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7/28/2019 Snoqualmie Valley Flooding Booklet
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Snoqualmie Valley
Flood Guidebook!
!!!Jeremy Westlake - June, 12th 2013
Geology 106 Service Day Project
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Table of Contents!1 Introduction to Flooding in the Snoqualmie Valley
• Flood Related Facts
• Intro• Current Projects
o The Upper Snoqualmie Valley or River Residential
Flood Mitigation
o Middle Fork Snoqualmie Ricer Corridor
Management Plan
o Lower Valley Floodplain Management Actions
1
2
2
3
3
2 Flood Safety Information
3 Local Flood Phases
4 Flood Map: North Bend 7
5 Flood Maps: Snoqualmie 86 Additional Flood Maps 10
7 Flood Alert Information 10! About This Project!The following booklet is a guide to basic flooding and background
information in the Snoqualmie Valley, including the cities of North Bend
and Snoqualmie. Flood maps are provided for both cities, in addition to
references and links to FEMA maps for other cities as well.
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Chapter 1: Introduction to Flooding in the Snoqualmie Valley
Flood Related Facts
• There are about 8,000 properties located in a King County Floodplain
• River flooding has led to 12 presidential declared disasters in King Countysince 1990
• Even though local flooding most commonly occurs between November and
February, King County rivers have flooded in every month of the year exceptAugust
• The leading cause of flood related deaths is from motorists driving through
standing water or around barricades or road closure signs• Federal financial assistance is only available following a federal disaster
declaration• Most homeowners insurance policies do not cover flood damage
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Intro
The Snoqualmie Valley is a wide, low gradient floodplain mostly comprised ofagricultural lands with several smaller residential communities, such as the cities ofNorth Bend, Snoqualmie, Fall City, Carnation and Duvall. The mainstream
Snoqualmie River can be characterized by low velocities and a mild gradient, butstill causes substantial erosion. The Snoqualmie River is composed of three maintributaries which include the North Fork, South fork, and Middle Fork. The starts of therivers originate from the Cascade Mountain Range near North Bend and join near
Snoqualmie just above Snoqualmie Falls. After the falls, the river flows North throughrich farmland and meets the Skykomish river in Monroe to form the Snohomish River.
Flooding is commonly associated with damage to farms, houses, barns, and theroads that parallel or cross the mainstream Snoqualmie River. Damage is often dueto large areas of inundation along with localized erosion of outer river banks and
revetments, overtopping of flood protection levees, and road embankments.
Problems generally relate to constrictions where energy builds up and becomesconcentrated. One example is the Carnation Farm Road, where fill embanked
forces flood water through two small bridge openings. Both bridges were washed
out during the Thanksgiving flood of 1990 when two flood flows exceeded their
capacity.
Particularly in the later fall months, early snowfall in the mountains mixed with warm,melting rains creates conditions prone to cause flood events. Because the rivers thatcarry runoff out of this basin are located in steep valleys, floodwaters collect on the
flat valley floor where the communities are located. Most of the historic portions of
downtown Snoqualmie and the residential neighborhoods of North Bend lie withinthe floodplain of the Snoqualmie River. In the lower Snoqualmie valley, flooding due
to the flat topography and massive drainage basins that they reside in also regularlyimpacts towns like Carnation, Fall City and Duvall. It is very important for residentswho reside in the community to be prepared for the next flood event.
Current Projects:
The Upper Snoqualmie Valley or River Residential Flood Mitigation
The Snoqualmie Valley is the most flood prone community in the state of
Washington. The Upper Snoqualmie Valley Residential Flood Mitigation Projectprovides funding to mitigate flood impacts to local residents. The King County Water and Land Resource Division is partnering with the cities of North Bend andSnoqualmie to take a comprehensive approach to identifying hazards andmitigation needs in the community. An initial assessment of the community identified
315 homes, which have living space below the base flood level and 12 at homes atrisk from channel migration. The cost to mitigate these flood dangers is close to $32
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million. The goal of this project is to collaborate with the two cities to mitigate floodrisks for all identified properties mentioned above.
