Delwyn Oki is a hydrologist with the Pacific Islands Water Science Center in Honolulu, Hawaiʻi.
Science and Products
Filter Total Items: 37
December 23, 2021, Red Hill synoptic groundwater-level survey, Hālawa area, O‘ahu, Hawai‘i
On December 23, 2021, groundwater levels were measured in selected wells in the Hālawa area, O‘ahu, Hawai‘i, constituting a synoptic groundwater-level survey (shortened herein to “synoptic survey”) of the area. Groundwater levels were measured mainly from 9:00 a.m. to 12:00 p.m. (times listed in Hawai‘i standard time) and provide a snapshot of groundwater levels during the survey period. Following
Numerical simulation of the effects of groundwater withdrawal and injection of high-salinity water on salinity and groundwater discharge, Kaloko-Honokōhau National Historical Park, Hawaiʻi
Kaloko-Honokōhau National Historical Park (KAHO) is located on the west coast of the island of Hawaiʻi and contains water resources exposed in fishponds, anchialine pools, and marine waters that are cultural resources and that provide habitat for threatened, endangered, and other culturally important native species. KAHO’s water resources are sustained by and dependent on groundwater discharge. In
Numerical simulation of groundwater availability in central Moloka‘i, Hawai‘i
Since the 1990s, increased chloride concentrations of water pumped from wells (much of which is used for drinking water) and the effects of withdrawals on groundwater-dependent ecosystems have led to concerns over groundwater availability on the island of Molokaʻi, Hawaiʻi. An improved understanding of the hydrologic effects of proposed groundwater withdrawals is needed to ensure effective managem
Managing effects of drought in Hawai’i and U.S.-affiliated Pacific Islands
How is drought expressed in Hawai‘i & USAPI? Drought is a significant climate feature in Hawai‘i and the U.S.-Affiliated Pacific Islands (USAPI), at times causing severe impacts across multiple sectors. Below average precipitation anomalies are often accompanied by higher than average temperatures and reduced cloud cover. The resulting higher insolation and evapotranspiration can magnify the effec
Estimated groundwater recharge from a water-budget model incorporating selected climate projections, Island of Maui, Hawai‘i
Demand for freshwater on the Island of Maui is expected to increase by 45 percent between 2015 and 2035. Groundwater availability on Maui is affected by changes in climate and agricultural irrigation. To evaluate the availability of fresh groundwater under projected future climate conditions and changing agricultural irrigation practices, estimates of groundwater recharge are needed. A water-budge
Comparison of a simple hydrostatic and a data-intensive 3D numerical modeling method of simulating sea-level rise induced groundwater inundation for Honolulu, Hawai'i, USA
Groundwater inundation (GWI) is a particularly challenging consequence of sea-level rise (SLR), as it progressively inundates infrastructure located above and below the ground surface. Paths of flooding by GWI differ from other types of SLR flooding (i.e., wave overwash, storm-drain backflow) such that it is more difficult to mitigate, and thus requires a separate set of highly innovative adaptati
Groundwater-level, groundwater-temperature, and barometric-pressure data, July 2017 to February 2018, Hālawa Area, Oʻahu, Hawaiʻi
The Red Hill Bulk Fuel Storage Facility, operated by the U.S. Navy and located in the Hālawa area, Oʻahu, Hawaiʻi, includes 20 underground storage tanks that can hold a total of 250 million gallons of fuel. In January 2014, the U.S. Navy notified the Hawaiʻi Department of Health and U.S. Environmental Protection Agency of release of an estimated 27,000 gallons of fuel from the Red Hill Bulk Fuel S
Investigation of geochemical indicators to evaluate the connection between inland and coastal groundwater systems near Kaloko-Honokōhau National Historical Park, Hawai‘i
