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Alenaio Stream - Floodwall A, B - RB & Lined Channel (ASFA)
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Location City, County, and State of the levee system. Determined by the levee alignment location not the leveed area.
Hilo, Hawaii County, Hawaii
System ID Unique identifier code for the levee system using 10 or 12 numbers in length.
3205010101
Operation and Maintenance Organization Entity responsible for day-to-day management of the levee.
County of Hawaii, Department of Public Works
Floodplain Management Entities responsible for regulating activities that occur in areas prone to flooding.
FEMA Region 9
Oversight Organization Entity responsible for oversight of the levee and ensuring it is maintained.
USACE - Honolulu District
Last Assesment Date Last Risk Assessment or Formal Inspection.
7/7/2016
Levee Length Combine length of all the levee system features including the embankments, floodwalls, closures where they exist for this system.
Levee Length Graphic 0.273 Miles
Average Levee Height The average height of the levee system. The levee profile viewer on the mapping window will show the actual levee height values for the length of the levee if available.
Levee Height Graphic 5 Feet
Year Levee Constructed Year levee system was fully completed as a flood reduction project.
Timeline Graphic 1997
Summary General text description of the levee system with a summary of why the levee is there, and the benefits it provides.
The Alenaio Stream Flood Control Project (FCP) extends from Chong’s Bridge to the stream’s outlet at Waiolama Canal. The federally constructed project is now owned and operated by the County of Hawaii. Since completion of the original project in November 1997, the Alenaio Stream FCP has experienced several damaging flood events, including its flood of record flow (6,300 cfs) in November 2000. The project was designed to reduce flood risks for the 1-percent annual chance exceedance (100-year) flood event, which was estimated to be 7,200 cfs. In response to flood damages in 2000 and 2008, the project was repaired by USACE under the authority of Public Law 84-99. Damages included erosion, scour, and concrete damage of the channel invert and floodwall toe. The right bank levee system includes “Floodwall A” and “Floodwall B,” in addition to 1,790 feet of concrete channel. “Floodwall A” consists of a 365-foot concrete rubble masonry (CRM) floodwall ranging in height from 2.0 to 4.5 feet. “Floodwall B” consists of a 480-foot long concrete cast-in-place (CIP) floodwall with a maximum height of approximately 10 feet that ties into a 150-foot earthen levee reinforced with mortared riprap. Since the project was built, nearly $75 million in property damages have been prevented.
Performance & Condition General text description of the historical and anticipated performance of the levee, the people and property benefitting from the levee and who may be at risk of flooding, and actions to address areas of concern.
Although the Alenaio Stream FCP has a history of being well maintained by the County of Hawaii, there are still residual risks that could lead to a breach or overtopping somewhere in the levee system. Past performance of the project during major flood events, such as the record-setting flood in November 2000, indicates that overtopping is likely to first occur over the channel walls upstream of the Kapiolani Street Bridge. “Floodwall B” has a history of localized erosion occurring at the base of the floodwall during large events that has since been repaired, but both floodwalls are still anticipated to perform as designed (to withstand the 1% annual chance exceedance event). In the event that one or more of the floodwalls experiences a breach failure, people and properties immediately adjacent to the floodwalls would be at the greatest risk. The initially high and fast-moving water at the breach location could be life threatening and cause significant property damage. As the water spreads into the leveed area, however, it would slow down rapidly and cause shallow flooding (typically less than 1 foot in height) to streets and low-lying areas as it flows toward the ocean. The State and County have extensively planned their response to a variety of emergencies, including a multi-layered system to alert residents and non-residents of their risk of imminent flooding. There is no site-specific emergency response plan, however, which would reduce the overall risk for this specific levee system. The leveed area includes residential, commercial, and public structures. A flood would likely have social consequences to the Hilo community, negatively impact the regional economy, and may disrupt law enforcement services located within the inundated area.
Flooding Hazard
Historic Loading by Percentage of Height
Info Bubble Representative loading associated with historical flood information as a percentage of the levee height or overtopping.
Loading by Percentage of Heigth Graphic Background 0 Occurrences 0 Occurrences 0 Occurrences 1 Occurrences