Middle Fork Snoqualmie River Corridor Management Plan
This project addresses the existing flood protection facilities along the lower fivemiles of the Middle Fork of the Snoqualmie River. Sections from Tanner to the NorthFork are relatively short and discontinuous. The plan will develop a corridor management plan that will lead to well informed, strategic approaches to
conducting flood hazard reduction projects in a way that optimizes expenditure ofpublic funds to reach flood safety and habitat protection. The Water and LandResources Development team is concerned about the impacts of flood hazards for
human safety along the Middle Fork and its adjacent floodplain which include floodwater inundation, swift water in floodways and channel migration hazards. Flow inexcess of 30,000 cubic feet per second have occurred three times since the 1960’s
and this reach being on the Middle Fork alluvial fan is dynamic with respect to
channel migration and frequently transports high volumes of sediment. The areaslevees do not contain flooding and have been subject to repetitive damagerequiring nonstop repairs. The goal of this project is to develop floodplain
management actions to address flood and erosion hazards and by doing so,avoiding or minimizing environmental impacts of channel migration hazardmanagement by implementing a capital improvement project that will reduce the
likelihood of emergency repairs needed due to flood events. Also to reduce longterms costs of flood hazard management by designing and implementing a stablebank that will not need repairs over the long run.
Lower Valley Floodplain Management Actions
King county’s river and floodplain management vision and strategies includeworking with partner’s valley wide to balance floodplain management goals withfarming and habitat needs in mind. In channel migration areas, they want to allowmore from for natural channel movement and increase capacity for floodwaters
and sediment through levee setbacks and voluntary acquisitions, and coordinatewith affected landowners. In the broader valley where flows are slower, they plan tocontinue to work with farmers to reduce flooding impacts. Outside the Tolt and
Raging alluvial fan areas, they plan to reduce flood impact on farming whileprotecting floodplain functions by elevating houses and barns.
Between 2006 and 2012, the King County Flood Plan accomplished the following:
• Technical and permitting help for 34 farm pads• Elevated two barns and twelve homes• Acquired 36 acres of land and 15 residencies to reduce flood hazards
• Repaired two levees after the November 2006 flood• Submitted a draft flood insurance study of the lower Snoqualmie river to the
federal emergency management agency, which is awaiting adoption
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The following are plans for 2013-2018:
• Balance King County’s interest in fish, farms, and flood safety• Build more farm pads and elevate more barns
• Study recent changes at Snoqualmie Falls
• Elevate homes and farm buildings and acquire homes in high erosionlocations
• Study flood and erosion reduction measures to see how they could affectwood accumulation and recreational safety. Study the type and extent of
recreational use in the Lower Snoqualmie River
• Acquire at risk structures in the Fall City area• Support monitoring and adaptive management of restoration projects on
mainstream Snoqualmie downstream of Carnation• Repair the Sinnema Quaale Upper Revetment, the Winkelman Revetment,
and the Dutchman Road Revetment
• Conduct channel mitigation mapping of the Lower Snoqualmie River
• Continue gravel monitoring and implement gravel management actions ifappropriate in the river segments below the Tolt and Raging Rivers
Chapter 2: Flood Safety Information
One of the most important things you can do to protect your home and family
before a flood is to purchase flood insurance. If you do not already have floodinsurance, talk to a representative. Homeowners’ insurance policies do not cover damage from floods. Because the Snoqualmie participates in the National Flood
Insurance Program, you can purchase separate flood insurance policies. Somepeople have purchased flood insurance because the bank requires it beforepurchasing a home or obtaining a home loan.
Your home and property can be protected from floods in many ways. Elevatinghomes has been the most frequently used method of protecting homes inSnoqualmie. The use of water resistant materials, structural reinforcement to
withstand water pressure, and placement of mechanical elements in the upper parts of the building are a few other ways to flood proof your home.
