Flood Mitigation Measures Research Articles

Statistical analysis of flood risk perception: a case study for Eastern Black Sea Basin, Turkey

It is very essential in terms of flood risk management to consider social expectations such as risk perception, flood awareness, preparedness, and socio-economic dynamics together with engineering designs. Understanding the way people perceive flood risk can enhance our capability of improving existing flood risk management methods, thus helps us creating disaster resilient societies. In this study, results of a questionnaire which was used for a previous study and had been administered to participants from Eastern Black Sea Region of Turkey were further investigated using statistical methods. The main aim was to understand how demographic factors such as age, gender and education level affect people’s flood risk perception. It was also desired to see that whether they were aware of the parties responsible for taking mitigation measures, or whether they know about possible flood mitigation measures or not. Using the same data with the previous study, but in addition using SPSS software to do statistical analysis, questionnaire results were investigated using convenient statistical tests for each parameter, analysis results were interpreted, and conclusions were drawn. Same tests were conducted using weight coefficients adopted using a certain methodology which is explained in the paper, in order to make a better investigation. Also, results were compared with the results of the previous study. It was seen that there were some consistencies and contradictions between the results of the previous study and this study’s results.

Urban planning for flood resilience under technical and financial constraints: The role of planners and competence development in building a flood-resilient city in Matola, Mozambique

Today, urban flood resilience constitutes an academic and political discourse as well as a ‘proposed state’ to be achieved within urban management, planning, and development. Matola, a major Mozambican coastal city, has witnessed many floods, mainly caused by rainfall, the most devastating of which happened in 2000. This study analyses the actions the urban planners took during that major flood event, what flood mitigation and adaptation strategies and measures for increased flood resilience they have developed since that flood event, and the contribution of urban planning to building flood resilience under financial and technical constraints. The study is based on interviews with 32 urban planners from Matola and observations in the field. In addition to financial limitations, the main challenge in promoting flood resilience in Matola is the deficient and insufficient coordination in mitigation and adaptation actions among urban planners, political elites, and members of low-income urban communities, who use floodplain areas for purposes that contradict resilience-building actions. During the 2000 floods, mitigation actions were carried out by rescuing people and goods and placing them in accommodation centres. After the 2000 floods, gradual adaptation strategies and measures were carried out, such as hiring and training staff, designing a new urban plan, gradual resettlement, opening drainage channels, and allocating water pumping systems in some areas to promote flood resilience. The study concludes that urban planning contributed significantly to the building and promotion of flood resilience in Matola: the strategies and measures taken so far have contributed significantly to reducing the exposure and vulnerability to flooding of the population, their assets, and urban infrastructure, as well as improving the ecosystem in lowlands and coastal protection wetlands. The study brings a contribution from retrospective and prospective resilience thinking to the debate on building and promoting resilience in urban socio-ecological systems, showing the role of urban planners, and planning and management activity since the 2000 floods, and perspectives on the future. The study demonstrates that the development of competences or technical skills to plan and manage strategies and measures to promote resilience is a key factor in promoting socio-ecological resilience.

Comparing Remote Sensing and Geostatistical Techniques in Filling Gaps in Rain Gauge Records and Generating Multi-Return Period Isohyetal Maps in Arid Regions—Case Study: Kingdom of Saudi Arabia

