Geology topics

Nathan R. vanArendonk

Publications and source records attributed to Nathan R. vanArendonk.

6 recordsLinked to original sources

USGS2024

Dynamic modeling of coastal compound flooding hazards due to tides, extratropical storms, waves, and sea-level rise: A case study in the Salish Sea, Washington (USA)

The Puget Sound Coastal Storm Modeling System (PS-CoSMoS) is a tool designed to dynamically downscale future climate scenarios (i.e., projected changes in wind and pressure fields and temperature) to compute regional water levels, waves, and compound flooding over large geographic areas (100 s of kilometers) at high spatial resolutions (1 m) pertinent to coastal hazard assessments and planning. This research focuses on advancing robust and computationally efficient approaches to resolving the coastal compound flooding components for complex, estuary environments and their application to the Puget Sound region of Washington State (USA) and the greater Salish Sea. The modeling system provides coastal planners with projections of storm hazards and flood exposure for recurring flood events, spanning the annual to 1-percent annual chance of flooding, necessary to manage public safety and the prioritization and cost-efficient protection of critical infrastructure and valued ecosystems. The tool is applied and validated for Whatcom County, Washington, and includes a cross-shore profile model (XBeach) and overland flooding model (SFINCS) and is nested in a regional tide–surge model and wave model. Despite uncertainties in boundary conditions, hindcast simulations performed with the coupled model system accurately identified areas that were flooded during a recent storm in 2018. Flood hazards and risks are expected to increase exponentially as the sea level rises in the study area of 210 km of shoreline. With 1 m of sea-level rise, annual flood extents are projected to increase from 13 to 33 km 2 (5 and 13% of low-lying Whatcom County) and flood risk (defined in USD) is projected to increase fifteenfold (from 14 to USD 206 million). PS-CoSMoS, like its prior iteration in California (CoSMoS), provides valuable coastal hazard projections to help communities plan for the impacts of sea-level rise and storms.

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USGS2023

Compound flood model for the lower Nooksack River and delta, western Washington—Assessment of vulnerability and nature-based adaptation opportunities to mitigate higher sea level and stream flooding

Higher sea level and stream runoff associated with climate change is expected to lead to greater lowland flooding across the Pacific Northwest. Increases in stream runoff that range from 20 to 32 percent by the 2040s and from 52 to 72 percent by the 2080s is expected to steadily increase flood risk. Flood risk is also expected to increase in response to the landward shift in high tides and storm surge, which will retard downstream conveyance. The combination of higher stream runoff, which is expected to drive greater fluvial sediment delivery to the coast, and more frequent, higher coastal waters relative to present-day (2023) levels, which will retard streamflow, is projected to cause more sedimentation across coastal and estuarine systems, exacerbating the flood risk. In the Nooksack River delta of western Washington, as in many Puget Sound deltas, resilient adaptation planning to mitigate impacts to community assets and infrastructure, nationally essential agricultural areas, and valued habitats and restoration investments that support endangered and threatened salmon recovery are underway but are in need of more informed projections of compound flood hazards. A Delft3D Flexible Mesh hydrodynamic model was constructed and used to assess changes in the extent, frequency, and timing of flood exposure associated with higher sea level and stream runoff projected to occur in the 2040s and 2080s. The model was also used to evaluate the change in and potential mitigating effects to flood exposure associated with individual and cumulative salmon-habitat-restoration strategies. Model simulations also evaluated the sensitivity of sedimentation to the individual and cumulative effects of higher fluvial delivery, trapping by sea-level rise, and changes in hydrodynamics associated with the rerouting of flows by proposed restoration strategies. The model performed well, having mean absolute errors for water levels below 1 foot (0.3 meters) when tested during a 2-year period for two recent flood events of record, the February 2, 2020, “Super Bowl flood” and the January 8, 2009, stream flood, both of which caused substantial flooding and damage across the study area. Fluvial discharge was found to dominate flood hazard at higher elevations in the study area, whereas near the coast, sea-level rise is computed to turn a less extreme 2-year (50 percent annual exceedance probability [AEP]) bankfull streamflow, which, at present (2023), causes nuisance flooding, into a more extreme 5-year (20 percent AEP) and 10 percent AEP stream-flood event by the 2050s and 2100, respectively. The February 2020 Super Bowl flood was calculated to be a 10-year or 10 percent AEP peak-flow event, and the January 2009 flood was calculated to be a 25-year (4 percent AEP) peak-flow event. Extreme events such as the February 2020 Super Bowl flood and the January 2009 flood caused extensive damage across the Nooksack River floodplain, and model computations predict these magnitudes of events would have notably greater effect in the 2040s and 2080s in response to higher projected sea level and stream runoff. The modeled January 2009 flood is predicted to transform into a flood event, causing flood exposure that is comparable to the 100-year or 1 percent AEP flood by the 2040s. The modeled January 2009 flood is also predicted to exceed the flood exposure of the recent November 16, 2021, flood, which caused substantial damage in the lower Nooksack River floodplain and restricted access for emergency-management efforts on important arterial roadways in the area; the measured peak discharge during the November 16, 2021, flood exceeded that of the January 2009 flood. Two of several identified alternative strategies that reroute floodwaters to restore salmon habitat were projected to reduce exposure to the increasingly impactful 10 and 4 percent AEP stream-flood events through the 2080s. The effects of the suggested alternatives, however, were found to reduce flow velocities, promote additional sedimentation, and reduce flow conveyance in the main-stem Nooksack River, a concern to flood-management efforts, navigation, and fishing. The model also suggests that main-stem channel sedimentation is likely, given projected climate change. Higher stream runoff that increases fluvial-sediment delivery and higher sea levels that retard downstream flow are expected to lead to greater sedimentation. Lastly, the model was used to assess the sensitivity of flood exposure to the individual and cumulative effects of climate changes, alternative strategies, and sedimentation, including recently observed decadal-scale aggradation patterns. These results indicate that sediment is likely to continue to be a challenge to flood-management efforts and that nature-based alternatives that benefit ecosystem restoration may also mitigate flood exposure for several decades.

