US Army Corps of Engineers
Honolulu District

Ala Wai Flood Risk Management Project

The Ala Wai Canal Flood Risk Management Project completed the Feasibility Stage in December 2017 when the Chief of Engineers for the US Army Corps of Engineers submitted the Chief's Report to Congress.  The Record of Decision for the Environmental Impact Statement was signed by the Assistant Secretary of the Army for Civil Works in September, 2018 and was transmitted to the state of Hawaii for adoption.  The Project was funded for Construction by the Bi-Partisan Budget Act of 2018 under the Long-term Disaster Recovery Investment Program with an authorized cost of $345,076,000.  The program allows for single phase design and construction, as well as a deferred payment option to expedite funding and execution of projects.

The Honolulu District is negotiating project partnership with the state of Hawaii and the City and County of Honolulu.  The team is currently in the early stages of Exploration and Survey to refine data gathered during the Feasibility phase and develop the feasibility designs into full designs

HAWAII DEPARTMENT OF LAND AND NATURAL RESOURCES AND

CITY AND COUNTY OF HONOLULU DEPARTMENT OF DESIGN AND CONSTRUCTION

 

DAVID Y. IGE
GOVERNOR

KIRK CALDWELL
MAYOR

 

TOWN HALL MEETING FOR ALA WAI FLOOD RISK MANAGEMENT PROJECT

 

FOR IMMEDIATE RELEASE

Wednesday, March 13, 2019

HONOLULU – The Hawaii Department of Land and Natural Resources and the City and County of Honolulu Department of Design and Construction, in partnership with the United States Army Corps of Engineers, have scheduled a town hall meeting on the Ala Wai Flood Risk Management Project.

The meeting will be held at Mānoa Valley District Park, Gymnasium No. 1, on Tuesday, March 19, from 6:30 p.m. to 8:30 p.m. The presentation portion of the program will take place from 6:30 p.m. to 7:15 p.m., with a question and answer session to follow.

The agenda will consist of presentations about the need for resiliency on the island of O‘ahu in the face of climate change, emergency preparedness, and an update on the project.

Members of the public who have questions about the Ala Wai Flood Risk Management Project, or want to find out more information, are encouraged to attend. There is no cost to enter the gymnasium and free parking is available at Mānoa Valley District Park.

If you require special assistance, auxiliary aid and/or service to participate in this town hall meeting (i.e. sign language interpreter; interpreter for language other than English, or wheelchair accessibility), please contact James Kurata of DLNR at least four days prior to Tuesday, March 19 by calling (808) 587-0227.

For questions or comments about the Ala Wai Flood Risk Management Project, please contact the United States Army Corps of Engineers at (808) 835-4026, or email at AlaWaiFloodProject@usace.army.mil. Information about the project is also available at the following website: https://www.poh.usace.army.mil/Missions/Civil-Works/Civil-Works-Projects/Ala-Wai-Flood-Risk-Management-Project/

Background

The Ala Wai Flood Risk Management Project completed the Feasibility Stage in December 2017 when the Chief of Engineers for the US Army Corps of Engineers submitted the Chief's Report to Congress. The Record of Decision for the Environmental Impact Statement was signed by the Assistant Secretary of the Army for Civil Works in September of 2018 and was transmitted to the state of Hawaii for adoption. The Project was funded for Construction by the Bi-Partisan Budget Act of 2018 under the Long-term Disaster Recovery Investment Program with an authorized cost of $345,076,000. The program allows for single phase design and construction, as well as a deferred payment option to expedite funding and execution of projects.

The team is currently in the early stages of Exploration and Survey to refine data gathered during the Feasibility phase, and to develop the feasibility designs into full designs.

Contacts:

Dino Buchanan, U.S. Army Corps of Engineers (808) 835-4003

Dan Dennison, Department of Land and Natural Resources (808) 587-0396

Andrew Pereira, City and County of Honolulu, (808) 768-5824

 

 

