The URL can be used to link to this page

Home My WebLink AboutTIS 2022-04-18 Item 2B - Discussion - Introduction to LeveesCity of Tukwila Allan Ekberg, Mayor Public Works Department - Hari Ponnekanti, Director/City, Engineer INFORMATIONAL MEMORANDUM TO: Transportation and Infrastructure Services Committee FROM: Hari Ponnekanti, Public Works Director/ City Engineer BY: Sherry Edquid, Project Manager CC: Mayor Allan Ekberg DATE: April 15, 2022 SUBJECT: Tukwila 205 Levee Certification Project Project No. 91341203 Introduction to Levees ISSUE Provide the Council with a general overview of levees within the City and an introduction to the Tukwila 205 Levee Certification Project. BACKGROUND Levees are manmade structures typically built parallel to a river designed to contain, control and/or divert floodwaters thereby reducing the risk from temporary flooding on the landward side. However, they do not eliminate flood risk altogether. In the Green-Duwamish watershed, an integral part in minimizing flood risk is the Howard A. Hanson Dam, which is located in the upper watershed, 21 miles upstream from the City of Auburn. The dam's primary purpose is to provide flood risk reduction in the winter and provide additional flow for fish in the summer and early fall. Flood risk reduction is accomplished by capturing water runoff from the upper watershed and releasing it under controlled conditions. Both the dam and the levee system work in conjunction to reduce flooding in the lower Green River to a fraction of what it once was. The dam was formerly thought to control water up to a 500 -year flood event but recently the Army Corps of Engineers (Corps) revised the dam capacity to just 140 -year flood event. DISCUSSION There are several levees along the Green River and within the City that provide various levels of flood protection. The King County Flood Control District (District), as a special purpose government, assists the City in managing, maintaining, funding, and oversight of these levees. The levee certification process is expected to lead to additional levee repair projects that are required to meet the certification criteria. Certification is valid for a 10 -year period. A levee assessment has been completed for the Tukwila 205 Levee. The study found approximately 80% of the levee could not be certified in its current condition and will require repair or reconstruction. The City and the District are working jointly to maintain Federal Emergency Management Agency (FEMA) certification along with making levee improvements to withstand 500 -year flood events, all while integrating habitat restoration, flood storage, and recreation. 17 The City has petitioned the King County Flood Control District to make levee improvements to upgrade the 205 Levee to provide a minimum of 100 -year level of protection, and where construction is needed, construct to a 500 -year level of protection. KCFCD has agreed to begin design of several projects in 2020, which will take approximately 15 years to complete and will require extensive work with the City of Tukwila and property owners. FINANCIAL IMPACT The overall construction costs of the Tukwila 205 Levee is estimated to be around $200 million and the majority of that is funded by the King County Flood Control District (KCFCD). RECOMMENDATION Discussion only. Attachments: 2021 CIP pg. 86 Levees Presentation Tukwila Levees 18 CITY OF TUKWILA CAPITAL PROJECT SUMMARY 2021 to 2026 PROJECT: Tukwila 205 Levee Certification Project No. 91341203 DESCRIPTION: Reconstruct the Tukwila 205 Levee to provide 500 -year level of flood protection and obtain levee certification. The US Army Corps of Engineers no longer provides levee certification services to federally authorized levees. The existing certification expired in August 2013. Certification is required for the Federal Emergency JUSTIFICATION: Management Agency to accreditate the levee system as providing a 100 -year level of flood protection. A study of the Tukwila 205 Levee found approximately 80% of the levee could not be certified in its current condition and will require repair or reconstruction. STATUS: A levee assessment has been completed. MAINT. IMPACT: Certification process is expected to lead to additional levee repair projects that are required to meet the certification criteria. Certification is valid for a 10 -year period. The City has petitioned the King County Flood Control District to make levee