A map of the lower Snoqualmie River flood hazard management plan can be
seen here: http://your.kingcounty.gov/dnrp/library/water-and-
land/flooding/flood-hazard-mgmt-plan-update-2012/basin-strategy-fact-
sheets/1211_2797lowerSNOQ.pdf
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The following chart lists flood safety tips:
Preparing for a Flood When a Flood Comes After a Flood
1. Learn the safest
evacuation routefrom your home.
2. Keep a portable
radio, emergencycooking equipment,and flashlights on
hand.3. Have emergency
food, water, andmedical supplies on
hand.
4. Store valuables inhigh areas.
5. Install check valvesin sewer traps toprevent floodwater
from backing upinto your house.
6. Keep sandbags,plywood, plastic
sheeting, and other
materials to protectproperty.
7. Move to a safe area
before you looseaccess. Stay put tillrescue teams come.
8. Do not drive over aflooded road or around barricades.
9. Do not walk throughfloodwaters.
10. Stay away frompower lines and
electrical wires.
Electrical currentscan travel through
water.11. Turn off all utilities at
the main power
switch in your houseand close the maingas valve.
12. Look before you
step. The groundand floors after aflood may be
covered withdebris.
13. Be alert for gas
leaks. Use aflashlight to searchfor damage.
14. Keep electricity off
until an electrical
has inspected your system for safety.
Chapter 3: Local Flood Phases
The following table shows response in relation to phase thresholds:
Phase PhaseThreshold
Response
1 6,000 CFS County personnel are put on alert and preparations are
made to open the flood warning center
2 12,000 CFS The flood warning center is opened. Staff at the center monitor river gauges and flood conditions around the
clock. Gage information is updated on an hourly schedule
3 20,000 CFS Flood investigation crews are sent out to monitor floodcontrol facilities such as levees
4 38,000 CFS Warnings issued to police and fire departments, schools,and other agencies. The public is informed through newsand the media.
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The following tables shows roads susceptible of flooding in relation to phase
thresholds:
Phase PhaseThreshold
Description Roads that may overtopand close
1 6,000 CFS Internal Alert
2 12,000 CFS Lowland Flooding Neal Rd, SE Reinig Rd, WestSnoqualmie River Rd NE,
SnoqualmieMeadowbrook Rd, MillPond Rd
3 20,000 CFS Flooding of varied depthsoccurs in the entireSnoqualmie Valley
(Those listed above) FallCity-Carnation Rd, Tolt HillRd, Ne 124th St
4 38,000 CFS Some residential areas mayexperience dangerous high
velocities and flooding ofhomes
(Those listed above)Woodinville-Duvall Rd, SR
203 between Duvall andCarnation, Moon ValleyRd, South Fork Rd
Chapter 4: North Bend Flood Map
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Chapter 5: Snoqualmie Flood Maps
Legend (above)
Gray: 100 Year Flood
Blue: 200 Year Flood
To view interactive maps from FEMA visit this link:https://msc.fema.gov/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&catalogId=10001&langId
=-
1&categoryId=12001&parent_category_rn=12001&type=CAT_MAPPANEL&stateId=13054&countyId=15930&c
ommunityId=359909&stateName=WASHINGTON&countyName=KING+COUNTY&communityName=N.BEND%
2CCTY%2FKING+CO&dfirm_kit_id=&future=false&dfirmCatId=null&isCountySelected=&isCommSelected=&us
erType=G&urlUserType=G&sfc=0&cat_state=13054&cat_county=15930&cat_community=359909
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To view interactive maps from FEMA visit this link:https://msc.fema.gov/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&catalogId=100
01&langId=-
1&categoryId=12001&parent_category_rn=12001&type=CAT_MAPPANEL&stateId=13054&countyId
