Geology topics

Liv M. Herdman

Publications and source records attributed to Liv M. Herdman.

14 recordsLinked to original sources

USGS2026

A spatial analysis of the groundwater emergence flood hazard in Long Island, New York, and coastal areas surrounding Long Island Sound in New York, Connecticut, and Rhode Island

Long Island, New York, and nearby coastal areas surrounding Long Island Sound are densely populated and, like other coastal areas, are susceptible to flooding from several potential sources, including stormwater from precipitation events, tidal flooding and storm surge, and groundwater emergence flooding. Groundwater emergence fooding refers to the intersection of a rising water table with land surface or critical infrastructure. Many studies of flood drivers either neglect or only briefly discuss how shallow groundwater conditions may contribute to or exacerbate flood conditions. As a part of a comprehensive study of compound flood hazards in the coastal areas of Long Island and Long Island Sound, a spatial analysis was completed by the U.S. Geological Survey, in cooperation with the Environmental Protection Agency’s Long Island Sound Partnership, formerly called the Long Island Sound Study, using available regional datasets to characterize the potential hazard for groundwater emergence flooding. The approximately 3,100 square mile study area was subdivided into 11,407 grid cells that were 900 meters by 900 meters (approximately 3,000 feet by 3,000 feet), for the purpose of integrating the spatial datasets to calculate and map the groundwater emergence flood hazard. The depth to the water table, hydrologic soil groups, and National Land Cover Database were harmonized to the common grid. A groundwater emergence flood hazard score was calculated for each grid cell for current average conditions following a set of rules accounting for the depth to the water table and the percentage of area within each cell with slow infiltrating soils. A scenario with a higher sea-level position was also calculated for the Long Island part of the study area. The calculated groundwater emergence flood hazard score was reviewed in conjunction with the National Land Cover Database to identify developed areas and associated infrastructure that may be at risk of potential groundwater emergence flooding. Study results indicate that the groundwater emergence flood hazard is highest in coastal areas and near surface water where the water table is close to ground surface. Inland areas away from surface waterbodies are not likely to be exposed to groundwater emergence flooding. For Long Island, in the scenario with higher sea-level position, a greater groundwater emergence flood hazard is calculated for some locations closer to the coast and where land is submerged. Away from the coast and surface-water drainage, the groundwater emergence flood hazard is similar between the current average sea-level condition and the higher sea-level position scenario.

Connecticut, New York, Rhode Island↗

USGS2026

Hazard potential of compound flooding from rainfall, storm surge, and groundwater in coastal New York and Connecticut

Compound flood events, the co-occurrence of multiple flood drivers, can result in flood hazard potential exceeding that of any single driver alone. To evaluate compound flooding in a semi-urbanized coastal area, historical records dating back to 1970 are used to study the co-occurrences of high precipitation, storm surge, and shallow groundwater conditions along the coastlines of New York and Connecticut. Joint return periods for coincident precipitation-surge events were computed using statistical dependence models and compared to the assumption of independence as a ratio, referred to here as a return period adjustment. Results indicate distinct seasonality where compound events in the area disproportionately occur in the cold season between October and April. Return period adjustments range from a factor of 1 to almost 9, demonstrating the range in precipitation-storm surge dependence across the study area. Across all 24 station triad locations, groundwater levels were elevated during times of precipitation- surge co-occurrence, reflecting the tendency for coastal storms and shallow groundwater conditions to co-occur seasonally. The result is a pseudo-trivariate compound flood hazard score and corresponding hazard map that integrates dependence between daily precipitation-surge events and overall monthly groundwater levels (as a precondition) into a relative compound hazard score. The location with the highest compound flood hazard score is on the south shore of Long Island, as well as locations across coastal Connecticut where groundwater levels compound the co-occurrence of heavy precipitation and storm surge.

