Coastal Flooding Research Articles

Rob Flood Control on the North Coast of Java (Study on coastal areas of Pekalongan and Semarang)

Flooding on the coasts of Pekalongan and Semarang, North Coast of Java (Pantura), has become a severe problem for the Indonesian government. Factors causing the flood are rainfall, climate, land subsidence and rob, river conditions, tidal influence, poorer areas, land change, inappropriate flood control, damage to flood control buildings, excessive groundwater utilization, inappropriate flood management, river sedimentation, reduced water catchment areas, and runoff floods. Therefore, there is a need for an appropriate handling study to deal with these problems. This research aimed to determine the achievements of coastal flood control on the North Coast of Java. Data was collected through a literature review for secondary data, field studies for primary data, in-depth interviews with relevant stakeholders, and observation. The results showed that handling Rob flooding in coastal Pekalongan focuses on four locations: Bremi River, Meduri River, Mrican pump house, and Silempeng. Rob flood handling methods on the Pekalongan coast include the construction of concrete barriers with corrugated sheet pile (CCSP), compacted soil embankments with bamboo mattress reinforcement, and submersible pumping machines at the Mrican pump house. In comparison, rob flood management in coastal Semarang focuses on the Sringin and Tenggang rivers. The flood handling methods conducted are the provision of pumps, construction of Rob embankments and retention ponds, normalization, drainage improvements, and interconnection channels. However, handling coastal flooding needs a comprehensive and sustainable follow-up.

Spatial vulnerability assessment of climate-related disasters in the Rebana Metropolitan Coastal Area, West Java Province

Human activities have become the main significant factor of the occurrence of climate change. Because of this phenomenon, the negative impacts of climate change influence human life itself, especially for the people who live in coastal area. One part of the Rebana Metropolitan Area in West Java Province is the coastal area consisting of Indramayu, Subang, and Cirebon regencies, which is closely related to climate-related disasters issues, such as coastal flooding and sea-level rise. To adapt the negative impacts of climate change, the local decision-makers should know the vulnerability to climate-related disasters. Therefore, the vulnerability assessment of climate-related disasters should be conducted. The spatial assessment was applied in this study to give a deeper perspective on the spatial vulnerability index. This study used georeferenced statistical data of three aspects (physical, geological, and socio-economical). These data then were overlaid with the support of the Geographical Information System (GIS) and eventually produced the vulnerability index for each zone. Based on the result, the Rebana Metropolitan Coastal Area has high vulnerability indexes (9 of 16 districts in these three coastal areas are very vulnerable). Two reasons have been identified. First, the intensity of rainfall and sea-level rise index that occurs annually in Indramayu and Subang is very high. Second, at the same time, these regencies have many vital infrastructures that make the massive potential of losses when climate-related disasters happen in the future. For the Cirebon case, the lack of supportive socio-economy situation in the coastal area has become the main factor for its vulnerability index. Based on these findings, the decision-makers could create different approaches to improve the resilience of each area. In Indramayu and Subang cases, their resilience could be strategically improved by strengthening their physical aspects, especially by ensuring the government protects their vital infrastructures. Meanwhile, for the Cirebon case, the government could be more concerned with its population density and income per capita for each district so that more people could avoid the coastal disaster directly and push their livelihood up in the more uncertain environment.

A National‐Scale Coastal Flood Hazard Assessment for the Atoll Nation of Tuvalu

AbstractAtoll nations such as Tuvalu are considered to be amongst those most vulnerable to the effects of climate change. Here we present a national‐scale coastal flood hazard assessment for Tuvalu based on high‐resolution Light Detection and Ranging (LiDAR) topography and bathymetry. We follow a fully probabilistic approach, considering sea level anomalies, tides, and extreme wave conditions from a mixed climate (i.e., from distant extra‐tropical storms and local tropical cyclones). Nearshore processes such as wave setup and runup are also accounted for. Hazard maps were calculated for the present sea level, as well as for sea level rise projections corresponding to different shared socioeconomic pathways (SSP2 4.5 and SSP5 8.5) and time horizons (2060 and 2100). With a mean elevation of 1.55 m above mean sea level (1.37 m above mean high water spring) >25% of land area is inundated once every 5 years and >50% of land area floods once every 100 years nationally. Results indicate that present day 1‐in‐50 years floods (>45% of land area flooded) will occur more than once every 5 years by 2060 (annual exceedance probability >20%), even under the moderate SSP2 4.5 sea level rise projections. Results of this study highlight the pressing need for ambitious and large‐scale adaptation solutions which are commensurate with projected sea level rise and marine hazard impacts. The methodologies presented in this paper can easily be applied to other low‐lying islands in the tropical Pacific, where mixed climates (i.e., regular and TC conditions) and non‐linear nearshore processes dominate extreme water levels and flooding.