Kaloko-Honokōhau National Historical Park (KAHO) is a coastal sanctuary on the western side of the Island of Hawai‘i that was established in 1978 to preserve, interpret, and perpetuate traditional Native Hawaiian culture and activities. KAHO contains a variety of culturally and ecologically significant water resources and water-related habitat for species that have been declared as threatened or e
Water-chemistry data collected in and near Kaloko-Honokohau National Historical Park, Hawaii, 2012–2014
Kaloko-Honokōhau National Historical Park (KAHO) on western Hawaiʻi was established in 1978 to preserve, interpret, and perpetuate traditional Native Hawaiian culture and activities, including the preservation of a variety of culturally and ecologically significant water resources that are vital to this mission. KAHO water bodies provide habitat for 1 threatened, 11 endangered, and 3 candidate thr
Trends and shifts in streamflow in Hawaii, 1913-2008
This study addresses a need to document changes in streamflow and base flow (groundwater discharge to streams) in Hawai'i during the past century. Statistically significant long-term (1913-2008) downward trends were detected (using the nonparametric Mann-Kendall test) in low-streamflow and base-flow records. These long-term downward trends are likely related to a statistically significant downward
Changes of freshwater-lens thickness in basaltic island aquifers overlain by thick coastal sediments
Freshwater-lens thickness and long-term changes in freshwater volume in coastal aquifers are commonly assessed through repeated measurement of salinity profiles from monitor wells that penetrate into underlying salt water. In Hawaii, the thickest measured freshwater lens is currently 262 m in dike-free, volcanic-rock aquifers that are overlain by thick coastal sediments. The midpoint depth (depth
Hydrogeology of the Hawaiian islands
Volcanic-rock aquifers are the most extensive and productive aquifers in the Hawaiian Islands. These aquifers contain different types of groundwater systems depending on the geologic setting in which they occur. The most common groundwater systems include coastal freshwater-lens systems in the dike-free flanks of the volcanoes and dike-impounded systems within the dike-intruded areas of the volcan
Characterization of Flood-Producing Mechanisms in Watersheds with a High-Elevation Area in Southeast Alaska and Hawaiʻi
Major floods in Southeast Alaska and Hawaiʻi that potentially threaten life, property, and culturally significant resources and ecosystems are caused by mechanisms related to intense precipitation for both locations as well as snow melt-based processes for Alaska. Small, high-gradient, and heavily vegetated watersheds with direct contribution to the ocean are common in both locations. To understan...
Changes in Water Flow through Hawaiian Forests due to Invasive Species and Changing Rainfall Patterns
Precipitation in Hawaiʻi’s higher elevation upland areas provides needed water to both people and ecosystems. Once it reaches the ground, rain can either run off and contribute to water flow in streams, or it can infiltrate into the ground and provide water for plants and recharge aquifers and groundwater. The exact route that water takes is controlled by many factors, including the duration and i...
Influences of Climate Change, Climate Variability, and Drought on Human Communities and Ecosystems in Hawaiʻi
Over the past century, Hawaiʻi has experienced a pronounced decline in precipitation and stream flow and a number of severe droughts. These changes can have wide-reaching implications, affecting the water supply, native vegetation and wildlife, wildfire patterns, and the spread of invasive species. Several climate-related factors are influencing Hawaiˈi’s landscapes and contributing to these chang...
Assessing the Potential Effects of Climate Change on Vegetation in Hawaiʻi Volcanoes National Park
Climate change in Hawaiʻi is expected to result in increasing temperatures and varying precipitation through the twenty-first century. Already, high elevation areas have experienced rapidly increasing temperatures and there has been an increase in the frequency of drought across the Islands. These climatic changes could have significant impacts on Hawaiʻi’s plants and animals. Changes in temperatu...
