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Research about O'ahu

Source-linked reports with geographic coverage including O'ahu.

12 recordsLinked to original sources
USGS2025

Wave driven cross shore and alongshore transport reveal more extreme projections of shoreline change in island environments

Coastal erosion, intensified by sea level rise, poses significant threats to coastal communities in Hawaiʻi and similar island communities. This study projects long-term shoreline change on the Hawaiian Island of O‘ahu using the data-assimilated CoSMoS-COAST shoreline change model. CoSMoS-COAST models four key shoreline processes: (1) Alongshore transport, (2) Recession due to sea level rise, (3) Cross-shore transport due to waves, and (4) Residual processes represented by a linear trend term. This study marks the first application of CoSMoS-COAST for an oceanic equatorial island with narrow beaches and a dynamic wave climate. The model is informed with a novel combination of shoreline data derived from high-resolution imagery from Planet, Sentinel-2, and Landsat satellites, wave-climate hindcasts specific to Hawai‘i, and regional beach-slope surveys. On a dynamic northern Oʻahu beach, the model achieved a root mean square error of 9.4 m between observations and model output. CoSMoS-COAST predicts that 81% of O‘ahu’s sandy beach coastline could experience beach loss by 2100; with 39.8% of this loss happening by 2030. This represents an increase, 43.3%, in net landward shoreline change compared to previous erosion forecasts, for 0.3 m of sea level rise (2050). Additionally, dynamic processes such as cross-shore equilibrium processes and alongshore sediment transport, play a large contribution to gross shoreline change within the next decade, particularly on O ‘ahu’s north and west shores. In the long term, we find that recession due to sea level rise and residual processes dominate, but dynamic, wave-driven processes (longshore and cross-shore transport) still account for 34% of shoreline change between present and 2100. We assert dynamic, wave-driven processes are a crucial addition for accurate modeling of island sandy beach environments. These findings have implications for O‘ahu’s coastal planning and development, suggesting updates to shoreline policies that rely upon erosion forecasting, and highlights the importance of incorporating wave and alongshore transport in erosion models for other Pacific islands.

Hawaii↗
USGS2022

The Hawai'i groundwater recharge tool

This article discusses the design and implementation of the Hawai’i Groundwater Recharge Tool, an application for providing data and analyses of the impacts of land-cover modifications and changes in precipitation on groundwater-recharge rates for the island of O’ahu. This application uses simulation data based on a set of 29 land-cover types and 2 precipitation conditions to provide users with real-time recharge calculations for interactively defined land-cover modifications. The tool provides two visualizations, representing the land cover for the island and the resultant groundwater-recharge rates, and a set of metrics indicating the changes to groundwater recharge for relevant areas to present a set of easily interpretable outcomes based on user-defined scenarios. Users have varying degrees of control over the granularity of data input and output, allowing for the quick production of a roughly defined scenario, or more precise land-cover definitions. These modifications can be exported for further analysis. Heuristics are used to provide a responsive user interface and performant integration with the database containing the full set of simulation data. This tool is designed to provide user-friendly access to the information on the impacts of land-cover and precipitation changes on groundwater-recharge rates needed to assist in making data-driven decisions.

Hawai'i↗
USGS2021

Hawaiian hoary bat acoustic surveys on Marine Corps Base Hawaii, 2019–2021

The endangered Hawaiian hoary bat ( Lasiurus semotus, Vespertilionidae, also known as Aeorestes semotus and ‘ōpe‘ape‘a) occurs on all the principal volcanic islands in Hawai‘i. Advances in acoustic bat monitoring techniques have contributed to the body of knowledge of bat activity and behavior in many areas of the State of Hawai‘i; however, there is still much that is unknown about the population and seasonal distribution of Hawaiian hoary bats on O‘ahu. A two-year acoustic survey for presence of Hawaiian hoary bats was conducted at 17 stations across four Marine Corps Base Hawaii (MCBH) properties on O‘ahu to document distribution, seasonal patterns, and foraging activity. Bats were confirmed present at all properties; MCBH Kaneohe Bay on Mōkapu Peninsula, Marine Corps Training Area Bellows (MCTAB) in Waimanalo, Camp H M Smith in Halawa Heights, and Puuloa Range Training Facility (RTF) on the ‘Ewa coastal plain. Hawaiian hoary bats were recorded in airspace at all four properties during important periods of Hawaiian hoary bat life history, including periods of pregnancy, lactation, and pup fledging; however, overall presence was low. Foraging activity as identified from characteristic feeding buzzes was very rare and was recorded on only three nights over the entire study. Within-night bat detection pooled for all nights and stations at each property showed that bat activity was mostly confined to the first several hours of the night at MCBH Kaneohe Bay and Puuloa RTF, whereas bat activity was spread throughout the night at Camp H M Smith and MCTAB. Overall, detection frequency was low (year 1 = 0.009, year 2 = 0.007, average = 0.008) at the study sites on O‘ahu compared to results from acoustic monitoring studies on the islands of Maui and Hawai‘i. However, the low rate of bat presence on MCBH properties is consistent with recent studies at other locations on the Island of O‘ahu. Monitoring the seasonal presence and distribution of Hawaiian hoary bats on MCBH facilities, especially at forest and wetland habitats, could contribute to the broader scientific understanding of islandwide distribution and behavior on O‘ahu, which is essential for species recovery planning and implementation of best management practices.