Comparative Studies Of Residual Water Level In Manado And Melonguane Coastal Area During Tropical Cyclone In 2021

North Sulawesi Province, directly bordering the Pacific Ocean, is located in an area with the highest level of tropical cyclone (TC) activity in the world. As a result, the province is vulnerable to the impacts caused by cyclones, including storm surges. The increase in water levels due to this event has the potential to cause coastal flooding. Previous studies in Manado have identified that sea level rise can be detected through residual water level (RWL), making studying the characteristics of RWL in North Sulawesi important. This research focuses on Manado and Melonguane, allowing for a comparison of characteristics. The data used includes tropical cyclone data from the China Meteorological Administration (CMA) and tidal data from the Geospatial Information Agency. The Unified Tidal Analysis and Prediction (UTide) method is used to identify RWL. The analysis was carried out by using a t-test to compare data at the two locations. The results showed that RWL at those locations had significant differences with Melonguane having the higher value between them. Generally, the increase in RWL in Melonguane occurs shortly after the cyclone period, while the RWL in Manado maximum increases 86 hours after TC's first occurrence. Keywords: tropical cyclone; residual water level; UTide.

Unveiling the Hidden Threat: Drought‐Induced Inelastic Subsidence in Expansive Soils

AbstractExpansive soils pose a significant challenge in geotechnical engineering, especially in coastal areas. While research has mainly focused on their elastic properties, this study explores the overlooked aspect of inelastic subsidence during prolonged droughts, utilizing decade‐long GPS datasets from the University of Houston Coastal Center. Our findings reveal substantial subsidence, approximately one to two dm, during the summer droughts of 2018, 2020, 2022, and 2023, due to compaction within the upper 4 m of expansive soils. Inelastic subsidence constitutes roughly 10% of the total subsidence, resulting in step‐like permanent land elevation loss over time. Notably, drought‐induced subsidence is prominent in open‐field areas with expansive soils but is minor in built‐up areas or in non‐expansive soil regions. The occurrence of inelastic subsidence challenges traditional assessments of relative sea‐level rise and coastal flooding, emphasizing the need to consider it in coastal infrastructure planning for enhanced resilience against climate uncertainties.

A Science and Community-Driven Approach to Illustrating Urban Adaptation to Coastal Flooding to Inform Management Plans

Academic research plays a pivotal role in illustrating and testing potential future adaptation strategies to sea level rise in low-lying coastal communities and enhances local municipalities’ adaptation plans. In Waikīkī, Hawai‘i, the built environment is increasingly impacted by flooding from multiple drivers: sea level rise-induced direct marine inundation, storm-drain backflow, and groundwater inundation (GWI), compounded by high-wave runup, extreme tides, heavy rainfall, and a shallow groundwater table. Given Waikīkī’s economic and cultural importance, in-place accommodation of flooding is desired, yet implementation plans have not been developed. By combining current scientific research, urban design visualizations, and community feedback, the interdisciplinary research team advanced intentional communication between the many parties seeking increased flood resilience through the end of the 21st century. Site-specific architectural renderings were a key tool to prompt structured community input on the coordination, prioritization, policy, and feasibility of adaptation measures for buildings, utilities, transportation, and open space. Public outreach reports document that the majority of participants thought all adaptation strategies presented were applicable, especially relocating critical equipment in buildings and streets. Proposed methods to develop sea level rise-adjusted minimum building elevation requirements may inform local municipalities’ future codes to minimize coastal property damage. The multi-year iterative process fostered growing participation in hosted and invited events, further improving the publicly distributed research products.

