HURRICANE OLIVIA PROJECTED FLOODING FROM RAINFALL-RUNOFF

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1 INFRASTRUCTURE IMPACT ASSESSMENT September ; 2300 EDT HURRICANE OLIVIA PROJECTED FLOODING FROM RAINFALL-RUNOFF ASSESSMENT The Department of Homeland Security (DHS)/National Protection and Programs Directorate (NPPD)/National Risk Management Center (NRMC) has modeled the extent of freshwater flooding likely to result in the Hawaiian Islands from heavy rainfall associated with Hurricane Olivia. Modeling was based on precipitation forecasts published by the National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS). NMRC assesses that heavy rainfall will result in local flooding and elevated risk of landslides in susceptible areas. Approximately 2 feet of freshwater flooding is expected to affect: Hilo Harbor and the Waimea Water Treatment Plant on the Big Island of Hawaii Kahului Harbor on Maui Nu'uanu Dam. 4 on Oahu Critical infrastructure assets in areas at risk of landslide event initiation include: Waimea Water Treatment Plant on the Big Island of Hawaii Maui Memorial Medical Center and one electric power substation on Maui Four undersea cable landing stations, Wahiawa Dam, one electric power substation, an agricultural chemical manufacturer, and a cement manufacturing facility on Oahu Alexander Dam and Kaloko Dam on Kauai BACKGROUND Olivia is currently a Category 1 hurricane, with maximum winds near 85 miles per hour (mph). It is forecast to weaken to a strong tropical storm before passing over Hawaii. Tropical storm conditions will reach Hawaii starting the evening of Tuesday, September 11. Along with high winds, Olivia will bring rainfall accumulations of inches, with isolated areas of up to 20 inches, leading to widespread rainfall runoff flooding, especially one the eastern side of Maui and the Big Island (figure 2). 1 In addition to the risk of dangerous flash flooding, Olivia will bring heavy rains to areas susceptible to landslides and debris slides in Hawaii. Large amounts of cumulative rainfall, such as those forecast as a result of Olivia, can trigger landslides, as top layers of ground become saturated and heavy. Large sections of earth can then break loose and slump downhill, sliding on an underlying layer. Debris slides (often called mudslides) are turbulent rivers of water-saturated soil and rock fragments that travel downslope as muddy slurries, bearing rocks, vegetation, and other natural and man-made debris at speeds of up to 35 mph. Debris slides are more likely to be triggered by very intense rainfall; the precipitation rate for Olivia is not forecast to reach the threshold for debris slides. Figure 3 shows the location of critical infrastructure assets in areas of greatest landslide susceptibility (due to geological structure, slope, and other factors). 2 1

2 METHOD NMRC used its Rapid Infrastructure Flood Tool (RIFT) to model the depth and extent of flooding due to precipitation, based on the precipitation forecast from the NOAA NWS. 3 Rainfall-runoff flooding depends on both the spatial and temporal distribution of precipitation for a given area. For this analysis, NMRC used the rain total from NWS forecast temporally distributed over 24 hours such that most of the rain falls near the beginning of the event. Because of uncertainties in the forecast and the complexity of real-world flooding events, actual flooding will differ somewhat from the model results. Analysts used the location of critical infrastructure assets with respect to the modeled flooding to assess the impacts to people and critical infrastructure. SECTOR IMPACTS Chemical Impacts to the Chemical Sector from precipitation associated with Olivia are expected to be minimal. An agricultural chemical manufacturer (Crop Production Services, Inc.) is in the area expected to receive 2 feet of flooding on the Big Island and a cement manufacturer (Hawaii Cement) is located in areas that are susceptible to landslide events on Oahu. If a landslide were to occur, it could damage these facilities and could potentially result in release of chemicals. Communications undersea cable landing stations are at risk from freshwater flooding, although several are located in areas where landslides could occur. If undersea cable connections were to be severed, there could be significant disruptions to trans-pacific communications. However, the onshore equipment is typically housed in robust concrete facilities and so is impervious to freshwater flooding and unlikely to sustain damage from landslides. Dams dam failures are expected, although one dam is expected to receive approximately 2 feet of freshwater flooding, and three others are in areas that are susceptible to landslides. Dam operators normally manage water levels in advance of storms in order to minimize stress to the dam and the risk of overtopping. Nu'uanu Dam. 4 (Oahu) is a high hazard 4 earthen dam in the area expected to receive approximately 3 feet of freshwater flooding. It is managed by the Board of Water Supply for flood control and recreational purposes. 5 The earthen embankment extends 60 feet up to the spillway and 65 feet to the top of the dam; the reservoir has a maximum capacity of 3,600 acre-feet. Operators have typically kept water levels about 30 feet below the top of the dam in the past. 6 The dam has recently been repaired and rehabilitated. 7 Wahiawa Dam (also called Waialua, on Oahu) is a high-hazard earthen dam located in an area susceptible to landslide events. It impounds Lake Wilson, which surrounds the town of Wahiawa on three sides. The dam is owned by the Dole Company and used for irrigation. Lake Wilson can hold up to 9,200 acre-feet of water. 8 Water levels have dropped 4 feet over the last several days, indicating that the dam operators are likely releasing water in advance of the storm, in order to reduce any risk of damage to the dam. 9 Water levels are currently about 15 feet below the top of the dam. 10 Alexander Dam and Ka Loko Dams (Kauai) are high hazard earthen dams in an area susceptible to landslide events. They respectively impound the Alexander Reservoir, which is used for hydroelectric generation and irrigation and the Ka Loko Reservoir, used primarily for irrigation. Lake Alexander has a maximum capacity of 2,540 acre-feet of water. 11 The Ka Loko Reservoir has a maximum capacity of 1,400 acre-feet. 12 The Ka Loko Dam failed in 2006 following heavy precipitation, resulting seven deaths. 13 Water level information is not available for either of these two dams.

