Fluvial Flood Research Articles

Impact of Tides and Surges on Fluvial Floods in Coastal Regions

Fluvial floods in coastal areas are affected by tides and storm surges, while the impact is seldom quantified because the dynamics of seawater levels are often not represented in river routing models. This study established a model framework by coupling a surge model with a global hydrodynamic model at a higher spatiotemporal resolution than previous studies so that flood processes affected by seawater level fluctuation in small river basins can be investigated. Model implementation in Zhejiang Province, China, shows that the integration of dynamic seawater levels increases the stress of flooding along the Zhejiang coasts. The ocean effect varies in space, as it is much stronger in northern Zhejiang because of the lower landform and strong tidal amplification, while the mountainous rivers in southern Zhejiang are dominated by river flow regimes. Typhoon Lekima resulted in compound flood events (i.e., rainfall-induced riverine flood, tides, and surges), during which the maximum water level at the outlet of Qiantang River was 0.80 m in the default model settings with a constant downstream seawater level (i.e., 0 m), while it increased to 2.34 m (or 2.48 m) when tides (or tides and surges) were considered. The maximum increase due to tides and surges was 2.09 m and 1.45 m, respectively, while the maximum increase did not match the time of the flood peak. This mismatching indicates the need to consider different processes in physical models rather than linearly summing up different extreme water levels (i.e., river flood, tide, and surge) found in previous studies. The model framework integrating various flow processes will help to prevent risks of compound events in coastal cities in practical and future projections under different scenarios.

Unraveling the complexities of urban fluvial flood hydraulics through AI

As urbanization increases across the globe, urban flooding is an ever-pressing concern. Urban fluvial systems are highly complex, depending on a myriad of interacting variables. Numerous hydraulic models are available for analyzing urban flooding; however, meeting the demand of high spatial extension and finer discretization and solving the physics-based numerical equations are computationally expensive. Computational efforts increase drastically with an increase in model dimension and resolution, preventing current solutions from fully realizing the data revolution. In this research, we demonstrate the effectiveness of artificial intelligence (AI), in particular, machine learning (ML) methods including the emerging deep learning (DL) to quantify urban flooding considering the lower part of Darby Creek, PA, USA. Training datasets comprise multiple geographic and urban hydraulic features (e.g., coordinates, elevation, water depth, flooded locations, discharge, average slope, and the impervious area within the contributing region, downstream distance from stormwater outfalls and dams). ML Classifiers such as logistic regression (LR), decision tree (DT), support vector machine (SVM), and K-nearest neighbors (KNN) are used to identify the flooded locations. A Deep neural network (DNN)-based regression model is used to quantify the water depth. The values of the evaluation matrices indicate satisfactory performance both for the classifiers and DNN model (F-1 scores- 0.975, 0.991, 0.892, and 0.855 for binary classifiers; root mean squared error- 0.027 for DNN regression). In addition, the blocked K-folds Cross Validation (CV) of ML classifiers in detecting flooded locations showed satisfactory performance with the average accuracy of 0.899, which validates the models to generalize to the unseen area. This approach is a significant step towards resolving the complexities of urban fluvial flooding with a large multi-dimensional dataset in a highly computationally efficient manner.

Impact of climate change on spatiotemporal variations in the vegetation cover and hydrology of district Nowshera

Abstract This research seeks to validate climate change in the district of Nowshera, as well as its impact on NDVI (vegetation) and hydrological events such as monsoon rains. Modified Mann-Kendall and Sen's statistics were used to examine climate parameters. Using climate factors and MODIS NDVI (Normalized Difference Vegetation Index) data, regression analysis was used to study a 20-year (2001–2020) spatiotemporal climate-vegetation relationship. Landsat 5 and 7 NDWI (Normalized Difference Water Index) data, as well as SRTM DEM (Digital Elevation Model) data, were used to map extreme weather events such as floods caused by climate change. For mapping and data processing, ArcGIS and R tools were used. The findings revealed significant trends in climate parameters, which has led to climate change in the area, affecting NDVI and water cycles. The NDVI showed a generally good trend, however some places were damaged. Monsoon rain patterns and rates have been substantially disrupted, resulting in flash and fluvial floods. The risk of future floods owing to the Kabul and Indus rivers was shown through watershed delineation, which is compounded by climate change and anthropogenic activities. It is advised that government officials and policymakers establish climate change mitigation plans for regional sustainable development and vegetation restoration.