Dynamically downscaled coastal flooding in Brazil’s Guanabara Bay under a future climate change scenario

Dynamically downscaled coastal flooding in Brazil’s Guanabara Bay under a future climate change scenario

Effects of multiple future environmental changes on flooding in coastal area: Case study in Qianshan River Basin, South China

Due to their unique geographical characteristics, coastal areas are not only impacted by climate change and urbanization but also by sea level rise-induced lower boundary jacking. This makes them vulnerable to rapid, intense, and short-duration flooding events. In this study, a comprehensive analysis was conducted considering future climate change, land use change, and sea level change. By employing a hydrological model, potential flood scenarios in Qianshan River Basin were simulated in efforts to understand the combined impact of multiple environmental changes on coastal flooding. The results indicate that the flood characteristics of Qianshan River Basin will increase due to multiple future environmental changes. Notably, Dachong experiences the most significant surge in peak discharge, while Hongwanchong and Guangchangchong experience the highest increase in peak water depth under normal and extreme conditions, respectively. The inundation area’s location remains predominantly situated in the southern part of the basin, with high-risk zones substantially increasing, particularly in Tanzhou Town and the outlet of Qianshanshuidao. The observed pattern of increasing flood characteristics follows a clear trend across future scenarios SSP126, SSP245, SPP370, and SSP585. The flood characteristics resulting from a design rainfall of grade n correspond to those produced by a design rainfall of grade (n + 1), (n + 2), (n + 3), and (n + 4) in the current period, respectively.

C-HAND: near real-time coastal flood mapping

The Texas Gulf Coast region contains significant centers of population, infrastructure, and economy and is threatened by intensifying tropical storms. The flooding from these tropical storms often has multiple compounding drivers. This characteristic presents a complex numerical problem where a simulation must consider multiple hydrologic forcings. While several procedures exist for addressing this problem numerically, they tend to be resource-intensive and cannot be conducted in near real-time. We extend GeoFlood, a reduced physics approach for fluvial flood forecasting, to rapidly predict coastal and compound fluvial-coastal inundation. This method is validated against a numerical ocean circulation model (ADCIRC) simulation of Hurricane Ike, a major coastal flooding event that happened on the Texas Gulf Coast in 2008. We show that the inundation map generated by coastal HAND (c-HAND) has reasonable agreement with the ADCIRC simulation while taking about 1.7% of the time currently needed to run ADCIRC on a supercomputer. While our model correctly predicts 99% of ADCIRC-inundated DEM cells, it also overpredicts inundated area by a factor of approximately 27%. We combine c-HAND with the GeoFlood framework for fluvial flood forecasting to create a compound fluvial-coastal inundation mapping workflow that can be run in near real-time. c-HAND's fast wall-clock time and low CPU requirements can support decision making by first response personnel. The method provides timely and convenient access to crucial information, such as the locations of flooded roads and inundated coastal areas.

Sea level rise and extreme events along the Mediterranean coasts: the case of Venice and the awareness of local population, stakeholders and policy makers

Sea level rise (SLR) is among the major climate change effects threating the coasts of the Mediterranean basin, which are increasingly exposed to coastal flooding, especially along the low lying coastal plains, river deltas, lagoons and reclamation areas. Coastal erosion, beach retreat and marine flooding are already causing unprecedented environmental and socio-economic impacts on coastal populations. According to the Intergovernmental Panel on Climate Change (IPCC) these effects are expected to worsen by 2100 and beyond with a projected global SLR up to about 1 m above the current level. This study provides an overview of the Mediterranean basin, focusing on the vulnerable city of Venice, which is particularly exposed to marine flooding due to SLR and land subsidence. We show the current and future sea level trend as well as a flooding scenarios in the absence of the Experimental Electromechanical Module (MoSE), which is protecting the city of Venice since 2020. To understand the awareness of citizens in Venice to address SLR, we have engaged a group of stakeholders through a structured participatory process to develop solution-oriented, case-specific and site-specific Policy Tools. Our results show that the Policy Tools contain relevant, effective and implementable actions stemming from stakeholder interaction and consensus building, identifying relevant issues that should be considered for SLR adaptation policies. A more extensive participation in public processes is required to materialize the Policy Tools into concrete actions to help vulnerable areas adapt to the expected SLR by the end of this century.

