Flood Hazard Mitigation Research Articles

Flood frequency analysis in the lower Burhi Dehing River in Assam, India using Gumbel Extreme Value and log Pearson Type III methods

Flood is a widespread climate-related hazard with the potential to occur in almost any geographical location where fluvial processes are active and can occur due to the involvement of multiple factors. Flood frequency analysis (FFA) is considered a valuable hydrologic tool to know the magnitude and frequency of the recurrence of floods. In this research, we have examined the Lower Burhi Dehing River (LBDR) in Assam, India, which frequently experiences severe flooding due to its meandering course induced by heavy monsoon rainfall. Therefore, the present research aims to analyze past flood events and current trends and predict future flood frequencies using Gumbel’s extreme value distribution and Log Pearson Type III Method. In this particular investigation, 25 years of annual maximum peak discharge data from 1972 to 1997 was employed to examine the discharge records of LBDR. This research estimated the return periods of different flood magnitudes, quantifying the likelihood of future floods with varying degrees of severity. In this regard, the return periods are estimated at 2, 5, 10, 20, 50, 100, and 200 years. The study reveals that the largest flood event occurred in 1972, with a discharge of 1134.4 m3/s, and the smallest flood event occurred in 1997, with a discharge of 214.65 m3/s. The 2-year flood is a relatively common event with a 50% probability of occurring in any given year, characterized by a moderate discharge of 1384.90 m3/s and minor impacts of 0.3665. The 5-year flood, occurring with a 20% chance annually, brings a significantly higher water level of 2008.81 m3/s and moderate-to-severe impacts of 1.4999, potentially causing widespread flooding. In the 10-year and 50-year return period, which has a probability of returning 10% and 2% chance annually, the discharge will reach 2421.89 m3/s and 3331.01 m3/s, respectively. The outcome of this research will sustainably guide policymakers and environmental planners to mitigate flood hazards.

Performance of low impact development techniques in flood hazard mitigation in a closed urbanised catchment for extreme precipitation events

ABSTRACT Sealing of surfaces alters the natural hydrological conditions, thereby increasing the urban flood risk. Rainwater management in urban environments has traditionally been performed using conventional urban drainage systems (UDS). However, low impact development (LID) solutions have been recognised in recent decades as effective in controlling runoff. The present work aims to evaluate the efficiency of LID techniques in flood control in a closed basin characterised by high urbanisation for three extreme precipitation events in the city of Natal, Brazil, using 1D/2D modelling. Two techniques were tested, namely bioretention cells (BCs) and rain barrels (RBs) alone or combined. The existing UDS in the area proved unable to control flooding of the basin. Water depths exceeded 0.5 m in all events. The efficiency of the LID solutions evaluated was extremely low, with reductions of less than 1% for highest hazard class. Combining the techniques produced better performance than implementing isolated techniques.

Assessment of a geomorphological-based design for coastal protection: The case of a wave-cut platform on the Bogliasco coast (Liguria Region, NW Italy)

Coastal erosion processes and the associated risks pose a significant challenge for coastal urban settlement administrations. Coastal managers are often seeking new approaches and solutions for coastal protection. Introducing protective structures such as breakwaters and groins often poses problems for management, e.g. modification of the natural panorama, changes within the local coastal dynamics and associated implications with regard to coastal hazards and risks. This paper describes a geomorphological-based approach to coastal structure design, taking as its study case the Bogliasco coast in the region of Liguria, near the eastern border of the municipality of Genova (Northwest Italy). Bogliasco is a stretch of rocky coast exposed to the most intense storms of the Liguria Sea and where the urban settlement reaches the edge of the cliff. To prevent cliff collapse and coastal flooding (and mitigate the associated risks), this study proposes an approach based on the structural recovery of an ancient wave-cut platform currently consumed by erosion. The recovered structure dissipates incoming waves, helping to mitigate both the erosive phenomena at the foot of the cliff and the risk of coastal flooding. The performance of the coastal protection project was evaluated by comparing the results of the XBeach model simulations for ante-operam and post-operam scenarios. The results indicate that the adopted solution contributes to a reduction of wave impact on the coast and the mitigation of flood hazards and risks. A geomorphological-based approach is therefore seen as a winning approach from both an engineering and management viewpoint.

