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Home My WebLink AboutCOW 2026-03-23 Item 4A - Briefing - December 2025 Flood Recap & Levee StatusCity of Tukwila Thomas McLeod, Mayor Marty Wine, City Administrator AGENDA BILL ITEM NO. 4.A. Agenda Item December 2025 Flood Response and Levee Briefing Sponsor Jen Tetazin, Public Works Director Sherry Edquid, Project Manager Legislative History March 23, 2026 Committee of the Whole Recommended Motion El Discussion Only ❑ Action Requested EXECUTIVE SUMMARY This is an informational briefing to City Council with a status update regarding the impact, initial response and recovery efforts following the December 2025 flood event. BACKGROUND Heavy rain during the week of December 8-11 pushed rivers to record floods and with abnormally high snow -levels and unseasonably warm temperatures much of the precipitation fell as rain onto already saturated soils. Five of the county's six major rivers surged to Phase 4 (severe flooding) including Green River which hit 12,000 cfs on December 9th. During this period of time infrastructure within Tukwila faced critical stress and/or failure: 1. Tukwila 205 - Segale Sinkhole 2. Minkler P-17 Pump Station 3. West Valley Highway Stormwater Outfall 4. Desimone Levee Breach 5. Fort Dent Pump Station #19 The City's Maintenance and Operations team implemented 24/7 flood patrol operations from December 9th through 22nd. The County also had their own flood patrol. ATTACHMENTS Presentation 4 December 2025 Flood Recap and Levee Briefing Jen Tetatzin, PE, PMP Public Works Director and Sherry Edqu'd, CFM Levee and Floodplains Project Manager The City of opportunity, the community of choice. 5 Agenda • Background • 2025 Flood Recap • LeveeStatus • Future Planning 160,1,-AN, VI:A.014,0d FiCAU61,1,q Majcz 4eact NIA sit Estuary ershed Grun River Subwatershed King County Department of 'hiattu70 Re,f,ourre5 and, Pardo Water and Land Resturces Division Green River Watershed a City of Tukwila Middle Green River u bwateesited Rrodured Dc-part-rent of Natura erl Park:. tdfi,ffl Corum ur4catQn &W4th Unit Fglu Maw. 0.60S9 Upper GreenRiver Sulavatergheci 7 Green / Duwamish River and the Tukwila Levee System Green River - Shared Responsibility City of Tukwila and Neighbor Cities • Public Works is local sponsor for federal levee, local partner for county levees • Parks & Recreation operates and maintains trails, parks, and golf course along river. King County • Maintains County -owned levees, parks, and trails • Multiple departments are involved KC Flood Control District separate entity State Agencies • Provide resources and regulatory roles Federal Agencies and Tribal Nations • Provide resources and regulatory roles • Federal treaty rights and significant cultural resources along the river system \1908i 8 Flood Management Partners -Federal FEMA US Army Corps of Engineers® Federal Emergency Management Agency's (FEMA) mission is to help people and communities before, during and after disasters. This includes managing floodplains by mapping flood risks (Flood Insurance Rate Maps), establishing minimum floodplain management standards for community development, and administering the National Flood Insurance Program (NFIP). U.S. Army Corps of Engineers (USACE) acts as a primary federal agency managing flood risks by designing, inspecting, and rehabilitating federal flood control levees. During flood events they can provide direct assistance in flood fighting. Regionally, they operate and manage the Howard Hanson Dam, among others. 9 Flood Management Partners -State DEPARTMENT OF ECOLOGY State of Washington Department of Ecology provides technical assistance and grants to reduce flood risks; protect lives and properties within floodplains; and improve habitat and the essential environmental functions that floodplains offer. Washington Emergency Management Division leads and coordinates mitigation, preparedness, response and recovery in the state to minimize the impact of disasters and emergencies on the people, property, environment and economy. 