Flood Hazard Assessment.pdfED MC CUTI11", IN) E � a PS
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July 28, 2014
Ms. Christy Dopp
Sundquist Homes, a Family of Companies
16108 Ash Way, Suite 201
Lynnwood, WA 98087
Re: Shoreshire Plat — :sots 6 and 7
Lake Ballinger Flood Hazard Assessment
Dear Ms. Dopp:
99:5 171 9(%V.:,GNNUE SE
R=N 10GN, OVA °; 80,,,59
(4V5) 271-5734
I've completed a flood hazard assessment for Lots 6 and 7 within the Shoreshire Plat
located off 243`d Place SW in Edmonds. This assessment meets the requirements of
Edmonds City Code 23.70.020 for special studies and reports.
The subject properties are located on the west shore of Lake Ballinger and are in all area
mapped by FEMA as a Zone A flood hazard area (Attachment A). Zone A areas have a
one percent annual chance of flooding. Because Zone A flood areas do not have a
FEMA -approved flood study, no depths or base flood elevations are shown within these
zones on the FEMA map.
I understand that new single-family structures will be constructed on Lots 6 and 7. The
proposed finished floor elevations of the structures are as follows:
® Lot 6: 288.23 feet NAVD 88
,, Lot 7: 288.33 feet NAVD 88
The City of Edmonds Building Department has adopted an operational policy to adopt a
base flood elevation of Lake Ballinger. The City has adopted a base flood elevation
(BFE) of 286.14 feet NAVD 88 for the lake (Figures I and 2). This elevation is based on
the highest observed water level in the lake, which occurred during a storm in January
1997.
Hydrologic studies for Lake Ballinger have been conducted as part of past basin and
flood studies for the City of Edmonds and the City of Lake Forest Park (Aqua. Terra, June
Ms. Christy Dopp
Page 2
July 28, 2014
1999; Clear Creek Solutions, June 2008; Clear Creek Solutions, January 2009; Otak,
December 2009). None of the studies have resulted in a base flood elevation for the lake
that has been approved by FEMA. Based on HSP -F hydrologic modeling, the elevations
of the lake have been predicted to be 284.14 feet NAVD 881 for the 10 -year, 284.90 feet
NAVD 88 for the 50 -year, and 285.19 feet NAVD 88 for the 100 -year flood elevation
(Clear Creek Solutions, June 2008). I could not find any reference to the estimated return
period of the January 1997 storm that resulted in an observed peak flood elevation that is
higher than the 100 -year flood elevation predicted by Clear Creek Solutions.
Stormwater System
Stormwater from the roofs of the proposed structures on Lots 6 and 7 (Figures 1 and 2)
will be collected and dispersed in gravel -filled trenches adjacent to the lake's shoreline.
The surface elevations of the trenches are at about the same elevation as the City's
operational policy BFE. Stormwater from the trenches is designed to sheet flow through a
Category IV wetland and its buffer and then to the edge Lake Ballinger. This dispersion
design is appropriate in consideration of gentle site topography and the presence of the
adjacent wetland. During lower lake levels, Stormwater from the lot roofs will be
dispersed from the trenches through the wetland to help sustain its hydrology. During
higher lake levels, stormwater from the dispersion trenches will still have a direct flow
path to the lake.
A stormwater vault and filter cartridge system to manage runoff from the plat's entry
road have been approved by the City and constructed. The vault is located at the east end
of 243`d Place SW, between Lot 6 and Lot 7. The outfall pipe from the proposed
stormwater vault discharges to the edge of the lake. In my opinion, in conveying
stormwater from the developed area of the site to the lake, the vault stormwater system
provides a suitable flood flow path on the site.
Recommendations
The applicant must follow local building code requirements in construction of the new
structure. I recommend the following flood control related measures, provided they are
not in conflict with any of the City's building requirements:
® The finished floor elevation of the proposed structure on the project site must be a
minimum of 1 foot above the City's adopted operational policy BFE of 286.14
feet NAVD 88. Given the lack of an approved FEMA flood study, I recommend
constructing the finished floor for the new structure two feet above the City's
' The original report cites these elevations using a vertical datum of NGVD29. The following conversion
was used: NAVD 88 = NGVD 29 + 3.60
Ms. Christy Dopp
Page 3
July 28, 2014
adopted BFE. Under this recommendation, the finished floors of Lots 6 and 7
would not be lower than El. 288.14 feet NAVD 88.