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USGS2022

Assessment of vulnerabilities and opportunities to restore marsh sediment supply at Nisqually River Delta, west-central Washington

A cascading set of hazards to coastal environments is intimately tied to sediment transport and includes the flooding and erosion of shorelines and habitats that support communities, industry, infrastructure, and ecosystem functions (for example, habitats critical to fisheries). This report summarizes modeling and measurement data used to evaluate the sediment budget of the Nisqually River Delta, the vulnerability of the largest estuary restoration project in Puget Sound at the Billy Frank Jr. Nisqually National Wildlife Refuge, and the role of coastal hydrodynamics and potential restoration alternatives for recovering sediment delivery to its marshes. The 2009 Brown’s Farm Restoration achieved many goals toward recovering salmon habitat, but the understanding of the delta and restoration area sediment budgets remain poorly quantified. Specifically, quantitative estimates of the amount of sediment delivered to the delta and restored marsh areas, which had subsided in response to historical diking and draining for grazing, were identified as important information needs. Forecasts of potential outcomes of proposed adaptive distributary channel restoration actions were also prioritized to inform potential solutions. These estimates can be used to evaluate whether sufficient sediment is available for marsh recovery downstream from Alder Lake, which traps about 90 percent the Nisqually River sediment load that could reach the delta . Additionally, quantitative sediment information was identified to help prioritize opportunities to recover and maintain the area marshes and guide ecosystem restoration investments across the delta to reduce the vulnerability of the system to drowning under projected sea level rise. A coupled, numerical hydrodynamic-sediment transport model and measurements of the sediment load just upstream from the delta were used to evaluate the (1) availability of sediment for marsh recovery, (2) sediment transport dynamics across the estuary, and (3) potential outcomes of distributary reconnection alternatives under existing and projected conditions of streamflow and sea level. Modeling and measurements indicated that the volume of fluvial sediment load reaching and accumulating in the restoration area ranges from 7 to 32 percent and identified that restoration alternatives could recover about an additional 10–12 percent under current and projected sea-level rise by the year 2100. At these rates of sediment delivery, 85–200+ years may be necessary to fill for marsh vegetation development and maintenance. The model also reveals the sensitivity of sediment transport and accumulation to sediment properties, hydrodynamics, and wave conditions. The low sediment accumulation results in large part because of the role of waves in directing sediment transport offshore and challenges of restoring geomorphic processes suited to maintaining habitat structure where opportunity exists or least conflicts with land use. The findings therefore have implications for siting, phasing, and implementing strategies to route and retain sediment. This study shows that opportunities to recover sediment higher in the tidal prism, where a greater hydraulic gradient and gravity could promote progradation and greater sediment retention, may be more effective than alternatives lower in the tidal prism implemented to date and assessed in this study. Furthermore, the modeling indicates that distributary channel restoration also may provide additional benefits to society by reducing flood stage, and therefore, flood hazards surrounding the delta.

