Reconstructing coastal flood occurrence combining sea level and media sources: a case study of the Solent, UK since 1935

Using newly digitised sea-level data for the ports of Southampton (1935–2005) and Portsmouth (1961–2005) on the south coast of the UK, this study investigates the relationship between the 100 highest sea-level events recorded at the two cities and the incidence of coastal floods in the adjoining Solent region. The main sources of flood data are the daily newspapers The Southern Daily Echo, based in Southampton and The News, based in Portsmouth, supported by a range of local publications and records. The study indicates a strong relationship between the highest measured sea levels and the incidence of coastal floods and highlights the most vulnerable areas to coastal flooding which include parts of Portsmouth, Southampton, Hayling Island, Fareham and Cowes. The most severe flood in the dataset resulted from the storm surge events of 13–17 December 1989 when eight consecutive extreme high waters occurred. The data suggest that while extreme sea-level events are becoming more common, the occurrence of flood events is not increasing. This is attributed to improved flood remediation measures combined with a reduction of storm intensity since the 1980s. However, several recent events of significance were still recorded, particularly 3 November 2005 when Eaststoke on Hayling Island (near Portsmouth) was flooded due to high sea levels combined with energetic swell waves.     

Synthetic impact response functions for flood vulnerability analysis and adaptation measures in coastal zones under changing climatic conditions: a case study in Gippsland coastal region,Australia

There is an increasing concern that the current management practices for many coastal regions are unsustainable. Very few countries have planned to deal with the exacerbation of environmental decline in the face of sea level rise. It is therefore necessary to assess socioeconomic and environmental impacts of sea level rises to better understand the vulnerability of coastal zones, as part of devising adaptive and integrated management principles. This paper presents a systematic approach by which relevant stakeholders can be actively engaged in prioritising flood impact issues and deriving information for quantification of impacts for adaptation measures and demonstrates the approach through implementation in the Gippsland coastal region. As outcomes of the project, we have identified key issues of concern for this region for flood impacts and constructed synthetic response functions for quantification of impacts of floods on some of the key issues in the region. The analysis also showed that stakeholders consider that some of the issues are not likely to be significantly affected by floods and thus may not require adaptation measures. The analysis did not provide high agreement on some issues. Different approaches are required to assess the importance of these issues and to establish impact response functions for them.     

An integrated flood inundation model for coastal urban watershed of Navi Mumbai,India

Most urban agglomerations located in the Mumbai coastal region in India are vulnerable to flooding due to increasing frequency of the short-duration heavy rainfall, by virtue of their location at foothills on one side and tidal variations on the other side. Steep slopes in the catchment ensure fast runoff and tidal variation adds to backwater effect in the drainage system, which together are favorable for flooding. The present study simulates the flood inundation due to heavy rainfall and high-tide conditions in a coastal urban catchment within Mumbai region with detention pond. Overland flow is modeled using a mass balance approach, which can adapt to hilly slopes and smoothly accommodate detention pond hydraulics. Dynamic wave channel routing based on finite element method captures the backwater effects due to tidal variation, and raster-based flood inundation model enables direct use of digital elevation model. The integrated model is capable of simulating detention pond hydraulics within the raster flood model for heavy rainfall events. The database required for the model is obtained from the geographical information system (GIS) and remote sensing techniques. Application of the integrated model to literature problems and the catchment of the study area for two non-flooding events gave satisfactory results. Further, the model is applied to an extreme rainfall event of July 26, 2005, coinciding with high-tide conditions, which revealed vulnerability of the area to flooding despite of an existing detention pond. A sensitivity analysis on the location of detention pond indicated that catchment response can be better governed by relocating the detention pond to upstream of existing detention pond especially when heavy rainfall events are becoming frequent.     