Does Flooding Undermine the Management Capacities of the COVID-19 Pandemic? A Study of Lagos State, Nigeria

Given the dynamics of climate events (hazards) and their linkages to human health, it is imperative to continuallly check the impacts of these events on the public health system. While efforts have been made to understand fluvial flood and COVID-19 vulnerability and impacts, substantial gaps about impacts of their simultaneous occurrence on densely-populated communities abound. This paper presents an assessement of the occurrence of fluvial flooding and its potential to undermine the management of the COVID-19 pandemic in Lagos State, Nigeria. This study applied the indicator-based risk assessment method to determine the pattern of COVID-19 risk in the study area. Flood hazard and health facilities datasets of Lagos State were also used to determine the flood extent and pattern of flood-exposed health facilities in ArcGIS 10.7.1. Results revealed that Apapa, Eti Osa, Ibeju Lekki, Mushin, and Lagos Mainland local government areas (LGAs) were at a very high risk of COVID-19. Results also highlight six LGAs that should be prioritized in managing COVID-19 due to the exposure of the majority of its health facilities to flood. Far-reaching recommendations on the need to prioritize these flood-exposed health facilities for COVID-19 risk reduction, humanitarian aid and prevention strategies is made. Also, future research in the study area should explore sustainable strategies to adapt to COVID-19 and flood events from an interdisciplinary perspective.

A classification scheme for sedimentary architectures arising from aeolian-fluvial system interactions: Permian examples from southeast Utah, USA

• Novel classification scheme for types of aeolian-fluvial interaction in ancient erg deposits. • Scheme applied to outcrops of Permian Cutler Group to enable 3D architecture analysis. • Classification scheme is generally applicable. • Classification scheme assists palaeoenvironmental interpretation. The preservation of the sedimentary deposits of arid environments is determined by both geomorphic and geologic processes. Sedimentary evidence of aeolian-fluvial system interactions in arid-climate settings are preserved in both recent and ancient sedimentary successions. However, despite considerable prior sedimentological research, there is no unifying scheme to provide generalized definitions of commonly occurring types of preserved aeolian-fluvial interactions. This study addresses this shortcoming by introducing a novel classification scheme for sedimentary architectures arising from such system interactions. The scheme is demonstrated through reference to examples from the Permian Cutler Group, Paradox Basin, Southeast Utah, USA – a sedimentary record of competing aeolian dune-field and fluvial-fan systems along a palaeo-coastline. Well-preserved, laterally continuous outcrops arranged in different orientations enable three-dimensional architectural characterization. The sedimentary record of eight distinct types of aeolian-fluvial interaction are identified: (i) water-table-controlled interdune sedimentation; (ii) deposits of low-energy fluvial floods; (iii) isolated fluvial channel-fills originating from episodic and confined flooding of interdunes in orientations parallel to the trend of dune crestlines; (iv) channel fills oriented perpendicular to the trend of dune crestlines; (v) amalgamated fluvial channel elements resulting from persistent, long-lived but confined dune-field flooding; (vi) deposits of unconfined sheet-like flood deposits; (vii) fluvial breaching of dunes and their reworking by catastrophic flooding; (viii) aeolian reworking of fluvial deposits. Each interaction type is characterized in terms of preserved sedimentary facies, architectural element geometries and associated proprieties, to demonstrate sedimentary variability in three dimensions. Results provide a guide with which to make sedimentological comparisons and interpretations between active systems and their preserved depositional record.

Palaeohydrology from the Northern Salado River, a lower Parana river tributary (Argentina)

