area of Ghardaïa-Algeria

17 Pages·2016·8.48 MB·English

by  Kheira Yamani

Model.EarthSyst.Environ.(2016)2:147
DOI10.1007/s40808-016-0183-x
ORIGINAL ARTICLE
Mapping of vulnerability of flooded area in arid region. Case
study: area of Gharda¨ıa-Algeria
Kheira Yamani1,2 • Abdelkrim Hazzab3 • Mohamed Sekkoum1 • Toumi Slimane1
Received:15June2016/Accepted:27June2016/Publishedonline:4August2016
(cid:2)SpringerInternationalPublishingSwitzerland2016
Abstract The issue of natural hazards in general and RAS 1D). After comparison of the results obtained by
flooding in particular is a hot topic which marks memo- various simulations, the vulnerable zones are thus charted.
rable actions in the world and specifically in Algeria.
Managing this risk is becoming more of a necessity that Keywords Vulnerability (cid:2) Cartography (cid:2) HEC-HMS 1D (cid:2)
must include all stakeholders and all possible means HEC-RAS 1D (cid:2) Arid region
available. The objective of this work is the vulnerability
mapping of flood areas in the arid region Oued M’zab-
region Ghardaia. It’s about implement predictive models Introduction
and flood control. This allows the development of a risk
prevention plan to flooding. To achieve this goal we The risings and the floods in the Mediterranean often
evaluated the hazard and vulnerability. The evaluation of originate in of the torrential rains. They are complex
theriskpassesbyastudyofthemodeofrising.Thisstudy weatherphenomenaandofagreatviolence.Inanyseason,
leads to the determination of the synthetic hygrogram the pouring rain can involve destroying risings and floods.
which are taken into account under the boundary condi- They thus represent the most widespread catastrophes in
tions upstream of a hydraulic model of the nonpermanent the Mediterranean (Ballais et al. 2005). In general, the
flows on free face. The results obtained for one period of floods at the origin of more than 80 % of the natural dis-
return given constitute the risk of the floods relating to asters are thus recorded in the world between 1996 and
these hydrograms. The vulnerability is represented by a 2006. They thus caused damage estimated at 500,000
rate which translates the objective of protection against a people deceased and of 600 billion dollars of economic
probable risk. Two types of models are tested on a section losses. So they are the natural disasters most spectacular
of Oued M’zab-region where the data are available. Ini- whichproducethemostdamage(Klijn2008).Accordingto
tially, are considered hydrological models (HEC-HMS the Blue Plan, 210 destroying floods touched the
1D). In the second place of the hydraulic models (HEC- Mediterranean circumference these 20 last years. They
struck 3,220,000 people, causing 4250 dead and economic
losses which would rise with more than 25 billion euros
& KheiraYamani (Em-dat, international disaster database 2004).
[email protected]
The forecast and the control of the damage caused by
AbdelkrimHazzab this type of disasters particularly require the identification
[email protected]
ofthevulnerableareasandthedeterminationofthefactors
1 CivilEngineeringDepartment,LaboratoryofWater andthedamagesgeneratedbythesecatastrophes(Hansson
Resource,SoilandEnvironment,UniversityofLaghouat, et al. 2008; Jonkman et al. 2008).
RoadofGharda¨ıa,P.O.Box:37G,Laghouat,Algeria Theriskoffloodisregardedasbeingtheproductofthe
2 UniversityofTahriMohammed,StreetofIndependence, probability of occurrence of risings and the consequences
P.O.Box417,Bechar,Algeria caused by these events (Raaijmakers et al. 2008). By
3 UniversityofMoulayTahar,20000Saida,Algeria havingadiagramtotalofthesituation,itwouldbenotonly
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possible to manage the risk, to take the necessary mea- (Nouh 2006; Hreiche et al. 2007; Kingumbi et al. 2007;
surements in order to eliminate the life losses and to limit Lajili-Ghezal 2007; McIntyre et al. 2007; Nasri 2007).
themateriallosses,butalsotohavediversifiedpossibilities (d) Space heterogeneity generates a progressive change in
to envisage an adapted dimensioning of the works water- the hydraulic capacity. The risks of flood are confirmed
supply engineering (Breton and Marche 2000). (Lebdi et al. 2006).
Algeria is among the countries which are affected by ThestudyoftherisingsinAlgeriaremainsanunknown
risings which generally generate floods due to the over- field. Thearid andSaharan areas, suffer fromlackof data,
flows of the river crossing the cities and the agglomera- only some very specific indications can be available in the
tions. These risings are of sudden appearance, often not Algerianhydrologicaldirectories.Therisingsrepresentone
easily foreseeable, of fast relatively significant specific of the fundamental features of the mode of a river of this
flow and boarding time. They are generally related to type of area. However, the information concerning the
intense rainy episodes and appear on basins of moderate series of risings is not available. This fact no conclusion
size (Merabet 2006; Yahiaoui 2012). total can be drawn.