Hawaii↗
USGS2019

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 adaptation strategies to manage. To spur consideration of GWI in planning, data-intensive numerical modeling methods have been developed that produce locally specific visualizations of GWI, though the accessibility of such methods is limited by extensive data requirements. Conversely, the hydrostatic (or 'bathtub') modeling approach is widely used in adaptation planning owing to easily accessed visualizations (i.e., NOAA SLR Viewer), yet its capacity to simulate GWI has never been tested. Given the separate actions necessary to mitigate GWI relative to marine overwash, this is a significant gap. Here we compare a simple hydrostatic modeling method with a more deterministic, dynamic and robust 3D numerical modeling approach to explore the effectiveness of the hydrostatic method in simulating equilibrium aquifer effects of multi-decadal sea-level rise, and in turn GWI for Honolulu, Hawai'i. We find hydrostatic modeling in the Honolulu area and likely other settings may yield similar results to numerical modeling when referencing the local mean higher-high water tide datum (generally typical of flood studies). These findings have the potential to spur preliminary understanding of GWI impacts in municipalities that lack the required data to conduct rigorous groundwater-modeling investigations. We note that the methods explored here for Honolulu do not simulate dynamic coastal processes (i.e., coastal erosion, sediment accretion or changes in land cover) and thus are most appropriately applied to regions that host heavily armored shorelines behind which GWI can develop.

Hawaii↗
USGS2017

Reproductive success of Mariana swiftlets (Aerodramus bartschi) on the Hawaiian island of O'ahu

Mariana Swiftlets ( Aerodramus bartschi ) are federally listed as endangered, with populations currently limited to just three islands in the Mariana Islands plus an introduced population on the Hawaiian island of O'ahu. Before efforts are made to reintroduce Mariana Swiftlets to other islands in the Mariana archipelago, additional information is needed concerning their breeding biology. Therefore, our objective was to examine the reproductive biology of Mariana Swiftlets over five annual cycles on the Hawaiian island of O'ahu. This introduced population used a human-made tunnel for roosting and nesting, and was studied as a surrogate to negate interference with endangered populations in the Mariana Islands. Active nests ( N = 478) were observed in every month of the year, with peak nesting activity between May and September. All clutches consisted of one egg. Mean duration of incubation and nestling periods were 23.9 d (range = 18–30 d, N = 233) and 55.0 d (range = 41–84 d, N = 228), respectively. Estimated nest success was 63%. Over half (52%) of nest failures were attributed to eggs found on the tunnel floor. Predation by rats ( Rattus spp.) was also an important cause of nest failure and often resulted in the loss of most active nests. However, Mariana Swiftlets did re-nest after these predation events. Our results suggest that rat predation of both nests and adults may limit growth of the Mariana Swiftlet population on O'ahu, and could also affect the chances for successful establishment of relocated populations in the Mariana Islands. Another limiting factor on O'ahu is that only one nesting site is apparently available on the island. Current goals for downlisting Mariana Swiftlets from endangered to threatened include establishing populations on Guam, Rota, Aguiguan, and Saipan. To meet these goals, the population of Mariana Swiftlets on O'ahu can be important for testing reintroduction techniques, learning more about the natural history of these swiftlets, and providing individuals for reintroduction efforts in the Mariana Islands.

Hawai'i↗
USGS2017

Small-scale genetic structure in an endangered wetland specialist: possible effects of landscape change and population recovery

The effects of anthropogenic landscape change on genetic population structure are well studied, but the temporal and spatial scales at which genetic structure can develop, especially in taxa with high dispersal capabilities like birds, are less well understood. We investigated population structure in the Hawaiian gallinule ( Gallinula galeata sandvicensis ), an endangered wetland specialist bird on the island of O`ahu (Hawai`i, USA). Hawaiian gallinules have experienced a gradual population recovery from near extinction in the 1950s, and have recolonized wetlands on O`ahu in the context of a rapidly urbanizing landscape. We genotyped 152 Hawaiian gallinules at 12 microsatellite loci and sequenced a 520 base-pair fragment of the ND2 region of mitochondrial DNA (mtDNA) from individuals captured at 13 wetland locations on O`ahu in 2014–2016. We observed moderate to high genetic structuring (overall microsatellite F ST = 0.098, mtDNA F ST = 0.248) among populations of Hawaiian gallinules occupying wetlands at very close geographic proximity (e.g., 1.5–55 km). Asymmetry in gene flow estimates suggests that Hawaiian gallinules may have persisted in 2–3 strongholds which served as source populations that recolonized more recently restored habitats currently supporting large numbers of birds. Our results highlight that genetic structure can develop in taxa that are expanding their range after severe population decline, and that biologically significant structuring can occur over small geographic distances, even in avian taxa.