Palaeofloods and drainage palaeostage can be approached from sedimentological, stratigraphical, geomorphological, geodetic, and geophysical information. This allows us to supply pre-instrumental and historical data and to assess a particular flood-prone area. It has been proved that the study of Late Holocene fluvial sediments is valuable source to estimate 1 × 102-1x103yr. scale occurrence and long-term recurrence of maximum events. The geological evidence of palaeofloods in lowlands in Central Argentina may reveal higher discharges likely occurred in the near past.In this work, we attempt to identify sedimentological evidence of past floods in Late Holocene sediments from the northern Salado River (NSR), an important tributary of the lower Paraná River basin (Chaco-Pampean plain region). In the yr. 2003, the lower reaches of the NSR recorded an extreme flood event that provoked a disaster in Santa Fe, a city of 500,000 inhabitants located at the river mouth.Considering the importance of this event, we developed a geomorphometry methodology for discriminating different levels of fluvial terraces and flood indicators in a representative area of the NSR, using multi-scale resolution Digital Elevation Model (DEM) data. Descriptions of flood-associated fluvial landforms and sedimentological stratigraphic attributes were performed in the field. High-resolution geodetic information and digital optical images were obtained from UAV photogrammetry. Ground Penetrating Radar (GPR) cross-sections were achieved and addressed to detect extreme flood evidence. A geomorphometric routine was applied to simulate the extreme flood scenarios, based on the data obtained from the field. The map resulting from the simulation was compared to satellite images recorded in the yr. 2003 extreme flood. A series of slackwater deposits and other palaeostage indicators (SWD-PSI) showed elevations higher than those reached over the yr. 2003 extraordinary flood (instrumentally recorded) and in the yr. 1914 historic flood event. The geomorphometric simulation of a flood event, calibrated from these diagnostic landforms, allowed us to extend the flood-prone area beyond the boundaries of the current active floodplain and channel. The integrative methodology enabled the mapping of areas potentially prone to flooding. The estimations of the discharges associated to the inferred palaeofloods could be 50–80% larger than the maximum events historically documented and instrumentally measured.

The role of susceptibility, exposure and vulnerability as drivers of flood disaster risk at the parish level

Fluvial flooding continues to be a process that has a major impact on society, the environment and the economy. Although its natural triggering factors, the spatial configuration of exposure and vulnerability is expected to play a relevant role in explaining the damage records. The starting point of this research is the use of existing flood susceptibility, exposure and social vulnerability mapping, produced at the parish level, as input data in a Classification and Regression Trees’ (CART) model. Two models were ran, autonomously, that use two databases of flood damage as dependent variables: one including the human damages (fatalities, missing, injured, displaced and evacuated people) from flood events—the DISASTER database; another one that sums the DISASTER cases and the lower impact damages (damages to roads, railroads and buildings). The results show a quite distinct classification of parishes, whether one database is used or the other. The DISASTER database reveals susceptibility as the most relevant flood risk driver in explaining the damage patterns, while the database with all the flood cases identifies exposure as the more relevant driver. In the end, the degree of damages as documented in databases is conditioned by the geographical distribution and overlay configuration of the three flood risk drivers. Finally, the CART classification groups are analyzed at the light of the European Union’s Floods Directive areas of significant potential flood risk. This analysis showed that the Directive’s parishes are interpreted differently—in terms of their positioning in face of the risk drivers—which is explained by the use of distinct impacting-criteria in the construction of the flood damage databases.

Assessment of the effects of natural and anthropogenic drivers on extreme flood events in coastal regions

With climate change leading to sea level rise and frequent occurrence of extreme weather events, extreme flood disasters occur frequently in coastal cities, especially under the combined influence of heavy rainfall, fluvial floods, and storm surges. Compound floods from multiple sources are prone to superimposed effects, greatly aggravating flooding. In addition, the influence of anthropogenic activities such as man-made flood control projects in coastal regions also need to be explored. Using the Ling River Basin on the east coast of China as a case study, this study investigated the impacts of natural and human drivers on the spatiotemporal distribution of extreme floods based on a 1D–2D coupled hydrodynamic model. The hydrodynamic model was calibrated and validated based on historical flood events, and the validated model was further used to reproduce the devastating flood caused by Typhoon Lekima in 2019. The results show that the model has great capability and accuracy in simulating both the flood occurrence process and its inundation extent under natural and anthropogenic influences. The results also indicate that the high amount of discharge from the upper reaches of the Ling River was the main driver that caused the catastrophic consequences, and 83% of the inundation is caused by this factor. Comparatively, the failure of flood protection measures, which was a human driver, aggravated the influence of floods in local regions. Assessing the individual and superimposed effects of natural and human drivers on flooding may help enhance the resilience of flooded coastal areas.

Application of Unmanned Aerial Vehicle DEM in flood modeling and comparison with global DEMs: Case study of Atrak River Basin, Iran.

