjectConditionsRiver = MayCreek Reach = Reach 1 RS = 362Station (ft)Elevation (ft)LegendWS 100YrFloodGroundBank Sta.06.073DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
ATTACHMENT 3
Terrane Survey
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
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.KINGDocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC
ATTACHMENT 4
HEC-RAS Model
Provided as a separate
digital attachment
DocuSign Envelope ID: ABD8D32C-16ED-4293-9B4E-C0989EDCD6FC