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A dam is an artificial barrier constructed across a stream channel or a man-made basin for the purpose of storing, controlling or diverting water. Dams typically are constructed of earth, rock, concrete or mine tailings. The area directly behind the dam where water is impounded or stored is referred to as a reservoir.
A dam failure is the partial or total collapse, breach or other failure of a dam that causes flooding downstream. Dam failures can result from natural events such as a flood event, earthquakes or landslides, human-induced events such as improper maintenance, or a combination of both. In the event of a dam failure, the people, property and infrastructure downstream could be subject to devastating damage.
The potential for catastrophic flooding due to dam failures led to passage of the National Dam Safety Act (Public Law 92-367). The National Dam Safety Program requires a periodic engineering analysis of every major dam in the country. The goal of this effort, implemented by the U.S. Army Corps of Engineers (USACE) with monitoring from FEMA, is to identify and mitigate the risk of dam failure so as to protect the lives and property of the public.
In Hawai’i, over 80% of dams and reservoirs were built before 1940 to support sugarcane plantations. Today, in addition to agriculture, dams and reservoirs within the state provide storage for drinking water, flood control, hydropower, and recreation. The Hawai’i Dam Safety Program was created in 1987 by the state legislature and was followed up in 1989 with the Hawai’i Administrative Rules, which were set up by the Hawai’i Department of Land and Natural Resources (DLNR). Only dams of a certain size criteria (height and volume) are regulated by the State’s Dam and Reservoir Safety Program. Regulated dams are identified as having artificial barriers which are 25 feet or more in height or have an impounding capacity of 50 acre-feet (approximately 17 million gallons) or more.
Dam failures can occur due to a variety of reasons. Prolonged periods of rainfall and flooding are the primary cause of most failures. Other factors that can lead to failures include inadequate spillway capacity resulting in excess flow overtopping the dam, internal erosion caused by embankment or foundation leakage, improper maintenance and design, negligent operation, failure of an upstream dam on the same waterway, landslides into reservoirs, high winds, and earthquakes.
Maui County contains many streams that have been dammed for either flood control or water storage. In total, Maui County has 57 dams and reservoirs. Use the RAMP application to explore the location of these dams.
There has been one recorded historic dam failure incident in Maui County. Horner Reservoir, located in the West Maui community planning area, failed on November 13, 1994. However, limited information was available regarding the impacts of this incident.
The extent of dam failure is difficult to determine given minimal historic incidents and limited details associated with the historic events. The ranking provided by the National Inventory of Dams can be used as an indicator for the potential severity of dam failure. Hazard rankings are not reflective of the potential for a dam to fail, but instead represent the potential impact if a dam was to fail. Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life. Significant hazard potential are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss. Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and environmental losses. Of the 57 dams in Maui County, 54 are ranked as high hazard, 2 are ranked as significant, and 1 is ranked as low hazard.
Potential impacts may be gleaned from failures of similar dams. In 2006, the privately owned Ka Loko Dam on the Island of Kauai failed. This dam had similarities in dam construction, ground topography, and rainfall intensity to dams in Maui County. During the failure event, a 120-foot long portion of the dam breached after an unusually long period of torrential rainfall. Approximately 300million gallons of water and debris destroyed several homes, devastated a 300-foot long portion of state highway, overturned several utility poles and lines, and killed seven people. An independent civil investigation identified conditions and practices that could have contributed to the failure: inadequate inspections, non-permitted grading operations, inadequate maintenance, and non-enforcement of regulations. The failure of a dam or reservoir in Maui County could have similar impacts, and more severe impacts than the event described on Kauai are possible
All current and future buildings, infrastructure, and populations in dam inundation areas are considered at risk to dam failure. Specific impacts to buildings, infrastructure, socially vulnerable populations, life safety, public heath, and the economy from coastal erosion are described below. Climate-related impacts to coastal erosion are also described. You can explore any of this data in the RAMP application.
Buildings and Infrastructure: All buildings, including critical facilities, located in dam inundation areas are at risk to dam failure. Several community planning areas (Wailuku-Kahului, West Maui) have greater vulnerability to dam failure in terms of building exposure. Overall, there are 4,731 structures within dam inundation areas in Maui County, with an estimated value of almost $13.5 billion; and an additional 42 critical facilities. In addition to buildings and identified critical facilities, utility lines, roads, and bridges are vulnerable to dam inundation. Flooding from dam inundation can undermine roads, scour bridges, and expose underground utilities. When utility lines are damaged by flooding, functionality of water, sewer, gas, and electricity systems may be compromised. Because of their geographic extent, roads and utility lines can have a greater chance of being impacted by dam failure and are difficult to move out of hazard areas. Further, if any section of a road or utility line is damaged, the entire system may be impacted. In addition, dam failure can cause damage to the dams themselves, which are important infrastructure for water retention and flood control. Dam failure may cause failure of dams located downstream along the same watercourse. Several major roads in Maui County are within dam inundation areas, including Honoapiilani Highway in the West Maui community planning area, portions of Kahului Beach Road in the Wailuku-Kahului community planning area, as well as sections of North and South Kīhei Road in the Kīhei-Mākena community planning area.
Health and Safety: All populations within dam inundation areas are considered at-risk to dam failure. This includes populations who reside in inundation areas, as well as populations in the inundation area for work or recreation. Tourists and visitors may be at a higher risk if they are not familiar with the County’s evacuation routes and procedures. Dam failure can result in injuries and loss of life. Warning time may range from several hours to just minutes. Dam failure can have many negative impacts on public health, which are similar to the public health issues associated with flooding (see this section’s equivalent under the Flood hazard profile). In particular, having water and wastewater treatment facilities within dam inundation areas results in vulnerability to sewage spills and water contamination.
Household composition: Special accommodations should be considered for people with access/functional needs and other dependent populations, such as seniors and children, to support advance warning and evacuation efforts during a time-critical evacuation.
Socioeconomic status: Low-income households living in coastal erosion zones may lack funds to support mitigation efforts as well as a financial buffer to recover after a major disaster event such as a dam failure.
Access to information: Populations with language and technology barriers may experience delays in receiving and acting upon urgent hazard warning information.
Housing characteristics: Homes built before 1950 and prior to the enactment of modern building codes are more susceptible to structural damages and even permanent losses to homes and property as a result of hazard events.
Access to lifelines: Populations with limited vehicle access or transportation routes, especially those living in isolated areas, are more likely to experience mobility challenges during an evacuation, and have difficulty accessing needed supplies and services before, during and after a hazard event.
Economic Impacts: Economic impacts resulting from flooding from dam failure are similar to those from flooding, though generally contained to inundation areas . (see this section’s equivalent under the Flood hazard profile).
Climate Change Impacts: Climate change can have many indirect impacts on dam failure. The cause of most dam failures is flooding from prolonged periods of rainfall. In Maui County, expected increases in extreme rainfall events can increase the likelihood of dam failure due to increased flooding or inadequate spillway capacity. Further, many dams, including the ones analyzed for this plan, were constructed 80 or more years ago, and were originally designed based on climate conditions effective at the time of construction. Dam upgrades and renewals should consider changing climate conditions; such actions are typically addressed in a dam management plan and are out of the scope of this plan.
