Showing papers by "Francois Clemens published in 2011"

Quantitative fault tree analysis for urban water infrastructure flooding

Abstract: Flooding in urban areas can be caused by heavy rainfall, improper planning or component failures. Few studies have addressed quantitative contributions of different causes to urban flood probability. In this article, we apply probabilistic fault tree analysis for the first time to assess the probability of urban flooding as a result of a range of causes. We rank the causes according to their relative contributions. To quantify the occurrence of flood incidents for individual causes we use data from municipal call centres complemented with rainfall data and hydrodynamic model simulations. Results show that component failures and human errors contribute more to flood probability than sewer overloading by heavy rainfall. This applies not only to flooding in public areas but also to flooding in buildings. Fault tree analysis has proved useful in identifying relative contributions of failure mechanisms and providing quantitative data for risk management.

Analysis of pluvial flood damage based on data from insurance companies in the Netherlands

Abstract: Insurance databases form a promising data source that can be used to improve pluvial flood damage estimations. This paper describes the key characteristics of an insurance database on water related damages to private buildings and content in the Netherlands that has been made available for research. The paper presents preliminary results of a case study where insurance data are explored to find relationships between rainfall characteristics and pluvial flood damage. The results show that variations in damage are partly related to rainfall characteristics. More research on rainfall characteristics and other explanatory variables of flood damage is needed to capture the processes causing damage.

Collecting data for quantitative research on pluvial flooding

Abstract: Urban pluvial flood management requires detailed spatial and temporal information on flood characteristics and damaging consequences. There is lack of quantitative field data on pluvial flooding resulting in large uncertainties in urban flood model calculations and ensuing decisions for investments in flood protection. In this paper four different data sources are discussed, based on literature and expert consultation, that are believed to be of value for the acquisition of quantitative data on pluvial flooding. Data assembled by insurance agencies on flood damage, call databases held by water authorities and emergency services and remote sensing images cover years of observational data that can be mined to obtain data on flood characteristics and occurrence. Flood monitoring using sensor technology can be effective to collect additional pluvial flood data, that is not captured by existing data sources.

Impact of sewer condition on urban flooding: a sens itivity analysis based on Monte Carlo simulations on full hydrodynamic models

Abstract: In-sewer defects are directly responsible for affec ting the performance of sewer systems. Notwithstanding the impact of the condition of the assets on serviceability, sewer performance is usually assessed assuming the absence of in-sewer defects. This leads to an overestimation of serviceability. This paper presen ts the results of a study in two research catchments on the impact of in-sewer defects on urb an pluvial flooding. Impacts are assessed using Monte Carlo simulations with a full hydrodynamic model of the sewer system. The studied defects include root intrusion, surface dam age, attached and settled deposits and sedimentation. These defects are based on the resul ts of field observations and translated to two model parameters (roughness and sedimentation). The calculation results demonstrate that the return period of flood events, number of f looded locations and flooded volumes are substantially affected by in-sewer defects. Irrespe ctive of the type of sewer system, the impact of sedimentation is much larger than the impact of roughness. Further research will focus on comparing calculated with measured behaviour in the research catchments.

Guidelines on capacity reducing gas pockets in wastewater mains

Abstract: Pressurised wastewater mains in urbanised delta regions include many inverted siphons to cross channels, motorways, railways and other infrastructure. Accumulating gas pockets in these inverted siphons cause significant capacity losses. These gas pockets are responsible for an estimated annual CO2 release of 10,000 ton in the Netherlands, equivalent to the electric power consumption of 5,400 households. Other consequences of the presence of gas pockets include combined sewer overflows, increased maintenance costs and less reliable operation.

Seven years of research in the joint industry project CAPWAT

Abstract: The CAPWAT project is a Dutch joint industry project (JIP) on capacity losses in pressurized wastewater mains. The project has been primarily funded by the Dutch water boards, consultants and a pump manufacturer. Since its start in 2003, the JIP CAPWAT included a scientific track and a track on practical implications. This set-up has guaranteed a continuous two-way interaction between practice and research. Feedback from practice has focused and adjusted the research questions during the project and the project set-up has enabled an immediate transfer of scientific results towards practical guidelines. This paper addresses a number of issues, both managerial and technical: 1 It sketches the context from which the CAPWAT project was initiated. 2 It details the research track and practical track. 3 Furthermore, the paper addresses the key findings of the CAPWAT project, as well as its implications for the water industry.