Arid regions are susceptible to flash floods and severe drought periods, therefore there is a need for accurate and gap-free rainfall data for the design of flood mitigation measures and water resource management. Nevertheless, arid regions may suffer from a shortage of precipitation gauge data, whether due to improper gauge coverage or gaps in the recorded data. Several alternatives are available to compensate for deficiencies in terrestrial rain gauge records, such as satellite data or utilizing geostatistical interpolation. However, adequate assessment of these alternatives is mandatory to avoid the dramatic effect of using improper data in the design of flood protection works and water resource management. The current study covers 75% of the Kingdom of Saudi Arabia’s area and spans the period from 1967 to 2014. Seven satellite precipitation datasets with daily, 3-h, and 30-min temporal resolutions, along with 43 geostatistical interpolation techniques, are evaluated as supplementary data to address the gaps in terrestrial gauge records. The Normalized Root Mean Square Error by the mean value of observation (NRMSE) is selected as a ranking criterion for the evaluated datasets. The geostatistical techniques outperformed the satellite datasets with 0.69 and 0.8 NRMSE for the maximum and total annual records, respectively. The best performance was found in the areas with the highest gauge density. PERSIANN-CDR and GPM IMERG V7 satellite datasets performed better than other satellite datasets, with 0.8 and 0.82 NRMSE for the maximum and total annual records, respectively. The spatial distributions of maximum and total annual precipitation for every year from 1967 to 2014 are generated using geostatistical techniques. Eight Probability Density Functions (PDFs) belonging to the Gamma, Normal, and Extreme Value families are assessed to fit the gap-filled datasets. The PDFs are ranked according to the Chi-square test results and Akaike information criterion (AIC). The Gamma, Extreme Value, and Normal distribution families had the best fitting over 56%, 34%, and 10% of the study area gridded data, respectively. Finally, the selected PDF at each grid point is utilized to generate the maximum annual precipitation for 2, 5, 10, 25, 50, and 100-year rasters that can be used directly as a gridded precipitation input for hydrological studies.

Designing effective educational storymaps for flood disaster mitigation in the Ciliwung River Basin: An empirical study

Flood disasters, notably in the Ciliwung River Basin, Indonesia, pose grave challenges to urban communities. The recurrent nature of these floods accentuates the importance of holistic educational resources to bolster community resilience and lessen flood risks. This study endeavors to assess the efficacy of StoryMaps—a digital platform fusing geographic information with narrative—as an instrument for flood disaster education in the Ciliwung Basin. Recognized for its interactive and immersive nature, StoryMaps transforms intricate disaster management data into digestible, interactive modules for the public. The research methodology encompasses an exhaustive literature review, offering insights into optimal StoryMaps design and its educational role in disaster mitigation. Subsequent content analysis of pertinent StoryMaps identifies effective design elements, shaping the prototype tailored to the Ciliwung milieu. This prototype amalgamates regional geospatial data with educational narratives on robust flood mitigation measures, undergoing rigorous expert evaluation and usability tests. Academically, the study augments the existing discourse on digital tools in disaster education, presenting a pertinent StoryMaps case study. Practically, it equips local stakeholders with a potent tool to counter flood threats and fortify resilience. Summarily, this research underscores the transformative capacity of geospatial tools and interactive narratives in democratizing vital disaster knowledge, thus catalyzing community involvement in disaster management.

Exploring a spatiotemporal hetero graph-based long short-term memory model for multi-step-ahead flood forecasting

Operational flood prevention platforms and systems rely upon the advance notice provided by flood forecasts to formulate efficient measures for flood mitigation. Capturing complex spatial heterogeneity and correlation of hydro-meteorological variables is fundamentally challenging for artificial neural networks. This challenge becomes even more significant when the complexity involved introduces systematic biases and time-lag phenomena in flood forecasts. For the first time, this study proposed a Spatiotemporal Hetero Graph-based Long Short-term Memory (SHG-LSTM) model for multi-step-ahead flood forecasting. The case study focused on the Jianxi basin in China. 25,341 hydro-meteorological data, with a temporal resolution of three hours, collected during flood events were divided into training and test datasets for model construction purpose. The model was fed with 3-h streamflow and precipitation data from 23 gauge stations, covering a time span of the preceding 21 h, for generating flood forecasts at 1 up to 7 horizons. To make a comparative analysis, both LSTM and the Spatiotemporal Graph Convolutional Network (S-GCN) were constructed. This study conducted multiple rounds of model training with varying initial parameters to assess the accuracy, stability, and reliability of the LSTM, S-GCN, and SHG-LSTM models. The results demonstrated that the SHG-LSTM model outperformed LSTM and S-GCN models, with an average reduction in the volume error (VE) of 6.5% and 11.1%, respectively, a decrease in the Mean Absolute Error (MAE) of 6.7% and 8.1%, respectively, and a reduction in the Root Mean Square Error (RMSE) of 5.0% and 12.9%, respectively. Furthermore, the SHG-LSTM model not only could efficiently overcome the under-prediction bottleneck, but also could largely mitigate the time-lag phenomenon in flood forecasts, even during the testing stages. These findings indicate that the proposed SHG-LSTM model can provide a general framework for modelling the spatial heterogeneity and correlation of hydro-meteorological variables and achieve accurate and reliable flood forecasts, thereby enhancing the model’s applicability in flood prevention platforms and systems.

