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Research paper
Integrated modelling for flood risk mitigation in Romania:case study of the TimisBega river basin
I. POPESCU,UNESCO IHE Institute for Water Education, Westvest 7, 2601 DA Delft, The Netherlands.
E-mail: [email protected](Author for correspondence)
A. JONOSKI,UNESCO IHE Institute for Water Education, Westvest 7, 2601 DA Delft, The Netherlands
S.J. VAN ANDEL, UNESCO IHE Institute for Water Education, Westvest 7, 2601 DA Delft, The Netherlands
E. ONYARI,UNESCO IHE Institute for Water Education, Westvest 7, 2601 DA Delft, The Netherlands
V.G. MOYA QUIROGA, UNESCO IHE Institute for Water Education, Westvest 7, 2601 DA Delft, The Netherlands
ABSTRACTAn integrated flood modelling approach has been applied in a demonstrator of a flood management system, which was developed within the frameworof a collaborative project between Romania and the Netherlands. The developed demonstrator system had two objectives: (a) operational water management under extreme conditions when actions have to be taken quickly; (b) off-line analysis and design of flood mitigation measures and alternativeThis article presents the applied approach and the achieved results for meeting the second objective. The pilot basin for the development of the systemwas theTimis Bega river basin, in which therivers Timis and Bega were considered jointly. The system is based on modelling the flood generation anrouting processes by combined development and application of hydrological and hydrodynamic models. The modelling system HEC-HMS was usefor the hydrological model, HEC-RAS for the one-dimensional hydrodynamic model and SOBEK for the two-dimensional (2D) model used for downstream flood analysis and design of mitigation measures and alternatives. The 2D model includes alternatives of deliberate dike breaching as part of th
analysis of the system response. The analysis presented is concentrated on a specific flood event that occurred in April 2005, which occurred due to dikbreaches along the Timis river. The combination of models is first used for reconstruction of inundation patterns resulting during this flood event. Subsequently the models were used for testing flood mitigation alternatives of deliberate (planned) breaches of flood protection dikes located in the downstream part of the Timis river at the same location where they had occurred during the 2005 flood event, but at different times with respect to the arrivaof the flood hydrograph. The demonstrated approach can enable decision-makers to analyse the behaviour of the physical system and design possiblpreventive and/or mitigation measures.
Keywords:Flood modelling; flood mitigation; dike breaches; decision support system
1 Introduction
Floods remain one of the most frequent and devastating natural
hazards worldwide. While existing forecasting and warning
systems have made a significant contribution to the reduction
of losses due to floods, nevertheless there remains a consider-
able potential for further prevention of losses by making use
of technological advances for better integration of data and
models and consequently design of better flood mitigation
measures and issuing of more accurate forecasts and possible
warnings. In on-line situations, flood modelling is central in
forecasting and warning systems as it can help us to understand
flood generation and identify the potential areas to be inun
dated. This allows issuing of targeted early warning to down
stream communities located in the floodplains which will b
affected. In off-line situations flood modelling also enable
long-term planning for flood damage reduction, which is com
monly carried out by using the models for evaluating variou
flood mitigation measures in order to determine which alterna
tive will be economically and environmentally feasible, given
the prevailing conditions. Models have different requirement
for on-line and off-line applications. On-line models, fo
flood forecasting, require fast and accurate simulation of dis
charge peaks for a known water system. Often, capabilities o
Received 5 January 2010. Accepted 29 July 2010.