Meandering streamflows across landscapes and scales: a review and discussion

The study of meandering patterns created by geophysical flows is important for a number of fundamental and applied research topics, including stream and wetland restoration, land management, infrastructure design, oil exploration and production, carbon sequestration, flood-hazard mitigation and planetary palaeoenvironmental reconstructions. This volume, Meandering Streamflows: Patterns and Processes across Landscapes and Scales , contains 13 papers that present field, laboratory and numerical investigations of meandering channels found in distinct environmental and geological contexts and focus on how the interactions of different autogenic and allogenic processes, both in the horizontal and the vertical dimension, affect meander kinematics and the resulting morphology, sedimentology and stratigraphic architecture. In this introductory chapter, we offer an overview of the evolution of scientific research on meandering streams over time, aiming to review and discuss meandering patterns in both fluvial and non-fluvial settings. Additionally, we present a new compilation of data on meander morphological features, drawn from both existing literature and novel sources, encompassing over 8000 meander bends discovered across a diverse array of environments.

UAV Mapping for Flood Routing in Steep and Densely Vegetated Areas: Insights from the Contok River Basin, Garang Watershed, Indonesia

This research utilizes photogrammetry to assess flood routing dynamics in the Contok river basin, a sub-watershed with a challenging landscape characterized by steep slopes, dense vegetation, and meandering patterns. The objectives are to assess Unmanned Aerial Vehicle (UAV) mapping accuracy, evaluate the river's capacity for design flood volumes, quantify the impact of land cover changes on surface runoff, and provide insights for early warning systems and watershed conservation strategies. The study area, encompassing the Contok River Basin, a sub-watershed of the Garang Watershed, covers 7,413 km² and includes a stream length of 5,274 meters in Semarang City, Central Java, Indonesia. This research employed image processing of aerial photographs and satellite imagery. Aerial photos captured using UAV data were utilized to derive elevation data and cross-sectional profiles of the Contok River, essential for understanding channel morphology and hydraulic characteristics. Concurrently, satellite imagery was used for land cover analysis, identifying vegetation and built-up areas that influence surface runoff dynamics. Hydrological analysis was performed to quantify discharge magnitudes, simulated against river cross-sections to evaluate flood behavior under varying scenarios. Our proposed UAV mapping provides adequate accuracy for small and local areas. Furthermore, it remains reliable for flood routing analysis. We discovered that the capacity of the Contok River channel in the downstream area allows it to convey design flood discharges up to a 50-year return period, contrary to the upstream area, it overflows. Notably, the shift from vegetated to built-up and agricultural areas significantly contributes to the 10.6% increase in surface runoff. This research highlights the role of UAV-based photogrammetry in assessing and mitigating flood hazards amidst evolving land cover patterns. It also enhances the understanding of flood dynamics and thus provides insights that will serve as a reference for flood early warning systems, flood management practices, and watershed conservation.

A Sponge Village Flood Response Method Based on GIS and RS Analysis Formation—A Case Study of Jiangou Village

This study was conducted in response to the Beijing–Tianjin–Hebei mega heavy rainfall event at the end of July 2023, and the severely affected and representative Jiangou village in Beijing was selected as the study area. A variety of methods were used to synthesize and analyze the situation and propose an adaptive response to heavy rainfall and flooding in the village. Based on multi-source remote sensing (RS) data, a comprehensive topographic and hydrological characterization was carried out, and the precipitation before and after the disaster was analyzed; the flood inundation area was extracted using the improved normalized water body index (MNDWI) and OTSU thresholding methods, and the changes of water bodies during the flooding period were quantitatively analyzed; and an improved convolutional-neural-network-based building identification and extraction model was constructed to extract the research distribution of buildings in the area. The sponge city construction (SPCC) method was improved to obtain a method that can mitigate flood risk and adapt to villages by constructing small artificial lakes and local topographic buffers to improve the water storage and drainage capacity of villages. The study shows that these methods are innovative in flood hazard analysis and mitigation but still need further improvement in data accuracy, simulation depth, and system evaluation.