Impact of Structural and Non-Structural Measures on the Risk of Flash Floods in Arid and Semi-Arid Regions: A Case Study of the Gash River, Kassala, Eastern Sudan

Sediment precipitation in riverbeds influences the effectiveness of structural and non-structural measures for flash flood mitigation and increases the potential for flooding. This study aimed to disclose the effectiveness of the implemented measures for flood risk mitigation in Kassala town, eastern Sudan. We employed remote sensing (RS) and GIS techniques to determine the change in the Gash River riverbed, the morphology, and the leveling of both the eastern and western sides of the river. Flood model simulation and a 3D path profile were generated using the digital elevation model (DEM) with a data resolution of 12.5 m from the ALOS BILSAR satellite. The main purpose of this study is to extract the layer of elevation of the riverbed on both the western and eastern banks and to determine the variations and their relationship to flood occurrence and mitigation. The construction of dikes and spurs near Kassala town has led to sediment precipitation, causing the riverbed to rise. The results show that it is now 1.5 m above the eastern Kassala town level, with a steep slope of 2 m/km, and the cross-section area at Kassala bridge has shrunk, which indicates that the bridge body will partially impede the river’s high discharge and increase the potential for flood risk in the study area. The eastern part of Kassala town has a higher likelihood of flooding than the western side. This study suggests redesigning structural measures like widening the Gash River, extending Kassala bridge for normal water flow, strengthening early warning systems, and implementing soil conservation activities for normal water flow.

Urban inundation response law analysis to characteristics of designed rainstorms based on coupled hydrodynamic and rainfall-tracking model

Extreme stormwater and high-impervious area, caused by climate change and high-urbanization, are widely considered as the essential factors for causing urban flood. Understanding the response law of urban inundation to characteristics of rainstorms is helpful to implement integrated flood mitigation measures. Therefore, this paper is focused on exploring the urban inundation response law based on designed rainstorms by coupled hydrodynamic and rainfall-tracking model. Pilot area of Guyuan sponge city, which is divided into 5 source areas, is adopted to conduct 36 types of rainfall scenario simulations with the combination of different rainfall amounts and durations as well as peak coefficients. Inundation analysis methods is used to obtain the relationship between maximum inundation maps and characteristics of rainstorms, and source tracking analysis method is novelty proposed to excavate the response law of the connectivity among source areas to characteristics of rainstorms. First, Results of inundation analysis reveal that rainfall amount, duration and peak value are the first, second and third critical rainstorm characteristics that determine the severity of disasters, the variation of inundation volume are 140 %, 30 % and 4.2 % when precipitation and duration as well as peak value double. Second, the inundation area that water depth more than 0.5 m increases quickly is the major reason that inundation volume varies with 2 times as the increasing of precipitation; the transferring runoff volume between source areas and land use reaches 0–6 % and 0–10 % of inundation volume. Third, SA 1 and 2 are the critical sub-areas to manage the runoff, when precipitation equals to 200 mm, SA 1 contributes 19.5–33.7 % of inundation volume in SA 2, and SA 2 contributes 28–30 % of inundation volume in SA 3. The study is helpful to further understand the response law of inundation and relationship among source areas to characteristics of rainstorms, provide novel insights for constructing integrated flooding intervention practices.