Digital Elevation Models (DEMs) play a significant role in hydraulic modeling and flood risk management. This study initially investigated the effect of Unmanned Aerial Vehicle (UAV) DEM resolutions, ranging from 1m to 30m, on flood characteristics, including the inundation area, mean flow depth, and mean flow velocity. Then, the errors of flood characteristics for global DEMs, comprising ALOS (30m), ASTER (30m), SRTM (30m), and TDX (12m) were quantified using UAV DEM measurements. For these purposes, the HEC-RAS 2D model in steady-state conditions was used to simulate the flood with return periods of 5- to 200 years along 20km reach of Atrak River located in northeastern Iran. Results indicated when UAV DEM resolution decreased from 1m to 30m, inundation area and mean flow depth increased 17.0% (R2=0.94) and 10.2% (R2=0.96) respectively, while mean flow velocity decreased 16.8% (R2=-0.94). Validation of the hydraulic modeling using the modified normalized difference water index demonstrated that the HEC-RAS 2D model in conjunction with UAV DEM simulates the flood with ⁓92% accuracy. Comparing the global DEMs with UAV DEM showed that the root mean square error (RMSE) values of the flow depth for ASTER, SRTM, ALOS, and TDX DEMs were 1.77, 1.12, 1.02, and 0.93m, and the RMSE values of the flow velocity for the same DEMs were 0.81, 0.66, 0.55, and 0.47m/s, respectively. Furthermore, TDX DEM with a 6.15% error in the inundation area was the nearest to UAV measurements. Overall, TDX DEM revealed a better performance in hydraulic modeling of the fluvial flood characteristics. Hence, it is recommended for environments where high-resolution topography data is scarce. The results of this study could potentially serve as a guideline for selecting global DEMs for hydraulic simulations.

Are Pluvial and Fluvial Floods on the Rise?

The aim of this paper is accurately framed in its title: Are pluvial and fluvial (river) floods on the rise? First, physical mechanisms that drive changes in hazard of pluvial and fluvial floods were examined. Then, a review of literature was undertaken on detection and an attribution of changes in hazard of pluvial and fluvial floods in observation records for past to present, as well as in model-based projections for the future. Various aspects, factors, processes and mechanisms, as well as various indices of interest were considered. There is quite a common, even if not scientifically justified, belief that, generally, floods are on the rise. However, in this paper, a balanced, knowledge-based assessment was undertaken, with discussion and interpretation, including caveats and indicating considerable departures from such a flat-rate statement. Observation records show that precipitation extremes have been intensifying on a global scale and for many regions. A formal detection and attribution analysis shows that intensification of rainfall events may have been influenced by greenhouse gas forcing of anthropogenic origin. Frequency and magnitude of pluvial floods is on the rise with increasing intense precipitation, while changes of river floods are more complex. High river discharges were found to increase in some regions, but to decrease in other regions, so that no general corollaries can be drawn at the global scale. Heavy rainfall events and pluvial floods are projected to become, almost ubiquitously, more frequent and more intense with progressing climate change, while frequency and magnitude of fluvial floods are likely to increase in many but not all regions.

Assessing the Role of Extreme Mediterranean Events on Coastal River Outlet Dynamics

River mouths are highly dynamic environments responding very rapidly to changes in wave energy or river floods. While the morphological response during floods or during marine storm events has been widely documented in the literature, little is known about the mechanisms acting during the co-occurrence of fluvial and marine hazards. This concomitance of river flood and marine storm is quite common in the western Mediterranean Sea, and was the case for the Gloria event, considered to be the most extreme event in recent decades. During this event, monitoring of hydrodynamics and morphological evolution was implemented, making it possible to better understand the impact of concomitant marine storm and fluvial flood during an extreme meteorological event on spit breaching of a small Mediterranean river mouth. Monitoring using a combination of high-resolution hydrodynamic measurements, topographic and bathymetric surveys, and sediment cores was used before, during, and after the storm “Gloria”. The results suggest an amplification of the morphological impact of the events and a different morphogenic response than if each of the events had acted independently on the system. The marine storm, occurring first, weakened the spit and initiated its breaching, which was continued by the extreme fluvial flood, thus leading to the complete destruction of the mouth. The destruction of the spit acted as a sediment source for subaqueous large delta deposition amounting to 50% of the total volume. The contribution of the river, estimated at 30%, was quite low for an exceptional event, showing the importance of locating rainfall in a catchment area controlled by a dam. For this event, extreme morphological evolution was observed, as well as the importance of water levels in the river mouth, which probably increased flood hazards, demonstrating the importance of including the compounding effect of extreme coastal water levels in river flood risk management.