ISSN 1571-5124 print/ISSN 1814-2060 onlineDOI:10.1080/15715124.2010.512550http://www informaworld com
Intl. J. River Basin ManagementVol. 8, Nos. 34 (2010), pp. 269280
# 2010 International Association for Hydro-Environment Engineering and Research
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hot-starts and data assimilation are a pre-requisite to fulfil these
requirements. Off-line models need to provide a physically
based reliable simulation of the water system behaviour for a
wide range of conditions and for changes in the modelled
water system itself, to allow design and analysis of structural
flood management measures. The off-line modelling systems
need to allow users to translate proposed measures into
changes in the model, e.g. flood plain adjustments. Integrated
flood modelling is increasingly being demonstrated to be a
necessity due to the complexity of the interactions among
different components of the river and its floodplain. Various
flood modelling studies have been carried out that show how
interactions between rivers and floodplains can lead to accurate
flood forecasting and prediction at critical points. Flood model-
ling systems usually combine rainfallrunoff models with flood
routing models. The flood routing is carried out either by
hydrologic routing approaches, which are used to obtain theflood peak by routing flood events between streamflow
gauging stations, or by more complex one-dimensional (1D)
hydrodynamic models which simulate flood propagation
based on detailed channel geometry (Blackburn and Hicks
2002). However, in areas with complex river flow conditions,
especially in the presence of complex riverfloodplain inter-
actions, two-dimensional (2D) models need to be used for
off-line spatial hydraulic analysis (Horrit and Bates 2002).
The Netherlands has a long history of water management,
during which significant knowledge and experience related to
flood protectionhas been accumulated.In thiscountry, flood man-agement is currently approached as an integral part of wider water
management and spatial planning processes. The practical
implementation of this approach relies heavily on integrated
flood modelling. The accumulated knowledge and experience
in the field of forecasting excessive rainfall events, predicting
and controlling high river water levels as well as mitigation of
floods, can be exported to other countries in Europe and the rest
of the world. Similar to the Netherlands, Romania is a country
where rivers discharge into the sea. Romania is, however, a
much larger country also characterized by mountainous catch-
ments, which are absent in the Netherlands. Romanian Waters
(the National Agency responsible for overall water resources
management) complies with the legislation compatible with the
EU regulations regarding water resources management and the
preservation of aquatic ecosystems and water areas. In this
respect, this agency is responsible for the ways in which surface
and groundwater resources in the Romanian territory are used.
The same agency is also responsible for flood management and
control. In this area, the agencyis currently developing andimple-
menting new, technologically advanced decision support systems
(DSS) for flood forecasting and warning, as well as long-term
flood risk planning and management. In these efforts, the
agency is facing numerous challenges due to lack of modellingexperience as well as data availability and data quality assurance.
As part of these ongoing activities, within the framework of a
flood forecasting system demonstrator has been develope
which can support operational water management und
extreme conditions when rapid action has to be taken. Th
system had a comparatively simpler (with short running time
modelling component (only rainfall runoff model develope
with HEC-HMS), and the focus was on the on-line integratio
of this component with meteorological and hydrologic
data. Next to the on-line system, integrated flood modellin
approaches for off-line analysis and design of flood mitigatio
alternatives were implemented, which are the focus of this pape
This was achieved by combining the HEC-HMS model with
1D hydrodynamic model developed with HEC-RAS and
SOBEK 1D-2D model for flood inundation modelling. In th
modelling approach, the Timis and Bega rivers were considere
jointly, since their joint hydrodynamic response are conditione
by the operation of existing hydraulic structures used for wat
transfer between the two rivers. The present paper describes thapproach taken in the off-line integrated flood modelling an
the usage of the models for analysis and design of possibl
flood mitigation measure and alternatives. The focus is on th
analysis of a particular flood event that occurred in April 2005
when a large area close to the Romanian border with Serb
was inundated as a consequence of dike breach failures alon
the river Timis.Actual breaches of the dikes occurred due to stru
tural failure (induced by poor maintenance), even though th
water levels were barely at the overtopping level. Initially, th
integrated modelling approach was applied for reconstructin
this particular flood event. Subsequently the same models weused for analysis and testing of possible flood mitigation alterna
tives. Assuming that high flood water levels and discharg
would anyhow lead to eventual dike breaches due to overtoppin
(even if dikes are well maintained), alternatives have been teste
in which deliberate (planned) dike breaches are carried out at th
same locations as those occurring during April 2005, but at diffe
ent timingwith respect to thearrival of the flood hydrograph. Th
approach has not been extensively researched in the past and,
the results demonstrate, it can leadto the reduction of flood impa
in terms of lower flood volumes and reduced area of inundatio
2 The Timis Bega river system
2.1 Case study location
In terms of flooding problems, one of the most vulnerab
regions in Romania is in the west. Furthermore, many rivers i
this region are of a trans-boundary nature: their basins a
either in Romania and Serbia or in Romania and Hungary. An
event occurring in these rivers is advected downstream to th
neighbouring country. A typical example of this situation is th
river Timis, which in the recent past has caused severe floo
ing in the two neighbouring countries of Romania and Serbia. the past, many dikes were constructed along this river for floo
protection, which in return made the downstream floo
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May 1912 was the highest, with a maximum recomputed dis-
charge of approximately 1600 m3/s, and estimated to have a
return period of 1 in 50 years (Hunteret al.2007).