Amphibious Architecture: A Biomimetic Design Approach to Flood Resilience

Amphibious buildings use the buoyancy principle in the design of their foundation systems to mitigate flood impact. In some cases, amphibious buildings are fitted with mechanical systems that further aid the buoyancy element to temporarily raise the building and guide its descent to natural ground level. These mechanical systems require external operation, preventing the amphibious building from passively responding during flood events as is one of the requirements of a robust flood mitigation measure. Additionally, buildings in flood environments are often left with stains on the exterior facade from floodwater contamination from sewage and chemicals, among others. This paper distinguishes three main components of an amphibious foundation: the buoyancy element, vertical guidance post, and structural sub-frame, and discusses their functionality. The natural world provides solutions to tackling environmental issues such as flooding. When systematically studied and transferred, nature can inspire innovative ideas for functional and sustainable designs for the built environments. Although there are many existing designs and a small number of constructed amphibious buildings, there are very few studies that discuss how the designs are derived, and even fewer on a framework emulating natural systems for transfer into amphibious building design. In that context, this research uses the biomimetic transfer process to abstract relevant biological systems, illustrating their potential for transfer into amphibious foundation design. The aim is to understand how these biological systems passively and continuously respond and adapt to their environment. Organisms such as the Venus flower basket, giant kelp, and red mangrove, among others, are discussed, to understand how they perform the identified functions. The steps of the biomimetic transfer process are used to integrate functions of amphibious buildings and processes of the studied biological systems. The final output of this paper is a discussion of the ways in which these derived relationships can be adopted in amphibious building design.

Investigating Flood Characteristics and Mitigation Measures in Plain-Type River-Connected Lakes: A Case Study of Poyang Lake

The flow of plain-type river-connected lakes is affected by both upstream and downstream rivers, and the hydrological conditions are very complex. Poyang Lake, situated in Jiangxi Province, is the largest river-connected lake in the Yangtze River Basin. Its unique geographical features and complex hydrological conditions have made it a heavy disaster area and a frequent area of floods since ancient times. As typical mitigation measures of Poyang Lake, semi-restoration polder areas and flood storage and detention areas play a crucial role in the flood control of Poyang Lake. Taking Poyang Lake as an example, this article studies the flood characteristics of Poyang Lake based on the measured hydrological data. Furthermore, by using the weir (gate) outflow formula to construct the hydraulic model of semi-restoration polder areas and DHI MIKE to construct the hydrodynamic model of Kangshan flood storage and detention area, the flood diversion capacity of the two, and the flood diversion effect under the super-historical flood in 2020 are analyzed. The results show that compared with the non-use of mitigation measures, the maximum cumulative reduction in Xingzi water level can be reduced by 0.68 m and 0.48 m when semi-restoration polder areas and Kangshan flood storage and detention areas are used alone. Finally, the article puts forward some thoughts and suggestions on the flood control of Poyang Lake. The research results can offer some reference to the flood risk management of plain-type river-connected lakes.

Urban Flood Mitigation by Implementing LIDs (Case Study: Bendung Watershed in Palembang City)

Urban areas continue to be affected by flooding, necessitating more sustainable and effective adaptation strategies and mitigation initiatives. This study investigates the potential flood reduction capability achieved through implementing various green infrastructures known as low-impact development (LID). The Bendung watershed, in the center of Palembang City, with a total area of 18.37 km2, is used as the study area to evaluate the performance of LID infrastructure in reducing flood parameters, including total runoff volume, peak runoff discharge, runoff coefficient, and flooding area. Five types of LID infrastructure were simulated, namely bio-retention cells, rain gardens, permeable pavements, rain barrels, and recharge wells. The flood simulations were performed using four design storms with 2-, 5-, 10-, and 25-year return periods. Hydrologic and hydraulic modeling and simulations were carried out using PCSWMM Professional 2D, and the results were integrated with ArcMap to map the flood inundation. The results of this study demonstrate that with only 9.81 percent of the area occupied by LIDs, a flood reduction of more than 30% can be achieved. In addition, implementing LIDs can help restore the watershed’s hydrological condition to its natural state, as indicated by the decrease in the runoff coefficient. Thus, implementing LIDs in a sustainable urban drainage system must be widely promoted in many urban areas, especially in developed countries like Indonesia. This study can be used as a reference for the local government and authorities to create policies and regulations to establish sustainable flood mitigation measures in Palembang City.