SUTRA model used to evaluate groundwater availability in central Molokai, Hawaii
A three-dimensional, variable-density solute-transport model (SUTRA) was developed to evaluate the effects of nine selected withdrawal/recharge scenarios on salinity of groundwater and discharge of freshwater to the nearshore environment of central Molokai, Hawaii. The model was constructed using water-level and salinity data available for the period from 1940 to 2012. Groundwater recharge for the
Science and Products
- Publications
Filter Total Items: 37
December 23, 2021, Red Hill synoptic groundwater-level survey, Hālawa area, O‘ahu, Hawai‘i
On December 23, 2021, groundwater levels were measured in selected wells in the Hālawa area, O‘ahu, Hawai‘i, constituting a synoptic groundwater-level survey (shortened herein to “synoptic survey”) of the area. Groundwater levels were measured mainly from 9:00 a.m. to 12:00 p.m. (times listed in Hawai‘i standard time) and provide a snapshot of groundwater levels during the survey period. FollowingNumerical simulation of the effects of groundwater withdrawal and injection of high-salinity water on salinity and groundwater discharge, Kaloko-Honokōhau National Historical Park, Hawaiʻi
Kaloko-Honokōhau National Historical Park (KAHO) is located on the west coast of the island of Hawaiʻi and contains water resources exposed in fishponds, anchialine pools, and marine waters that are cultural resources and that provide habitat for threatened, endangered, and other culturally important native species. KAHO’s water resources are sustained by and dependent on groundwater discharge. InNumerical simulation of groundwater availability in central Moloka‘i, Hawai‘i
Since the 1990s, increased chloride concentrations of water pumped from wells (much of which is used for drinking water) and the effects of withdrawals on groundwater-dependent ecosystems have led to concerns over groundwater availability on the island of Molokaʻi, Hawaiʻi. An improved understanding of the hydrologic effects of proposed groundwater withdrawals is needed to ensure effective managemManaging effects of drought in Hawai’i and U.S.-affiliated Pacific Islands
How is drought expressed in Hawai‘i & USAPI? Drought is a significant climate feature in Hawai‘i and the U.S.-Affiliated Pacific Islands (USAPI), at times causing severe impacts across multiple sectors. Below average precipitation anomalies are often accompanied by higher than average temperatures and reduced cloud cover. The resulting higher insolation and evapotranspiration can magnify the effecEstimated groundwater recharge from a water-budget model incorporating selected climate projections, Island of Maui, Hawai‘i
Demand for freshwater on the Island of Maui is expected to increase by 45 percent between 2015 and 2035. Groundwater availability on Maui is affected by changes in climate and agricultural irrigation. To evaluate the availability of fresh groundwater under projected future climate conditions and changing agricultural irrigation practices, estimates of groundwater recharge are needed. A water-budgeComparison of a simple hydrostatic and a data-intensive 3D numerical modeling method of simulating sea-level rise induced groundwater inundation for Honolulu, Hawai'i, USA
Groundwater inundation (GWI) is a particularly challenging consequence of sea-level rise (SLR), as it progressively inundates infrastructure located above and below the ground surface. Paths of flooding by GWI differ from other types of SLR flooding (i.e., wave overwash, storm-drain backflow) such that it is more difficult to mitigate, and thus requires a separate set of highly innovative adaptatiGroundwater-level, groundwater-temperature, and barometric-pressure data, July 2017 to February 2018, Hālawa Area, Oʻahu, Hawaiʻi
The Red Hill Bulk Fuel Storage Facility, operated by the U.S. Navy and located in the Hālawa area, Oʻahu, Hawaiʻi, includes 20 underground storage tanks that can hold a total of 250 million gallons of fuel. In January 2014, the U.S. Navy notified the Hawaiʻi Department of Health and U.S. Environmental Protection Agency of release of an estimated 27,000 gallons of fuel from the Red Hill Bulk Fuel SInvestigation of geochemical indicators to evaluate the connection between inland and coastal groundwater systems near Kaloko-Honokōhau National Historical Park, Hawai‘i