improvements to upgrade the 205 Levee to provide a minimum of 100 -year level of protection, and where construction is needed, construct to a COMMENT: 500 -year level of protection. KCFCD has agreed to begin design of several projects in 2020, which will take approximately 15 years to complete and will require extensive work with the City of Tukwila and property owners. A full time employee to monitor this project will be required and listed in 2021 through 2026. FINANCIAL Through Estimated (in $000's) 2019 2020 2021 2022 2023 2024 2025 2026 BEYOND TOTAL EXPENSES Certification Phase I 350 350 Certification Phase II 229 500 500 500 500 500 500 3,229 Design 0 Const. Mgmt. 150 150 150 150 600 Construction 0 TOTAL EXPENSES 579 0 500 500 650 650 650 650 0 4,179 FUND SOURCES KC Flood Control 236 150 150 150 150 836 Proposed Grants 0 Mitigation Actual 0 Mitigation Expected 0 Utility Revenue 343 0 500 500 500 500 500 500 0 3,343 TOTAL SOURCES 579 0 500 500 650 650 650 650 0 4,179 Project Location: Entire System 2021 - 2026 Capital Improvement Program 86 19 Introduction to Levees Presentation April 18, 2022 Agenda • Watershed Overview • History • Howard A. Hanson Dam • Levee Vocabulary • Flood Hazard Management • Flood Control Basics • Levees in Tukwila • Future Floodplain Management • Flooding Notification 2) Green-Duwamish River Watershed Duwamish Estuary Subwatershed URIEN ti RE NTO NORM PAR DY SEATAC Middle Green River Subwaters hed WASHINGTON STATE DER WAY Marine Nearshore Subwatershed Lower Green River Subwatershed ACK DIAMOND' F. R Howard Hanson Darn • Howard Horton Rt envatr River Major Road WRIA 9 Subwatershed Boundary WRIA 9 Boundary 1110111111111 Open Water Unincorporated King County Upper Green River Subwatershed 0 2 4 6 Miles AAarch 2009 King County Department of Natural Resources and Parks 0903_W9MAPpptai LPRE z.:mew V 14401:4.14- I.4 Historical Flooding November 22 & 23, 1959 Flood Event Howard A. Hanson Dam Definition of a Levee Manmade structure(s) typically built parallel to a river designed to contain, control and/or divert floodwaters thereby reducing the risk from temporary flooding on the landward side. However, they do not eliminate flood risk altogether. 5C4 YR. .1, 1±u S C L 100 YR WSEL 4' CARTH BERM OVERBUILD °SCALLOP` I I.OoD MEAN DALLY WSEL 1C.S''[ APPROXIMATE DIIWM,I; WSEL 12.4' LAUI;ICIIABLE ROCK TOE PRDTECT1CIt PAVED WALKING PATH EXISTING GRADE if kou.TIE RIPnkI, I1 HABITAT 12:.37..1',E RECREATION - `- - - �'-EARTHEN LEVEE TERRESTRIAL HAS I'TAT PASSI VE RECREATION, .PPRC?RI'•1ATE 125' lfr'".1:111T. CDRR!DOR 25 How do we measure floods on the Green River? • i Flood Phase Thresholds for Green River Phase Green River at Auburn Gage (RM 32) * � Flood Frequency 1 5,000 cfs Routine wet season high flow 2** 7,000 cfs Peak flow exceeded 15 of last 20 years 3 9,000 cfs Median estimate of 2 -year flood 4 12,000 cfs 10- to 100 -year flood (2006 and 2009 floods) * Auburn - US Geological Services Gauge https://waterdata.usgs.gov/monitoring- location/12113000/#parameterCode=00060&period=P7D ** King County Flood Warning Center Opens 26 Levee Failure Rates Over 30 -Year Period * Likelihood of Levee E di Over a 30 -Year Residential Mortgage LEVEL OF FLOOD RROTECTION 100 year 200 yea• 300 ye 400!rt+1r 500 year 0% 5% 1 15% 20% 25% SOURCE NatLona f Committee on Lease Saifit°a= Figure 1. Likelihood of flooding from a 100 to 500 year -flood event during a 30 -year period. (From the National committee on Levee Safety). 27 Why do levees fail? Height deficiency Erosion 165.1•••• Stability 1 -- Stability Seepage 29 Desimone Levee Seepage occurring and water pooling on landward side of the levee. February 7, 2020 Damage Occurred —11,700 CFS Lei King County Department of Natural PPesources and Parks For Official Use Only 1-2O1?.aa2O17Gr 4.6 Miles Long Tukwila 205 Levee • Levee last built/modified in 1964 • Levee is currently not certified nor accredited by FEMA due to: • Embankment and foundation stability • Steep riverward slopes • Not meeting freeboard elevation 30 Lower Green River Corridor Flood Hazard Management Plan 22,000 people living in Over 100,000 jobs the Valley and floodplain Major transportation routes and public facilities, including hospitals and schools Threatened salmon and other aquatic animals Over $37 million in income from businesses of all sizes, including companies like Boeing, Starbucks, REI, IKEA, and Blue Origin Farming The 2nd -largest industrial park on the West Coast and the 3rd - largest warehouse and distribution center in the country Parks, trails, and natural areas 31 Be Prepared F https://green2.kingcounty.goy/floodalertsystem/ or download the Flood Warning App BE FLOOD READY YOUR GUIDE TO FLOOD PREPAREDNESS IN KING COUNTY https://your.kingcounty.goy/dnrp/librarv/water-and- land/flooding/Flood-Brochures/2021-2022-flood- brochures/KCFCD Mailer2021 County Final.pdf L41 King County King County Flood Warning Center and Information Line: Connect to a representative during a flood and year-round access to automated flood phase information, river gage readings, and emergency sandbag distribution locations. 