Connecticut, New York↗

USGS2025

A spatial analysis of the groundwater emergence flood hazard in Long Island, New York and near coastal areas surrounding Long Island Sound in New York, Connecticut, and Rhode Island

Long Island, New York and near coastal areas surrounding Long Island Sound are densely populated and, like other coastal areas, are susceptible to flooding from several potential sources, including stormwater from precipitation events, tidal flooding and storm surge, and groundwater inundation or groundwater emergence flooding. The latter refers to the intersection of a rising water table with land surface or critical infrastructure. Many studies of flood drivers either neglect or only briefly discuss how shallow groundwater conditions may contribute to or exacerbate flood conditions. As part of a comprehensive study of compound flood hazards in the near coastal areas surrounding Long Island and Long Island Sound, a spatial analysis was completed, in cooperation with the Environmental Protection Agency’s Long Island Sound Study, using available regional datasets to characterize the potential hazard for groundwater emergence flooding. The approximately 3,100 square mile study area was subdivided into 11,407 900-meter by 900-meter (approximately 3,000-feet by 3,000-feet) grid cells, for the purposes of integrating the spatial datasets to calculate and map the groundwater emergence flood hazard. The depth to the water table, hydrologic soil groups, and National Land Cover Database were harmonized to the common grid. A groundwater emergence flood hazard rank was calculated for each grid cell for current average conditions following a set of rules accounting for the depth to the water table and the percent of area within each cell with slow infiltrating soils. A higher sea level position scenario was also calculated for the Long Island part of the study area. The calculated groundwater emergence flood hazard rank was reviewed in concert with the National Land Cover Data Base to identify developed areas and associated infrastructure that may be at risk to groundwater emergence flooding. Study results indicate that the groundwater emergence flood hazard is highest in coastal areas and near surface water where the water table is close to ground surface. Inland areas away from surface water bodies are not likely to be exposed to groundwater emergence flooding. For Long Island, under a scenario with higher sea level position, a greater groundwater emergence flood hazard is calculated in some locations closer to the coast and where land is submerged. Away from the coast and surface-water drainage, the groundwater emergence flood hazard is similar between the current average sea level condition and a higher sea level position scenario.

EarthArXiv↗

USGS2025

Present and future coastal flooding hazard for Long Island, NY and Long Island Sound (NY/CT), USA

Coastal flooding and the associated damages due to storms are increasing with sea level rise around the world, with regional variability in the severity of impacts., Researchers and resource managers need to better understand and predict the future shifts in coastal flooding due to these processes to plan for resilient and sustainable communities. Here we present an analysis of long-term historical records of water levels, tides, and modeled present-day wave climatologies, to characterize the present-day inundation extent in Long Island Sound and Long Island, NY. To understand the potential future changes in inundation extent, we provide a similar analysis of future climate projections of non-tidal residuals (storm surge) for the year 2050 and compare these projections with our present-day results. We examine both the magnitude of relatively frequent events with a 0.99 annual exceedance probability to more extreme events with a 0.01 annual exceedance probability (or the 1 in 100-year event). This range of events is relevant for local managers to understand the spatial variability in coastal inundation, in addition to planning for larger more catastrophic events.

EarthArXiv↗

USGS2024

Unlearning Racism in Geoscience (URGE): Summary of U.S. Geological Survey URGE pod deliverables

The U.S. Geological Survey (USGS) is in a unique position to be a leader in diversity, equity, inclusion, and accessibility in the Earth sciences. As one of the largest geoscience employers, the USGS wields significant community influence and has a responsibility to adopt and implement robust, unbiased policies so that the science it is charged to deliver is better connected to the diverse communities it serves. Meaningful and effective improvements in implementation of diversity, equity, inclusion, and accessibility principles made within the USGS will be seen across the geoscience community. Despite this opportunity, however, the community, including the USGS, has struggled to diversify the geoscience workforce, which does not reflect the Nation’s diversity. This disparity suggests that the implementation of past policies did not achieve their desired outcomes in sustainable ways. The persistent lack of diversity across the geosciences and the racial justice protests of 2020 motivated a group of geoscience scholars to launch a global, virtual initiative known as Unlearning Racism in Geoscience (URGE) in the winter of 2021. The 16-week facilitated URGE curriculum was designed to highlight existing literature, share expert opinions, and foster discussion within groups (pods) around the world to build action plans for affecting change within their home institutions ( https://urgeoscience.org/ ). Whereas most of the approximately 4,500 participants were university faculty and students or from professional societies and nonprofit organizations, 6 pods totaling over 120 participants from the USGS joined the program—the largest participation of any Federal science agency. Summarizing the recommendations of over 100 USGS employees across the USGS who participated in URGE, this Circular represents a grassroots plan for making the USGS workforce more diverse and inclusive. To identify how peer-reviewed best practices could be implemented at the USGS, participants read existing literature, reviewed USGS policies and procedures, explored new and existing demographic data, and listened to and discussed primary interviews with scholars, all facilitated by the URGE program. This Circular leverages the efforts and momentum of the USGS URGE participants to catalyze and support positive, systemic change throughout the organization in a holistic way that represents an achievable departure from past policies that fell short of success. These recommendations are starting points. Reflecting the overall lack of diversity in the USGS workforce, the USGS URGE participants were predominantly White, meaning recommendations in this document can and should continue to evolve to include the lived perspectives and input from the broader USGS community. Finally, this summary document only highlights some of the key findings of these working groups. Additional details that may be more suitable to specific USGS Centers and programs can be found in the primary documents developed by each USGS URGE pod; a list of all registered pods can be found at https://urgeoscience.org/pods/ .