The impacts of rainfall and soil moisture to flood hazards in a humid mountainous catchment: a modeling investigation

Floods pose a significant threat to the safety of countries with severe societal, economic, and environmental consequences, especially the flash floods in mountainous regions. Previous studies have shown that many floods were caused by intense rainfall with highly saturated soil. In this study, we applied a physically-based distributed hydrological model (Integrated Hydrology Model, InHM) to a warm humid mountainous catchment in Southwest China, the Shouxi River. The main objective of our research is to investigate the relative importance of rainfall and antecedent soil moisture on flood generation in our study region. Our results show that an increase in rainfall return period and antecedent soil saturation ratio significantly increased peak flow and shortened peak time. There is a correlation between the ratio of antecedent soil saturation ratio to rainfall (SPR) and peak flow. When SPR <1, there is a positive correlation; when SPR >1, there is a negative correlation. Additionally, with the increase in drainage area, the relative importance of rainfall tends to decrease, while the relative contribution of soil saturation ratio tends to increase. The findings could provide support for the determination of the dominant factors influencing runoff generation in humid regions, offering scientific support for the timely and effective flood prevention and mitigation measures in mountainous regions.

Modelling public social values of flood-prone land use using the GIS application SolVES

Abstract Social values of land use are often excluded when undertaking integrated flood management as they are harder to quantify. To fill this research gap, a geographic information system application called Social Values for Ecosystem Services was used to assess, map and quantify the perceived social values of flood-prone land use in Kuala Selangor, Malaysia. This approach was based on a non-monetary value index (VI) calculated from responses to a quantitative social survey on the public's attitude and preference towards flood management across different land uses. The study outcome is the geospatial representation of flood-prone land use with their social values, which local communities perceive as crucial for flood management. The VI was influenced by elevation and slope, with lower elevations and flatter slopes associated with higher values. Farmland is highly favoured by the local community for flood management, whereas oil palm and rubber plantations are opposed. Tourism received the highest monetary allocations from survey respondents, with the popular firefly park consistently associated with the highest social values. This practical framework contributes to integrated flood management in facilitating decision-makers to evaluate land-use trade-offs by considering their social values when prioritising flood mitigation measures or investments.

Flood Risk Mapping of Kamla River Basin using HEC-RAS 2D Model

Flood is a natural disaster that occurs repeatedly in Nepal and causes significant losses in terms of life and property particularly in low land areas around the river courses. Kamla basin is highly susceptible to flooding and had experienced many disastrous floods in the past. Flood mitigation measures generally consists of two main methods which are structural and non-structural methods. Nowadays, the importance of using nonstructural method such as flood hazard map and flood risk map are increasing because of environmental and economic aspects. In this study, the assessment of flood hazard and risk was carried out for Kamla River basin. Floods are simulated using the HEC-RAS 2D hydraulic model. The flood hazard map was prepared using the simulation result by classifying into four hazard level, corresponding to different inundation depth. The exposed elements considered for the vulnerability assessments are building, population and agriculture area. Finally, to evaluate the flood risk, a flood risk map of wards under the study area was prepared for 25year,50year and 100-year return period flood events based on the product of flood hazard and vulnerability weightage. The study’s findings may help in the planning and management of Kamla River flood plain region to avoid future likely disasters.

Rainfall-Runoff Response of A Suburban Area

Batu Pahat experiences flash floods whenever intense rainfall coincides with high tide. Among the factors which cause flash floods are due to Batu Pahat river catchment's flat and low-lying geographical features as well as high-intensity rainfall. The goals of the study are to analyse the frequency of rainfall events for SMK Munshi Sulaiman station and to investigate runoff due to severe rainfall events within the study area. The observed daily rainfall depth record between 2010 and 2021 was obtained from the Department of Irrigation and Drainage (DID) Malaysia. The frequency of rainfall events within the 11-year period is examined using empirical rainfall intensity formulation. Rainfall-runoff of the five most heavy rainfall events in 2021 within the study area are simulated using HEC-HMS. It has been found that most daily rainfall events have a frequency of a 1-year return period. Only three events were found to have a return period of up to 2-year ARI, with a maximum rainfall depth of 110.67 mm. Five heaviest rainfall events in 2021 were obtained from DID's real-time online platform for rainfall-runoff simulations. One of the events, which occurred in June 2021 has a frequency larger than a 100-year return period while other events have return periods ranging from 1-year to 5-year. Simulations produced by HEC-HMS for these events in January, April, May, June, and September 2021 have resulted in peak flow of 6.7 m3/s, 26.8 m3/s, 24.7 m3/s, 39.9 m3/s, and 39.9 m3/s, respectively. Based on frequency analysis, rainfall-runoff simulations, and field observations, it can be concluded that flash floods are highly possible due to high-intensity rainfall as well as lowland topographical features of the study area. Therefore, flood mitigation measures need to be carried out to improve the drainage system for the suburban area.