For comparison purposes, the hydrographs of four recorded
floods, including the 2005 flood, are represented on the graph
in Figure 2 and centred at the time of peak. The 2005 total
flood volume was three times greater (about 720 million m3)
than that of the flood in 2000, though the peaks of these two
events were very close. In 2005, as a result of the high flood
peak, the embankment of the right-side bank of the river Timis
was barely overtopped, but still collapsed and multiple dike
breaks were reported. The volume of inundation was approxi-
mately 300 350 million m3. After the 2005 flood, a significant
financial investment was made to restore the structural com-
ponents of the various affected water dikes.
In these conditions, the question naturally arises as to what
measures need to be taken so that new flood events of thesame magnitude as the one in 2005 will not cause further
damage in the future.
The current flood forecasting and warning system in the
TimisBega basin is based on empirical models which show
the relationships of the flow at a downstream point versus the
one at an upstream station. During the flooding crisis in Banat
in 2005, specifically with regard to the Timis and Bega River
basins, there were three significant time periods with high rain-
fall. Warnings of high water levels associated with these three
high rainfall periods were issued, but the established procedure
did not provide sufficiently accurate forecasts, which led to flood-ing and consequently to severe flood damage. While the precipi-
tation data have been quite reliable, lack of good rainfall runoff
model that could produce forecasts of upstream discharges
together with the unreliable empirical approach used for flood
routing were the main reasons for the inaccurate forecasts.
This event proved that better, more accurate models were
required. It led to the conclusion that the elaboration of an inte-
grated hydrological-hydraulic model for the TimisBega river
basin is needed, comprising different flooding scenarios and
indicating the spatial extension of the inundation, water depths
and velocities.
2.3 Availability of data for a flood event in the basin
Before setting up an integrated model for the TimisBeg
system, the analysis of the April 2005 flood which was carrie
out by the Romanian Banat Water Board was taken into conside
ation. This analysis was done on the basis of the dischargrecords at 20 gauging stations. The analysis checks the degre
of reliability of the data concerning the gauged and ratin
curve, i.e. the extrapolation discharges.
The check was made for the total runoff hydrograph, th
surface runoff and the base runoff. This analysis reported unu
sually high estimates of the runoff coefficients a (surfac
runoff versus rainfall) (Stanescu and Drobot 2005).
The analysis of the available observed data for the Timis
Bega basin for the year 2005 refers to the amount of precipitatio
and climatic conditions prior to the flood period and to the perio
of the flood itself (1422 April 2005) (Figure 3).The period covering two weeks before the flood event wa
characterized by comparatively small amounts of rainfall (10
15 mm recorded between 27 March and 1 April). Howeve
the same period, especially the days between 8 and 13 Apri
was characterized by a sudden increase in temperature (468
daily average in the hilly and mountain zones). These condition
contributed to significant snow melt in the mountainous zones.
was estimated that the increase in soil moisture during this perio
ranged between 24 and 40 mm, and the larger part of this so
moisture increase was because of snowmelt (compared wi
the contribution from precipitation).
By the time of the big precipitation events that eventuall
caused the flooding, the snow cover in the catchment has bee
limited to very small areas at very high altitudes. Under the alt
tude of 1000 m.a.s.l (corresponding to 96% of the entire area o
the river basin) there was no snowpack. However, due to th
above-described conditions in the previous period, the who
catchment was already quite wet when the big flood-causing pr
cipitation events came.
This analysis led to the conclusion that the flood event itse
was in fact entirely of pluvial nature and there was insignifican
snowmelt contribution provided by the small mountainous area
which was anyhow retained in two reservoirs in the basin (PoianMarului at 650 m.a.s.l. and Trei Ape at 870 m.a.s.l.)
