A multiple-plan evaluation model for small ungauged watersheds

A computer solution model is proposed for simulation of the effect of alternative measures for flood damage reduction. The goal of the model is to optimize the value of an objective function which will maximize the amount of net benefits returned by the project. The evaluation includes unit hydrograph synthesis, direct runoff construction, computation of average annual damages, and optimization of an objective function. A test application of the model is made on a small community affected by floods from a small ungauged stream --Abstract, page iii

Review article "Assessment of economic flood damage"

Damage assessments of natural hazards supply crucial information to decision support and policy development in the fields of natural hazard management and adaptation planning to climate change. Specifically, the estimation of economic flood damage is gaining greater importance as flood risk management is becoming the dominant approach of flood control policies throughout Europe. This paper reviews the state-of-the-art and identifies research directions of economic flood damage assessment. Despite the fact that considerable research effort has been spent and progress has been made on damage data collection, data analysis and model development in recent years, there still seems to be a mismatch between the relevance of damage assessments and the quality of the available models and datasets. Often, simple approaches are used, mainly due to limitations in available data and knowledge on damage mechanisms. The results of damage assessments depend on many assumptions, e.g. the selection of spatial and temporal boundaries, and there are many pitfalls in economic evaluation, e.g. the choice between replacement costs or depreciated values. Much larger efforts are required for empirical and synthetic data collection and for providing consistent, reliable data to scientists and practitioners. A major shortcoming of damage modelling is that model validation is scarcely performed. Uncertainty analyses and thorough scrutiny of model inputs and assumptions should be mandatory for each damage model development and application, respectively. In our view, flood risk assessments are often not well balanced. Much more attention is given to the hazard assessment part, whereas damage assessment is treated as some kind of appendix within the risk analysis. Advances in flood damage assessment could trigger subsequent methodological improvements in other natural hazard areas with comparable time-space properties

Bayesian Model Averaging Approach For Reducing Urban Flooding Damage Estimation Uncertainty

Uncertainty analysis is useful to define the level of reliability of a modelling application, but operational methods are needed to identify the best modelling structure for a specific problem based on uncertainty reduction criteria. One interesting example is given by flood damage estimation problem where different possible modelling solution and flood damage estimation can be used depending on the case study. Past literature showed that several modelling structures may be equally reliable in terms of calibration ability but they may produce different uncertainty levels. The use of the Bayesian approach for uncertainty analysis has been stimulated by its rigorous theoretical framework and by the possibility of evaluating the impact of new knowledge on the modelling predictions. Model structure uncertainty is associated with the assumptions reflected in model conceptualization and mathematical structure. An unfortunate truth in model development is that no matter how many resources are invested in developing a particular model, there remain conditions and situations in which the model is unsuitable to give an accurate forecast. Reliance on a single model typically overestimates the confidence and increases the statistical bias of the forecast. Bayesian model-averaging (BMA) techniques look to overcome the limitations of a single model by linearly combining a number of competing models into a single new model forecast. This method showed that a pooled forecast of competing models outperformed any single model forecast. The early applications of model-averaging for hydrological systems resulted in a point forecast. An extension of these approaches uses a multiple linear regression model to compute model weights while assuming a model Gaussian distribution, which allows for a probabilistic performance evaluation. In the present paper, BMA was applied to several flood damage estimation models in order to identify the best combination of models to analyse urban flooding distribution in Palermo city centre (Italy)

