A software program has been developed, which requires as input forecast rainfall data for Bulgaria, Turkey and Greece, and the reservoir elevation of the Bulgarian dams at the beginning of simulation. Subsequently the software program calculates (forecasts) a few days in advance the discharge of the river Evros at various critical places, according to the way the Bulgarians will manage the water of the dams

1. A DEDICATED COMPUTER SIMULATION OF
EVROS/MARITSA FLOODS WITH THE AIM OF MITIGATING
THE PROBLEM OF FLOODS WITH THE APPROPRIATE
MANAGEMENT OF THE BULGARIAN DAMS
Dr Kotsovinos N., Professor DUTH
Dr Angelidis P, Lecturer DUTH
Dr Maris F., Assistant Professor DUTH
Kotsikas M., MSc Environmental Engineer
DEMOCRITUS UNIVERSITY OF THRACE
SCHOOL OF ENGINEERING
DEPARTMENT OF CIVIL ENGINEERING
XANTHI - GREECE

2. Transboundary river Evros (Meric) and main tributaries

3. River Evros (Meric) and main tributaries
EVROS
ΑRDAS
ΤΟUΝΤΖΑ
ΕRGINE
ΕRYTHROPOTAMOS

4. AIM OF THE RESEARCH
The basic objective of this work is to contribute in the
fighting of the problem of floods in the border region of the
transboundary river Evros (Meric).
A software program has been developed, which requires
as input forecast rainfall data for Bulgaria, Turkey and
Greece, and the reservoir elevation of the Bulgarian dams
at the beginning of simulation.
Subsequently the software program calculates (forecasts)
a few days in advance the discharge of the river Evros at
various critical places, according to the way the Bulgarians
will manage the water of the dams.

5. AIM OF THE RESEARCH
The program also calculates the time that is needed for
flood waves that are created by the sudden opening of the
weir gates of the Bulgarian dams to reach the Greek
borders and the propagation of the flood wave along the
Greek-Turkey transboundary river Evros.
The software can be used to study various scenarios with
the aim of optimal management of the water release from
the Bulgarian dams a few hours before the occurrence of
strong rainfalls.
The software has the ability to simulate the hydroelectric
operation of dams, to calculate the produced energy for
various scenarios and to calculate the energy loss due to
the flood prevention management.

6. Why the management of the water release from the Bulgarian
dams is so important?
In the Bulgarian part of the watershed of Evros a significant
number of dams have been constructed. It is pointed out, that
the 15 greatest dams receive the flow of the 34% of the area
of the Evros watershed in Bulgaria
Consequently, it is obvious, that in the Greek-Turkish
downstream part of the river Evros there is no longer a direct
inflow of the waters of the watershed of Evros, as in the past,
but mainly the inflow of released quantities of water from the
Bulgarian dams.
Therefore, the management of these quantities of water, that
are released via the dams, is of decisive importance for the
floods that are created.

7. Are climatic changes responsible for resent floods?
Studying the biggest daily discharges, we found:
period 1844-1995 (151 years): 12 floods (less than one
flood each 12 years) are reported
period 1985-1995 (11 years): only one time flood
discharge was greater than 2500 m3/s
period 1996-2007 (12 years): seven times flood discharge
of 2500 m3/s was exceeded
As we prove in this work, NO

8. Results of Gumbel analysis to the maximum annual flood
discharges in Pythio of Evros for two distinguishable time
periods:
a) Period 1985 – 1994: the floods with a discharge of about
3000 m3/sec have a return period of 70 years
b) Period 1985 – 2007: the return period changes dramatically
to only 7 years
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1000
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400
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Fixed value Y = -LN LN(T/T-1)
GUMBEL DISTRIBUTION OF THE ANNUAL FLOOD DISCHARGES OF
THE RIVER EVROS (BRIDGE OF PYTHIO)
DISCHARGE,
m
3
/
sec
RETURN PERIOD T, YEARS
Comparison of the Gumbel distribution for two groups of flood data. From 1985 to
1995 and from 1985 to 2007. The dramatic change in the distribution is connected to
the changes in the management of the Bulgarian dams.