During the flood event period (1422 April 2005), significa
rainfall occurred in three distinct time intervals separated by n
rainfall periods which varied between 3045 h during 161
April and 9.0015.00 h on 21 April (Figure 4). Periods
time with reduced rainfall quantities continued after 22 Apr
but they only fed the high discharges without contributing
the increase of the water levels over the alarm threshold. Th
core of the biggest rainfall, in terms of quantity, in the floo
zone ranged between 15 and 24 h.
According to the data recorded at the pluvial stations, th
cumulative rainfall (1422 April) that caused the outstandin
April 2005 flood ranged between 60 and 221 mm. The small
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western mountainous zone. The spatial distribution of the
cumulative rainfall during the flood event period is presented
in Figure 4.
3. The integrated model for the TimisBega system
The Dutch Romanian project mentioned in this paper had
Timis Bega basin. Because of the high stakes involved concern
ing water management during a crisis, it is important that a fore
cast of the emerging situation occurs in a structured an
reproducible manner. These requirements are met nowadays by
making use of hydrologic and hydrodynamic models, which
are used by water managers in both forecasting situations awell as planning situations.
The development and implementation of a DSS demands an
integration of water management, knowledge management and
hydroinformatics (Abbott 1991, 1999). Besides extended knowl
edge of ICT and software development, attention to the quality o
modelling and also the users demands concerning the presen
tation and communication of the model results are require
(Abbott and Jonoski 1998). If not enough attention is paid to
these aspects, the DSS will not satisfy the users expectation
and consequently the adoption by its users may be difficu
(Jonoski and Popescu 2004).
The developed demonstrator system of the above-mentioned
Dutch Romanian project had two objectives: (a) operationa
water management under extreme conditions when actions hav
to be taken quickly; and (b) off-line analysis and design of floo
mitigation measures and alternatives. The focus of this paper i
to present the models which were used for developing the secon
objectivefor theDSS forfloodprotection in theTimis Bega basin
The integrated model used in the off-line analysis of th
system is based on a sequential combination of hydrologica
and hydrodynamic models. The integrated model starts wit
the development of a hydrological model using the USACE
HEC-HMS modelling system (a hydrological model). After thdevelopment of the HEC-HMS model, the second phase wa
the development of a 1D hydraulic model of the major river
Figure 3 Isohyets of precipitation, 14 22 April 2005
Figure 4 Temporal distribution of rainfall in the Timis Bega basin
between 14 and 22 April 2005
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hydrologic model. The third phase of the model development
entailed a refinement of the second phase by integrating the
1D-2D SOBEK model for modelling river floodplain inter-
actions. The whole suite of models used comprised therefore
HEC-HMS (0D), HEC-RAS (1D) and a 1D-2D SOBEK.
All the models were calibrated and checked for sensitivity.
Figure 5 shows the coverage of the various models as used in
the study. The rainfall runoff model HEC-HMS was used in
the whole catchment and the 1D hydraulic model HEC-RAS
was used in the main channel starting at the gauging stations at
Balint and Lugoj for the Bega and Timis rivers, respectively,
and up to their outlets. The SOBEK 1D-2D was used for
the floodplain starting at the gauging stations for Remetea
and Brod.
In transforming several rainfall time series into a flood inun-
dation map, various interconnected components were involved,
as shown in Figure 5. HEC-DSS was used for data storage.The measured precipitation was provided to the data storage
HEC-DSS, which was used as input for the HEC-HMS model.
The system, when provided with these rainfall time series, trans-
forms them into runoff through hydrologic simulations in HEC-
HMS. The hydrograph obtained from the rainfall runoff model
was fed into the hydraulic model HEC-RAS that computed the
water surface elevations. This computed discharge hydrographs
of the HEC-RAS model were used as input into the SOBEK 1D-
2D model that simulated the floodplain inundation.
The elements that were used to support the full integration
include HEC-RAS, HECDSS, HEC-HMS and SOBEK 1D-2Dmodel configurations.