Time to anoxia: Observations and predictions of oxygen drawdown following coastal flood events

The coastal terrestrial-aquatic interface (TAI) is a highly dynamic system characterized by strong physical, chemical, and biological gradients. In particular, shifting soil redox conditions and consumption of terminal electron acceptors, due in part to dynamic hydrologic conditions, is a strong driver of carbon availability and transformations across TAIs. However, while redox dynamics are well described, our ability to quantitatively forecast rates ofoxic to anoxic shifts in soils with different characteristics and inundation regimes is limited. We integrated field measurements, laboratory incubations, and model simulations to improve mechanistic understanding of oxygen consumption dynamics in coastal soils. Continuous in situ monitoring unexpectedly revealed that flooding caused temporary spikes in subsurface dissolved oxygen followed by rapid consumption in the wetlands. To further investigate these mechanisms in a controlled setting, we performed laboratory incubations using surface and subsurface soils from a TAI gradient (defined here as upland forest to transitional forest to wetland) in Western Lake Erie to measure oxygen consumption rates in TAI soils during flood events. In our experiments, wetland soils reached anoxia the fastest, in ∼ 9 h on average, whereas upland soils turned anoxic in ∼ 18 h. Subsurface upland soils did not turn anoxic even after two weeks of saturation in the lab, and their oxygen consumption patterns suggested carbon and/or nutrient limitation. These results are consistent with in-situ groundwater redox and oxygen measurements in the field, where wetland soils exhibited the highest rates of oxygen consumption along the TAI. Model simulations of oxygen consumption suggested that oxygen consumption had stronger abiotic controls in wetland soils but stronger biotic controls in upland soils, providing a useful framework for future incubation experiments. Microbial activity is a strong driver of oxygen consumption in TAI soils, although it is constrained by the availability of dissolved carbon in subsurface soils.

Improving our understanding of future tropical cyclone intensities in the Caribbean using a high-resolution regional climate model

The Caribbean region is prone to the strong winds and low air pressures of tropical cyclones and their corresponding storm surge that driving coastal flooding. To protect coastal communities from the impacts of tropical cyclones, it is important to understand how this impact of tropical cyclones might change towards the future. This study applies the storyline approach to show what tropical cyclones Maria (2017) and Dorian (2019) could look like in a 2 °C and 3.4 °C warmer future climate. These two possible future climates are simulated with a high-resolution regional climate model using the pseudo global warming approach. Using the climate response from these simulations we apply a Delta-quantile mapping technique to derive future changes in wind speed and mean sea level pressure. We apply this Delta technique to tropical cyclones Maria and Dorian’s observed wind and pressure fields to force a hydrodynamic model for simulating storm surge levels under historical and future climate conditions. Results show that the maximum storm surge heights of Maria and Dorian could increase by up to 0.31 m and 0.56 m, respectively. These results clearly show that future changes in storm surge heights are not negligible compared to end-of-the-century sea level rise projections, something that is sometimes overlooked in large-scale assessments of future coastal flood risk.

Coping Measures and Social Capital in Offsetting Effects of an Estuary Flash Flood in Bangladesh: A Case Study

The northern, northeastern, and southeastern parts of Bangladesh are highly susceptible to the impacts of flash flooding. Beyond these typical areas, flash floods also occur in the coastal areas of the country. The objective of this paper is to examine the ways residents of a coastal area have coped with the impacts of the flash flood event that took place on 5 August 2020 in 26 villages of Kamalnagar and Ramgati upazilas in the Lakshmipur district, Bangladesh. A household survey conducted in these villages revealed that nearly 83% of the respondents adopted two of the six broad groups of coping measures to recover from the impacts of the 2020 flash flood event. Unlike flash floods in typical areas, the survivors in the study area did not receive any emergency assistance either from local/national governments or NGOs, creating a cause of anger among the flash flood survivors. They offset the event effects largely by social capital through social networks and social relations. This study concludes that the government of Bangladesh should have effective policies to reduce the impacts of coastal flash flooding.