Compound flooding in convergent estuaries: insights from an analytical model

Abstract. We investigate here the effects of geometric properties (channel depth and cross-sectional convergence length), storm surge characteristics, friction, and river flow on the spatial and temporal variability of compound flooding along an idealized, meso-tidal coastal-plain estuary. An analytical model is developed that includes exponentially convergent geometry, tidal forcing, constant river flow, and a representation of storm surge as a combination of two sinusoidal waves. Nonlinear bed friction is treated using Chebyshev polynomials and trigonometric functions, and a multi-segment approach is used to increase accuracy. Model results show that river discharge increases the damping of surge amplitudes in an estuary, while increasing channel depth has the opposite effect. Sensitivity studies indicate that the impact of river flow on peak water level decreases as channel depth increases, while the influence of tide and surge increases in the landward portion of an estuary. Moreover, model results show less surge damping in deeper configurations and even amplification in some cases, while increased convergence length scale increases damping of surge waves with periods of 12–72 h. For every modeled scenario, there is a point where river discharge effects on water level outweigh tide/surge effects. As a channel is deepened, this cross-over point moves progressively upstream. Thus, channel deepening may alter flood risk spatially along an estuary and reduce the length of a river estuary, within which fluvial flooding is dominant.

Evaluating the Response of Hydrological Stress Indices Using the CHyM Model over a Wide Area in Central Italy

Central Italy is characterized by complex orography. The territorial response to heavy precipitation may activate different processes in terms of hydrogeological hazards. Floods, flash floods, and wet mass movements are the main ground effects triggered by heavy or persistent rainfall. The main aim of this work is to present a unique tool that is based on a distributed hydrological model, able to predict different rainfall-induced phenomena, and essential for the civil protection early warning activity. The Cetemps Hydrological Model is applied to the detection of hydrologically stressed areas over a spatial domain covering the central part of Italy during a weather event that occurred in 2014. The validation of three hydrological stress indices is proposed over a geographical area of approximately 64,500 km2 that includes catchments of varying size and physiography. The indices were used to identify areas subject to floods, flash floods, or landslides. Main results showed very high accuracies (~90%) for all proposed indices, with flood false alarms growing downstream to larger basins, but very close to zero in most cases. The three indices can give complementary information about the predominant phenomenon and are able to distinguish fluvial floods from pluvial floods. Nevertheless, the results were influenced by the presence of artificial reservoirs that regulated flood wave propagation, therefore, indices timing slightly worsen downstream in larger basins.

An Efficient Modeling Approach for Probabilistic Assessments of Present-Day and Future Fluvial Flooding

Risk-informed flood risk management requires a comprehensive and quantitative risk assessment, which often demands multiple (thousands of) river and flood model simulations. Performing such a large number of model simulations is a challenge, especially for large, complex river systems (e.g., Mekong) due to the associated computational and resource demands. This article presents an efficient probabilistic modeling approach that combines a simplified 1D hydrodynamic model for the entire Mekong Delta with a detailed 1D/2D coupled model and demonstrates its application at Can Tho city in the Mekong Delta. Probabilistic flood-hazard maps, ranging from 0.5 to 100 year return period events, are obtained for the urban center of Can Tho city under different future scenarios taking into account the impact of climate change forcing (river flow, sea-level rise, storm surge) and land subsidence. Results obtained under present conditions show that more than 12% of the study area is inundated by the present-day 100 year return period of water level. Future projections show that, if the present rate of land subsidence continues, by 2050 (under both RCP 4.5 and RCP 8.5 climate scenarios), the 0.5 and 100 year return period flood extents will increase by around 15- and 8-fold, respectively, relative to the present-day flood extent. However, without land subsidence, the projected increases in the 0.5 and 100 year return period flood extents by 2050 (under RCP 4.5 and RCP 8.5) are limited to between a doubling to tripling of the present-day flood extent. Therefore, adaptation measures that can reduce the rate of land subsidence (e.g., limiting groundwater extraction), would substantially mitigate future flood hazards in the study area. A combination of restricted groundwater extraction and the construction of a new and more efficient urban drainage network would facilitate even further reductions in the flood hazard. The projected 15-fold increase in flood extent projected by 2050 for the twice per year (0.5 year return period) flood event implies that the “do nothing” management approach is not a feasible option for Can Tho.