Circular↗

USGS2024

Advanced quantitative precipitation information: Improving monitoring and forecasts of precipitation, streamflow, and coastal flooding in the San Francisco Bay area

Advanced Quantitative Precipitation Information (AQPI) is a synergistic project that combines observations and models to improve monitoring and forecasts of precipitation, streamflow, and coastal flooding in the San Francisco Bay Area. As an experimental system, AQPI leverages more than a decade of research, innovation, and implementation of a statewide, state-of-the-art network of observations, and development of the next generation of weather and coastal forecast models. AQPI was developed as a prototype in response to requests from the water management community for improved information on precipitation, riverine, and coastal conditions to inform their decision-making processes. Observation of precipitation in the complex Bay Area landscape of California’s coastal mountain ranges is known to be a challenging problem. But, with new advanced radar network techniques, AQPI is helping fill an important observational gap for this highly populated and vulnerable metropolitan area. The prototype AQPI system consists of improved weather radar data for precipitation estimation; additional surface measurements of precipitation, streamflow, and soil moisture; and a suite of integrated forecast modeling systems to improve situational awareness about current and future water conditions from sky to sea. Together these tools will help improve emergency preparedness and public response to prevent loss of life and destruction of property during extreme storms accompanied by heavy precipitation and high coastal water levels—especially high-moisture laden atmospheric rivers. The Bay Area AQPI system could potentially be replicated in other urban regions in California, the United States, and worldwide.

California↗

USGS2021

Managing water resources on Long Island, New York, with integrated, multidisciplinary science

Nutrients, harmful algal blooms, and synthetic chemicals like per- and polyfluoroalkyl substances (PFAS) and 1,4-dioxane threaten Long Island’s water resources by affecting the quality of drinking water and ecologically sensitive habitats that support the diverse wildlife throughout the island. Understanding the occurrence, fate, and transport of these potentially harmful chemicals is critical to protect these vital resources. The U.S. Geological Survey (USGS) is collecting and analyzing data to support informed water-resource management decisions. This fact sheet introduces ongoing efforts and future areas of study aimed to help water professionals develop a comprehensive science strategy to address contamination of the Long Island aquifer system, the sole source of drinking water for nearly 3 million people. These studies include surface and groundwater collection and groundwater flow modeling. Funding for the data collection has been provided by the USGS, New York State Department of Environmental Conservation, New York City Department of Environmental Protection, Suffolk County Water Authority, Nassau County Department of Public Works, State and local agencies, and Tribal and Federal partners. Without the foresight and long-term commitment of these funding partners, evaluating sustainability and planning for future water needs would not be possible.

New York↗

USGS2021

Assessment of flood forecast products for a coupled tributary-Coastal model

Compound flooding, resulting from a combination of riverine and coastal processes, is a complex but important hazard to resolve along urbanized shorelines in the vicinity of river mouths. However, inland flooding models rarely consider oceanographic conditions, and vice versa for coastal flood models. Here, we describe the development of an operational, integrated coastal-watershed flooding model to address this issue of compound flooding in a highly urbanized estuarine environment, San Francisco Bay (CA, USA), where the surrounding communities are susceptible to flooding along the bay shoreline and inland rivers and creeks that drain to the bay. The integrated tributary-coastal forecast model (Hydro-Coastal Storm Modeling System, or Hydro-CoSMoS) was developed to provide water managers and other users with flood forecast information beyond what is currently available. Results presented here are focused on the interaction of the Napa River watershed and the San Pablo Bay at the northern end of San Francisco Bay. This paper describes the modeling setup, the scenario used in a tabletop exercise (TTE), and the assessment of the various flood forecast information products. Hydro-CoSMoS successfully demonstrated the capability to provide watershed and coastal flood information at scales and locations where no such information is currently available and was also successful in showing how tributary flows could be used to inform the coastal storm model during a flooding scenario. The TTE provided valuable feedback on how to guide continued model development and to inform what model outputs and formats are most useful to end-users.