The procedure was as follows:
(1) Inputting precipitation data into HEC-DSS for HEC-HMS.
(2) Executing HEC-HMS.
(3) Transferring flow values of HEC-HMS into HEC-RAS b
establishing connection points in HEC-DSS file (output o
HMS) and updating related input files.
(4) Executing HEC-RAS.
(5) Transferring discharge and waterlevel data from HEC-RA
as boundary conditions to SOBEK 1D-2D.
(6) Executing SOBEK 1D-2D (Figure 6).
A good understanding of the HEC-DSS system was critical i
this implementation to make available relevant time seri
records from the database time series tables to the HEC-HM
and HEC-RAS models and to allow the transfer of records.
unique identifier (model codification) to support the connectivi
between the features in each model was needed to spatially rela
features across the models.
Figure 6 Flow chart showing the coupling of HRC-HMS, HEC-RA
and SOBEK1D-2D
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The HEC-HMS model covers an area which includes the
HEC-RAS model. HEC-HMS output was used as upstream
boundary condition to the HEC-RAS model. Some sub-basin
HEC-HMS hydrographs located downstream of the upstream
boundary condition in HEC-RAS were provided as lateral
inflow to the HEC-RAS model.
The discharge hydrographs from the 1D HEC-RAS hydraulic
model were provided to the 1D-2D SOBEK model as boundary
conditions on the upstream part, and water levels were used as
downstream boundary conditions. 2D model simulations were
then performed with the aim of providing information about
the inundation patterns in the riverfloodplain system of the
TimisBega basins.
3.1 The HEC-HMS model
In the HEC-HMS model, the Timis Bega catchment was discre-
tized into 20 sub-basins, based on their common physical charac-
teristics. The other components of the system are junctions and
reaches, which collect water from different sub-basins and
route it downstream.
The river network was schematized from the upstream station
Sadova to the downstream station, at the border between
Romania and Serbia, which in total covers a distance of
about 275 km. In setting up the HEC-HMS model, each sub-
basin is associated with a schematization point, called a junction,
which represents the outlet of the sub-basin. The reaches repre-
senting the channels are straight line connections of the junc-tions, through which the routing takes place from upstream to
downstream.
The HEC-HMS model was calibrated for the year 2003, a year
without any extreme events, and then used to reproduce the 2005
flood event.
Each sub-basin was assumed to have uniform hydrological
characteristics, thus the model parameters were lumped at the
sub-basin level. The characteristics that are required in the
model include precipitation, evaporation, physical character-
istics such as slope, Manning roughness, channel length, etc. Pre-
cipitation was given as input according to measuring gauges in
the basin. The spatial distribution and contribution of the precipi-
tation for various sub-basins, according to the measuring gauges,
was provided by the Romanian water hydrology department,
along with the gauge weights. The soil moisture accounting
method (SMA) (Bennett 1998) was used to compute the losses
in the catchment, taking into account the precipitation and poten-
tial evapotranspiration. This method uses different storage reser-
voirs to represent components of the runoff generation processes,
such as canopy, soil, surface and groundwater storages. The
exchange of water in between the components is controlled by
exchange parameters. The storage capacity of each component,
i.e. canopy, soil, surface and groundwater, together with theexchange parameters, was inputted into the model. The initial
conditions of canopy, soil, surface, and groundwater were speci-
beginning of the simulation. The potential evapotranspiration
in the catchment was computed using the Blaney Criddl
method, where the monthly percentage of daylight hours in the
year, p, was computed using the maximum possible sunshin
hours for the latitude 468north.
Besides the junctions, the other routing elements from
upstream to downstream are the reaches. The runoff wa
routed downstream using the Kinematic wave method, and there
fore the sub-basin length, slope and roughness coefficient neede
to be specified.
The simulation results of this HEC-HMS model for the floo
event of 2005 were hydrographs at junctions, some of which
were further used as upstream boundary condition for th
HEC-RAS model, which was developed and calibrated only
for the 2005 event. The resulting hydrographs from th
HEC-HMS model for the river Timis at Lugoj was compared
with the observed discharge at the same station. The result is presented in Figure 7.