Numerical modelling of the saline interface in coastal karstic aquifers within a conceptual model uncertainty framework

Numerical modelling is increasingly used as a tool for improving management strategies in aquifers and to support the design of comprehensive projects considering natural and anthropogenic processes. Overall, numerical simulation in karstic aquifers poses a major scientific challenge due to the non-Darcian groundwater flow dynamics. In specific cases, the equivalent porous medium approach has shown acceptable results, particularly in poorly karstified aquifers with regional/subregional scales such as this case. The Yucatan coastal karstic aquifer (Mexico) has been defined as a complex regional heterogeneous system, partially confined, thus allowing the discussion of multiple conceptual models. In this research, a two-dimensional numerical model of flow and transport was implemented using SEAWAT for the NW Yucatan aquifer. Four likely conceptual models were audited, calibrated and verified using hydrogeological field data, to select the best one, considering their fit and complexity. The numerical model accuracy was evaluated using the root-mean-square error, Nash Sutcliffe efficiency and the Pearson coefficient. The Akaike information criterion and Bayesian information criterion were included for evaluating the complexity of the numerical models. In addition, the signal of tide propagation into the aquifer was assessed as a proxy to improve the numerical calibration process. Results show that the most complex numerical model has a better calibration than the simpler models, but the model accuracy is worse when compared to less complex numerical models in the verification exercise. This research offers enhancement in the knowledge of numerical modelling in heterogeneous coastal aquifers within a conceptual-model uncertainty setting.

     

Occupational transitions in three coastal villages in Central Java, Indonesia, in the context of sea level rise: a case study

The transition from one system to another as a mechanism of adaptation to an external disturbance is widely discussed in terms of ‘regime shifts’ in resilience research. But occupational transitions by communities due to coastal hazards such as coastal erosion and strong waves have not been studied in depth from a systems perspective. Such a perspective can contribute towards a better understanding of the process and pattern behind transformation among coastal societies. The present case study of coastal occupational communities in Central Java province, Indonesia, includes fishers, brackish pond farmers and labourers. It investigates the historical occupational transitions and the factors that drive them. The study draws on Participatory Rural Appraisal exercises such as historical timeline analysis and participatory discussions along with a socio-economic survey to study the factors and processes that led these communities to transitional pathways. Historical narratives of the community reveal the significance and influence of livelihood capitals such as social, human, financial, physical and natural capital in the transitions. Through the ‘Marble and Cup’ conceptual framework of the systems transitions, the irreversibility of occupational transitions due to the destruction of natural assets is outlined. This depicts a multi-locale and one-dimensional transition to a singular occupational mode (essentially labourers) in the face of a disturbance like sea level rise, necessitating transformation and building of the livelihood capitals across geographical scales.     

Origin of composite dikes in the Gouldsboro granite, coastal Maine

Composite dikes, consisting of aphyric basaltic margins and phenocryst-rich rhyolitic interiors, cut the Gouldsboro granite of coastal Maine at many localities. Limited hybridization (exchange of crystals, commingling, and mixing) occurs in most of the dikes and indicates that the two magmas were contemporaneous with emplacement of rhyolitic magma following closely in time the initial emplacement of the basaltic dike. Petrographic characteristics and geochemistry indicate that the source of the rhyolite was resident magma in the Gouldsboro granite magma chamber. The composite dikes formed when basaltic dikes ruptured the Gouldsboro magma chamber, permitting partly crystallized magma from the margin of the chamber to flow outward into the center of the basaltic dikes. Field relations of similar composite dikes in other areas (e.g., Iceland, Scotland) are consistent with this model. A second type of composite dike (silicic margins with chilled basaltic pillows) commonly cuts mafic intrusions along the Maine coast and probably formed when a granitic dike ruptured an established chamber of mafic magma, permitting resident mafic magma to collapse downward into the still Liquid granitic dike. Most composite dikes have probably formed when a magma chamber was disrupted by a dike of contrasting magma rather than by tapping a stratified magma chamber.     

