snoqualmie valley flooding booklet

7/28/2019 Snoqualmie Valley Flooding Booklet

http://slidepdf.com/reader/full/snoqualmie-valley-flooding-booklet 1/14

Snoqualmie Valley

Flood Guidebook!

!!!Jeremy Westlake - June, 12th 2013

Geology 106 Service Day Project



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



! 5!

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.



! 6!

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



! 9!

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



! 10!

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



! 11!

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

snoqualmie valley flooding booklet

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