High-resolution sequence stratigraphy and facies assemblage in flood-dominated and mixed deltaic systems: Insights from early Eocene Figols Group, South-central Pyrenean basin

The upper part of the Early Eocene Figols Group cropping out near the town of Tremp (province of Lerida, Spain), is a wonderfully exposed sedimentary succession mainly constituted by mouth bar deposits and delta-front sandstone lobes, forming a fluvio-deltaic system dominated by catastrophic fluvial floods. These deltaic sandstones are vertically associated with carbonate and hybrid (mixed carbonate and siliciclastic) sediments that are physically related to a carbonate ramp platform which crops out in the southernmost part of the study area. The vertical and lateral juxtaposition of these depositional systems allows investigating how the stratigraphic controls (as climate and relative sea level) affect the resulting facies assemblages. The studied succession has been subdivided following a pragmatic physical stratigraphic approach into three 3rd order large-scale depositional sequences (FG2, FG3, and FG4), six 4th order small-scale depositional sequences and 21 EDSs (elementary depositional sequences). The latter are considered the stratigraphic building block of the succession, made of 10s of meter scale forestepping sandstones followed by, backstepping sandstones, bioclastic and mudstone sediments. During the lowstand system tract (LST), the depositional sequences FG2 and FG3 are characterized by the occurrence of flood-dominated deltaic systems (mouth bars and lobes). These deltaic deposits mainly developed in the northern sector characterized by higher subsidence. The overlain transgressive system tract (TST) is dominated by hybrid sediments and carbonates that initially accumulated in the southern zone and then progressively spread out over the entire area. The highstand system tract (HST) is mainly constituted by shelfal fine-grained sediments reflecting the reactivation of the fluvial input and deltaic clastic deposition in a more landward position. This sequential model resulted to be applicable at all hierarchical scales and in particular to the EDS scale. In FG4, the fluvio-deltaic systems became coarser-grained and channelized, the carbonate production on the shelf decreased and lagoonal fines were accumulated so as to separate vertically the fluvio-deltaic bodies. Syn-sedimentary tectonic activity capable to produce local variations of the available accommodation space is inferred by the geometry and facies distribution shown in the high-resolution correlation framework, particularly if considered at the physical scale of EDSs.

Drivers of future fluvial flood risk change for residential buildings in Europe

Flooding is the most costly natural hazard in Europe. Climatic and socioeconomic change are expected to further increase the amount of loss in the future. To counteract this development, policymaking, and adaptation planning need reliable large-scale risk assessments and an improved understanding of potential risk drivers.In this study, recent datasets for hazard and flood protection standards are combined with high resolution exposure projections and attributes of vulnerability derived from open data sources. The independent and combined influence of exposure change and climate scenarios rcp45 and rcp85 on fluvial flood risk are evaluated for three future periods centered around 2025, 2055 and 2085. Scenarios with improved and neglected private precaution are examined for their influence on flood risk using a probabilistic, multivariable flood loss model — BN-FLEMOps — to estimate fluvial flood losses for residential buildings in Europe.The results on NUTS-3 level reveal that urban centers and their surrounding regions are the hotspots of flood risk in Europe. Flood risk is projected to increase in the British Isles and Central Europe throughout the 21st century, while risk in many regions of Scandinavia and the Mediterranean will stagnate or decline. Under the combined effects of exposure change and climate scenarios rcp45, rcp85, fluvial flood risk in Europe is estimated to increase seven-fold and ten-fold respectively until the end of the century. Our results confirm the dominance of socioeconomic change over climate change on increasing risk. Improved private precautionary measures would reduce flood risk in Europe on an average by 15%. The quantification of future flood risk in Europe by integrating climate, socioeconomic and private precaution scenarios provides an overview of risk drivers, trends, and hotspots. This large-scale comprehensive assessment at a regional level resolution is valuable for multi-scale risk-based adaptation planning.

