Ala Wai Canal Project Flood Risk Management Project Open House Meetings Athline Clark Project Manager Civil and Public Works Branch U.S. Army Corps of Engineers Honolulu District Honolulu District May 20 and 21, 2014 US Army Corps of Engineers BUILDING STRONG ®
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Ala Wai Canal ProjectjFlood Risk Management Project
Open House Meetings
Athline ClarkProject ManagerCivil and Public Works BranchU.S. Army Corps of EngineersHonolulu DistrictHonolulu District
May 20 and 21, 2014
US Army Corps of EngineersBUILDING STRONG®
Ala Wai Canal ProjectProject
Authority:Section 209 of the Rivers & Harbors Act of 1962
Non-Federal Sponsor:State of Hawaii (DLNRState of Hawaii (DLNR Engineering Division)
Key Partner:Cit d C t fCity and County of Honolulu (ENV)
Product:Integrated Feasibility Report and Environmental Impact Statement
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(EIS)2
Historical PerspectiveAla Wai Canal was built toAla Wai Canal was built to provide drainage, not for flood protection (estimated capacity for 10-percent chance flood)Non-systematic flood projects result in reduced capacityresult in reduced capacity
Aging and inadequate drainage infrastructuredrainage infrastructureMultiple flood events have overtopped Canal in past
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pp pcentury, resulting in property damage and loss of life
PROJECT DEVELOPMENT PROCESSPROJECT DEVELOPMENT PROCESS
Approaches/Tradeoffs Considered in Alternati es Formulation ProcessAlternatives Formulation Process
Approaches: Tradeoffs:Approaches:Attenuate water where the highest volume of peak flows occur upper Manoa
Tradeoffs:Potential issues with public acceptability of one measure over anotherflows occur – upper Manoa
and PaloloAttenuate water within
tl d l d
measure over anotherUse of the golf course and/or park space for d t ti i t tcurrently developed
portions of the watershedMaximize solutions where h j i f h fl d
detention versus impacts to forest reserve landsHolding large volumes of
i Mthe majority of the flood risk occurs – the lower watershed, including Waikiki
water in upper Manoa versus building higher levees in Waikiki
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Alt. 3A. 3(Conceptual)
F th l i d• Further analysis and refinement may result in variations
f lt tiof alternative
• Tentatively Selected Plan to be identifiedPlan to be identified from these variations
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Detention Basins (Mid to Upper Watershed)
Earthen berm across channel
20-24 feet highArch culvert (allows small storm flows to pass)Vegetation to be kept clear within 20’ perimeter around bermEmergency spillway (riprap)N t id d l t d dNot considered regulated damMitigation to be incorporated
8' wide concrete pad Steel posts (Up to 7' high), p ( p g ),spaced every 4' along concrete pad Excavation to allow high fl it ( tflows across site (at Innovation Center)Mitigation to be incorporated
O&M i tO&M requirementsDebris removal
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Manoa In-Stream Debris Catchment
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Ala Wai Canal FloodwallsWall / berm set back from existing walls
Up to 5’ feet highUp to 5 feet highFlap/slide gates and pump stations to prevent back flow via existing drainage featuresg gBridges and roadways to be maintained (possibly some impacts along Ala Wai Blvd)Recreational access to be maintained (design features to be determined)Aesthetic improvements may beAesthetic improvements may be added by non-federal sponsorImpacts to historic floodwalls to be considered, with mitigation
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20be considered, with mitigation as appropriate
Ala Wai Canal Floodwalls
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Conceptual Renderings ofRenderings of Ala Wai Canal
Floodwalls
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Detention Basins (Lower Watershed)Earthen berm around detention area
Up to 5 feet highUp to 5 feet highPassive drainage back into Ala Wai CanalSlide/sluice gates at HaustenSlide/sluice gates at HaustenBridge
Multi-purpose featuresDetention area currentlyDetention area currently floods in 1% chance stormRecreational activities to be maintained during non-flood gperiods
O&M requirementsSediment and debris removal
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23Slide/sluice gate maintenance (Hausten Ditch)
Ala Golf Course Detention Basin
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Hausten Ditch Detention Basin
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ConceptualConceptual Renderings of
i iDetention BasinsAla Wai Golf Course
Hausten Ditch
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Key Challenges and Opportunitiesy g ppChallenges:
Funding for future phases Opportunities:
Stakeholder support for g pof the project (both federal and local)No solution will eliminate
ppcontinued fundingFlood risk planning is a necessity now and in theNo solution will eliminate
all risk of floodingNon-federal sponsors are
necessity, now and in the futureSpecial area designation p
responsible for operations/maintenanceS
p gmay help resolve O&M constraintsP t ith kSome measures may
benefit from aesthetic improvements
Partner with key organizations to aesthetically improve
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flood measures27
Schedule to Complete Study
MILESTONE ANTICIPATED COMPLETION DATE
Public Review of Draft Feasibility Report Public Review of Draft Feasibility Report and Environmental Impact Statement (EIS) Fall 2014
Development of detailed design and cost for Wi t 2014 S i 2015
Development of detailed design and cost for Final Feasibility Study/EIS
Winter 2014 – Spring 2015
R l Fi l F ibilit R t/EIS F ll 2015Release Final Feasibility Report/EIS Fall 2015
Chief’s Report (USACE Recommendation Fall 2015
(to Congress) Fall 2015
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Questions?Q
For more information contact:For more information contact:Athline M. Clark