Evaluation of drought and flood risks in a multipurpose dam under climate change: a case study of Chungju Dam in Korea

The purpose of this study was to evaluate the effects of climate change on the drought and flood risks of a multipurpose dam. To achieve this, A2 climate change scenarios of RegCM3 were collected about Chungju Dam in Korea. To analyze drought risks, weather data obtained by the statistical downscaling method were entered to produce runoff series by runoff modeling and water balance was analyzed based on water use scenarios to review changes in the storage volume under climate change. To analyze flood risks, changes in water levels of the dam in future flood seasons were reviewed based on the current dam operation method. The results of the review indicated that both the drought and the flood risks of the dam would increase in the future. The reason was considered to be the movement of the flood season’s runoff characteristics from July and August to August and September because of climate change. Therefore, for climate change adaptation planning, not only quantitative changes in hydrologic values but also changes in temporal characteristics should be considered and given importance.     

Flood risk assessment in a coastal lagoon under present and future scenarios: Ria de Aveiro case study

Iranian strong motion records as well as detailed conditions of their instrument sites and the characteristics of their causative seismic sources are compiled and processed. The dataset consists of 2286 three-component records from 461 Iranian earthquakes with at least two high-quality records having moment magnitude from 3.9 to 7.3. These records are about 20% of the Iranian database and are suitable for seismic hazard analysis and engineering applications. Perhaps for the first time in the literature, the distance to the surface projection of the fault is reported for a great number of records corresponding to earthquakes with M > 6.0. The raw accelerations are processed using the wavelet de-noising method. Having corrected and filtered these raw data, the pseudospectral accelerations are calculated for each of the three components of time series, separately. In addition to the ground motion parameters, a large and comprehensive list of metadata characterizing the recording conditions of each record is also developed. Moreover, careful revision of the characteristics of the earthquakes such as location, magnitude, style of faulting and fault rupture plane geometry, if available, is carried out using the best available information in a scientifically sound manner. Finally, we also focus on special ground motion records including records with peak ground acceleration (PGA) >300 cm/s² and distances less than 30 km. These are “exceptional” records in the Iranian dataset and include less than 2% of the selected dataset.     

Modelling coincidence and dependence of flood hazard phenomena in a Probabilistic Flood Hazard Assessment (PFHA) framework: case study in Le Havre

Many coastal urban areas and many coastal facilities must be protected against pluvial and marine floods, as their location near the sea is necessary. As part of the development of a Probabilistic Flood Hazard Approach (PFHA), several flood phenomena have to be modelled at the same time (or with an offset time) to estimate the contribution of each one. Modelling the combination and the dependence of several flooding sources is a key issue in the context of a PFHA. As coastal zones in France are densely populated, marine flooding represents a natural hazard threatening the coastal populations and facilities in several areas along the shore. Indeed, marine flooding is the most important source of coastal lowlands inundations. It is mainly generated by storm action that makes sea level rise above the tide. Furthermore, when combined with rainfall, coastal flooding can be more consequent. While there are several approaches to analyse and characterize marine flooding hazard with either extreme sea levels or intense rainfall, only few studies combine these two phenomena in a PFHA framework. Thus this study aims to develop a method for the analysis of a combined action of rainfall and sea level. This analysis is performed on the city of Le Havre, a French urban city on the English Channel coast, as a case study. In this work, we have used deterministic materials for rainfall and sea level modelling and proposed a new approach for estimating the probabilities of flooding.

     

Public perception of flood hazard and flood risk in Iceland: a case study in a watershed prone to ice-jam floods

Understanding and improving the public perception has become an important element in the management of flood risk worldwide. In Iceland, studying perception of flood hazard and flood risk is, however, in its early stages. This paper presents a case study on the public perception of flood hazard and flood risk in an Icelandic town prone to ice-jam floods. Awareness of the population regarding historical inundations, self estimation of flood risk and worry is considered. The factual knowledge of the residents is deconstructed in flood hazard parameters accessible to the lay population: number of events, dates, genesis and boundaries. The performance of the respondents is rated for each parameter and the influence of several predictors evaluated. The research shows three significant patterns: there is poor awareness and little worry about historical inundations in the area; experience of the past flooding events in town is the most effective source of knowledge; awareness, risk estimation and worry are not correlated.     