Selecting this finished floor elevation would help protect against uncertainty in
the adopted BFE. In addition, a conservative selection of the finished floor
elevation would help protect the structure against the potential effects of wind
generated waves. For instance, the wind fetch across the lake from the northeast is
a distance of approximately 2,250 feet. Assuming a 30 mph wind velocity across
the lake from the northeast, a wave height of 0.8 feet could develop as a result of
the wind (Washington State Department of Ecology, 1993).
If any portion of the structure is to be located below the BFE, the structure must
be designed and constructed to resist flotation, collapse, and lateral movement
when subjected to base flooding conditions. All materials installed below the base
flood elevation must be flood resistant materials, such as concrete and corrosion
resistant metals
Vents are required in any enclosed space below the BFE not designed to resist
hydrostatic forces to relieve hydrostatic pressure on the structure. A minimum of
one (1) square inch of vent area is required for each square foot of enclosed space.
Vents must be installed on a minimum of two sides of the structure, with the
bottom of the vent within one (1) foot of the exterior adjacent grade and the top of
the vent no higher than the BFE. Vents may be equipped with screens or louvers
which allow for the automatic entry and exit of floodwaters.
All machinery and equipment should be elevated above the BFE or be designed,
constructed and installed to prevent floodwaters from entering or accumulating
within its components.
Edward J. McCarthy, Ph.D., P.E.
Ms. Christy Dopp
Page 4
July 28, 2014
References
City of Edmonds, June 2011. Building Department Operation Policy 062011 — Flood
Plain Elevation of Lake Ballinger.
Clear Creek Solutions Inc., 2008. Lake Ballinger Lake Level and Outlet Study. Prepared
for the City of Edmonds.
Hammond, Collier & Wade Livingstone Associates and Aqua Terra Consultants, 1999,
McAleer and Lyon Creeks Drainage Basin Study. Prepared for the City of Lake
Forest Park.
Otak, 2009. Flood Reduction Planning Study Lyon Creek/McAleer Creek Drainage
Basins. Prepared for the City of Lake Forest Park.
Washington State Department of Ecology, 1993. Dam Safety Guidelines- Part IV Dam
Design and Construction. Water Resources Program — Dam Safety Office.
Olympia, Wash.
Attachment A. FEMA Flood Map
U.S. DEPARTMENT OF HOMELAND SECURITY ELEVATION CERTIFICATE
FEDERAL EMERGENCY MANAGEMENT AGENCY
National Flood Insurance Program IMPORTANT: Follow the instructions on pages 1-9.
OMB No. 1660-0008
Expiration Date: July 31, 2015
SECTION A - PROPERTY INFORMATION FOR INSURANCE COMPANY USE
Al. Building Owner's Name Ardsley Homes, LLC Policy Number:
A2. Buildin Street Address (including Apt., Unit, Suite, and/or Bldg. No.) or P.O. Route and Box No. Company NAIL Number:
7534 - 243rd PL SW
City Edmonds State WA ZIP Code 98026
A3. Property Description (Lot and Block Numbers, Tax Parcel Number, Legal Description, etc.)
Lot 6 - plat of Shoreshire, as recorded under Snohomish County Auditor's File No. 201407165001
A4. Building Use (e.g., Residential, Non -Residential, Addition, Accessory, etc.) Residential
A5. Latitude/Longitude: Lat. 47 7788° Long. -122.3335' Horizontal Datum: ❑ NAD 1927 ® NAD 1983
A6. Attach at least 2 photographs of the building if the Certificate is being used to obtain flood insurance.
A7. Building Diagram Number
A8. For a building with a crawlspace or enclosure(s): A9. For a building with an attached garage:
a) Square footage of crawlspace or enclosure(s) sq ft a) Square footage of attached garage sq ft
b) Number of permanent flood openings in the crawlspace b) Number of permanent flood openings in the attached garage
or enclosure(s) within 1.0 foot above adjacent grade within 1.0 foot above adjacent grade
c) Total net area of flood openings in A8.b sq in c) Total net area of flood openings in A9.b sq in
d) Engineered flood openings? ❑ Yes ❑ No d) Engineered flood openings? ❑ Yes ❑ No
SECTION B - FLOOD INSURANCE RATE MAP (FIRM) INFORMATION
B1. NFIP Community Name & Community Number
B2. County Name
Charles A. Richardson
B3. State
Citv of Edmonds 530163
Snohomish
Address
12606 - 82nd Ave, Iq
WA
B4. Map/Panel Number
B5. Suffix
66. FIRM Index Date
B7. FIRM Panel Effective/
B8. Flood Zones)
B9. Base Flood Elevation(s) (Zone
Revised Date
AO, use base flood depth)
53061C / 1315
E
11/08/1999
11/08/1999
A
286.14 ft
810. Indicate the source of the Base Flood Elevation (BFE) data or base flood depth entered in Item B9:
❑ AS Profile ❑ FIRM N Community Determined ❑ Other/Source:
Bll. Indicate elevation datum used for BFE in Item B9: ❑ NGVD 1929 R NAVD 1988 ❑ Other/Source:
812. Is the building located in a Coastal Barrier Resources System (CBRS) area or Otherwise Protected Area (OPA)?
Designation Date: / / ❑ CBRS ❑ OPA
❑ Yes N No
Cl. Building elevations are based on: ® Construction Drawings* ❑ Building Under Construction* ❑ Finished Construction
*A new Elevation Certificate will be required when construction of the building is complete.
C2. Elevations - Zones Al -A30, AE, AH, A (with BFE), VE, V1 -V30, V (with BFE), AR, AR/A, AR/AE, AR/A1-A30, AR/AH, AR/A0. Complete Items
C2.a-h below according to the building diagram specified in Item A7. In Puerto Rico only, enter meters.
Benchmark Utilized: WCCS SURVEY DATABASE Pt. ID 175 Vertical Datum: NAVD 88
Indicate elevation datum used for the elevations in items a) through h) below. ❑ NGVD 1929 ® NAVD 1988 ❑ Other/Source:
Datum used for building elevations must be the same as that used for the BFE. Check the measurement used.
a) Top of bottom floor (including basement, crawlspace, or enclosure floor) 288. 89 ® feet ❑ meters
b) Top of the next higher floor 414 89 R feet ❑ meters
c) Bottom of the lowest horizontal structural member (V Zones only) ❑ feet ❑ meters
d) Attached garage (top of slab) 287 93 ® feet ❑ meters
e) Lowest elevation of machinery or equipment servicing the building 289. 43 N feet ❑ meters
(Describe type of equipment and location in Comments)
f) Lowest adjacent (finished) grade next to building (LAG) 287 , 35 N feet ❑ meters
g) Highest adjacent (finished) grade next to building (HAG) 287 , 35 N feet ❑ meters
h) Lowest adjacent grade at lowest elevation of deck or stairs, including 287 , 35 N feet ❑ meters
structural support
SECTION D - SURVEYOR, ENGINEER, OR ARCHITECT CERTIFICATION
This certification is to be signed and sealed by a land surveyor, engineer, or architect authorized by law to certify elevation
information. I certify that the information on this Certificate represents my best efforts to interpret the data available.
I understand that any false statement may be punishable by fine or imprisonment under 18 U.S. Code, Section 1001.
❑ Check here if comments are provided on back of form. Were latitude and longitude in Section A provided by a
❑ Check here if attachments. licensed land surveyor? ® Yes ❑ No
Certifier's Name
License Number
29291
Charles A. Richardson
Title
Land Surveyor
Company Name
Summit Surveying Inc.
Address
12606 - 82nd Ave, Iq
City
Kirkland
State
WA
I ZIP Code
198034
Signature
Date
Telephone
814-8487
FEMA Form 086-433 (Revised 7/12) See reverse side for continuation.
Replaces all previous editions.
U.S, DEPARTMENT OF HOMELAND SECURITY ELEVATION CERTIFICATEOMB No. 1660-0008
FEDERAL EMERGENCY MANAGEMENT AGENCY Expiration Date: July 31, 2015
National Flood Insurance Program IMPORTANT: Follow the instructions on pages 1-9.
SECTION A ® PROPERTY INFORMATION FOR INSURANCE COMPANY USE
Al. Building Owner's Name Ardsley Homes, LLC Policy Number:
A2. Building Street Address (including Apt., Unit, Suite, and/or Bldg. No.) or P0. Route and Box No. Company MAIC Number:
7532 - 243rd PL SW
City Edmonds State WA ZIP Code 98026
A3. Property Description (Lot and Block Numbers, Tax Parcel Number, Legal Description, etc.)
Lot 7 - plat of Shoreshire, as recorded under Snohomish County Auditor's File No. 201407165001
A4. Building Use (e.g., Residential, Non -Residential, Addition, Accessory, etc.) Residential
A5. Latitude/ Longitude: Lat. 47 7790' Long. -122.3334° Horizontal Datum: ❑ NAD 1927 ® NAD 1983
A6. Attach at least 2 photographs of the building if the Certificate is being used to obtain flood insurance.