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USGS2021

Long-term changes in kelp forests in an inner basin of the Salish Sea

Kelp forests form an important biogenic habitat that responds to natural and human drivers. Global concerns exist about threats to kelp forests, yet long-term information is limited and research suggests that trends are geographically distinct. We examined distribution of the bull kelp Nereocystis luetkeana over 145 years in South Puget Sound (SPS), a semi-protected inner basin in a fjord estuary complex in the northeast Pacific Ocean. We synthesized 48 historical and modern Nereocystis surveys and examined presence/absence within 1-km segments along 452 km of shoreline. Compared to the earliest baseline in 1878, Nereocystis extent in 2017 decreased 63%, with individual sub-basins showing up to 96% loss. Losses have persisted for decades, across a range of climate conditions. In recent decades, Nereocystis predominantly occurred along shorelines with intense currents and mixing, where temperature and nutrient concentrations did not reach thresholds for impacts to Nereocystis performance, and high current speeds likely excluded grazers. Losses predominated in areas with elevated temperature, lower nutrient concentrations, and relatively low current velocities. The pattern of long-term losses in SPS contrasts with stability in floating kelp abundance during the last century in an area of the Salish Sea with greater wave exposure and proximity to oceanic conditions. These findings support the hypothesis that kelp beds along wave-sheltered shorelines exhibit greater sensitivity to environmental stressors. Additionally, shorelines with strong currents and deep-water mixing may provide refugia within sheltered systems.

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USGS2021

Nearshore water quality and coral health indicators along the west coast of the Island of Hawaiʻi, 2010–2014

Coral reefs worldwide are experiencing rapid degradation in response to climate and land-use change, namely effects of warming sea-surface temperatures, contaminant runoff, and overfishing. Extensive coral bleaching caused by the steady rise of sea-surface temperatures is projected to increase, but our understanding and ability to predict where corals may be most resilient to this effect is limited owing to a lack of knowledge of nearshore habitat conditions and the role of compromised coral health in preconditioning bleaching vulnerability. On high islands and most atolls, fresh to brackish groundwater discharges to the coast through the beach face and seafloor, where it mixes with marine waters and commonly creates cool estuarine nearshore waters that are important to wildlife and ecosystem services that benefit people. Here, we summarize results of a study to evaluate the ecosystem services and effects of groundwater on coral reef health and the potential role of groundwater to maintain cold-water refugia that can buffer corals from thermal stress during temperature maxima. Across 75 kilometers of the west coastline of the Island of Hawaiʻi, paired time-series and discrete measurements of water quality, coral-community and colony size structures, and coral health indicators, including bleaching, at 33 stations grouped into 12 study areas were made from July 2010 to December 2013. The results show that nearshore water temperatures are depressed by groundwater across extensive areas of the nearshore. Persistent cold-water refugia ranging from 1 to 5 degrees Celsius below surrounding marine water temperatures are shown to be associated with identified groundwater inputs. Significant correlations were found between metrics of coral health and water temperature. Because areas of temperature refugia were notable along the west coast of the Island of Hawaiʻi and are identified by ecologists as increasingly important to valued wildlife, improved understanding of groundwater flux to the long-term resilience of coral reefs is likely important. In particular, evaluating the extent that the magnitude and timing of groundwater discharge across the nearshore mitigate thermal bleaching stress may help inform the fate of coral reefs projected to experience rising sea-surface temperatures worldwide.

Hawaii↗

USGS2019

Extreme coastal water level in Washington state: Guidance to support sea level rise planning

This document provides guidelines for assessing exposure to future coastal flooding during extreme coastal water level events – whether these are due to tides, surge, wave run-up, or, more likely, a combination of the three. These guidelines provide information about the current and future magnitude of extreme coastal water levels across Washington State and the underlying processes that influence them. This information is intended to be combined with sea level projections to assess future exposure to coastal flooding along Washington’s coastline. Although the results of our analyses can be combined with any available sea level projections, this report is intended as a companion to the localized sea level rise projections (Miller et al., 2018) developed as part of the Washington Coastal Resilience Project. The Washington Coastal Resilience Project was a three-year effort to rapidly increase the state’s capacity to prepare for sea level rise. The project aimed to improve risk projections, provide better guidelines for land use planners and strengthen capital investment programs for coastal restoration and infrastructure. Partners in the Washington Coastal Resilience Project included Washington Sea Grant, Washington Department of Ecology, Island County, King County, NOAA Office for Coastal Management, Pacific Northwest National Laboratory, Padilla Bay National Estuary Research Reserve, The City of Tacoma, The Nature Conservancy, U.S. Geological Survey, University of Oregon, University of Washington Climate Impacts Group, University of Washington Department of Earth and Space Sciences, Washington Department of Fish and Wildlife and Western Washington University. The 2018 sea level projections are described in an accompanying technical report, along with a review of the science related to sea level rise (Miller et al., 2018). The report and all associated supporting information are available on the Washington Coastal Hazards Resilience Network website (http://www.wacoastalnetwork.com/).

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