Une aide à la décision pour le choix des interventions en zone inondable

Cet article a été réalisé dans le cadre d'un projet de trois ans visant à développer une méthodologie d'analyse, de prévision et de contrôle des risques d'inondation au Québec. Il présente une approche concrète pour calculer les impacts potentiels et le risque d'inondation et utiliser ces résultats afin d'évaluer la situation du risque local, de décider si les impacts doivent être minimisés et de choisir les moyens d'intervention appropriés. Le risque d'inondation est considéré comme étant le produit de la probabilité d'occurrence des crues et des conséquences occasionnées par ces événements. Les pertes de vies potentielles et les dommages directs sont évalués en simulant les niveaux d'eau de différents scénarios d'inondation à partir d'un modèle d'écoulement unidimensionnel non permanent, et en intégrant ces résultats à un logiciel géoréférencé de calcul des dommages d'inondation. L'analyse des impacts et du risque calculé permet de dresser un portrait du montant des dommages annuels potentiels sur les sites habités le long du cours d'eau et un portrait de l'évolution des impacts en fonction de l'amplitude des crues. Cette analyse mène à l'identification des sites où existe un risque jugé inacceptable selon des critères préétablis. Pour chaque site où des interventions sont justifiées par le niveau de risque, des scénarios de minimisation des impacts tenant compte des mécanismes d'inondation sont élaborés et ensuite simulés afin d'en mesurer l'efficacité. Un exemple d'application à un site de la rivière Châteauguay illustre la méthode et les gains pouvant découler de son utilisation.Each year, several rivers in Quebec are responsible for severe flooding and these events generate major socio-economic impacts. The frequency and magnitude of these episodes highlight the existence of a real flood risk. Using global information concerning level and extent of flood risk, authorities would be more likely to make appropriate decisions in the management of flood risk. This article results from a three year project aimed at developing a methodology for the analysis, forecasting and control of flood risk in Quebec. It suggests a concrete approach for the evaluation of the potential impact of floods in order to obtain a better knowledge of local risk in inhabited areas and exploits there results to evaluate the acceptability of the calculated risk and to plan appropriate risk minimisation interventions.Risk is defined as the product of the mathematical expectation of a specified occurrence with the expected consequences of the event. In floodplain studies, flood risk is the probability of the occurrence at a given flood multiplied by the expected consequences resulting from this event. Different types of consequences may be observed, clearly the easiest to evaluate being direct or material damages and potential loss of life. The risk calculated using the proposed definition is attributable in variable proportions to the frequency of the floods and the amount of damages. A given calculated global risk on a site could be the result of frequent floods, each causing moderate damage or of a single (or more) extreme event, with very low probability of occurrence, but causing severe damage. Risk associated with rare events could be considered as an acceptable risk, a risk we decide to live with, since the resources available to prevent flood damage are often limited and a decision is taken to optimise the allocation of these resources. The flood level corresponding to the limit between acceptable and unacceptable risk must be determined by the population concerned and be based on a good knowledge of the risk situation.The proposed methodology to evaluate and minimise flood risk for a site localised in a river flood plain involves six steps:1. the realisation of a hydrologic frequency analysis to determine the amplitude of the floods associated with the flood frequency,2. the hydraulic simulation of floods to predict water level and velocity in the stream for each scenario, 3. the assessment of direct damage and potential loss of life for each flood simulated, 4. the calculation of risk, 5. the risk analysis considering the limit of acceptable risk and 6. the choice and planning of appropriate intervention to eliminate unacceptable risk.This approach has been applied to the study of a site along the Châteauguay River, a tributary of the St Laurence River, a river that experiences flood events every two years or so. Seven flood scenarios (the 2, 3, 10, 20, 100, 1 000, and 10 000 year flood) are used to evaluate the risk for a site localised in the village of Huntingdon. Hydraulic characteristics, water level and velocity, associated with each flood scenario are determined using the DAMBRK model, a one-dimensional unsteady flow model. The results are incorporated in DOMINO, a geo-referenced software calculating flood impacts. This software allows the user to create a three-dimensional numerical model of the site based on topographic information. The superposition of hydraulic results provides the flow depth at any point within the site. Damage is evaluated by integrating the municipal roll number of Huntingdon, which provide the site location and value of each building, and gives an estimate of the population threatened by each flood event at the site. These results of direct damages are used to calculate the risk related to each flood event simulated on the Huntingdon site. For this application, the unacceptable risk has generally been agreed to be the risk resulting from the 20 year flood, or more frequent floods, for the material damages and to the number of potential losses of life associated with the 100 year flood or more frequent flood. The analysis indicates that an unacceptable risk of 23 993 $ per year for material damages and potential loss of life of 50 persons exist. Different site scale interventions to eliminate this risk have been simulated and proven to be efficient only if complemented with a few local modifications to the more exposed buildings.This approach may be extended to the study of any river because it takes into consideration local hydrologic and hydraulic conditions. It has the advantage of being based on existing information and to be automated, which limits the time and resources required to obtain the base data and perform the necessary simulations

Mutagenic impact on fish of runoff events in agricultural areas in south-west France

When heavy rainfall follows herbicide application, the intense surface runoff causes stream water contamination. Aquatic organisms are then briefly exposed to a complex mixture of contaminants. The aim of the present study is to investigate the genotoxic impact of such events on fish. A model fish, the Crucian carp (Carassius carassius) was exposed in controlled conditions, for 4 days, to water sampled daily in the Save River (France). The watershed of this stream is representative of agricultural areas in southwest France. Three hydrological conditions were compared: basal flow, winter flood, and spring flood. Chemical analysis of the water samples confirmed the higher contamination of the spring flood water,mainly explained by a peak of metolachlor. Genotoxicity was evaluated by micronucleus (MN) test and comet assay in peripheral erythrocytes. A significant increase in DNA breakdowns compared to controls was detected by the comet assay for all conditions. Exposure to spring flood water resulted in the highest damage induction. Moreover, induced chromosomal damage was only detected in this condition. In addition, fish were exposed, for 4 days, to an experimental mixture of 5 herbicides representative of the spring flood water contamination. Fish exhibited moderate DNA damage induction and no significant chromosomal damage. The mutagenicity induced by field-collected water is then suspected to be the result of numerous interactions between contaminants themselves and environmental factors, stressing the use of realistic exposure conditions. The results revealed a mutagenic impact of water contamination during the spring flood, emphasizing the need to consider these transient events in water quality monitoring programs

Satisfaction issues in the reinstatement of flood damaged domestic property

The frequency of flooding is forecast to increase in the UK, as is the number of properties at risk of flooding. Following major floods in England and Wales in recent years, questions have been raised concerning the quality of service received by insured homeowners during the repair of their properties. At present there is little existing research that evaluates homeowners' perceptions and their levels of satisfaction with respect to the performance of their insurers, repair and restoration companies and loss adjusters during flood damage reinstatement claims. As part of a wider investigation, a review is presented of issues relating to satisfaction and service quality. A proposed approach is put forward for measuring satisfaction of insured homeowners in flood claims. Knowledge of the determinants of insured homeowners' satisfaction in flood damage repair works would be beneficial to all stakeholders involved in the claim chain and should lead to an improved service for homeowners

Using Space Syntax For Estimation Of Potential Disaster Indirect Economic Losses

The study of applicable network measures shows that Normalised Angular Choice can be used as criteria for selecting alternatives for minimizing indirect costs caused by road network damages. At the same time, this methodology cannot be used for monetizing indirect costs or identifying losses in different economic sectors. The study approach does not contradict the main theoretical approaches and it gives new opportunities for research on disasters recovery