The effects of urban drainage system functioning on building structure and content damage

The effects of urban drainage system functioning on building structure and content damage

Koole, M.A.

Van de Giesen, N.C. (mentor)
Ten Veldhuis, J.A.E. (mentor)
Spekkers, M.H. (mentor)

Civil Engineering and Geosciences

Water Management

Water Resources

2014-10-29

As a result of expected increase of rainfall intensities due to climate change, there is an increasing demand for reliable flood damage models for urban areas. Most existing models focus on damage prediction using stage-damage curves, which mainly apply to fluvial or coastal floods on a regional scale. Pluvial flood- ing, however, often takes place at smaller spatial and temporal scales. Therefore, damage assessments for pluvial floods require more detailed approaches. Uncer- tainties in existing damage models for pluvial flooding are high due to the limited availability of reliable damage data and insufficient knowledge of the occurrence of the underlying damage processes. In this study, a database of insurance claims on water-related damages to building structure and content in Rotterdam was analysed, with the aim to study the extent to which failures of public sewer systems cause building damage. The insurance claims were manually classified in order to identify the damage causes, using additional data from municipality complaints. For this study only damage causes that relate to the functioning of the urban drainage system were considered, such as flooding via streets or sewer backups through toilets/sinks in houses. Rainfall data from weather radar were used to examine into relationships between insurance claims and extreme rainfall conditions. A Poisson generalized linear model is used to predict the number of sewer- related insurance claims per day. Two different rainfall characteristics were de- rived from the radar data as input variables for this model: (1) The calculated return period of the observed rainfall and (2) the effective rainfall volume, which is determined using a conceptual reservoir model of the sewer system with a fixed volume and outflow capacity. Effective rainfall is only generated when the storage of the sewer system is exceeded. A database of municipality complaints was analysed next to the insurance data, as an additional source of information about flooding from urban drainage systems. Complaints that were reported on the same day and near an insurance claim were studied qualitatively to investigate whether they were related to the same flood event. The complaint information was used to distinguish between flooding due to rainfall overloading of sewer systems, sewer malfunctioning or local blocked house connections. Results show that for rainfall events that exceeded sewer design standards, in around half of the cases the two sources of information complemented each other, indicating that the scale of the flood exceeded the household level. For claims associated with minor rainfall, which did not result in exceedance of the sewer design capacity, additional information is hardly found in the complaint data. This implies that for these claims, the damage is likely to be caused by local problems, for example blocked house connections.

http://resolver.tudelft.nl/uuid:a77d2246-a97c-4133-9acf-25ac3460c796

2015-10-29

Student theses

master thesis

(c) 2014 Koole, M.A.