206-296-8200 or 800-945-9263 32 5.5 • reen/Duwamish River .. \y A` GD1 -2017 Levee/Revetment 1/10 River Mile King County Outfall City Boundary • h 0 400 I I I Feet LKing County Department of Natural Resources and Parks For Official Use Only S '108th -St 56• ••ph s' ° _ e ittl e i�r -�� Tukwila ll'�ll�l'1�� N • 0) -, h 1 - v cQ c) v � e rs, O. 9AcRd 1 N 0 N S 111th PI n � • V k-'-'1:-- ...-4:' it-- '- 1� NI* . . :.411g Rda rjri U ` •6.4 4. Q -, •i✓ x��r , . Access �a 6.8 - ^ -p 6.7 A S 116th way ' ;6 Gateway Lowest Rai b+ , _ rr , . - c0. . . ane•.mn.nl ...r.....I I k' , #0. /- "%; .. r.a' I. 1....1 ::" IU..•t. �. •.e f • . t� GD1-2017.ai/2017Greenl iverFloodMaps/GreenRiver/1709_6• p8m_FloodPatrolBooks ver Tri 6.9 • • 6.8 w Gate �ay Lowest w J • 6.9 w • • S 115th St S 115th St Interurban South "" s 11 • S 119th B rg • • i - .Q Tukwila - Green/Duwamish River GD2-2017 Levee/Revetment 1/10 River Mile King County Outfall City Boundary N 0 400 I I I Feet \ . .. I. King County Department of Natural Resources and Parks For Official Use Only • Offillnal a a) 0 ViApillifr Pit S 124th St GD2-2017.ai/2017GreenRiverFloodMaps/GreenRiver/ 1Z09_6908m_FloodPatrolBooks UIiF. -C ,p _iL N' ew k istrkii /� 1 V ) ,4 4 4' —co a) Q imr S 124th St Banchero o� `Right' •8 Codlga 34 Green/Duwamish River GD3-2017 Levee/Revetment 1/10 River Mile King County Outfall City Boundary N 0 400 I I I Feet rzy 0 L.41 King County Department of Natural Resources and Parks For Official Use Only Of S j"�6 • `ham' �� h ti. o N N CO S *�1D 0 N GD3-2017.aQ01.7GreenRiverFloodMaps/GreenRiver/1709_6908m_FloodPatrolBooks Green/Duwamish River GD4-2017 Levee/Revetment Primary Access 1/10 River Mile King County Outfall City Boundary im King County Department of Natural Resources and Parks For Official Use Only Black River Pump Station enton Pedestrian Walk S 149th St GD4-2017.ai/27Gre 908m F1podPatrolBooks. 36 -570 (.2 00 sRQ' Green/Duwamish River GD5 - 2017 r 1 S153rdSt" M hilirr 4v. f ^? Tukwila 4. 31 CD Levee/Revetment Primary Access Point 1/10 River Mile Tukwilla Outfall King County Outfall Evacuation Route City Boundary 0 400 I I I Feet IV King County Department of Natural Resources and Parks For Official Use Only S 156th St Tukwl Evans Black Dr Q II 41 P_ 1=1 lir C cc 2 a) .c GD5-20117.-a /2017GreenRiverFloodM reenRiver/1709 6908m FloodPatrolBooks _Bakj Tukwila lell -Zr.e.ck Dr Green/Duwamish River GD6-2017 Levee/Revetment Primary Access Point Secondary Access Point 1/10 River Mile • Tukwilla Outfall King County Outfall Approximate Olympic Pipeline Crossing City Boundary N 0 400 Feet King County Department of Natural Resources and Parks For Official Use Only Ren P-17 Pump Station •': �pS if.i.r.;:f-;..l r. mss_..,` 7.ai/2017Green9iverFloodMaps/ GreenRiver/1709_6908m_FloodPa 38 Green/Duwamish River GD7-2017 Levee/Revetment Primary Access Point 1/10 River Mile aid Tukwilla Outfall King County Outfall Evacuation Route City Boundary N Inland Dr Feet 400 I. King County Department of Natural Resources and Parks For Official Use Only wile S 18' rid St _. l` Y 7-2017.ai/2017Gree 8m FloodPatrolBooks 411 Green/Duwamish River GD8-2017 Levee/Revetment Primary Access Point Secondary Access Point 1/10 River Mile Kent Outfall King County Outfall City Boundary 0 400 Feet u King County Department of Natural Resources and Parks For Official Use Only Tukwila Ra "Et 1 n ' a!' air e 1. 709 6 oodMa /G,teenRt', _ 908m_FloodPatrolBooks 40 'v1 Green/Duwamish River GD9 - 2017 Levee/Revetment Primary Access Point 1/10 River Mile Kent Outfall King County Outfall City Boundary u 0 400 I I I Feet I. � King County Department of Natural Resources and Parks For Official Use Only 16.9*\ LI\ Al \ til n� N O 0 LI '1 Pedestrian Walk S 20/1 th St 4 GD9-2017.ai/2017GreenRiverFloodMaps/Green River/1709_6908m_FloodPatrolBooks