Pemanfaatan Sig Untuk Untuk Mengurangi Resiko Bencana Banjir Di Kota Demak

The application of Geographic Information Systems (SIG) has become an important tool in combating the risk of flood disasters in many areas, including Demak City. This research aims to explore and evaluate the possible benefits of implementing SIG to reduce the danger of flooding in Demak City. The study approaches used include stakeholder interviews, field surveys, and geographic data analysis. The research results show how useful SIG is for creating early warning systems, identifying air flow patterns, and mapping areas vulnerable to flooding. The use of SIG also enables improved coordination of flood mitigation and management among various interconnected entities. This study makes a significant contribution to our understanding of the function of geospatial information technology in disaster management and provides useful insights for stakeholders to create more effective methods for mitigating flood hazards in Demak City.

Small-Scale Experiments’ Ability To Augment Large Lab Testing For Designing Nature-Based And Hybrid Solutions For Coastal Flood Hazard Mitigation

Mangroves and other natural coastal defenses have the potential to augment or replace traditional engineered coastal structures in preventing adverse events such as wave overtopping. Natural, or “green” systems may reduce maintenance costs, reduce sediment erosion, and increase biodiversity compared to traditional “gray” infrastructure built from stone and concrete. To effectively inform the design of hybrid green-gray infrastructure, experimental results must be reliable, but testing at 1:1 scale is time-consuming, expensive, and available at only a few facilities worldwide. This study addresses a knowledge gap in defining the nature of the interactions between green and gray coastal defenses with a focus on overtopping and scaling experimental results. This study will compare data from mangrove-related experiments conducted at scales including 1:2 and 1:8 as part of a collaborative effort between Oregon State University (OSU) and the United States Naval Academy (USNA). The study aims to analyze this data and contribute to the joint compilation of a methodology for designing prototype-scale tests from small-scale experiments to identify the relative importance of friction and scaling effects between prototype and small-scale experiments. Testing conducted at USNA as part of this study included a 1:8 scale, 0.61m-wide (2ft.) flume that replicates the conditions of 1:2 scale experiments at Oregon State University. The experimental setup includes a model Rhizophora mangrove forest placed in front of a seawall, behind which overtopping is measured as volume per unit length either computed from overtopped water weight or directly measured by overtopped volume. Mangroves are modeled as central trunks with stilt roots, as this study focuses on the effects of the root structures on overtopping. Waves generated for the 1:8 experiments include regular waves with heights between 5cm and 10cm and periods between 1 and 2 seconds, scaled according to Froude similitude. Implications of scaled-up measurements of overtopping are also discussed.

UAV based comprehensive modelling approach for flood hazard assessment and mitigation planning