Hawai'i↗
USGS2015

Spatially distributed groundwater recharge for 2010 land cover estimated using a water-budget model for the Island of O‘ahu, Hawai‘i

Owing mainly to projected population growth, demand for freshwater on the Island of Oʻahu is expected to increase by about 26 percent between 2010 and 2030, according to the City and County of Honolulu. Estimates of groundwater recharge are needed to evaluate the availability of fresh groundwater. For this study, a water-budget model with a daily computation interval was developed and used to estimate the spatial distribution of recharge on Oʻahu for average climate conditions (1978–2007 rainfall and 2010 land cover) and for drought conditions (1998–2002 rainfall and 2010 land cover). For average climate conditions, mean annual recharge for Oʻahu is about 660 million gallons per day, or about 36 percent of precipitation (rainfall and fog interception). Recharge for average climate conditions is about 34 percent of total water inflow, which consists of precipitation, irrigation, septic leachate, water-main leakage, and seepage from reservoirs and cesspools. Recharge is high along the crest of the Koʻolau Range, reaching as much as about 180 inches per year in the north-central part of the range. Recharge is much lower outside of the mountainous areas of the island, commonly less than 5 inches per year in unirrigated areas. The island-wide estimate of groundwater recharge for average climate conditions from this study is within 1 percent of the recharge estimate used in the 2008 State of Hawaiʻi Water Resource Protection Plan, which divides the Island of Oʻahu into 23 aquifer systems for groundwater management purposes. To facilitate direct comparisons with this study, these 23 aquifer systems were consolidated into 21 aquifer systems. Recharge estimates from this study are higher for 12 of the aquifer-system areas and lower for 9. Differences in mean rainfall distribution and the inclusion of irrigation in this study are the primary reasons for discrepancies in recharge estimates between this study and the 2008 Hawaiʻi Water Resources Protection Plan. For drought conditions, mean annual recharge for Oʻahu is about 417 million gallons per day, which is about 37 percent less than recharge for average climate conditions. For individual aquifer-system areas, recharge for drought conditions is about 25 to 70 percent less than recharge for average climate conditions.

Hawai'i↗
USGS2014

Monitoring Hawaiian waterbirds: evaluation of sampling methods to produce reliable estimates

We conducted field trials to assess several different methods of estimating the abundance of four endangered Hawaiian waterbirds: the Hawaiian duck ( Anas wyvilliana ), Hawaiian coot ( Fulica alai ), Hawaiian common moorhen ( Gallinula chloropus sandvicensis ) and Hawaiian stilt ( Himantopus mexicanus knudseni ). At two sites on Oʽahu, James Campbell National Wildlife Refuge and Hamakua Marsh, we conducted field trials where both solitary and paired observers counted birds and recorded the distance to observed birds. We then compared the results of estimates using the existing simple count, distance estimates from both point- and line-transect surveys, paired observer count estimates, bounded count, and Overton estimators. Comparing covariate recorded values among simultaneous observations revealed inconsistency between observers. We showed that the variation among simple counts means the current direct count survey, even if interpreted as a proportional index of abundance, incorporates many sources of uncertainty that are not taken into account. Analysis revealed violation of model assumptions that allowed us to discount distance-based estimates as a viable estimation technique. Among the remaining methods, point counts by paired observers produced the most precise estimates while meeting model assumptions. We present an example sampling protocol using paired observer counts. Finally, we suggest further research that will improve abundance estimates of Hawaiian waterbirds.

Hawai'i↗
USGS2009

Ecological assessment of wadeable streams on O`ahu, Hawai'i, 2006-2007: A pilot study