9. We argue this dramatic change of flood
frequency is connected with the change of the
way of management of the Bulgarian dams
afterwards 1994
and not with the climatic changes.
The effect of climatic changes should be
sought and proved in the meteorological
parameters (main rainfall, which surely did
not present a 6 times increase) and not in the
floods, as the flow is controlled now mainly
by the dams.

10. Why most of resent floods happen?
The Bulgarian private electricity production company (which
is in charge of the managements of the Bulgarian big dams)
tries to “to maximize” the produced hydroelectric energy,
following the simplified principle of the maintenance of the
water level in the reservoir above the crest of the spillways,
keeping the floodgates closed (maximizing the piezometric
head and the volume of stored water in reservoir).
When a strong rainfall occurs in the watershed of the dams
(which already operate at the highest reservoir level), face the
danger of dam overtopping.
To avoid this danger of dam overtopping, the operators of the
dams open the gates.

11. As we prove in our work, the peak of the discharge
hydrograph due to the outflow hydrograph from the
spillway can be much greater than the peak of the
discharge hydrograph of the natural river, without the
existence of the dams, under the same meteorological
conditions.

12. It seems therefore that a hypothetical
simplified management strategy on behalf of
the owners of the dams causes floods, that
would not be created under the same
meteorological characteristics (rain) without
the existence of the dams.
Therefore, a better strategy for appropriate
management should be advanced, which
prevents floods downstream with
compensating the economic losses due to the
diminishing energy production upstream.

13. We developed a new computer software for the simulation of the
management of flood flows of the river Evros, named EvroFloods

14. INPUT:
forecast rainfall data for Bulgaria, Turkey and Greece
the reservoir elevation of the Bulgarian dams at the
beginning of simulation
OUTPUT:
the discharge of the river Evros at various critical places,
according to the way the Bulgarians will manage the water
of the dams
the travel time that the peaks from the flood waves
(created by the release of water from the gates of the
Bulgarian dams) need to reach Greek boundaries
calculation of the produced energy for various scenarios
and calculation of the energy loss due to the flood
prevention management

15. OUTPUT:
The Evrofloods software can be used to
study various scenarios with the aim of
optimal management of the water release
from the Bulgarian dams a few days before
the occurrence of strong rainfalls
The optimal management has as basic
objective the prevention of floods
downstream with minimum hydroelectric
energy loss upstream.

16. Friendly graphical interface

17. Simple input of forecast rainfall

18. Hydrograph computation using Snyder’s method

19. Basic input: Dam’s general data, Spillway data and
Hydropower Plant data

20. Rooting through rivers’ network and hydrograph
prediction at any place

21. Variation of water elevation in a reservoir as a function of
time

22. Comparison between EvroFloods and HEC-HMS:
Results (hydrographs) are very closed

23. SOME RESULTS
Senario 1:
What happens at a storm event, if
(hypothetically) the dam of Ivaylovgrad does
not exist?

24. • Suppose a 24 hr rain of totally 100 mm on the area (1)
• Suppose a 24 hr rain of totally 100 mm on the area (2),
which starts 8 hours later
• We also suppose, that the dam of Ivaylovgrad
(downstream area 2) does not exist.
1
2
1

25. Peak discharges of the two hydrographs arrive at the same time(45.1
hr), which is the worst senario.
So we have a very high peak discharge of 2968 m3/s that means flood
1
2
1

26. Senario 2:
What happens for the same storm event, if the
dam of Ivaylovgrad has been constructed and
operates?
We suppose that:
At the beginning of the rain, the water level in the reservoir
is 1.0 m above the crest of the spillways, keeping the
floodgates closed.
In order to maximize the volume of stored water in the
reservoir and the produced hydroelectric energy, the
managers of the dam keep the floodgates closed.
If the water level in the reservoir reach the maximum
allowed lever, then the floodgates will open.

27. The peak discharge is now 3913 m3/s, that is about 1000 m3/s
higher compared with SENARIO 1, when the dam of
Ivaylovgrad does not exist.
1
2
1
Input to the reservoir
Outflow hydrograph
from the spillway, when
the floodgates open
Total hydrograph
entering Evros,
downstream
Edirne

28. Senario 3:
What will happen for the same storm event, if
the managers of the dam start to release
water through hydropower plant, in order to
lower the water level so that incoming water
volumes can be stored?
It is pointed out, that there is a hydroelectric
energy loss (cost), releasing water through
hydropower plant.