California↗

USGS2021

Drivers of extreme water levels in a large, urban, high-energy coastal estuary – A case study of the San Francisco Bay

Reliable and long-term hindcast data of water levels are essential in quantifying return period and values of extreme water levels. In order to inform design decisions on a local flood control district level, process-based numerical modeling has proven an essential tool to provide the needed temporal and spatial coverage for different extreme value analysis methods. To determine the importance of different physical processes to the extreme water levels we developed a process-based numerical model (Delft3D Flexible Mesh) and applied it to simulate a large, urban, high-energy coastal estuary (the San Francisco Bay). The unstructured grid with 1D/2DH model elements, allows for efficient model simulations and therefore it was possible to simulate over 70 years between 1950 and 2019. Results show significant skill in reproducing observations for the entire modeled time period with an average root-mean-square error of 8.0 cm. A process-based modeling approach allows for the explicit in- and exclusion of different physical processes to quantify their importance to the extremes. For the 100-year still water level (SWL), tide (70%) and non-tidal residual (NTR) (25%) explain the majority of the simulated high water levels in the Bay relative to Mean Higher High Water (MHHW). However, closer to the Delta, local fluvial inflow increases in importance. For longer return periods, the importance of tide decreases and the importance of remote NTRs and fluvial inflow increases.

California↗

USGS2020

Effect of fluvial discharges and remote non-tidal residuals on compound flood forecasting in San Francisco Bay

Accurate and timely flood forecasts are critical for making emergency-response decisions regarding public safety, infrastructure operations, and resource allocation. One of the main challenges for coastal flood forecasting systems is a lack of reliable forecast data of large-scale oceanic and watershed processes and the combined effects of multiple hazards, such as compound flooding at river mouths. Offshore water level anomalies, known as remote Non-Tidal Residuals (NTRs), are caused by processes such as downwelling, offshore wind setup, and also driven by ocean-basin salinity and temperature changes, common along the west coast during El Niño events. Similarly, fluvial discharges can contribute to extreme water levels in the coastal area, while they are dominated by large-scale watershed hydraulics. However, with the recent emergence of reliable large-scale forecast systems, coastal models now import the essential input data to forecast extreme water levels in the nearshore. Accordingly, we have developed Hydro-CoSMoS, a new coastal forecast model based on the USGS Coastal Storm Modeling System (CoSMoS) powered by the Delft3D San Francisco Bay and Delta community model. In this work, we studied the role of fluvial discharges and remote NTRs on extreme water levels during a February 2019 storm by using Hydro-CoSMoS in hindcast mode. We simulated the storm with and without real-time fluvial discharge data to study their effect on coastal water levels and flooding extent, and highlight the importance of watershed forecast systems such as NOAA’s National Water Model (NWM). We also studied the effect of remote NTRs on coastal water levels in San Francisco Bay during the 2019 February storm by utilizing the data from a global ocean model (HYCOM). Our results showed that accurate forecasts of remote NTRs and fluvial discharges can play a significant role in predicting extreme water levels in San Francisco Bay. This pilot application in San Francisco Bay can serve as a basis for integrated coastal flood modeling systems in complex coastal settings worldwide.

California↗

USGS2018

Storm surge propagation and flooding in small tidal rivers during events of mixed coastal and fluvial influence

The highly urbanized estuary of San Francisco Bay is an excellent example of a location susceptible to flooding from both coastal and fluvial influences. As part of developing a forecast model that integrates fluvial and oceanic drivers, a case study of the Napa River and its interactions with the San Francisco Bay was performed. For this application we utilize Delft3D-FM, a hydrodynamic model that computes conservation of mass and momentum on a flexible mesh grid, to calculate water levels that account for tidal forcing, storm surge generated by wind and pressure fields, and river flows. We simulated storms with realistic atmospheric pressure, river discharge, and tidal forcing to represent a realistic joint fluvial and coastal storm event. Storm conditions were applied to both a realistic field-scale Napa river drainage as well as an idealized geometry. With these scenarios, we determine how the extent, level, and duration of flooding is dependent on these atmospheric and hydrologic parameters. Unsurprisingly, the model indicates that maximal water levels will occur in a tidal river when high tides, storm surge, and large fluvial discharge events are coincident. Model results also show that large tidal amplitudes diminish storm surge propagation upstream and that phasing between peak fluvial discharges and high tide is important for predicting when and where the highest water levels will occur. The interactions between tides, river discharge, and storm surge are not simple, indicating the need for more integrated flood forecasting models in the future.