=15930&communityId=359914&stateName=WASHINGTON&countyName=KING+COUNTY&commun
ityName=SNOQUALMIE%2CCTY%2FKING+CO&dfirm_kit_id=&future=false&dfirmCatId=null&isCounty
Selected=&isCommSelected=&userType=G&urlUserType=G&sfc=0&cat_state=13054&cat_county=1
5930&cat_community=359914
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Chapter 6: Additional Flood Maps
Carnation:
https://msc.fema.gov/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&
catalogId=10001&langId=-1&categoryId=12001&parent_category_rn=12001&type=CAT_MAPPANEL&stateId=1
3054&countyId=15930&communityId=359901&stateName=WASHINGTON&countyName=KING+COUNTY&communityName=CARNATION%2CCTY%2FKING+CO&dfirm_kit_id=&future=false&dfirmCatId=null&isCountySelected=&isCommSelected=&userType=G&urlUserType=G&sfc=0&cat_state=13054&cat_county=15930&cat_community=
359901
Duvall:
https://msc.fema.gov/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&
catalogId=10001&langId=-1&categoryId=12001&parent_category_rn=12001&type=CAT_MAPPANEL&stateId=13054&countyId=15930&communityId=360096&stateName=WASHINGTON&countyName=KING+COUNTY&communityName=DUVALL%2CTWN%2FKING+CO&dfirm_kit_id=&future=false&dfirmCatId=null&isCountySelected=&isCommSelected=&userType=
G&urlUserType=G&sfc=0&cat_state=13054&cat_county=15930&cat_community=360096
FEMA Database for other Communities:
https://msc.fema.gov/webapp/wcs/stores/servlet/CategoryDisplay?storeId=10001&catalogId=10001&langId=-1&categoryId=12001&parent_category_rn=12001&type=1&stateId=13054&countyId=15930&communityId=359901&stateName=WASHINGTON&countyName=KING+CO
UNTY&communityName=CARNATION%2CCTY%2FKING+CO&dfirm_kit_id=&future=false&dfirmCatId=null&isCountySelected=1&isCommSelected=1&userType=G&urlUserType=G&sfc=0&cat_state=13054&cat_county=15930&cat_community=360096
Chapter 7: Flood Alert Information
Sign up to receive flood alerts!https://green.kingcounty.gov/FloodAlertSystem/default.aspx
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The following links provide information for several tributaries on the Snoqualmie
River, such as discharge rates:
Directory of all Snoqualmie River Flooding Information:
Includes stages of river, discharge (CFS), and flow change.
http://green.kingcounty.gov/rivergagedata/gage-data.aspx?r=snoqualmie
North Fork http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12142000
Middle Fork http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12141300
South Fork http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12143400
Near Snoqualmie http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12144500
Near Carnation http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12149000
Near Duvall http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12150400
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Works Cited
• http://green.kingcounty.gov/rivergagedata/gage-data.aspx?r=snoqualmie • http://www.kingcounty.gov/environment/wlr/sections-programs/river-
floodplain-section/capital-projects/upper-snoq-res-flood-mit.aspx
• http://www.ci.snoqualmie.wa.us/DesktopModules/Bring2mind/DMX/Download.aspx?Command=Core_Download&EntryId=7118&PortalId=0&TabId=273
• http://www.fema.gov/mitigationbp/brief.do?mitssId=6730 • http://www.kingcounty.gov/environment/wlr/sections-programs/river-
floodplain-section/capital-projects/mid-fork-snoq-corridor.aspx
• http://your.kingcounty.gov/dnrp/library/water-and-land/flooding/flood-hazard-mgmt-plan-update-2012/basin-strategy-fact-
sheets/1211_2797lowerSNOQ.pdf • http://www.co.snohomish.wa.us/documents/Departments/Public_Works/Surf
aceWaterManagement/Flooding/Snoskyreport.pdf
• http://green.kingcounty.gov/rivergagedata/gage-data.aspx?r=snoqualmie