A framework for coastal flood hazard assessment under sea level rise: Application to the Persian Gulf

Coastal areas are of paramount importance due to their pivotal role in facilitating a wide range of socio-economic activities and providing vital environmental services. These areas, as the meeting points of land and sea, face significant risks of flooding due to the ongoing rise in sea levels caused by climate change. Additionally, they are susceptible to extreme events like king tides and large waves in the future. This paper introduces a framework for estimating the extreme total water level (TWL) by considering the effects of regional sea level rise (RSLR) resulting from a warming climate under RCP 8.5. It also incorporates the contributions of high tides, 100-year storm surge, and 100-year wave setup and run-up. The proposed framework is utilized to evaluate the occurrence of extreme coastal flooding along the Persian Gulf coast of Iran, an area that is home to significant industries in the country. The results offer an estimated increase of RSLR by 0.23 m from 2020 to 2050 considering an ensemble of climate model projections. Extreme wave setup values are estimated to range between 0.19 and 0.66 m, while storm surge is projected to vary from 0.4 to 1.44 m across the studied coastline. These together yield in a projected extreme TWL along the coastline within the range of 3.18 and 3.90 m above the current sea level. This significant increase in sea level could lead to the inundation of approximately 513 km2 of low-lying coastal land, which accounts for about 16% of the studied domain and could pose serious flooding threat to the people and their assets in this region. Finally, relative ranking of flooded zones (i.e., 6 zones) helps determine the areas with higher chance of flood exposure, at which investment in flood mitigation measures should be prioritized.

Floods in Dinaric Karst fields: a case study of the Dicmanjsko-Bisko Polje (Croatia)

ABSTRACT Karst areas are characterized by extreme heterogeneity and variability of geologic, morphologic, hydrogeologic, hydrologic, hydraulic, ecologic and other parameters in space and time. Therefore, the occurrence of floods under such condition manifests in different forms, intensities, and durations. Heavy precipitation in karst areas leads to a considerable increase in groundwater levels and the activation of temporary springs. Karst fields that have not been properly meliorated are particularly vulnerable to such phenomena and, can remain flooded for several weeks. In Dalmatia, in the southern Croatian region, there are 12 karst poljes with an area larger than 1000 ha, including Dicmanjsko-Bisko polje (1700 ha). Our study presents a conceptual model of the interaction of underground and surface water in the Dicmanjsko-Bisko polje, as well as the process of flooding. The input data were geological mapping and measured precipitation. The paper describes the December 2021 flood in detail. The average 11-day precipitation recorded in the field catchment area was 292 mm, which led to the flooding of 230 ha (approximately 14% of the field area). The main cause of the flooding in the western part of the field was a large amount of surface runoff, resulting in insufficient capacity of the existing drainage channels. In the eastern lowest part of the field, flooding was even more intense due to the insufficient capacity of the sinkhole. The flood caused damage to agricultural lands, infrastructure, and economic facilities. The paper proposes flood mitigation measures. The study is an example of the practical application of karst research, that can be used for different purposes (spatial planning, hydrologic monitoring, modeling hydrogeological processes).