The assessment of flood hazard in semi-arid region under the scare data situation is a challenging task under the changing climatic situation. Therefore, the present research is carry out for Rel river catchment, Gujrat, India as case study and presented the comprehensive approach to identify the possible flood extend and flood mitigation measures for better flood assessment. The UAV based high resolution (3.6 cm × 3.6 cm) DEM is generated for most flood vulnerable area (i.e. Dhanera city), whereas scare precipitation data under ungauged condition is generated using GEE and National Aeronautics and Space Administration (NASA) Global Precipitation Measurement Mission (GPM) system. The HEC-HMS based hydrologic model is utilized for simulation of stream flow under the observed data, however, the 2D HEC-RAS based open-source model is used for flood assessment in 2D under extreme flood, dam break and levees condition. The flood decision making maps i.e water surface elevation, flood inundation, flood arrival time, and flood velocity are prepared for flood event 2017. The six flood hazard classes were selected from H1 (Low) to H6 (High) categories. The hazard maps of flood for different scenario i.e., 2D hydrodynamic analysis, 2D dam breach, 2D analysis with extended levees, and Dam break analysis with extended levees are derived. The model was validated with observed river gauge (water level) and discharge data at Dhanera City of flood 2017. The developed UAV based comprehensive modelling approach for flood hazard and mitigation planning provides the systematic approach for flood hazard assessment and would be adopted as a system framework for flood risk assessment for any similar case worldwide.

Advances in Dam-Break Modeling for Flood Hazard Mitigation: Theory, Numerical Models, and Applications in Hydraulic Engineering

Despite significant advancements being made in recent decades (e [...]

The influence of microtopography to road inundation caused by extreme flood

Microtopography plays a critical role in road inundation during urban flood events. The microtopography in this paper was defined as terrain-scale features that encompass surface roughness, slope, road network and urban building layout. This paper aims to explore the mechanism of depression storage and road inundation under different microtopography. Simulations under 4 rainfall intensities (144.0– 182.88 mm/h) and 14 slope combinations (four transverse slope and five longitudinal slope) were implemented in an 800 by 70 cm local model. The correlation heat map directly reflected that longitudinal slope had higher influence on drainage than other factors. Then real topographical and hydrological data was applied to predict road inundation with five different extreme rainfall events in Jiangning District (Nanjing City, China). The microtopography characteristics of frequent inundation road were extracted, which further verified the conclusions of the local model. Results show that: the microtopography depressions drainage process could be divided into six main stages: filling stage, interaction stage, unstable drainage stage, stable flow stage, drainage stage and stage of drainage end. Water was stored on depressions of road, and the storage volume and discharge efficiency were affected by the surface relief and slope. The emergence of slope provided an altered path and power for water drainage. Only 0.3 % slope could contribute a 28.4 % to discharge efficiency. Upon comparation, the best combination for drainage was 2.0 % transverse slope with 3.0 % longitudinal slope. These findings provided meaningful insights and perspectives for urban flood hazard mitigation and were a more detailed reference for road design.

Evaluating Flood Hazard Mitigation through Sustainable Urban Drainage Systems in Bor, Jonglei State, South Sudan

Evaluating Flood Hazard Mitigation through Sustainable Urban Drainage Systems in Bor, Jonglei State, South Sudan

Flood Hazard Mitigation at Tarusan Watershed, South Pesisir District, West Sumatera Province

Floods are the most common natural disasters in Indonesia and have enormous potential. This study aims to determine the flood hazard zone and regional arrangement in the Tarusan Watershed, South Pesisir Regency. To determine the flood hazard zone using the GIS approach. The indicators used to determine flood hazard are slope, rainfall, soil type, landform, geology, and land use. Determine the direction of regional arrangement with an Interpretative Structural Modeling (ISM) approach. The results showed that the high flood hazard zone in the Tarusan watershed is about 22% of the total area, the medium index is around 58%, and the low flood hazard index is 20%. The high - hazard zone of flood disasters in the study area is caused by high rainfall and topographic conditions of the Tarusan Watershed. The main priority in the management of flood - hazard areas in the Tarusan Watershed is to find economic alternatives to reduce forest destruction. Increasing the economic value of the community can lead to reduced community activities in carrying out land conversion, especially in forest areas.