  • The U.S. Army Corps of Engineers (USACE) Honolulu District three-day Ala Wai Flood Risk Mitigation Project Design Charrette concluded in Honolulu Oct. 11, 2018 with stakeholders from the governor’s office, mayor’s office, state of Hawaii Department of Land and Natural Resources, as well as key technical experts from the USACE enterprise (Seattle District, New Orleans District, USACE Contracting Enterprise, and Risk Management Center) attending.
  • Honolulu District is currently negotiating particular terms of the Partnership Agreement with potential local non-Federal Sponsors (state of Hawaii and City and County of Honolulu). The project is to be cost-shared proportionately.
  • Recent flood damage done by April 2018’s intense rainfall on Kauai and Oahu, followed by Hurricane Lane’s more than 52 inches of rain on the island of Hawaii in four days, showcases the potential for extreme rain events in the future.
  • Project features include the following eleven individual structural elements and two non-structural components:
    • Six debris/detention basins in upper reaches of Makiki, Manoa, and Palolo streams
    • One in-stream debris catchment structure
    • Three multi-purpose detention basins
    • Flood Control Elements along the Ala Wai Canal
    • Flood warning system (non-structural)
    • Fish and wildlife mitigation (non-structural)
  • These are not just separate projects throughout Honolulu but are all integral pieces to an overall system that will reduce the risk to life, safety, and property for the communities in the Project Area and watershed.
  • Understanding the stakeholder plans, projects, processes; as well as the mutual respect for the historic, cultural, and economic significance of the Ala Wai Canal amongst all affected and interested stakeholders is key to advancing current design plans into a final product.
  • Stakeholders are HIGHLY encouraged and invited to participate throughout the entire design and construction to keep communication and collaboration moving in the direction of project completion.
  • By acquiring portions of land for the project we reduce the flooding risk and project footprint throughout other areas of the watershed community.
  • The USACE is strongly committed to working with our local and state partners and integrating public participation in the planning and construction of the Ala Wai FRM project to ensure public safety, quality of life, and enhance flood protection within the Ala Wai Watershed and Ala Wai Watershed FRM project areas.  We (USACE) do not do anything alone. We work in partnership with local/regional/state leaders, contractors, and affected public.
  •  Sea level Rise/Climate Change:  From USACE Adaptation Policy Statement: “It is the policy of USACE to integrate climate change preparedness and resilience planning and actions in all activities for the purpose of enhancing the resilience of our built and natural water-resource infrastructure and the effectiveness of our military support mission, and to reduce the potential vulnerabilities of that infrastructure and those missions to the effects of climate change and variability. USACE shall continue undertaking its climate change preparedness and resilience planning, in consultation with internal and external experts and with our districts, divisions, and Centers, and shall implement the results of that planning using the best available – and actionable – climate science and climate change information.”
  • USACE is on the forefront of federal construction agencies in integrating climate change (including sea- level change) into project planning and climate change adaptation into project design, construction and repair. Honolulu District works closely with State and local partners to provide a better understanding of (and ways to reduce) erosion, within our missions and authorities.
  • The watershed encompasses 19 square miles (mi2) (12,064 acres) and extends from the ridge of the Ko‘olau Mountains to the near-shore waters of Māmala Bay. It includes Makiki, Mānoa, and Pālolo streams, which flow to the Ala Wai Canal, a 2-mile-long, man-made waterway constructed during the 1920s to drain extensive coastal wetlands. This construction and subsequent draining allowed the development of the Waikīkī District.
  • Overall, the Ala Wai Watershed contains approximately 200,000 residents and is the most densely populated watershed in Hawai’i. The upper portion (approximately 7.5 mi2 or 40 percent of the watershed) is zoned as Conservation District, which is intended to protect natural and cultural resources, including the island’s aquifer. The remaining approximately 11 mi2 of the middle and lower watershed is heavily urbanized, supporting a high density of single-family residences, condominiums, hotels, and businesses, as well as many public and private schools, including the University of Hawai’i at Mānoa (UH), the largest university in the state. Within this urban footprint, the population density is one of the highest in the nation with 12.36 persons per urbanized acre (Fulton et al., 2001).
  • In addition to a variety of residential, commercial, and institutional development, the watershed also includes the Waikīkī District, a prime tourist destination that attracts more than 79,000 visitors per day. In large part because of the tourism industry, Waikīkī is the primary economic engine for the state, providing 7 percent of the gross state product, 7 percent of the civilian jobs in the state, and 9 percent of the state and county tax revenue (DBEDT, 2013).
  • It was created in 1921 by Walter F. Dillingham's Hawaiian Dredging Construction Company, and completed in 1928. When the city was issuing permits for new buildings in Waikīkī, they required builders to build above sea level. Dillingham sold the spoil he had dredged in creating the canal so builders could increase the elevation of the newly-created land. Original design plan was a second outlet continuing from the Kapahulu library through Kapiolani Park and outlet near Kaimana Beach (near Natatorium).  The canal was constructed to drain the Waikiki marshlands to allow development was and was not designed for major flood control.  Since its construction, the drainages have been highly urbanized causing urban pollutants and runoff increase to the Canal.  The Canal is owned and maintained by the state of Hawaii. The canal has been dredged at least three times, in 1967, 1978 and 2002.
  • While much of the urban areas technically belong to the City and County of Honolulu (primarily residential properties), and state land areas are limited to the University of Hawaii, public schools, and state highway, all these areas drain into a tributary/drainage that eventually flows into the canal.  So the problem starts in city jurisdictional areas into a state maintained area. There is no federal responsibility for the pollution problems.
  • Early on, and certainly after the 2004 Manoa flood, the UH Office of Emergency Management and their planners became very involved in the AWCP.  Their involvement waned after the UH decided to address flooding separately on campus (diversion walls, directing surface flows to Manoa stream).  USACE has given numerous talks at the UH Water Resources Research Center (WRRC), that includes faculty and students, on USACE processes and individual projects.  Also during this time, the former USACE-Honolulu District Civil Works chief advised a senior class of the UH Natural Resources and Environmental Management (NREM) School on USACE processes and provided tours of the proposed Ala Wai Canal Project areas.
  • Cost / Funding: In July 2018, Congress appropriated $345 million toward that effort. Non-federal sponsor cost share is approximately $125M. The benefit-cost ratio is approximately 3.68 to 1.
  • Federal Sponsor: U.S. Army Corps of Engineers (Local: Honolulu District)
  • Non-Federal Sponsor: Potential non-Federal sponsor are the state of Hawai’i DLNR, (Engineering Division) and the City and County of Honolulu (Department of Environmental Services)
  • Project duration: Approximately 5 years