Kaloko-Honokōhau National Historical Park (KAHO) is a coastal sanctuary on the western side of the Island of Hawai‘i that was established in 1978 to preserve, interpret, and perpetuate traditional Native Hawaiian culture and activities. KAHO contains a variety of culturally and ecologically significant water resources and water-related habitat for species that have been declared as threatened or eWater-chemistry data collected in and near Kaloko-Honokohau National Historical Park, Hawaii, 2012–2014
Kaloko-Honokōhau National Historical Park (KAHO) on western Hawaiʻi was established in 1978 to preserve, interpret, and perpetuate traditional Native Hawaiian culture and activities, including the preservation of a variety of culturally and ecologically significant water resources that are vital to this mission. KAHO water bodies provide habitat for 1 threatened, 11 endangered, and 3 candidate thrTrends and shifts in streamflow in Hawaii, 1913-2008
This study addresses a need to document changes in streamflow and base flow (groundwater discharge to streams) in Hawai'i during the past century. Statistically significant long-term (1913-2008) downward trends were detected (using the nonparametric Mann-Kendall test) in low-streamflow and base-flow records. These long-term downward trends are likely related to a statistically significant downwardChanges of freshwater-lens thickness in basaltic island aquifers overlain by thick coastal sediments
Freshwater-lens thickness and long-term changes in freshwater volume in coastal aquifers are commonly assessed through repeated measurement of salinity profiles from monitor wells that penetrate into underlying salt water. In Hawaii, the thickest measured freshwater lens is currently 262 m in dike-free, volcanic-rock aquifers that are overlain by thick coastal sediments. The midpoint depth (depthHydrogeology of the Hawaiian islands
Volcanic-rock aquifers are the most extensive and productive aquifers in the Hawaiian Islands. These aquifers contain different types of groundwater systems depending on the geologic setting in which they occur. The most common groundwater systems include coastal freshwater-lens systems in the dike-free flanks of the volcanoes and dike-impounded systems within the dike-intruded areas of the volcan - Science
Characterization of Flood-Producing Mechanisms in Watersheds with a High-Elevation Area in Southeast Alaska and Hawaiʻi
Major floods in Southeast Alaska and Hawaiʻi that potentially threaten life, property, and culturally significant resources and ecosystems are caused by mechanisms related to intense precipitation for both locations as well as snow melt-based processes for Alaska. Small, high-gradient, and heavily vegetated watersheds with direct contribution to the ocean are common in both locations. To understan...Changes in Water Flow through Hawaiian Forests due to Invasive Species and Changing Rainfall Patterns
Precipitation in Hawaiʻi’s higher elevation upland areas provides needed water to both people and ecosystems. Once it reaches the ground, rain can either run off and contribute to water flow in streams, or it can infiltrate into the ground and provide water for plants and recharge aquifers and groundwater. The exact route that water takes is controlled by many factors, including the duration and i...Influences of Climate Change, Climate Variability, and Drought on Human Communities and Ecosystems in Hawaiʻi
Over the past century, Hawaiʻi has experienced a pronounced decline in precipitation and stream flow and a number of severe droughts. These changes can have wide-reaching implications, affecting the water supply, native vegetation and wildlife, wildfire patterns, and the spread of invasive species. Several climate-related factors are influencing Hawaiˈi’s landscapes and contributing to these chang...Assessing the Potential Effects of Climate Change on Vegetation in Hawaiʻi Volcanoes National Park
Climate change in Hawaiʻi is expected to result in increasing temperatures and varying precipitation through the twenty-first century. Already, high elevation areas have experienced rapidly increasing temperatures and there has been an increase in the frequency of drought across the Islands. These climatic changes could have significant impacts on Hawaiʻi’s plants and animals. Changes in temperatu... - Data
SUTRA model used to evaluate groundwater availability in central Molokai, Hawaii
A three-dimensional, variable-density solute-transport model (SUTRA) was developed to evaluate the effects of nine selected withdrawal/recharge scenarios on salinity of groundwater and discharge of freshwater to the nearshore environment of central Molokai, Hawaii. The model was constructed using water-level and salinity data available for the period from 1940 to 2012. Groundwater recharge for the