The two hydrographs show a very good match; however, th
computed hydrograph has a higher peak than the measured one
and a slightly later arrival of the peak. As mentioned earlier, the
HEC-HMS model was calibrated using data from 2003, and i
was not re-calibrated for the simulation of the 2005 event
Given that the SMA model that was used in this HEC-HMS
set-up requires physically meaningful parameters, the goo
match between the measured and modelled hydrographs for con
siderable extent can be attributed to the sufficient calibration o
the original HEC-HMS model. This contention could be confirmed by testing the model performance with other floo
events,but this could not be done due to thelack of available data
3.2 The HEC-RAS model
To schematize the river network, the river reach was introduced
first, and then the cross-sections were provided to the model
Figure 7 Measured and HEC-HMS modelled hydrograph on Timi
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An example of cross-sections that were provided is shown in
Figure 8 (Sag station).
Flow data were provided by the HEC-HMS-calibrated output
hydrographs.
The most upstream boundary condition was introduced as an
inflow hydrograph. Downstream boundary conditions werespecified as normal depths calculated for different flow con-
ditions. The initial conditions were provided as discharge. In
between the upstream and the downstream HEC-RAS points,
the sub-basins contributions were provided as lateral inflows,
as calculated by the HEC-HMS.
The initial purpose of the HEC-RAS model was to determine
water levels in the downstream part of the TimisBega river
system, especially during flood conditions. The development
of different models was carried out in stages. During the stage
of the HEC-RAS development, it became apparent that results
of the HEC-RAS model could not represent well the waterlevels in the most downstream part of the TimisBega catch-
ment, where most of the flooding occurred during the 2005
event. Therefore, in the next stage, it was decided to model
this last part with the SOBEK 1D-2D modelling system and
the results from HEC-RAS served only as inputs to this last
model (Figure 9).
3.3 The 1D-2D Sobek model
In general, the 1D models are computationally efficient.
However, when applied to flooding situations, especially whenfloodplain flows are modelled, there are a number of disadvan-
tages of 1D models, such as inability to model lateral diffusion,
than representing it as a surface (Popescu et al. 2007). The
are constraints, which have been addressed with the use o
1D-2D or 2D codes. The use of 1D-2D codes rather than ju
2D codes is necessary because during flooding events, it
critical to have a good representation of the channel conveyanc
processes.
The Sobek model was used in this paper for the 1D-2D mod
elling of the river in the downstream part of the catchment, whe
the area is very flat. The Timis and Bega rivers were schematize
as a 1D channel, and the floodplain was represented by a 2D gri
using cell sizes of 100 100 m. The elevations for the 2D gr
cells were obtained from a 30 30 m Digital Elevation Mod
(DEM). The flooding was allowed to occur from the 1
channel into the 2D grid. Two boundary nodes were introduce
at the upstream and downstream side of each river reach. Floo
ing was allowed to the 2D from 1D using a dummy branch whic
has a weir with a control structure. The weir crest level walowered over time to simulate gradual breach developmen
For a given crest level of the weir, the weir itself functions a
Figure 8 Cross-section example data for the river Timis at Sag station
Figure 9 Plan view schematizationof theTimis Bega system in HEC
RAS
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Boundary conditions for the Sobek 2D model were obtained
from the 1D hydraulic model HEC-RAS. For the upstream
boundary conditions flow hydrographs were used. The down-
stream boundary condition for both rivers Timis and Bega was
provided as water level.
Flood maps of the event are available from MODIS remote-
sensing images taken during the 2005 event. The extent of the
flood from the MODIS images (Flueraru et al. 2007) was com-
pared with the results of the Sobek model (Figure 10). The sat-
ellite image (available in colour online) presents flooded area
on 23 April 2005 (light blue colour, which is of our interest)
together with the flooded area on 30 April 2005 (dark blue
not of interest here as it was not covered by the model).
The comparison shows a good match between the flood
extent obtained from the Sobek model and the one registered
by the satellite. The model simulations show that an area of
22,088 ha was affected by the flood (at the time of theevent, this area was estimated at 25,000 ha).
