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

Sponsor R t NEPA

100% federally funded

Request NEPA

Purpose dependent Purpose dependent 100% non-federally funded

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19981998 Ala Wai Canal Flood Control Project initiated

Reconnaissance study for

Project History20002000

20022002

Reconnaissance study for ecosystem restoration; added to

Ala Wai Flood Control Project Cost Share agreement signed with DLNR, renamed Ala Wai20022002

20042004

with DLNR, renamed Ala Wai Watershed ProjectManoaManoa FloodFlood

Ala Wai Watershed Project

20062006

Ala Wai Watershed Project expanded to include upper watershed

NRCS funded to identify20082008

20102010

NRCS Manoa Technical Study incorporated into Ala Wai

NRCS funded to identify actions to reduce flooding in Manoa

20102010

20122012

Watershed Project Analysis of baseline conditions completed

Rescoping of remainder of feasibility study

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feasibility study20142014

Anticipated issuance of Final Feasibility Study and EIS

Anticipated issuance of Draft Feasibility Study and EIS

Project ObjectiveReduce riverine flood hazards to property and life safety in the Ala Waiwatershed, including:

Improving waterImproving water conveyance; Using environmentally

t i bl d i f fl dsustainable design for flood risk management features, where practicable; andIntegrating non-structural approaches, where practicable

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100-Year FloodplainFloodplain

(Existing Conditions)

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Estimated Damages•3,000+ properties in modeled floodplain for the 1% annual chance flood (100-year event)

•Estimated property damages ~$397 million (2013 price level)

•Life safety risk (~54 000•Life safety risk ( 54,000 residents, ~85,000 students/ workers, ~79,000 Waikiki visitors in existing floodplainvisitors in existing floodplain

•Flooding of surface streets, impacting emergency access

•Impacts to critical infrastructure (e.g., power, telecommunications, sewer,

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water)

Alternatives Formulation Process

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Variations based on further analysis

and refinement

Criteria Used in Alternative iFormulation Process

T h i l f ibilit Fl d i k d tiTechnical feasibilityImplementation costO&

Flood risk reductionLife safety risk reductionO&M requirements

Cost-effectiveness

reductionCommunity resilienceE i t l i tAvailability of land

Acceptability

Environmental impactArchaeological/cultural impactSocial fairness impact

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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

Inundation areaGenerally < 1 acre, drains in ~9-12 hours (1% chance storm)

O&M requirements

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qSediment/debris removal Vegetation clearing

Waihi Stream Detention Basin (Manoa)

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Conceptual Renderings of

DetentionDetention Basins

Waiakeakua Stream (Manoa)

Pukele Stream (Palolo)

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Conceptual Renderings of

DetentionDetention Basins

Woodlawn Ditch (Manoa) Makiki Stream

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Debris Catchment

Debris catchment structure

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

Project Manager, USACEj g ,808-835-4032

athline.m.clark@usace.army.mil

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