California↗

USGS2018

The influence of sea level rise on the regional interdependence of coastal infrastructure

Sea level rise (SLR) is placing both immediate and long‐term pressures on coastal communities to take protective actions. Projects in the United States, and in many locations throughout the world, generally involve local jurisdictions raising the elevation of shoreline protection elements, with limited or no analysis of the feedback between shoreline management decisions and the impacts to water levels regionally. Our study examines the impact of local shoreline development on regional flood risk and considers SLR scenarios up to 1.5 m using a large‐scale numerical model, as an example, for San Francisco Bay. Here we show that measures to prevent flooding along an embayment shoreline in one location or subregion may increase inundation elsewhere in the system. The network of interactions occurs not only within subbasins of the Bay but also across the greater geographic extent from one end of the Bay to the other, and local jurisdiction may have either reciprocal relationships with or asymmetric impacts on one other. Importantly, the nature of the interaction network is seen to evolve with SLR: interactions are purely subregional at current sea level but with higher sea level (e.g., 1 m of SLR), not only do the subregional interdependencies strengthen but also regional interdependences emerge.

California↗

USGS2017

Interactions of estuarine shoreline infrastructure with multiscale sea level variability

Sea level rise increases the risk of storms and other short‐term water‐rise events, because it sets a higher water level such that coastal surges become more likely to overtop protections and cause floods. To protect coastal communities, it is necessary to understand the interaction among multiday and tidal sea level variabilities, coastal infrastructure, and sea level rise. We performed a series of numerical simulations for San Francisco Bay to examine two shoreline scenarios and a series of short‐term and long‐term sea level variations. The two shoreline configurations include the existing topography and a coherent full‐bay containment that follows the existing land boundary with an impermeable wall. The sea level variability consists of a half‐meter perturbation, with duration ranging from 2 days to permanent (i.e., sea level rise). The extent of coastal flooding was found to increase with the duration of the high‐water‐level event. The nonlinear interaction between these intermediate scale events and astronomical tidal forcing only contributes ∼1% of the tidal heights; at the same time, the tides are found to be a dominant factor in establishing the evolution and diffusion of multiday high water events. Establishing containment at existing shorelines can change the tidal height spectrum up to 5%, and the impact of this shoreline structure appears stronger in the low‐frequency range. To interpret the spatial and temporal variability at a wide range of frequencies, Optimal Dynamic Mode Decomposition is introduced to analyze the coastal processes and an inverse method is applied to determine the coefficients of a 1‐D diffusion wave model that quantify the impact of bottom roughness, tidal basin geometry, and shoreline configuration on the high water events

Journal of Geophysical Research: Oceans↗

USGS2017

Behavior of a wave-driven buoyant surface jet on a coral reef

A wave-driven surface buoyant jet exiting a coral reef was studied in order to quantify the amount of water re-entrained over the reef crest. Both moored observations and Lagrangian drifters were used to study the fate of the buoyant jet. To investigate in detail the effects of buoyancy and along-shore flow variations, we developed an idealized numerical model of the system. Consistent with previous work, the ratio of along-shore velocity to jet-velocity and the jet internal Froude number were found to be important determinants of the fate of the jet. In the absence of buoyancy, the entrainment of fluid at the reef crest, creates a significant amount of retention, keeping 60% of water in the reef system. However, when the jet is lighter than the ambient ocean-water, the net effect of buoyancy is to enhance the separation of the jet from shore, leading to a greater export of reef water. Matching observations, our modeling predicts that buoyancy limits retention to 30% of the jet flow for conditions existing on the Moorea reef. Overall, the combination of observations and modeling we present here shows that reef-ocean temperature gradients can play an important role in reef-ocean exchanges.

Journal of Geophysical Research C: Oceans↗