29. Hydrograph inflow in the reservoir because of storm.
Outflow through hydropower plant, which begins when
the rain started.
0
200
400
600
800
1000
1200
1400
0 20 40 60 80 100 120 140 160 180 200
TIME, HOURS
DISCHARGE
(m
3
/s)
RESERVOIR'S INFLOW OUTFLOW THROUGH HYDROPOWER PLANT

30. Reservoir’s water level variation as a function of time because of
storm and water release through hydropower plant.
As we see, the final water level in the reservoir remains quite higher
than initial level. So there is a significant profit.
68.00
70.00
72.00
74.00
76.00
78.00
80.00
0 20 40 60 80 100 120 140 160 180 200
TIME, HOURS
RESERVOIR'S
WATER
LEVEL(m)

31. The peak discharge is now only 2297 m3/s, that is about 1615
m3/s lower compared with previous SENARIO 2, when no
release of water happened.
1
2
1
Input to the reservoir
Outflow hydrograph
from the spillway
Total hydrograph
entering Evros,
downstream
Edirne

32. In any case the developed software EvroFloods estimates the
cumulative produced energy.
CUMULATIVE PRODUCED ENERGY (MWh)
0
1000
2000
3000
4000
5000
6000
7000
0 24 48 72 96 120
TIME, HOURS
ENERGY
(MWh)

33. According to these various management scenarios
that we have studied in this research, we find that a
bad management of the Bulgarian the dams seeking
economic profit of some hundreds of thousands
Euros, causes floods and destructions of tens of
millions Euros in Greece and Turkey which are
downstream.
We quantitatively prove, that for extreme
meteorological episodes (strong rainfall) it is
possible with appropriate operation management of
the dams to avoid floods downstream, without (most
likely) any losses in the production of electric
energy.

34. The Evrofloods software is used to study various
scenarios with the aim of optimal management of
the water release from the Bulgarian dams a few
days before the occurrence of strong rainfalls.
The optimal management has as basic objective the
prevention of floods downstream with minimum
hydroelectric energy loss upstream.
The software has the ability to simulate the
hydroelectric operation of dams, to calculate the
produced energy for various scenarios and to
calculate the energy loss due to the flood prevention
management.

35. However, if due to the flood prevention dam
management, profit losses occur for the
Bulgarian electric energy production
company (mainly because of the decrease of
the water level in the reservoir and the non
realization of the expected rainfall), then it is
fair that the downstream countries Greece
and Turkey compensate the upstream country.

36. For example, for one scenario that was elaborated
with the developed software EvroFloods, the energy
loss occurred in order to avoid the flood is roughly 5
MWh, valued about 400.000 €.
According to this scenario, where a flood prevention
management has been applied but the failure of
rainfall forecast has as a consequence the loss of
energy production, the downstream countries
Greece and Turkey should pay for compensation of
the upstream country.

37. We point out the European and International
legislation which is related to the responsibilities of
the upstream country, which due to technical works
and wrong management, causes problems (floods,
damages, social and economic repercussions) to
the downstream country, that for the same
meteorological phenomena would not have
occurred, if the dams and their problematic
management did not exist.

38. The recent Community Directive 2007/60/EC/23-10-
2007, on “the assessment and management of flood
risks”, where it is quoted in the introductive text,
that :
“Member States should refrain from taking
measures or engaging in actions which significantly
increase the risk of flooding in other Member States,
unless these measures have been coordinated and
an agreed solution has been found among the
Member States concerned”.
The downstream countries may suspect that their floods
are due to the unilateral undertaking of actions from the
upstream country for the management of the dams, and
that for the same rainfall upstream, floods would not be
created if the dams did not exist.

39. This situation introduces an interesting legal
question of European Legislation and it has to
be examined properly.
That is to say, that Greece and Turkey can
claim compensations, if they can prove, that
the flood discharges that reached the Greek-
Turkish part of Evros were not due to extreme
meteorological phenomena, but due to wrong
management of the Bulgarian Dams.

40. We advocate therefore the best practice is the
cooperation of the three countries (Greece,
Bulgaria, Turkey), exchanging detailed
information’s regarding the rainfall in their
countries, the level and management of dams,
improving the technical part of the flood
generation mechanism, and in crucial
situations decide together the best
management.