Assessing flood hazard using flood marks and analytic hierarchy process approach: a case study for the 2013 flood event in Quang Nam,Vietnam

The production of flood hazard assessment maps is an important component of flood risk assessment. This study analyses flood hazard using flood mark data. The chosen case study is the 2013 flood event in Quang Nam, Vietnam. The impacts of this event included 17 deaths, 230 injuries, 91,739 flooded properties, 11,530 ha of submerged and damaged agricultural land, 85,080 animals killed and widespread damage to roads, canals, dykes and embankments. The flood mark data include flood depth and flood duration. Analytic hierarchy process method is used to assess the criteria and sub-criteria of the flood hazard. The weights of criteria and sub-criteria are generated based on the judgements of decision-makers using this method. This assessment is combined into a single map using weighted linear combination, integrated with GIS to produce a flood hazard map. Previous research has usually not considered flood duration in flood hazard assessment maps. This factor has a rather strong influence on the livelihood of local communities in Quang Nam, with most agricultural land within the floodplain. A more comprehensive flood hazard assessment mapping process, with the additional consideration of flood duration, can make a significant contribution to flood risk management activities in Vietnam.     

Evaluating typical flood risks in Yangtze River Economic Belt: application of a flood risk mapping framework

The Yangtze River Economic Belt is one of the three national strategies of China, while flood risk is one of the most important concerns in the development of Yangtze River Economic Belt. In order to decrease the risks caused by floods, complete flood management system and adequate pre-arranged planning are desiderated to be researched in advance. This study considers two typical situations of flood risk, in which one is sluice-control situation in flood detention area and another is dike-break situation in flood-protected area, and proposes a framework for flood risk mapping. The results show that the losses caused by flood hazards are massive both in the two typical cases when extreme floods happen. The economic losses of different indicators are of great difference in flood detention area and flood-protected area, respectively. The framework effectively handles the complex boundaries in the Yangtze River Economic Belt and provides more accurate flood routing information. The evacuation plan module which has been incorporated in the framework also provides informative assistance for emergent action of evacuation under urgent condition.     

Doubling of coastal erosion under rising sea level by mid-century in Hawaii

This study discusses the scaling properties of the spatial distribution of the December 26, 2004, Sumatra aftershocks. We estimate the spatial correlation dimension D ₂ of the epicentral distribution of aftershocks recorded by a local network operated by Geological Survey of India. We estimate the value of D ₂ for five blocks in the source area by using generalized correlation integral approach. We assess its bias due to finite data points, scaling range, effects of location errors, and boundary effects theoretically and apply it to real data sets. The correlation dimension was computed both for real as well as synthetic data sets that include randomly generated point sets obtained using uniform distributions and mimicking the number of events and outlines of the effective areas filled with epicenters. On comparing the results from the real data and random point sets from simulations, we found the lower limit of bias in D ₂ estimates from limited data sets to be 0.26. Thus, the spatial variation in correlation dimensions among different blocks using local data sets cannot be directly compared unless the influence of bias in the real aftershock data set is taken into account. They cannot also be used to infer the geometry of the faults. We also discuss the results in order to add constraints on the use of synthetic data and of different approaches for uncertainty analysis on spatial variation of D ₂. A difference in D ₂ values, rather than their absolute values, among small blocks is of interest to local data sets, which are correlated with their seismic b values. Taking into account the possible errors and biases, the average D ₂ values vary from 1.05 to 1.57 in the Andaman–Nicobar region. The relative change in D ₂ values can be interpreted in terms of clustering and diffuse seismic activity associated with the low and high D ₂ values, respectively. Overall, a relatively high D ₂ and low b value is consistent with high-magnitude, diffuse activity in space in the source region of the 2004 Sumatra earthquake.