A7. Building Diagram Number
A8. For a building with a crawlspace or enclosure(s): A9. For a building with an attached garage:
a) Square footage of crawlspace or enclosure(s) sq ft a) Square footage of attached garage sq it
b) Number of permanent flood openings in the crawlspace b) Number of permanent flood openings in the attached garage
or enclosure(s) within 1.0 foot above adjacent grade within 1.0 foot above adjacent grade
c) Total net area of flood openings in A8.b sq in c) Total net area of flood openings in A9.b sq in
d) Engineered flood openings? ❑ Yes ❑ No d) Engineered flood openings? ❑ Yes ❑ No
SECTION B ® FLOOD INSURANCE RATE MAP (FIRM) INFORMATION
B1. NAP Community Name & Community Number
B2. County Name
62
B3. State
Citv of Edmonds 530163
Snohomish
414
WA
B4. Map/Panel Number
B5. Suffix
B6. FIRM Index Date
B7. FIRM Panel Effective/
88. Flood Zone(s)
B9. Base Flood Elevation(s) (Zone
❑ meters
d) Attached garage (top of slab)
287
Revised Date
® feet
AO. use base flood depth)
53061C / 1315
E
11/08/1999
11/08/1999
A
286.14 ft
BIO. Indicate the source of the Base Flood Elevation (BFE) data or base flood depth entered in Item B9:
❑ FIS Profile ❑ FIRM ® Community Determined ❑ Other/Source:
B11. Indicate elevation datum used for BFE in Item 139: ❑ NGVD 1929 ® NAVD 1988 ❑ Other/Source:
B12. Is the building located in a Coastal Barrier Resources System (CBRS) area or Otherwise Protected Area (OPA)? ❑ Yes ®No
Designation Date: / / ❑ CBRS ❑ OPA
SECTION C ® BUILDING ELEVATION INFORMATION (SURVEY REQUIRED)
C1. Building elevations are based on: ® Construction Drawings* ❑ Building Under Constructions ❑ Finished Construction
sA new Elevation Certificate will be required when construction of the building is complete.
C2. Elevations - Zones Al -A30, AE, AH, A (with BFE), VE, V1 -V30, V (with BFE), AR, AR/A, AR/AE, AR/A1-A30, AR/AH, AR/A0. Complete Items
C2.a-h below according to the building diagram specified in Item A7. In Puerto Rico only, enter meters.
Benchmark Utilized: WCCS SURVEY DATABASE Pt. ID 175 Vertical Datum: NAVD 88
Indicate elevation datum used for the elevations in items a) through h) below. ❑ NGVD 1929 N NAVD 1988 ❑ Other/Source:
Datum used for building elevations roust be the same as that used for the BFE. Check the measurement used.
a) Top of bottom floor (including basement, crawlspace, or enclosure floor)
288.
62
® feet
❑ meters
b) Top of the next higher floor
414
_ 62
® feet
❑ meters
c) Bottom of the lowest horizontal structural member (V Zones only)
Date
Telephone
(425) 814-8487
❑ feet
❑ meters
d) Attached garage (top of slab)
287
66
® feet
❑ meters
e) Lowest elevation of machinery or equipment servicing the building
289.
16
® feet
❑ meters
(Describe type of equipment and location in Comments)
0 Lowest adjacent (finished) grade next to building (LAG)
287.
08
® feet
❑ meters
g) Highest adjacent (finished) grade next to building (HAG)
287.
08
® feet
❑ meters
Ill Lowest adjacent grade at lowest elevation of deck or stairs, including
287.
08
® feet
❑ meters
structural support
SECTION D ® SURVEYOR, ENGINEER, OR ARCHITECT CERTIFICATION
This certification is to be signed and sealed by a land surveyor, engineer, or architect authorized by law to certify elevation
information. I certify that the information on this Certificate represents my best efforts to interpret the data available.
I understand that any false statement may be punishable by fine or imprisonment tinder 18 U.S. Code, Section 1001.
❑ Check here if comments are provided on back of form. Were latitude and longitude in Section A provided by a
❑ Check here if attachments. licensed land surveyor? ® Yes ❑ No
Certifier's Name
License Number
29291
I
Charles A. Richardson
Title
Land Surveyor
Company Name
Summit Surveying Inc.
Address
12606 - 82nd Ave. NE
City
Kirkland
State 1
WA
ZIP Code
198034
Signature
Date
Telephone
(425) 814-8487
7- 1-
FEMA Form 086-0-33 (Revised 7/12) See reverse side for continuation. Replaces all previous editions.
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