The total volume of inundation was the second criteria to
evaluate the result obtained with the Sobek model. The simulated
volume of inundation was around 278.9 M m3, which is similar
to the 300 M m3 reported by Stanescu and Drobot (2005). The
simulated water depths in the inundated area were up to 2.5 m.
Some sensitivity analysis of the developed model was carried
out with respect to the friction coefficient used for the 2D
modelling grid. The Manning roughness for the 2D grid wa
varied with values of 0.12, 0.15 and 0.08. Lower Mannin
roughness coefficients resulted in higher velocities and increased
flood extent downstream, as expected.
4 Flood mitigation alternatives
The aim of the downstream 1D/2D modelling was to simulat
various flooding extents and propose different methods of mana
ging the flood.
The proposed alternatives for flood mitigation involved delib
erate inundation by making intentional dike breaches along th
Timis and Bega rivers.
Depending on the magnitude of flood events, differen
mitigation measures can be taken. One of the possible measure
is dike breaching, though is not always the preferred one, no
the best. However, in case of extreme events, and if the rive
shows a history of dike failures, intentional breaching is one o
the solutions for flood mitigation because it gives control on th
place where flooding occurs and it releases the stresses on
the dike.
The location of the intentional breaches were selected in thi
study, exactly at the same locations with the natural breaches
formed during the 2005 event. The difference with the bas
case is the timing of the breaches.
These alternatives were modelled and mapped out under th
same conditions as the 2005 flood. The section of the floodedpart of the river stretches from the gauging station Sag to Gran
iceri for the river Timis and from Remetea to Otelec for the rive
Bega. The total length of this section is about 120 km. The area i
between these rivers is a highly populated area with a high econ
omic value.
Before an intentional dike breach is made, hydrological fore
casts or measurements have to be carried out to realize that ther
is a flood event that might occur. Again, different authorities and
people have to be involved directly or indirectly either becaus
they have to give consent and/or because they will be affecte
by the decisions. Most important is when to take the decision
to breach, which means that the flood timeline becomes very
important. The flood timeline starts from the forecast moment
and runs up to the time when pre-established critical threshold
is exceeded. This timeline needs to be determined as accurately
as possible so that decisions are not taken too early or too late, to
ensure effectiveness.
Since areas with a high economic value were to be affected b
the flood, actions have to be taken in order to reduce the impac
on these areas. Thus, actions that would protect people and prop
erty from the rising water could include intentional breaching o
dikes and inundating areas that are of low economic value, whil
protecting areas of high economic value. This intentional breaching was modelled in this study and it was realized that the area
that were to be affected could be greatly reduced with intentionaFigure 10 Flood extent of Sobek model in comparison with MODIS
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The following mitigation alternatives were considered:
(1) Base case with no mitigation measures
(2) Dike breaching after the arrival of the peak.
(3) Dike breaching at the start of the flood event.
4.1 The base case
The 2005 flood event was modelled by taking into account the
breaching at three locations on right embankment of Timis
river. The breaches were located at 6.7, 6.9 and 8.25 km, respect-
ively, upstream of the Romanian Serbian border. The two
breaches at 6.7 and 6.9 km joined together very quickly,
forming just one breach, which in the model was considered
to be located at 6.8 km. The width of the breaches was modelled
to be 250 m for the one at 6.8 km and 180 m, for the one at
8.25 km. In all subsequent figures, the most upstream breach isreferred as breach 1 (8.25 km) and the most downstream one
is referred as breach 2 (6.8 km).
The model covered the period from 14 April 2005 to 24 April
2005, midnight. The breaches were reported to be formed on 20
April, around 15.00. The total inflow volume of the 2005 flood
event was up to 513.3 M m3 and the outflow volume as it was
modelled was 234.4 M m3, meaning that all the remaining
volume inundated the floodplain (278.9 M m3). Figure 10
shows the flood map for the TimisBega basin for the 2005
flood event, and the area of 22,088 ha which resulted to be
affected by the flood.
The model first overtops the dikes and overflows and then
finally the dike breach occurs. The simulation shows that the
area in between the Bega and Timis rivers is highly affected:
54% of the area was covered by a water depth of less than
1 m, 33% of the area was covered by a water depth of
between 1 and 2 m and the rest was covered by a water depth
that was more than 2 m. The total area that was actually
covered during the flooding event was estimated to be
25,000 ha (Stanescu and Drobrot 2005). The model was able
to show the areas that were affected by the flood as a total o
22,088 ha, which means that the model under-predicted we
with an error of about 12%.
