Transcript Slide 1

URBAN FLOODS IN GREECE
Current situation and major research and development
needs in Urban Flood Management
Cost meeting, Warsaw, 29-31/5/2008
Vassilopoulos A., Mamassis N., Evelpidou N, Koutsoyiannis D.
URBAN FLOODS IN GREECE
Main causes
1. Intense rainstorms. The 50-year maximum 24-hour rainfall depth (which can be
considered as a very rough indicator of the flood severity) is as high as 175 mm
in western Greece, a region that receives 1800 mm per year, but also in Athens
and Aegean islands, regions that receive less than 400 mm per year
2. Deforestation and urbanization. They are responsible for the increasing severity
and destructive power of floods. Deforestation, also related to soil erosion, is a
major problem in Greece and has been caused primarily by human activities such
as fire, illegal land uses, pasturing, etc.
3. Absence or inadequate protective measures and hydraulic works. Deficient
channel cross sections, inadequate storm drainage networks, encroach of torrents
beds, absence of intergraded river basin management.
Decrease of the cross section area of the river near the outlet
River’ bed upstream of the
entrance to the urban area
River’s cross section in the
urban area near the outlet
Urbanization of river basins (Kephisos river)
Western Athens (1870)
Western Athens (2007)
THE CASE OF ATHENS
Facts
• The Greater Athens area is the most urbanized part of Greece with a population of about
four million.
• 179 lives were lost during the last 100 years, 96 of them occurred during the last 35
years. These figures are higher than in any other part of Greece.
• Flooding is also the most costly natural hazard in terms of human life. Comparatively,
earthquakes claimed less than 50 lives during the last century in the Attica area that
surrounds Athens.
Flood Causes
• The dry climate of Athens (mean annual rainfall depth of about 400 mm) and the high
evaporation rate in combination with the natural relief, did not lead to the formation of
significant river networks.
• The cross-sections of the existing streams are small and unable to route high flows. However,
the intense flood-producing rainstorms in Athens are almost as severe as in other parts of
Greece
• The increase of residential, commercial, and industrial areas and the diminution of natural
parks and farmlands affected the flood rate significantly.
• The stream network was reduced as many streams were converted into streets. Buildings were
even constructed over the old streambeds.
• No priority was given to the flood protection.
Absence of intergraded river basin management (Kephisos river basin)
Basin and river outside of the urban area
Structures on riverbed
Roads and houses on streambeds
Inside the city river is lined
River
basin
City of
Athens
River is
transformed in
main drainage
channel
The drainage
channel is
combined with
the national
road
construction
Major research and development needs in
Urban Flood Management in Greece
The main aim of Greece in UFM for the next decade is the harmonization with
the Directive 2007/60/EC
The Directive is related to the assessment and management of flood risks and requires from
Member States to deliver
Flood hazard maps that will cover the geographical areas which could be flooded
according to 3 probability scenarios (low, medium, high). In the maps must be shown the
flood extent, water depths and the flow velocity
Flood risk maps that will show the potential adverse consequences associated with
probability flood scenarios and expressed in terms of the (a) indicative number of inhabitants
potentially affected, (b) type of economic activity of the area potentially affected, (c)
installations concerning integrated pollution prevention and control and (d) other information
which the Member State considers useful
Flood risk management plans that will focus on the reduction of potential adverse
consequences of flooding for human health, the environment, cultural heritage and
economic activity. FRM plans must take into account costs and benefits, flood extent, soil
and water management, spatial planning, land use, nature conservation, navigation and port
infrastructure. FRM plans must focus on prevention, protection, preparedness, including
flood forecasts and early warning systems. FRM plans may also include the promotion of
sustainable land use practices, improvement of water retention as well as the controlled
flooding of certain areas in the case of a flood event.
Major research and development needs in
Urban Flood Management in Greece
Other issues (except the obligations arisen from directive)
Issues related
to Greek design
regulations
Issues related
to study
Issues related to
measurements
Operational
issues
1. revision of the flood protection design criteria
2. revision of the methods for estimation of the design storm and flood
1. regional analysis of recorded intense storms and study of extreme rainfall
probability
2. development of rainfall runoff models for urban basins
3. assessment of the existing storm drainage system and the strategic planning
of necessary improvements (measures, construction works)
1. the improvement of the raingauge network
2. the installation of modern monitoring networks including weather radars
3. the development of experimental basins
1. operational use of rainfall runoff model
2. development of a monitoring, forecasting and warning system for
intense storms and floods
COLLECTIVE DATA BASE MEMORY OF FLOOD EVENTS
Connection with the Directive 2007/60/EC
Article 4.2
Based on available or readily derivable information, such as records and studies on long
term developments, in particular impacts of climate change on the occurrence of floods, a
preliminary flood risk assessment shall be undertaken to provide an assessment of
potential risks. The assessment shall include at least the following:
(a) maps of the river basin district at the appropriate scale including the borders
of the river basins, sub-basins and, where existing, coastal areas, showing
topography and land use;
(b) a description of the floods which have occurred in the past and which had
significant adverse impacts on human health, the environment, cultural
heritage and economic activity and for which the likelihood of similar future
events is still relevant, including their flood extent and conveyance routes and
an assessment of the adverse impacts they have entailed;
(c) a description of the significant floods which have occurred in the past, where
significant adverse consequences of similar future events might be envisaged;
COLLECTIVE DATA BASE MEMORY OF FLOOD EVENTS
Under construction