In 2006–07, the U.S. Geological Survey (USGS) Pacific Islands Water Science Center (PIWSC), in cooperation with the Hawai‘i Department of Health (HDOH), conducted a pilot study as a participant in the U.S. Environmental Protection Agency’s (USEPA) Wadeable Streams Assessment (WSA) program. Forty randomly selected sites on perennial streams on O‘ahu, Hawai‘i, were surveyed for habitat characteristics, water chemistry, and benthic macroinvertebrate assemblages. Of the original sampling frame of approximately 505.2 miles of perennial stream, roughly 96.7±30.7 miles were found to be nonperennial or estuarine and another 200.5±64.7 miles were judged to be inaccessible. The scope of this report presents an assessment of the remaining 208±57.6 miles of accessible, wadeable, perennial stream length on O‘ahu. Benthic macroinvertebrate assemblages were used to determine the ecological condition at each site. Components of the benthic macroinvertebrate assemblages were assessed using the multimetric Preliminary–Hawaiian Benthic Index of Biotic Integrity (P–HBIBI) developed by Wolff (2005). Based on the P–HBIBI scores, an estimated 5.8±5.8 percent of the island’s total stream length is in most disturbed condition, 56±13.5 percent is in intermediately disturbed condition, and 38.2±13.2 percent is in least disturbed condition. Windward O‘ahu had the highest percentage of stream length in least disturbed biological condition at 56.7±20.8 percent. Using the relative abundance of insects, one of the core metrics that make up the P–HBIBI, 43.4±14.2 percent of the islandwide stream length was classified in the most disturbed condition—52±31.2 percent of the Honolulu region stream length and 51.4±23.3 percent of the windward O‘ahu stream length. An analysis of total nitrogen (N) estimated approximately 41.1±13.7 percent of the stream length on O‘ahu was in most disturbed condition. Regionally, the Honolulu region had the largest proportion, 61.3±28.6 percent, of most disturbed stream length in terms of total N. An analysis of total phosphorus (P) classified approximately 43.2±14 percent of the stream length on O‘ahu as most disturbed. Regionally, windward O‘ahu had the largest proportion, 78.4±19.5 percent, of stream length classified as most disturbed. An analysis of embeddedness classified 30.3±14.7 percent of O‘ahu’s stream length as most. Regionally, windward O‘ahu had the largest proportion, 43.3±17.1 percent, of stream length classified as most disturbed as compared to the reference condition. An analysis of riparian disturbance, an index of the in-channel, riparian, and near-stream human activities, classified 43±13 percent of stream length on O‘ahu as most disturbed. The Honolulu region had the largest proportion of stream length, 86.3±13.7 percent, classified as most disturbed. The information in this report is the first attempt in Hawai‘i to assess the islandwide ecological condition of wadeable, perennial streams on O‘ahu using the USEPA WSA probabilistic design. This study has demonstrated that such an assessment is practical and that it can provide information that may help the USEPA and HDOH in determining the status of aquatic ecosystems on O‘ahu, Hawai‘i. This study provides a baseline assessment of the current islandwide ecological condition and identifies potential environmental stressors. It can be used, with future WSA studies in Hawai‘i, to measure the changes in those conditions and the effectiveness of management efforts to protect, restore, and maintain Hawai‘i’s aquatic environment.

Hawaii↗
USGS2003

Data report: geology of reef-front carbonate sediment deposits around Oahu, Hawaii

This Open-File Report presents data and derivative products from an investigation of carbonate sediment deposits on the reef front in four areas around the island of Oahu, Hawaii - in Kailua Bay off Oahu's windward (east) side, off the leeward (west) coast from Makua to Kahe Point, off the north coast from Waimea to Camp Erdman, and off the south coast around Waikiki (Figure 1). The primary purpose of the investigation was to assess the resource potential of the deposits, particularly as a source of sand for beach nourishment. This work builds on previous studies by researchers from the University of Hawaii (Moberly et al., 1975; Coulbourn et al., 1988; Barry, 1995). The field program included collection of high-resolution acoustic-reflection profiles and vibracore sediment samples in Kailua Bay and off the leeward and north coasts. In a related project, in collaboration with the Hawaii State Department of Land and Natural Resources and the University of Hawaii, sidescan images and vibracores were collected in the Halekulani channel and on the adjacent Makua Terrace off Waikiki along the south coast.

Hawai'i↗
USGS1971

Relation of drainage problems to high ground-water levels, Coconut Grove area, Oahu, Hawaii

Purpose and Scope In 1969, hydrologic data-collection sites were established in and around the Coconut Grove area for the purpose of measuring directly the relationship between rainfall, runoff, ground-water levels, the level of water in Kawainui Swamp and the canals, and tidal fluctuations. The primary objective was to identify the causes of the occurrence and persistence of flooding and to gain data on which to base recommendations for remedial action. The scope of the study included establishing and operating flow and stage-recording gages on the Swamp, Kawainui Canal, and the inner canal; periodic and repeated measurements of ground-water level in test borings throughout the residential area; collection and analysis of soil and construction borings made for engineering purposes; the assembly and analysis of all available data relating surface and subsurface flow conditions, and the development of conclusions as to the causes and means to alleviate the flooding. This report summarizes the information collected from October 1969 to June 1971, includes analysis of the data, and discusses the probable causes of flooding.

Hawai'i↗