Partnership Coordination: This is a project for the community made possible by the state and city and county. The U.S. Army Corps of Engineers, Hawaii State Department of Land and Natural Resources, and City & County of Honolulu have been working on a plan since 2001 to mitigate flooding in the Ala Wai Watershed in the event of a major storm.

  • A high risk of flooding exists within the Ala Wai Watershed due to aging and undersized flood conveyance infrastructure.  Based on the peak flows computed for the Flood Risk Feasibility study, it is estimated the Ala Wai Canal has the capacity to contain about a 20- to 10-percent annual chance exceedance (ACE) flood before overtopping the banks.  The risk of flooding is exacerbated by the flashy nature of the streams in the watershed, with heavy rains flowing downstream extremely quickly due to steep topography and relatively short stream systems.    The 1-percent ACE floodplain is the area that is inundated by a flood with a 1-percent chance (1 in 100) of occurring in any single year. These are also commonly referred to as the 100-year floodplain and 100-year flood (but does not necessarily mean that this degree of flooding occurs every 100 years). This definition also applies to floods of other magnitudes (e.g., a 20-year flood is a flood that has a 5-percent chance of occurring and, a 10-year flood has a 10-percent chance of occurring in any single year, respectively).
  • Flash-flooding conitions can materialize within an hour in the upper portion of the Ala Wai Watershed.
  • Army Corps of Engineers estimates a major flood in the watershed could damage 3,000 structures and cost more than $1.14 billion.
  • Repairs to the Waikiki area as the result of a 100-year flood event. An October 2004 rain storm flooded Manoa Valley, described as a 25-year event caused $85 million in damage.
  • The Ala Wai Canal topped its banks and caused flooding in Waikiki before — during storms in 1965 and 1967, as well as during the passage of Hurricane Iniki in 1992.
  • Hawai‘i streams are flashy by nature. Within the study area, rain often starts in the mountainous areas of the upper watershed, with little precipitation in the lower elevations. The peak flow rate from mountains to sea is approximately 30 minutes. Storms typically last for 24 hours or less. With the sudden nature of the flood events and the associated high velocities, floods within the watershed threaten life safety and may result in significant damages. Rarely does the watershed experience long periods of standing water from a flood event. When heavy rains do occur over multiple days, standing flood waters become a problem. Based on U.S. Army Corps of Engineers (USACE) hydrology and hydraulic modeling, the majority of the peak flow is from the Manoa Stream, with Palolo Stream being the second highest contributor and Makiki Stream the third.
  • The watershed’s highest elevation is about 3,000 feet, before dropping to 300 feet at valley floors and rolling to sea level — all over the span of about four miles. Given the combination of sheer slope, considerable rainfall — up to 150 inches a year in the Koolau Mountain Ridge — as well as the dense Waikiki population and growing climate-change concerns, the waterway is designated as “high risk” for flash flooding.

Ala Wai Watershed Overview

 

 

 

  

 

Full Size video

Ala Wai Watershed Overview

 

Photos

Contact Information

Civil & Public Works Branch
Building 230
Fort Shafter, HI  96858-5440
(808) 835-4026
 Jeffrey.A.Herzog@usace.army.mil