Improved efficient physics-based computational modeling of regional wave-driven coastal flooding for reef-lined coastlines

Coastal flooding affects low-lying communities worldwide and is expected to increase with climate change, especially along reef-lined coasts, where wave-driven flooding is particularly prevalent. However, current regional modeling approaches are either insufficient or too computationally expensive to accurately assess risks in these complex environments. This study introduces and validates an improved computationally efficient and physics-based approach to compute dynamic wave-driven regional flooding on reef-lined coasts. We coupled a simplified-physics flood model (SFINCS) with a one-dimensional wave transformation model (XBeach-1D). To assess the performance of the proposed approach, we compared its results with results from a fully resolving two-dimensional wave transformation model (XBeach-2D). We applied this approach for a range of storms and sea-level rise scenarios for two contrasting reef-lined coastal geomorphologies: one low relief area and one high relief area. Our findings reveal that SFINCS coupled with XBeach-1D generates flood extents comparable to those produced by XBeach-2D, with a hit rate of 92%. However, this method tends to underpredict the flood extent of weaker, high-frequency storms and overpredict stronger, low-frequency storms. Across scenarios, our approach overpredicted the mean flood water depth, with a positive bias of 7 cm and root mean square difference of 15 cm. Offering approximately 100 times greater computational efficiency than its two-dimensional XBeach counterpart, this flood modeling technique is recommended for wave-driven flood modeling in scenarios with high computational demands, such as modeling numerous scenarios or undertaking detailed regional-scale modeling.

Knowledge Graph Representation of Multi-Source Urban Storm Surge Hazard Information Based on Spatio-Temporal Coding and the Hazard Events Ontology Model

Coastal cities are increasingly vulnerable to urban storm surge hazards and the secondary hazards they cause (e.g., coastal flooding). Accurate representation of the spatio-temporal process of hazard event development is essential for effective emergency response. However, current knowledge graph representations face the challenge of integrating multi-source information with various spatial and temporal scales. To address this challenge, we propose a new information model for storm surge hazard events, involving a two-step process. First, a hazard event ontology is designed to model the components and hierarchical relationships of hazard event information. Second, we utilize multi-scale time segment integer coding and geographical coordinate subdividing grid coding to create a spatio-temporal framework, for modeling spatio-temporal features and spatio-temporal relationships. Using the 2018 typhoon Mangkhut storm surge event in Shenzhen as a case study and the hazard event information model as a schema layer, a storm surge event knowledge graph is constructed, demonstrating the integration and formal representation of heterogeneous hazard event information and enabling the fast retrieval of disasters in a given spatial or temporal range.

Crustal shear wave velocity and radial anisotropy beneath the Mississippi embayment from ambient noise tomography

Imaging of shallow multiple basins and middle to lower crustal structure beneath the Mississippi embayment is still limited. No tomography studies have delineated multiple basins as effectively as those from reflection and drilling experiments. Several studies have constructed different velocity models for the middle to lower crust. We take advantage of the Northern Embayment Lithosphere Experiment dataset and long-term deployment of 277 3-component broadband stations installed from 1990 to 2018 to image crustal shear wave velocity and radial anisotropy in the Mississippi embayment. We first construct 5–40s group velocity maps for Rayleigh wave and 5–30s ones for Love wave. In the 5 s group velocity map, we observe that low velocity features correlate spatially with the sediment thickness from the Crust 1.0 model. High velocity anomalies are associated with the Ozark uplift and the Nashville Dome. In the 32 s group velocity map, high-low velocity boundaries align with 40 km crustal thickness contours from the Crust 1.0 model. We then invert Rayleigh and Love group velocity dispersion for shear wave velocity and radial anisotropy at each grid point and construct a 3D model accordingly. At the depth of 0–5 km of the model, we find that low velocity features characterize the Mississippi Valley Graben, Rough Creek Graben, Black Warrior Basin, and coastal flood plain. High velocity features mark thinly sedimented regions, like the Ozark uplift and the Nashville Dome. Regions with high gravity anomalies are characterized with negative anisotropies. At the depth of 5–12 km, we observe low velocity features in the Missouri Batholith, centering around 10 km. This region is characterized with negative radial anisotropy (Vsh < Vsv), inferring possible intrusions. High-low velocity boundaries correlate with the Appalachian-Ouachita thrust front. At the depth of 12–24 km, the Mississippi Valley Graben is filled with high velocity material, which may be related to the formation of the graben due to isostatic equilibrium. At the depth of 24–43 km, high velocity anomalies characterize the lower crust of the Mississippi embayment, consistent with high density features from the inversion of free air anomaly. The high velocity anomaly might be responsible for the formation of the embayment due to isostatic adjustment. The average velocity in the lower crust is approximately 4.3 km/s. Mafic Pikwitonei granulite is a possible material, indicating relative strong lower crust. This work provides useful information to explain earthquake occurrence in the New Madrid Seismic Zone and regional tectonic settings.