10 Flood Management Partners - County KING COUNTY FLOOD CONTROL King County Water and Land Resources Division King County Flood Control District (KCFCD) is a special purpose district which implements flood risk reduction policies and projects to protect life and property while advancing various benefits including equity and social justice, sustainable livelihoods, habitat protection, salmon recovery, recreation and resilient communities. King County Water and Land Resources Division (WLRD) is the service provider to the KCFCD who is responsible for carrying out programs and projects that reduce flood damages and protect public safety for the major river systems. They also operate the County's flood warning center during flood events. 11 Flood Management Partners - Cities • Rivers and flooding are not bound by jurisdictional boundaries • Managing flood risk across the entire river system requires coordination • Mutual aid is essential during emergency responses WASH NGTON 12 December 2025 Flood Event Historic Event • Historic flows and longest flood in memory • King County Flood Warning Center operated 24/7 from Dec 8-30 • City's Levee Patrol operated 24/7 from Dec 9-22 • City's Emergency Operation Center (EOC) was activated from Dec 15 —Jan 2 • Emergency Management provided an After -Action Improvement Plan to you separately 14 Regional Context Howard Hanson Reservoir 520 161 203 isaquah 169 Hobart Auburn Gage KING COUNTY Howard Hanson Dam 0 Source:Wash.State*tofEcoQgy 2— , 5bffulap PIERCE COLIN Y Top c Dam ,„ 1228' Top .{.7207:c6d, 1188' 12/12/202s Streambed 1050' 11181111111111111116 15 Regional Context Howard Hanson Dam and USGS Auburn Gauge U.S Army Corps of Engineers (USACE) Dam • Began operation in 1961 • Primary function is flood protection • Located near headwaters of the Green River • Reservoir captures 220 square miles Operated by U.S. Geological Service • Began operating in 1952 • Located on left bank 1.2 miles east of Auburn • USACE manages reservoir releases using this gauge and tries to keep flows below 12,000 cfs 16 Flood Phase Thresholds for Green River Phase 1 2 3 4 22100 2.100H 100 Auburn Gauge Reading (Green River Mile 32) 5,000 cfs 7,000 cfs 9,000 cfs 12,000 cfs Flow 1,160.0 Monday Nov 3 1,2 45 prn Flood Frequency Routine, wet season high flow Frequent, peak flow exceeded in 15 of last 20 years Less frequent, median estimate of 2-year flood Infrequent, 10- to 100-year flood events 0 z Observed 1,230 cfe 125 Oi 30 PM TASOMP;Po,'" High Flow History - Auburn Gauge • Nov 1990 11,500 cfs • Dec 1995 11,200 cfs • Feb 1996 12,400 cfs • Jan 2006 12,200 cfs — Recent -- Forecast • Jan 2009 11,100 cfs • Jan 2011 10,400 cfs • Dec 2015 10,900 cfs • Feb 2020 11,700 cfs • Dec 2025 12,100 cfs o 10124125 10/29125 11[3725 11/13125 17 County -wide Impacts • Six river systems experienced Severe Flooding • Cedar • Green • Snoqualmie • South Fork Skykomish • White • Issaquah • 16 emergency repairs during and immediately following the flood • Approximately 32% of all KC FCD facilities were damaged • Green River accounted for 29% of County -wide flood facility damage Source: King County briefing to KCFCD Executive Committee 3/4/2026 18 Levee Damage Assessment Results Cedar River Green River Issaquah & Haider Creeks Raging River Sammamish River Snoqualmie River South Fork Skykomish and Miller Rivers Tait River White and Gre n niter Rivers Number of Damaged Facilities 41 47 27 1 1* 26 5 0 15 Total Facilities in River 67 141 41 19 1 195 8 14 22 Percentage of River's Facilities Damaged 66 63% 0% 68% Percentage Damage County -Wide 25% 29% 17% Source: King County briefing to KCFCD Executive Committee 3/4/2026 • 46 inspection teams • 163 facilities damaged • Total of $71.1M in damages submitted • Uses an approximate unit rate $3,750 per LF 19 Tukwila Flood Infrastructure Status Update 16 West Valley Highway Stormwater Outfall • Blockage and design of flap gate allowed river to flow into stormwater system • Lanes closed to provide room for pumps and crews to work • Bypass systems constructed with available hoses, pumps, plugs • Required 24/7 monitoring and maintenance 21 Fort Dent Pump Station #19 • City's stormwater pump station was overwhelmed and had to be augmented with temporary pumps • Bypass systems were constructed with available hoses, pumps, plugs • Required 24-hr monitoring and maintenance • Star Fire sports operations and facilities threatened 22 Minkler P 17 Pump Station • County stormwater facility was at max capacity • 1972 pump station was overwhelmed • 24-hr foot patrols needed due to compromised condition of levee • Emergency replacement of two pumps needed to keep up with flood conditions • City's public works operations and maintenance facility threatened (sewer, water, street, and traffic parts/equip) • Critical equipment was relocated to the Fleet and Facilities campus to ensure continuity of operations Fund Normal flow Flood 6IIInnth dinchnme In II. Crean Miner Station 17 hydraulic profile 23 Gilliam Creek at 66th Ave S • Inlet armored by City summer 2025 • Project protected culvert and road substructure • Repair held during recent flood event 24 Aki rScri't V>, Tukwila 205 Levee System • 4.4-mile levee located on the left bank of the Green River protecting Tukwila Urban Center • Federally recognized levee, eligible for PL84-99 emergency assistance (USACE) • The City is the designated local sponsor • King County provides the majority of technical and administrative support for the City • Pursuing levee certification with FEMA • Certification would ensure that FEMA does not map properties behind the levee in the 100-year floodplain Strom gp..#., 25 Tukwila 205 - Segale Sinkhole • Sinkhole opened up Dec 11th • Repaired same night by King County • Governor, King County and cities held press conference on site Dec 12th • County completed long-term repair at the end of December • No immediate action needed • Larger Tukwila 205 system has been assessed as "minimally acceptable" 26 Tukwila 205 - Gaco-Mitchell Segale Levee • Located behind Mitchell Moving and across river from Briscoe Park USACE completed repairs in 2024 and 2025 under PL 84-99 • Repairs held during recent flood event • Additional work planned to provide 500-year level of protection, but significant real estate challenges exist. • $1.9M total budgeted (KC FCD) • $1.1M spent to date 27 Tukwila 205 - Gunter Floodwall Located in Prato District • Project programmed to set back levee and provide 500-year level of protection (18,800 cfs) • $15.8M budgeted (KC FCD) • Status: On hold due to real estate negotiations .4.44 44.4 .44 1,.044 4-11, 4.1 Calf Wt... 4ti4 28 Fort Dent Levee • Damage occurred in 2019 and 2020 at the north end of the park • Construction planned summer 2026 • Project goal is to repair and revegetate the levee and improve aquatic and riparian habitat • Green River Trail will be permanently relocated landward • Existing trees were removed in February to avoid nesting season Relocate een Rive "1r41.1>a d,Ti ii,, to' Ex, Acss R+ad Ex, Access ad' Rem e Ex T:s. Extend slope setba' rah;;' 29 Desimone Levee • Feb 2020: Damaged during flood event, PL 84-99 assistance requested • Dec 2024: Design completed • Jan 2025: USACE canceled project due to real estate delays • Dec 9, 2026: Contingency Plan implemented • Dec 15, 2026: Levee breach • Jan 2026: New PL 84-99 request submitted • Current Status: KC FCD construction funds programmed for 2028-2029 30 Future Planning KC FCD Annual Budget Process • Advisory and Joint Basin Technical Committees meet throughout the Spring and Summer • Advisory Committee makes recommendation by August 31st • Final budget developed and voted upon in fall/early winter • Mid -year budget adjustment in early summer, primarily technical updates to actual expenses River System Snoqualmie-South Fork Skykomish Cedar-Sammamish Green-Duwamsh White District -wide Total 2026 CIP Budget $20,520,667 0,286,365 $8,760,980 43,228,256 $107,590,863 6-Year CIP Total >258,505,652 $95,008,367 374,730,270 $15,274,148 ►248,1 00,682 $991,619,119 32 King County Flood Control District CIP Tukwila Projects (2026 -2031) Project Name Desimone Levee Major Repair Fort Dent Levee 2020 Repair G. am Creek Fish Barrier Removal Tukwila 205 Levee Gunter Floodwall Tukwila 205 Levee Ratolo Floodwall Tukwila 205 Levee Gaco-Segale Segment Total 2026 Budget 97,049 $755,278 00,000 $0 $38,011 $2,490,338 6-Year Budget $59,717,853 $3,099,643 $300,000 $15,840,935 ,450,000 $67,515 $80,475,946 33 Planning Studies District — Lower Green River Corridor Flood Hazard Management Plan District — Lower Green River Study to Examine Downstream Impacts City — Lower Green Riverfront Master Plan PROJECT IMPLEMENTATION Report will examine downstream impacts from Howard Hanson Dam related to the December 2025 flood including rapid drawdown, increases in the amount and duration of water releases, modeling, and mitigation options. Plan will develop a strategic city vision for future flood protection projects that focus on integrative and multi - benefit approach serving as the city blueprint. 34 The City of opportunity, the community of choice. 35