Research on the relationships between flood characteristics and fatalities: based on the flooding in New Orleans caused by hurricane Katrina

Research on the relationships between flood characteristics and fatalities: based on the flooding in New Orleans caused by hurricane Katrina

Maaskant, B.

Vrijling, J.K. (mentor)
Vrouwenvelder, A.C.W.M. (mentor)
Jonkman, S.N. (mentor)
de Bruijn, K.M. (mentor)

Civil Engineering and Geosciences

2007-05

The new flood safety approach for the Netherlands includes, besides the probability of extreme water levels, other type of dike failures and the consequences of a flood. The consequences of a flood are economic damage, materialistic damage and the number of fatalities. To determine the possible number of fatalities during a flood, fatality functions have been proposed by Jonkman. The Jonkman functions are mainly based on the flooding in 1953 in the Netherlands. Fatality functions give the relationships between flood characteristics and the fatality rate. Flood characteristics are: water depth, rise rate, flow velocity and arrival time. To improve the insight in the relationship between the flood characteristics and the fatalities the flooding of New Orleans, caused by hurricane Katrina, is researched. To determine the flood characteristics of the New Orleans flood a part of the total flooding is simulated. The output of the simulations is used to determine relationships between the flood characteristics and the fatalities. In the New Orleans flood event, two relationships can be distinguished. The first is the breach zone relationship. In this zone the building damage is high and the flood conditions are severe. The flow velocity and the water depth are the characteristics that determine this zone. The second relationship is the remaining zone relationship. In the remaining zone the flood conditions are less severe and the water depth causes the fatalities. Compared to the existing Jonkman fatality functions the biggest difference is that the rise rate has no clear influence on the number of fatalities in New Orleans. In previous studies the rise rate is considered a very important flood characteristic, but in the New Orleans flooding it had almost no influence. The two approaches have been determined on two independent flood events. To compare the two approaches they have both been applied to a case study of dike ring 14 in the Netherlands. For this dike ring there are ten possible flood scenarios for which the number of fatalities is estimated with both approaches. The fatality estimations with both approaches are in the same order. The New Orleans relationships give a slightly higher number of fatalities. To use these numbers of fatalities in a risk analysis, the individual and societal risks are quantified. The individual risk is the probability that a person dies at a certain location given a flood. Comparison between the two approaches shows that the spatial distribution of the individual risk is relatively large. So on a local scale it is difficult to determine the risks. The societal risk is the probability of a certain number of fatalities. The societal risk is a measure for the safety of a larger area, like a dike ring. When the two approaches are compared the differences in societal risk are relatively small. The difference expressed in a protection water is only 0.40 meter. The New Orleans functions give a protection water level that is 0.40 meter higher than the one for Jonkmans functions. This difference is smaller than the uncertainty in the extreme water levels, which is approximately 0.80 meter. So on a larger scale the number of fatalities can be estimated reasonably well. Improvements on the assumptions and more information on for instance the evacuation rate will lead to a better model. But to what extent does a better model influences the decisions that have to be made in the new flood safety approach.

New Orleans
Katrina
fatality
fatalities

http://resolver.tudelft.nl/uuid:d9640e6b-5840-4a54-a85b-4d6980d33185

TU Delft, Civil Engineering and Geosciences, Hydraulic Engineering

Student theses

master thesis

(c) 2007 B. Maaskant