Integrated modelling for flood risk mitigation in Romania: case study of the Timis–Bega river...

8/10/2019 Integrated modelling for flood risk mitigation in Romania: case study of the TimisBega river basinmania

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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

270 I. Popescu et al.


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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

Integrated modelling for flood risk mitigation in Romania 27


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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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Figure 16 Computed hydrographs before breaches, after breaches and

at the breach location in the case of breaching before the arrival of theflood peak



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