By Dino W. Buchanan, Honolulu District Public Affairs
HONOLULU, Hawaii (Oct. 17, 2018) -- 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 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, proposing a way forward with construction of the $345 million project.
“An opportunity to execute a project of this magnitude does not occur every day, so it’s important for us to have everyone gain a common understanding of the project, from Congressional authorization and funding through local real estate policies,” said Ala Wai Flood Risk Mitigation Project Manager Jeff Herzog. “It’s also important to get expectations and perspectives presented with everyone in the same room. Communication and collaboration between the stakeholders and Corps enterprise will be the key element to the successful execution of a project this size.”
During the charrette participants were given tours of upper and lower watershed locations where retention basins and debris catchment areas are planned and also areas along the Ala Wai Canal where flood control features are planned.
Local stakeholders ranging from the City and County of Honolulu Department of Climate Change and Resiliency, City and County of Honolulu Department of Design and Construction, to the State of Hawaii Department of Land and Natural Resources Land Division, State of Hawaii Historic Preservation Division, and State of Hawaii Office of Planning participated to ensure understanding of the requirements and perspectives of the stakeholders. Enterprise personnel from USACE’s Seattle District, New Orleans District, USACE Contracting Enterprise, and Risk Management Center identified best practices, lessons learned and suggestions for how to execute the project.
“Having the Enterprise participate was invaluable,” Herzog said. “New Orleans District executed $14.6 billion in constructing the Hurricane Storm Damage Reduction System while working with the State of Louisiana from 2005 to 2011. Similarly, we are negotiating with the stakeholders to construct a Flood Control System here in Honolulu. These are not just separate projects throughout Honolulu but are all integral pieces to an overall system which will reduce the risk to life, safety, and property for the communities in the Project Area. New Orleans District didn’t accomplish that work alone - they used Engineers without Borders, engaged other USACE Districts. Honolulu District is planning to engage in a similar manner.”
The Ala Wai Watershed encompasses a drainage area of 16.2 square miles and is located on the southeastern side of the island of Oahu in urbanized Honolulu. The three major streams within the watershed include the Makiki, Manoa, and Palolo streams, all of which drains into the Ala Wai Canal. The Canal is a two-mile-long waterway constructed during the 1920s to drain extensive coastal wetlands, thus allowing development of the Waikiki district. 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 pegged as “high risk” for flash flooding. An October 2004 storm that flooded Manoa Valley, described as a 25-year event, caused $85 million in damage.
Honolulu District is currently negotiating particular terms of the Partnership Agreement with the stakeholders. The project is being funded under the Fiscal Year 2018 Emergency Supplemental and allocated $345 million for Pre-Construction Engineering & Design and construction to be cost-shared proportionately.
Project features include the following eleven individual structural elements and two non-structural components:
• Six debris/detention basins in upper reaches of Maikiki, 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)
“Having the City and County, and State participate in the design charrette helped to lay a foundation for future successes,” added Herzog. “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 the parties in the room is key to advancing current designs into a final product. They (stakeholders) will be encouraged and invited to participate throughout the entire design and construction to keep communication and collaboration moving in a direction of project completion.”
The proposed Ala Wai Flood Mitigation project will reduce riverine flood risks and help protect metropolitan Honolulu, the University of Hawaii, and Waikiki, Hawaii's economic center for tourism. The population at risk includes approximately 65,000 residents and an additional 200,000 transient visitors to the watershed daily (tourists, workers, students, etc.). The likelihood of flooding so severe that it encompasses all of Waikiki and the canal’s tributaries is approximately one percent (a 100-year event), with potential damage to 3,000 structures and requiring more than $1 billion in repairs. The construction of the Army Corps-led project would help protect Waikiki, the heart of Hawaii’s tourism industry and neighborhoods along the streams.