Several catastrophes caused by its risings were listed in The area of M’zab in Ghardaia in the south of Algeria
Algeria. The table hereafter summarizes the most signifi- representsoneofthesearidregionsthemosttouchedbythe
cant floods that Algeria knew in the last decade (Anony- phenomenon of flood. This zone knew floods in 2008: the
mous 1 2007) (Table 1). OuedM’zab,whichleftitsbedtowards4Hofthemorning
In Algeria particularly the arid areas are characterized has,indeed,carriedeverythingonitspassage.Thedamages
by not very frequent but sometimes very significant are enormous: death of 100 people, 89 wounded, 756
downpours (Colombani et al. 1984; Pedro et al. 2006). damaged disaster victim families, 19 schools damaged,
These downpours often give birth to floods whose conse- 7200 houses deprived of electricity and 2300 families
quences are sometimes unforeseen (Hansson et al. 2008). deprivedofwater.Morethan1200 haofmarketgardening,
However, the rivers in the arid areas are characterized by arboricoles and of palm plantations were rolled by water.
the irregularity of flow and a strong fluctuation hydrolog- Morethan1000headsofcattleperishedandmorethan300
ical (Arab et al. 2004). During the year, the intermittent vehicles were carried by water. A manufacturing plant of
flows dominate in the majority of the Wadis in these areas batteries under licence (Tudor), employing more than 200
(Argyroudietal.2009).Ittakesplacetonotethatthistype workmen, was completely ransacked by water. The toll of
of area whose majority of the rivers are transitory, do not thematerialdamagesbordersthe20.1billionDinars,thatis
have till now a global approach of treatment confirmed by tosaymorethan200millionEuros(Medejerab2009).The
several reasons. (a) The scarcity of the data which repre- cartography of the flooded zones is a tool of decision-
sents one handicap to study the variations of the hydro- making aid in the management ofthe urbanization and the
logical assessment (Sivapalan et al. 2003). (b) The development of plan ORSEC (Anonymous 2 2007). The
occasionalchangeoftheclimaticandanthropic conditions justificationsofthisworkarevariedandthoserelatedtothe
which leads to an imbalance of hydrological flows and the social stakes consisting in ensuring the good being of the
physical characteristics of the basin (Puigdefabregas and population, the economic stakes consisting in decreasing
Mendizabal1998;Xoplakietal.2004;Lo´pez-Morenoetal. thedamagescausedbythefloodsandoftheenvironmental
2007). (c) The strong variability and of the transitory stakes consisting in decreasing the impact of the floods on
events, the hydrology of the arid regions or semi-arid. the people and the goods. In this work we cartography the
Whatimpliesastrongnon-linearityoftheexploredmodels floodedregion(attherisk)inanaridregionthenwequote
Table1 Thelargestfloodsin
Region Date Humanloss
thelastdecade
Azazga(TiziOuzou) 12October1971 40dead;hundredsofhomes
TiziOuzou 28March1974 52deaths,18,000claims
ElEulma(Se´tif) 1September1980 44deaths
Annaba 11November1982 26deadand9500claims
Jijel 29December1984 29deadand11,000claims
BordjBouArre´ridj 23September1994 16deaths
(Bab-El-Oued)Algiers 10November2001 710deaths,115missing
Bechar November1994 13deaths;4300homesdestroyedordamaged
Sidi-Bel-Abes October2007 7wordsandmorethan100affectedfamilies
Gharda¨ıa October2008 Morethan100deaths,86wounded,and4missing
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Model.EarthSyst.Environ.(2016)2:147 Page3of17 147
the tools of evaluation and cartography of the risks related belonging to the Saharan flora (Abonneau 1983; Daoudi
to the floods and the sources of generated uncertainties. et al. 2011). Among the trees, Abonneau (1983) quoting,
The estimate of the damage is done by the means of a be´toum (Astacia atlantica) and tarfaou (Tamarix gallica)
hydrological modeling by HEC-HMS, the hydrodynamic and the shrubs are represented by the alenda (Ephedra
modeling by HEC-RAS. Finally the cartography of the fragilis), the arich (Calligonium commosum), the rtem
flooded regions and the regions at the risk of the studied (Retmaretam)andtheseder(Zigyphuslotus).Accordingto
region are given. the type of area, one notes the presence of a rather sig-
nificantgrouptheadventitiousoneswhereinthesandyand
dry places such as the regs. (Abonneau 1983; Zergoun
Study area 1991;Daoudietal.2011),announcingthefollowingplants
of Acheb:Aristida pungens (drinne) and Aristida obtusa
General information like graminaceous most frequent,the dhamrane (Trajanum
inidatum), the baguel (Haloxylon articulatum), the merkh
The area of Gharda¨ıa is located at the center of the Alge- (Genista saharae) and the cheih (Artemesia alba). Down-
rian septentrional Sahara, 600 km in the south of the stream from the Oued M’zab develop halophilous plants
Algerian capital and is localised between latitude 32290 suchastheguettaf(Atriplexhalemus),theguedem(Salsola
19.4000N and longitude 3400 27.9400E (Fig. 1). The town of vermiculata), the ajrem (Anabasia articulata), the negued
Gharda¨ıa,countytownofwilayaascalled,islocatedonthe (Astericus graveolus) and the chaaliat (Sysimbium iris)
top of the five historical cities which counts the pen- (Abonneau 1983).
tapole;’’gathered cities in series on the banks of the same Theoccupationofgroundshowsthatthemajorityofthe
valley, which takes, on both sides this grouping, the name activities are concentrated on the level of the valley of
of Oued El Biod upstream, and that of Oued M’zab M’zab, which generates significant damage in case of ris-
downstream’’. ing (Fig. 2).
