Authorization of Interlocal Agreement V,
Des Moines Creek Basin Plan
Presenter:
John Evered, Senior Manager
Aviation Environment & Sustainability
Item No: 8j_supp
Date of Meeting: December 10, 2024
Requested Action
Request Commission authorization for the Executive Director to
execute Interlocal Agreement (ILA) number V with the Cities of
Des Moines and SeaTac for continuation of the Des Moines Creek
Basin Plan Restoration Projects for a period of 20 years with a
financial contribution of $89,304 per year.
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History of Des Moines Creek Basin Plan ILA
• 1995: ILA I with Cities of Des Moines and SeaTac and King County to prepare a Basin
Plan for Des Moines Creek.
• 1997: Amendment to ILA I to include and additional task to develop pilot projects
and continue program.
• 1998: ILA II to prepare a Preliminary Design Report.
• 2000: ILA III with Cities of Des Moines and SeaTac and King County to continue
coordination.
• 2004: ILA IV with Cities of Des Moines and SeaTac, King County and Washington
Department of Transportation to construct a suite of projects and designate Port as
project manager for the Regional Detention Facility
.
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Des Moines Creek Basin Projects
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• Regional Detention Facility and By-Pass
– High flows are mitigated. High flows from Tyee are routed to NW Ponds for detention.
– Base flows are routed away from Des Moines Creek in by-pass. Overall flows to Des Moines Creek are
reduced.
– In-stream erosion in Des Moines Creek from high flows is reduced.
• Habitat Improvements
– Replacement of Marine View Drive culvert improved fish passage.
– Large wood and rock placement in Des Moines Creek increased channel and habitat complexity,
reduced and repaired areas of erosion, and reconnected floodplain-wetland habitats.
Basin Plan Projects – RDF and Habitat Improvements
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Des Moines Creek In-stream Project 2007 - 2012
Regional Detention Facility (RDF) Projects and
Elements
ILA V – Scope and Average Annual Costs*
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• Operations and Maintenance $54,813
• Invasive Vegetation Management $8,433
• Education and Outreach $7,267
• Assessment of Future Needs $10,000
• Replacement and Improvements $173,558
• Coordination, Monitoring and Administration $35,500
*Costs in 2024 dollars. Annual average of expected 20-year projected costs. Actual yearly costs will vary
depending task schedule and program needs
ILA V Future Annual Contributions *
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TOTALReplacement and Imp.O&M Fund
$89,304$66,978$22,326Port of Seattle
$110,739$83,054$27,685SeaTac
$39,957$22,968$9,989Des Moines
$240,000$180,000$60,000TOTAL
* Annual contributions may increase with inflation subject to Basin Committee approval.
Questions?
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ILA IV Construction Costs
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Project Costs Basin Committee Cost**
• Regional Detention Facility Project 12,848,064 12,848,064
• Stream Bypass Project 1,943,174 1,943,174
• Flow Augmentation Project * 540,370 135,093
• Habitat Restoration and Enhancement 938,848 157,200
• Marine View Drive Culvert Replacement 8,731,628 7,706,271
• Subtotal – Project-Specific Costs 25,002,084 22,789,802
• Other Non-Project Specific Cost 2,688,090 2,688,090
• Total Costs 27,690,174 25,477,892
* Flow Augmentation Project not completed.
** Basin Committee costs augmented by grants