Acoustic methods in physical geography: Applications and future development

Sound is produced by many geomorphic and hydrological processes, such as rockfalls and landslides, ocean waves, fluvial flood flows and collisions among moving bedload clasts. In these and other areas of study, acoustic methods have found useful application to detect and quantify the operation of important landscape processes. In some, such as the recording of river discharge, the occurrence of rare events such as exfoliation or the presence and movement of dust devils (willy-willies), the use of acoustic methods is still in a relatively early stage of development and testing. The use of acoustic methods in the recording of rainfall occurrence and intensity is also developing and has the capacity to yield data with higher temporal resolution than can be achieved using conventional rain gauges. Novel acoustic methods include the analysis of the sound recorded by security cameras, which potentially form a vast network of observing stations. The frequencies of sound generated by land-surface processes include audible sound, ultrasound and infrasound at frequencies below the human hearing range. All appear to provide opportunities for further development of useful research tools and methodologies.

Evaluating the Risk and Complexity of Pluvial Flood Damage in the U.S.

Flood hazard in the U.S. is typically separated into two categories: storm surge and inland. Inland flooding is frequently represented as fluvial, stemming from overflow of rivers and streams. However, significant inland flood risk also exists in the form of pluvial flooding, resulting from ponding of water, and often occurring due to insufficient drainage in urban areas. Pluvial flood risk can be complex to model and is often not shown on floodplain maps, leading to significant uninsured risk. While pluvial and fluvial flooding are sometimes lumped together for purposes of modeling, insurance, and risk management, we hypothesize that key differences exist in damage associated with these types of inland flooding. We investigate and quantify these differences through study of three datasets: (i) Tropical cyclone (TC) flood insurance claims; (ii) non-Tropical Cyclone (non-TC) flood insurance claims; and (iii) Hurricane Harvey flood insurance claims in the Houston area. From our data analyses, we find that fluvial claims involve greater damage on average and are more likely to occur within the mapped Special Flood Hazard Area (i.e., 100-year floodplain) than pluvial claims. However, pluvial flooding is more frequent overall being the cause of 74% of TC and 60% of non-TC flood insurance claims in the U.S. TC floods have a higher percentage of pluvial flood insurance claims and higher average pluvial damage than non-TC floods. Analysis of Hurricane Harvey claims shows that zip codes with higher-than-expected losses tend to have high percentages of pluvial claims. Pluvial flooding and its local nuances exhibit the potential to reduce the accuracy of catastrophe models of expected flood damage.

Flood modelling and proposed Blue-Green Solutions – A case study in Lisbon, Portugal

Abstract. This study assesses the potential benefit of Blue-Green Solutions (BGS), green rooftops, rain gardens, permeable pavements, and bioswales, in Lisbon, Portugal. These proposed mitigation measures are applied using TFM-DYN (Nilsson et al., 2021) to simulate potential fluvial flooding distributions from a 10- and 50-year rain event.Water depth of over 30 centimeters can cause damage to infrastructure. The model results show water depths of over 40 centimeters in some parts of the study area for the 10-year return period, raising the need for action. For the 50-year return period even more areas will be affected. These floods can occur at a relatively rapid pace. Four BGS were implemented for flood mitigation. Areas with green roofs and rain gardens showed a lowering in water depth for both return periods. This study shows that even relatively simple data allows for an estimation of urban flooding and the potential effect of BGS for specific locations can easily be determined.

Federally Overlooked Flood Risk Inequities in Houston, Texas: Novel Insights Based on Dasymetric Mapping and State-of-the-Art Flood Modeling

In the United States, the Federal Emergency Management Agency (FEMA) delineates 100-year flood zones to define risks, regulate flood insurance premiums, and inform flood management. Evidence indicates that FEMA flood maps are incomplete, calling much of our current knowledge of U.S. flood hazard inequities into question. We use a state-of-the-art flood hazard model and census tract-level dasymetrically mapped sociodemographic data to examine flood risk inequities in the Greater Houston area, where increasingly frequent and damaging flood events are occurring. We innovate by analyzing federally overlooked 100-year flood risks (100-year flood zones delineated by the flood hazard model that are outside of FEMA 100-year flood zones). Results indicate that nearly 1 million Greater Houston residents live in federally overlooked 100-year flood zones. Black and Asian neighborhoods experience disproportionate risk in federally overlooked pluvial and fluvial flood zones, and Hispanic neighborhoods experience disproportionate risk in all federally overlooked zones (coastal, pluvial, and fluvial). High flood risk and the relative lack of protective resources in federally overlooked 100-year flood zones doubly jeopardizes racial and ethnic minority communities. Our findings and recent flood disasters suggest that future flood impacts in Greater Houston will be catastrophic and unjust unless FEMA revises their risk mapping and management approach to promote long-term public safety and social equity.