Identification of motivating factors to help decision-making to minimise flood risk by applying private mitigation measures

Residential buildings in flood-prone areas have been observed to be vulnerable, resulting in high losses during flood events over the past few decades. Despite the development of private flood mitigation measures to reduce damage from future floods, many flood-prone residents have been hesitant to implement them. This article aimed to identify motivational factors to adopt resilient-type flood mitigation measures, i.e., elevation and wet flood-proofing, by flood-prone residents. To achieve the aforementioned objective, an extended framework of flood mitigation behaviour was proposed in this paper, which was then applied to data collected from household surveys conducted in flood-prone areas of Australia. The data were analysed using logistic regression with the AIC backward stepwise approach to identify the key incentive factors. The analysis showed that flood-coping appraisal (evaluating private mitigation measures based on their effectiveness, cost and capability to implement) and prior flood experience were the primary factors influencing decision-making by flood-prone residents to adopt resilient mitigation measures. These findings offer valuable insights into flood mitigation behaviour and the uptake of private mitigation measures. The research outcomes will inform the development of more effective floodplain management strategies by policymakers and practitioners.

Spatial Multi-Criteria Analysis for Discovering Nature-Based Solutions Location for Urban Flood Mitigation in Accra

In recent years, Nature-Based Solutions (NBS) have become instrumental in restoring ecosystems and reducing the negative effects of hard surface developments. Existing studies have shown the potential of NBS in mitigating urban floods and reducing overall hydrogeological risks, especially in high-income areas. However, there is limited knowledge on area-specific NBS implementation and the locational suitability of areas to support different NBS for urban flood mitigation in medium to low-income regions. A methodology based on Spatial Multi-Criteria Analysis (SMCA) has the potential to spatially combine and synthesize information to elicit spatially-specific opportunities for NBS implementation. However, an SMCA tool to determine suitable locations for different NBS measures for urban flood mitigation does not yet exist. In order to address this research gap, this study developed an SMCA methodology to identify different target areas where specific urban flood-related NBS measures can be implemented to minimize urban flood occurrence in Accra, Ghana. The study revealed different locations where urban flood-related NBS measures could be applied. It also demonstrated how specific NBS measures could be tailored to the characteristics of different areas in Accra to ensure effective urban flood mitigation. The suggested methodological approach provides a spatial knowledge base for flood management institutions to integrate NBS into flood management schemes. The approach has application potential for other geographic contexts facing urban flood risks. Future research could focus on possible ways of integrating NBS into the spatial development of cities.

Urban flood numerical modeling and hydraulic performance of a drainage network: A case study in Algiers, Algeria.

Urban sewer system management is challenging due to its higher vulnerability to flooding caused by rapid urbanization and climate change. For local decision-makers, storm water management is essential for urban planning and development. Therefore, the main objective of this study is to develop a numerical model for the sewerage network of the central catchment area of Algiers since it has experienced frequent overflows during the winter season. For this purpose, to model the sewerage networks, the model was built by coupling ArcGIS with MIKE URBAN. Its calibration and validation were performed using real-time measurements with a time step of 15 min. The model was evaluated by several statistical indicators, such as the coefficient of determination (R2), Nash-Sutcliffe efficiency (NSE), root mean square error (RMSE), and percent bias (PBIAS). The model results showed acceptable model performance, with an NSE superior to 0.50, R2 of approximately 0.63, RMSE of 7%, and PBIAS of 10% during the validation of the model. The performance parameters prove the reliability of the developed model. The employed model can be applied in other regions and could be helpful for policymakers and managers to improve flood mitigation measures based on the model prediction of the sewerage network.

Facing up to the inevitable: the experience of flood events and lessons learnt at St Michael and All Angels’ Church in Tirley, South West England

In July 2007, a disastrous flood struck Gloucestershire, in the southwest of England. The Grade I listed church of St Michael and All Angels in Tirley was inundated, resulting in its interior and churchyard being extensively damaged. Despite the disastrous flooding and the distress caused, Tirley’s church congregation, supported by the local community, the insurance company and many historic building professionals, resolved to renew their church. Their traumatic experience has presented opportunities to make the building more fit for purpose and more resilient to future flood events. It has deepened a sense of belonging and the valuing of heritage in the community and has ensured the historical continuity of the church and its many stories. Proactive planning will play a major part in facing up to future climate change-related challenges at Tirley church. New research is being planned to examine the effectiveness of existing flood mitigation measures, the overall condition of the building fabric and the church site. The anticipated outcome of this work is a bespoke Flood Impact and Protection Management Plan which will include a set of recommendations, which can be adopted to bolster flood resilience of this historic church, as well as other churches dealing with similar challenges.