Introduction to Flood Resilience - Flood Management

Introduction to Flood Resilience
Contents: This section introduces the term Flood Resilience and Flood Resilience
Management and gives an overview of their main aspects. It also gives a comparison
to the traditional Flood (Resistance) Management measures.
Flood Management-overview
Flood Management can be defined as a sum of activities or as overall processes
involved in mitigating the extent of flooding and in impact of flooding, before, during
and after the flood event. Based on the experience made in the last couple of years,
flooding is not a problem that occupies only water management experts, as the
solutions made and measures applied in flood prone areas considerably influence
landscape and urban planning. Consequently, each decision made, involves
expertise not only of water managers, but also of specialists on other fields, such as
urban planners, structural engineers or geologist. It is very important to consider this
necessity for cross sector work, involving experts from different fields. Urban and
landscape planning should be done based on the information about flooding, that
means for example that densely populated residential area shouldn't be alowed in the
area frequently flooded. Also, soil characteristics and processes in the soil can
influence runoff during flooding and should be considered when planning the
activities within the flood managements. It is predomonantely task of geologists. In
case of flooding the the most severe damage occurs in urban areas. Consequently it
is important to find the way to protect the buildings in such a manner that can resist
flooding or start with the policy to construct new buildings already adapted to
flooding. Structural engineer, as experts on the field, should be involved when
defining those measures.
There is no general solution to flood protection problems. Each case should be
treated separately considering given conditions. In most cases, the financial aspect
plays the decisive role in deciding on the most convenient flood measure.
Conventional Flood Management

Conventional flood management strategies which are targeting at the defense of
these flood prone areas by dikes and walls are often not an adequate answer. In the
past (up to 1950’s), dike heights were calculated on the basis of the maximum
recorded water level. In practice this resulted in a raising of the dikes after each
major flood. After that, an approach of establishing safety levels was adopted. The
desired safety level was defined as the acceptable probability of flooding,
corresponding to a “design discharge” having a certain occurrence probability.
However, the design discharge is rising and expected to continue to rise, as a result
of land use practices and climate change. Therefore, using the traditional approach
to flood risk management, this would imply a further rising of the dikes. In general the
investments for these defense structures can not be provided ad hoc. Additionally
they will reduce the retention capacity of the river which needs to be compensated to
avoid increased flood risk downstream. However the possibilities for these
compensation measures are limited. Looking for more economic and sustainable
flood defense strategies, a great potential is seen in improved flood resilience of
urban areas.
An example of an urban area protected by dikes is depicted in Figure 1. Red line
shows a part of the main dike line of the city of Hamburg, which is of considerable
length and consequently this solution to flood problems, requires high investment.

Figure 1.1 Main dike line of the City of Hamburg
[source(left): Behoerde fuer Inneres in Zusammenarbeit mit den Bezirksaemtern Hamburg-
Mitte, Altona, Bergerdorf und Harburg]
Flood Resilience and Resilient Flood Management
In order to define the resilience, we are coming to the definition of RISK. The risk is
defined as the probability or as a hazard that occurs and that creates a certain loss.
Or:
Figure 2 Definition of Risk
The term Resilienceoriginates from ecology and can be defined as the ability of a
system to resist the perturbation or it is the speed the system recovers after being
disturbed.

Resilient Flood Risk Management focuses on the ability of a system to resist the
flood, taking into account the consequences of floods. Applying the resilience
strategies, decision maker does not try to "fight against floods" but to find the way to
"live with floods" by minimizing their impact.
An area is more resilient if its vulnerability, i.e. potential damage of flooding is
lower.Resilient Flood Management is based on minimizing the impact on flooding
rather than improving the existing flood defense constructions. The underlying idea is
to foster the ability of areas to recover after they had been proned to flood which in a
general sense represents the resilience of a system to persist and absorb changes
and disturbances.
This implies that in a flood resilience policy flood damages have to be minimized and
normal life has to return as soon as possible after flood. In agreement to ecological
systems in which the rate of resilience is determined by many factors, like variability
of populations, their capability to adjust to the environmental conditions and to
repopulate, flood resilience touches a variety of sectors and measures.
Flood resistance strategies, on the contrary, focus on minimizing the probability of
flooding.
Figure 3 ResilienceVSResistance
In the last years many countries have released a new water policy to cope with
floods, e.g. (LAWA 1995, BMU 2004, IRMA 2003). Instead of fighting floods it gives
preference to strategies of living with floods which covers all measures of flood risk
management by which the negative impact of flood is minimized. This change of
paradigm is essential to find the optimal solution to flood problem nowadays.
These measures can be subdivided into four main groups:

• land use control
• risk awareness
• flood preparedness
• financial preparedness
Flood resilience is predominantly a matter of adequate land use. Thus spatial
planning needs to consider flood aspects and has to define land use concepts for
areas proned to flood which includes building regulations that are, building codes and
zone ordinances or even prohibits certain forms of land use.
Building codes and standards regulate the design, construction, use of building
materials and maintenance of buildings in order to protect the users of a
building.Building codes set the minimum acceptable requirements necessary for
protecting people and their properties.
Zone ordinances regulate landuse based on the flood hazard.
Risk awareness encompasses all measures which fosters the risk perception of
stake holders. The key issue in increasing the flood risk awareness is communication
of the potential flood risk to affected citizen. While in the past, water authorities and
communities were afraid to inform stake holders about their flood risk, the new water
policy targets at full and open information about flood risk. Hazard and risk maps
have been found to improve the risk perception considerably. Additionally, the
methods to improve risk awareness are construction of flood marks/signposts,
symbols and information centres, with the fundamental idea to make the symbols
visible to everybody i.e. using public places for their .
It is important that the information delivered to the people, appeals to the emotional
level. This helps to reach people in a deeper and more lasting sense. Information and
communication should always be clearly related to the local situation. This facilitates
the identification of the people with the problem.
Flood preparedness can be mainly influenced by methods of flood resistant building
and hazard awareness. The flood resistance of buildings can be improved by
retrofitting measures, such as holding back floodwaters through sealing the building
or through barriers installed temporarily at some distance from a house (shielding). In
case that a flooding of the building can not be prevented the flood resilience of a
building can be improved by using waterproof materials and evacuation of the water-

sensitive interior of the building. Sealing as well as shielding of buildings and
evacuation of the interior requires sufficient preparation time. Thus measures to
improve the flood resistance of building can be only effective if stakeholders are
aware of the imminent hazard. This can be accomplished by flood forecasting and
warning. However their reliability is strongly influenced by the quality of monitoring
systems and their promptness to transfer the recorded data to flood control centres.
Another aspect of flood preparedness is certainly related to psychological problems
following a flood. Flood damage usually implies losses of belongings sometimes of
great personal value, that causes an emotional stress to the affected citizen. This
aspect of flooding should be considered in advance with the objective toreduce the
impact of this experience through communication policy and instructions for proper
action.
Also, the recovery after flood can be accelerated by damage compensation
regulations and insurances.
Table 1: Resilience Strategies-Main groups of activities with corresponding
responsibility
Land Use Control
I) Spatial Planning
Flood risk adapted land use
II) Building regulations
Building codes
zoning ordinances
Public Responsiblity
Risk Awareness
I) Information:
Inundation maps
Risk maps
II) Education
Learning Groups
Brochures
Public and Private
Responsibility
Flood Preparedness
Financial
Preparedness
I) Flood resistant buildings
Waterproof materials
Sealing of buildings
Shielding of buildings
II) Hazard Awareness
Forecasting and Warning
of flood hazards
Emergency measures
Obligatory insurance
Private insurance of the
Public and Private
Responsibility
Private Responsibility

emaining risk
As it has already been shortly induced, integrative approach is the key word for
deciding on flood resilience measures.
For example, without land use control and risk awareness the efficiency of flood
preparedness will be limited. Without risk awareness the readiness of stakeholders to
invest in an improved flood resistance of their building is limited. Inconsistent land
use can lead to inefficiency of flood preparedness or higher investments to
accomplish flood resistance of the building.
In England even a Kitemarking institution for approving techniques and materials of
flood resilience has been established. In Germany many Governmental agencies and
municipalities have delivered brochures to the stakeholders in which they inform
about the risks of flood and possibilities to adapt their buildings to flood. However
little is known about the efficiency of those measures either for individual properties
or groups and total urban districts of communities. On this basis the benefit of flood
resilience can not be evaluated in an economic way. The economic soundness of
flood resilience compared to alternative flood defence concepts (e.g. conventional
methods of defence by dikes and walls) can not be proved and stakeholders have
difficulties to realize the payback and limits of their investments. Thus the Technical
University of Hamburg, Germany has carried out an investigation in which the
observed damages have been analysed in 9 communities along the river Rhine,
Elbe, Danube and their tributaries with the objective to quantify the damage due to
insufficient flood resilience. The work was done by order of the International
Commission for the Protection of the River Rhine (ICPR) which published some of
the results in (IKSR, 2003). For the first time it could be quantified in what way flood
awareness influences the construction of the fabric and interior of buildings and what
damage can be reduced by different measures of flood resistance at buildings.
In order to get better overview of the main characteristics of resistance and resilience
strategies, a short summary is given in Table 2.

Table 2: Comparison between Resistance and Resilience Strategies
Resistance strategies
One design discharge is applied for the whole
area, implying that all land use types (e.g.
cities, agricultural areas and nature reserves)
have the same probability of flooding.
Applying one safety level also means that it is
unknown which area will be flooded.
Little attention is given to the consequences
of possible floods. As a result of economic
development, the potential flood damage has
increased significantly. The resistance
strategy creates a false sense of safety which
explains why large investments are still being
made in the area. As a consequence, the
economic value at risk of flooding still
increases steadily
It causes an endless need for raising and
improving the water defence structures, thus
restricting the natural dynamics of a river
system and spoiling landscape qualities such
as cultural heritage and scenery.
Resilience strategies
Focus on reducing the impact of floods by
"living with floods" instead of "fighting
floods", as in the traditional strategy. They
aim at giving room to the floods but with
concurrent impact minimalization.
Consider measures to reduce the impacts of
flooding, such as the design of warning
systems and evacuation plans and the
application of spatial planning and building
regulations.
May also include measures to accelerate the
recovery after a flood, such as damage
compensation regulations and insurances