3 Electric Power Impacts to the bulk electric power sector from precipitation associated with Olivia are expected to be minimal. bulk electric power system assets (power generation stations or transmission substations) are located in areas expected to receive flooding greater than 3 feet, although one substation in Maui is in an area that is susceptible to landslide events. If a landslide were to occur, substation equipment would likely have to be replaced, but the utility would put temporary measures in place to restore power as quickly as possible while repairs were conducted. Depending on the exact location of transmission towers and the velocity and debris load of floodwater, some transmission towers could be damaged or toppled by flooding. If this occurs, power outages could be more widespread and restoration could be affected. Government Facilities The Wahiawa Annex, part of Joint Base Pearl Harbor-Hickam on Oahu, is in an area susceptible to landslide events. It is a communications hub for the U.S. Navy and Department of Defense in the Pacific. 14 The facility is likely to have robust emergency continuity plans. Healthcare and Public Health The Maui Memorial Medical Center is in the area expected to receive approximately 2 feet of freshwater flooding. It is Maui s only acute care hospital, with a staff of over 1, This level of flooding is not likely to require evacuation. Hospital evacuation is generally a last resort, as it increases the risk to patients. Transportation Systems Freshwater flooding may impede surface travel in some areas. Port facilities in Hilo on the Big Island and Kahului Harbor on Maui will experience freshwater flooding in addition to the impacts of storm surge and waves, but the damage is likely to be dominated by the saltwater impacts. Water and Wastewater Systems Impacts to the Water and Wastewater Systems Sector from precipitation associated with Olivia are expected to be minimal. One water treatment plant, the Waimea Water Treatment Plant on the Big Island of Hawaii, is in an area expected to receive 2 feet of flooding and susceptible to landslides. The plant has an operating capacity of 4 million gallons per day (MGD), although its average productions is much lower. 16 This level of inundation is unlikely to interfere with plant operations, although it is possible that floodwater could contaminate treated water, necessitating a boil water notice. If a landslide were to occur, the resulting damage could incapacitate the plant, requiring equipment replacement and alternative sources of water until it could be restored.

4 FIGURE 1 LOCATION OF CRITICAL INFRASTRUCTURE WITH RESPECT TO MODELED RAINFALL-RUNOFF FLOODING

5 FIGURE 2 LOCATION OF CRITICAL INFRASTRUCTURE WITH RESPECT TO AREAS OF ELEVATED LANDSLIDE RISK PDM18096

6 1 NOAA National Hurricane Center, Hurricane Olivia Advisory Number 40, September 10, 2018, 1500 UTC, at 2 USGS, Preliminary Landslide Susceptibility Maps and Data for Hawaii, at 3 For more information on RIFT, please request NMRC/Office of Cyber and Infrastructure Analysis Modeling and Simulation Capability Summary - Inland Flooding, July 12, High hazard dams are those whose complete failure would result in at least one death. 5 Hawaii Department of Land and Natural Resources, Dam Inventory System, Nuuanu Dam. 4, at 5fda f2-0d7e3ea2e1f4, 6 Drewes, Paul, More monitoring on the way for Hawaii's dams, KITV4 Web site, February 15, 2017, at 7 Board of Water Supply, News Release: Dam Improvements at the Nuuanu Reservoir, April 27, 2018, at 8 Hawaii Department of Land and Natural Resources, Dam Inventory System, Wahiawa Dam, at 42a2-a6cb-bf8668bb49b3, 9 USGS, USGS Wahiawa Reservoir at Spillway at Wahiawa, Oahu, HI, gage height data for September 3-10, 2018, 10 Hawaii Department of Land and Natural Resources, Dam Inventory System, Wahiawa Dam, at 11 Hawaii Department of Land and Natural Resources, Dam Inventory System, Alexander Dam, at 12 Hawaii Department of Land and Natural Resources, Dam Inventory System, Kaloko Dam, at 13 Godbey, Robert C., Report of the Independent Civil Investigation of the March 14, 2006, Breach of Ka Loko Dam (Volume 1), January 2007, at 14 Department of Defense, Joint Base Pearl Harbor-Hickam Wahiawa Annex: Hawaii, at 15 Maui Health System, Maui Memorial Medical Center, at 16 Force, Jim, Reservoirs, Rainwater and the Big Island of Hawaii, Treatment Plant Operator, vember 2015, at

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