Nonstationary coastal flood hazard analysis

It is well known that the increase in coastal flood hazard is expected to continue due primarily to climate change. While, previous studies have advanced probabilistic approaches for estimating future coastal flood hazard, two seminal issues have received little attention: (1) sea level trend projections that arise as a consequence of climate change not being incorporated in nonstationary coastal flood frequency analysis and (2) traditional stationary approaches that estimate return periods are not suited for analysis of nonstationary water levels. In this paper, a regression approach for sea level rise estimation is proposed to detrend water levels. The peak-over-threshold approach is used to analyze the probabilistic behavior of detrended water levels via a generalized Pareto distribution. Two interpretations of return period—the expected waiting time until an exceedance event occurs and the time associated with the expected number of exceedance events equal to one—are elaborated in a nonstationary context. By incorporating the existing sea level trend projections and using two interpretations of return period, flood hazard curves with uncertainty (i.e., water levels vs. return periods) are developed to describe the probabilistic behavior of future coastal flood hazards. Two case studies are conducted: one for Boston, Massachusetts, and one for New York City, New York.

DeltaDTM: A global coastal digital terrain model

Coastal elevation data are essential for a wide variety of applications, such as coastal management, flood modelling, and adaptation planning. Low-lying coastal areas (found below 10 m +Mean Sea Level (MSL)) are at risk of future extreme water levels, subsidence and changing extreme weather patterns. However, current freely available elevation datasets are not sufficiently accurate to model these risks. We present DeltaDTM, a global coastal Digital Terrain Model (DTM) available in the public domain, with a horizontal spatial resolution of 1 arcsecond (∼30 m) and a vertical mean absolute error (MAE) of 0.45 m overall. DeltaDTM corrects CopernicusDEM with spaceborne lidar from the ICESat-2 and GEDI missions. Specifically, we correct the elevation bias in CopernicusDEM, apply filters to remove non-terrain cells, and fill the gaps using interpolation. Notably, our classification approach produces more accurate results than regression methods recently used by others to correct DEMs, that achieve an overall MAE of 0.72 m at best. We conclude that DeltaDTM will be a valuable resource for coastal flood impact modelling and other applications.

Spatiotemporal changes of climatic disasters and population displacements in Africa

ABSTRACT Frequent global climatic disasters are posing a growing threat, especially in populous Africa. Understanding the intrinsic interactions between climatic disaster and the resulting affected population in Africa can provide a representative sample of developing countries for global governance of climate change. This study explored the spatiotemporal dynamics in climatic disasters and disaster-related displacements in Africa from a geographical perspective. The results showed that climatic disasters in Africa occurred with seasonality consistent with African climate characterized by distinct dry and rainy seasons, manifested as flood, storm, and heat wave events occurring in the rainy season, wildfire and cold wave events taking place in the dry season, and prolonged droughts spanning both dry and rainy seasons. Meanwhile, the spatial pattern and variation trend of climatic disasters and displacements varied greatly by the five African sub-regions. East Africa experienced the highest number of disasters and displacements, while Southern Africa bore the least. Flood and drought triggered a third of total displacements in the most populated West Africa. The least frequent disasters dominated by flood only affected less than 10.9% of the total in Central Africa. 6.8% of the total displacements were primarily induced by coastal flood in North Africa.

An efficient metamodel to downscale total water level in open beaches

A hybrid methodology is described to obtain the wave set-up and infragravity wave level components for estimating total water level (TWL) in coastal areas, taking into account the surf zone hydrodynamics involved. By combining statistical tools and numerical methods, high-resolution spatial distributions of wave height and water level components are calculated efficiently and seamlessly. The proposed methodology is tested and numerically validated on La Salvé beach (Cantabria, Spain), showing a robust performance for diverse scenarios. The resulting TWL can efficiently evaluate coastal hazards in forecast and hindcast mode, having strong potential as a guideline for coastal engineers, managers and emergency planners in the elaboration of adaptation and mitigation strategies. As an application of the metamodel to these coastal management tasks, significant past storm events have been reconstructed, and their associated TWL-driven coastal flooding hazard has been analyzed using a impact rank scale.