Buyout programme experiences and perspectives of local public officials in eastern North Carolina

ABSTRACT Eastern North Carolina (ENC) has been buffeted by compound coastal water events (CCWEs) making residential buyouts, that seek to move households and communities out of flood risk areas, an important flood hazard mitigation tool. However, little is known about the experiences of local public officials implementing buyout programmes in rural coastal regions such as ENC in the United States. Using data from focus group interviews conducted with 24 emergency managers, planners, elected officials, and other public officials, we examine residential buyout programmes in ENC from the perspective of local public officials. According to ENC officials, while property attachment, social ties in the community, and financial considerations are key drivers for residential property owners in rural ENC considering a buyout, the governance of buyout programmes remains a complex lengthy process lacking adequate communication and leads to uncertainties for local public officials and property owners during the buyout. The uncertainty can be temporal, economic, or related to housing security. ENC officials recommend providing alternative mitigation options for small rural communities and simplifying and streamlining the buyout process along with improving communication throughout the buyout cycle to mitigate uncertainties in the buyout programme.

Future sea level rise exacerbates compound floods induced by rainstorm and storm tide during super typhoon events: A case study from Zhuhai, China

Compound floods are becoming a growing threat in coastal cities against a background of global sea level rise (SLR), and may cause increasing impacts on societal safety and economy. How to quantify the impact of SLR and compound effects among various flood causes on compound flood have become important challenges. We propose a modeling framework which integrates atmospheric, storm tide and urban flood (IASTUF) models to characterize the various physical processes related to compound flood. Future SLR projections under various shared socioeconomic and respective concentration pathway emission scenarios are considered. Hengqin Island (Zhuhai City, China) frequently experiences typhoon conditions combined with rainstorm and storm surge events. Its population has increased more than sixfold during the past decade, stimulating urgent demands for assessments of the potential risks associated with future compound floods in the context of potential SLR. A compound flood event in northern Hengqin Island, caused by the super typhoon Mangkhut in 2018, is selected as a case study to verify the proposed modeling framework. Results show that the IASTUF modeling framework can capture well the combined processes of typhoon, rainstorm, storm tide and inland flooding and demonstrates good performance in quantifying compound flood magnitudes. Compared to the current scenario, the node flooding volume (from the drainage system) and the maximum inundation area (with inundation depths >1 m) in 2050 are projected to increase by 20–26 % and 41–85 %, respectively, and these increases rise to 46–84 % and 23–71 times by 2100. The inundation volumes and water depths due to compound events are larger than the sum of those caused by the corresponding single-cause events, indicating that concurrent rainstorm and storm surge induce positive compound effects on flood magnitude. These findings can provide guidance for the management and mitigation of future compound flood hazards driven by super typhoon events.

Modelling the compound floods upon combined rainfall and storm surge events in a low-lying coastal city

Low-lying coastal cities are highly vulnerable to compound floods, which may result from a simultaneous occurrence of storm surges and heavy rainfall. Systematic numerical analysis is essential for projecting flood scenarios upon compound events. In this study, a coupled model that integrates the 1D drainage module with the 2D overland flow module is developed and validated by taking Macau as the study area. The joint cumulative probability distribution between rainfall and storm tide are derived based on the historical typhoon data. The flood hazards are projected under designed scenarios, and an investigation is conducted on the backflow processes through drainage system and effectiveness of installing tide gates. The flood zones are delineated and the contributions of rainfall and storm tide to floods are analyzed. Storm surge exerts a greater influence on the maximum inundation depth in the western Macau Peninsula than heavy precipitation does. As the peak tidal level increases from a 10-year to a 200-year return period, the increments of flooded area ratio to the total land area are approximately 19 %. The backflows through underground drainage system could expand the tide affected area during storm events, as indicated by the backflows in the pipe 1.4 km away from the coastal boundary. By installing tide gates, backflows could be greatly eliminated in the corresponding pipes. The inundation area in the compound flood scenario is not equal to the superposition of the extents by the individual components. The transition area that is affected by both storm tide and rainfall extends from coast to inland areas under the combined effects. This study is expected to furnish valuable insights for flood risk assessment, flood hazard prevention and mitigation in low-lying coastal cities such as Macau.