The input hydrograph together with the hydrograph at the tw
breach locations and the outflow hydrograph as resulted from th
model are presented in Figure 11.
Due to the high volume of water flooding the area ju
before the border with Serbia, several pumps were used
evacuate the water. These pumps evacuated 99.6 M m3
water from 3 May to 5 July 2005 (Nicoara and Ion 2005). I
the same period, according to Stanescu and Drobrot (2005
from the measured hydrographs between the Sag station, o
Timis and Graniceri, at the border of the model, a volume o
213 M m3 more than the usual flow on the same sector, flo
out on Graniceri section. These two values add up to wh
the model simulated.
Figure 12 presents the area affected by floods in 2005, and thdepth of the flooding.
Figure 11 Computed hydrographs before the breaches after the
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4.2 Dike breach after the arrival of the flood peak
The second case taken into consideration was an intentional
breaching carried out after the arrival of the flood peak in
the TimisBega catchment, on 21 April 2005, at 15.00.
Taking such a mitigation measure reduced the floodingeffects, since the model shows that the total area affected by
the flood was 13,122 ha (Figure 13). In this case the inundation
water depths dropped, as compared with the base case; there
was only 10% of the area with water depth between 1.5 and
2.5 m. The volume of the inundation was computed to be
161 M m3.
The inflow, outflow and breaches hydrographs for the case of
dike breaching after the arrival of the flood peak are presented in
Figure 14.
4.3 Dike breach at the start of the flood event
The effect of dike breaching at the start of the event can beseen in
Figure 15. The start of the event was on 20 April, 4 h later than
the actual breaching, in the base case. In the case of breaching at
the start of the event, the simulation showed that the extent of the
flood on the area in between the Timis and Bega rivers can be
reduced considerably. In this case, the inundation water depth
were as high as in the base case, more than 50% of the are
with water depth between 1.5 and 2.5 m. The volume of the inun
dation was computed to be 141 M m3
.
Figure 13 The 2005 flood extent taking into consideration dike breach
Figure 14 Computed hydrographs before breaches, after breaches an
at the breach location in the case of breaching after the arrival of th
flood peak
Figure 15 The 2005 flood extent in the case of a dike breach at th
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The inflow, outflow and breaches hydrographs for the case of
dike breaching before the arrival of the flood peak are presented
in Figure16. The area affectedby the flood in this case is 10,127 ha.
5 Conclusion
The hydrodynamic model developed for the TimisBega system
is a demonstrator which presents forecasted water levels and dis-
charges for the rivers TimisBega. This is an efficient way todemonstrate the possibilities of implementation of a model,
with the aim of helping decision-makers to understand flood
propagation and take the appropriate mitigation measures in
case of a flooding event. In Romania these models could be of
great help to the Romanian authorities.
Modelling can support decision-makers in responding to a
flood event, although there are uncertainties that can be expected
from forecasting and the involved models. In the TimisBega
basin the flood timeline that was deduced from the 2005 flood
showed that there were 8 h in Timis and 6 h in Bega available
as the maximum possible warning time after the falling of the
peak rainfall to the arrival of the runoff peak at the outlet.
The timing for the intentional breaching was while the rainfall
was still on the rising limb of the hydrograph. Modelling of
breaching is a difficult task, because it requires description of
the breach development, which has a lot of uncertainties. Taking
into account the effects of breach development and the related
uncertainties of that process was beyond the scope of this study.
One of the consequences of applying different mitigation
measures, in order to protect one area in the basin, can have as
an effect, flooding of another area further downstream in the
basin. This type of problem was not part of the present study.
Although the work presented here in is case-specific, the pro-posed mitigation measures proved to be efficient in reducing the
impacts of flood downstream and therefore can be used in similar
Aknowledgements
The financial support for this work was provided by the Dutc
Government, through Partners for Water. All the data require
for modelling were provided by Romanian Waters, Ban
region.
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