A Bayesian updating framework for calibrating the hydrological parameters of road networks using taxi GPS data

Abstract. Hydrological parameters should pass through a careful calibration procedure before being used in a hydrological model that aids decision making. However, significant difficulty is encountered when applying existing calibration methods to regions in which runoff data are inadequate. To achieve accurate hydrological calibration for ungauged road networks, we propose a Bayesian updating framework that calibrates hydrological parameters based on taxi GPS data. Hydrological parameters were calibrated by adjusting their values such that the runoff generated by acceptable parameter sets corresponded to the road disruption periods during which no taxi points are observed. The proposed method was validated on 10 flood-prone roads in Shenzhen and the results revealed that the trends of runoff could be correctly predicted for 8 of 10 roads. This study demonstrates that the integration of hydrological models and taxi GPS data can provide viable alternative measures for model calibration to derive actionable insights for flood hazard mitigation.

AN INTER-COMPARISON STUDY OF GREEN AND GRAY STRUCTURE EFFECTS ON OVERLAND FLOW FLOODING AND FORCE ON COASTAL BUILDINGS

Coastal communities have been prone to extreme inundations generated by storm surges and tsunamis. Especially inundated overland flows adversely impact low-lying areas. Therefore, mitigation solutions are essential in protecting human lives and infrastructures. So far, hard structures (gray structures) have been widely used to protect coastal communities against severe flooding. Recently, Natural and Nature-Based Features (NNBF, green structures) also have been studied for flood hazard mitigation, such as mangroves (Tomiczek et al., 2020), dunes, reefs, etc. However, the inter-comparison studies of gray and green structures in the flooding and force reduction have not been investigated sufficiently. Therefore, the present study investigated the physical and numerical model comparison of gray and green structures regarding flooding hydrodynamics and forces on the buildings.

Frequency domain electromagnetic calibration for improved detection of sand intrusions in river embankments

Sand intrusions pose significant risks to river embankments due to potential flow pathways that can lead to instability during flood events. Visual inspection is a first step to recognize critical segments, but it does not deliver information about the subsurface. In this context, the electromagnetic induction (EMI) technique is a useful method for preliminary zoning at regional scale while the electrical resistivity tomography (ERT) method, widely used for hydrological purposes, is considered among the most reliable techniques for local subsurface imaging. A major sand intrusion within the levees of the Brenta River, located near Venice (northern Italy), resulted in water seeping during seasonal floods and posed severe threats to embankment stability. ERT and EMI techniques, along with geotechnical investigations, were the best survey choices to address the problem. Resistivity profiling successfully imaged the sand body geometry within and underneath the levee, and results correlated nicely with borehole stratigraphy. A first multiarray EMI device, which represented a faster and less expensive survey, was deployed to map further anomalies along nearby levees, but results were not satisfactory because the inverted profile failed to image the known intrusion. A second multiarray EMI device, with larger coil spacing, was also tested. Although it performed better in detecting the intrusion, results were still below expectations. A calibration procedure based on Pearson's coefficients and using ERT as a reference was then devised and implemented to correct the EMI data prior to carrying out inversion. The procedure was successful for both EMI data sets, leading to realistic subsurface resistivity in the inverted sections. EMI measurements could then be recovered and interpreted correctly to estimate subsurface textures. The possibility of calibrating EMI data and obtaining subsurface resistivity images comparable to standard ERT profiling is an important improvement for cost-effective EMI surveying of river embankments to mitigate flood hazards.

Study of Aquatic Sedimentation Using Electromagnetic Modeling in Flood Hazard Mitigation Scheme Study of Aquatic Sedimentation Using Electromagnetic Modeling in Flood Hazard Mitigation Scheme

Study of Aquatic Sedimentation Using Electromagnetic Modeling in Flood Hazard Mitigation Scheme Study of Aquatic Sedimentation Using Electromagnetic Modeling in Flood Hazard Mitigation Scheme