TheclimaticandgeographicalconditionsmakeM’zaba For the study of the risings and flood we chose seven
desertedregioninthenorthernlimitoftheabsolutedesert, under basins of the large basin of the Oued M’zab. It is
whichexplainsthescarcityofthevegetationwhichpushes about under basins that are the most touched by the floods
only in edge of the wadis and on the level of the palm (Fig. 3). Tables 2 and 3 summarizes the principal charac-
plantations. It is made up of herbaceous plants and shrubs teristics of each sub basin.
Fig.1 Locationmapofthestudyarea
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Fig.2 Mapofsoiloccupation
ofthecityofGhardaia
Fig.3 SubbasincomponentbasinVersantOuedM’zab-regionGharda¨ıa
Table2 MorphometricparametersofsubbasinsthatcomposedtheOuedM’zab:regionGharda¨ıa
Subbasinversant Perimeter(km) Area(km2) Compactnessindex(KC) Equivalentlength(km) Equivalentwidth(km)
ELHaimeur 91 386 1.30 33.74 11.44
BOUBrik 24 35 1.14 6.66 5.26
ELBIODH 132 822 1.29 48.63 16.90
Ghardaia 64 198 1.27 23.26 8.51
Bounoura 100 168 2.16 45.99 3.65
ElAtteuf 18 18 1.19 5.87 3.07
Step 29 43 1.24 10.17 4.23
Globaldrainagebasin 202 1670 1.38 79.20 21.09
OuedM’zab:regionGharda¨ıa
The zone of study is primarily associated with three Climate and precipitation
large wadis: Laadhira and Bou Brik Labiode of the West
which meet in the place named ‘‘Amlaga’’. This last is For the study of precipitations, we considered a pluvio-
indicatedinArablanguage‘‘Moultaka’’withthecommune metric series which comprises maximum daily precipita-
of Daya Ben Dahoua to give rise to Oued M’Zab (Fig. 4). tions for the longest possible period. This series was
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Model.EarthSyst.Environ.(2016)2:147 Page5of17 147
Table3 Characteristicofthe
Characteristic Parameter Unit Symbol Value
basinofOuedM’zab:region
Gharda¨ıa Morphologyofthewatershed Area km2 A 1670
Perimeter km P 202
Compactnessindex – K 1.38
c
Lengthoftheequivalentrectangle km L 79.20
Widthoftheequivalentrectangle km l 21.09
Relief Maximumaltitude m H 762
max
Minimumaltitude m H 432
min
Averagealtitude m H 639
moy
Indexofrockslope % I 5.19
p
Overallslopeindex % I 3.71
g
Averageangle % I 0.37
moy
Specificaltitude m D 355
s
Hydrographicnetwork Lengthofthemainthalweg km L 95
p
Coefficientofelongation – E 5.4
Drainagedensity km/km2 D 0.218
d
Coefficientoftorrentiality – C 0.23
t
Timeofconcentration h T 23
c
Reportofconfluence – R 0.93
c
Lengthratio – R 1.4
l
Fig.4 MapofslopesofthewatershedOuedM’zab-regionGharda¨ıa
provided by the National office of Meteorology (Anony- in 1993). However, other periods are of a remarkable
mous 3 2010). They spread out for the period of dryness (1992 and 1997) (Fig. 5).
1975–2013. The analysis of the series indicates that the Thefigureindicatesthatfortheyears1979and1993and
climate of the area of Gharda¨ıa is typically Saharien. It is 2003, the values of precipitations are maxima. The inten-
characterized by two seasons: one hot and dries season sitycurves—duration–frequencyIDFarebuiltwithanaim
(from April at September) and another moderate (from of allowing, to synthesize pluviometric information on the
October at March). A great difference between the tem- level of the station representative of the zone of study.
peratures of the summer and the winter is observed They allow, in addition to calculate the flows of project
(Table 4). It registered an annual average of 22 (cid:3)C. brieflyandtoestimatetheflowsofrisingandofrainwater
Theprecipitationsinthezoneofstudyarecharacterized and, they define the rain of project of the uniform type
by the fact that they fall primarily in the form of stormy characterized by a constant intensity for all its duration.
showers in autumn and in spring. Some years (temporal Curves IDFare plottedfor times ofreturn 2,5, 10,20,50,
apportionment) have an exceptional precipitation (58 mm 100, 1000 and 10,000 years (Fig. 6).
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Table4 Averagemonthlytemperaturesonanobservationperiod(1966/2012)
Month Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec
Tmoy((cid:3)C) 10.9 13.2 16 19.8 24.9 30.2 33.2 32.9 28.2 22.1 15.6 11.7
Fig.5 DistributionofmaximumdailyrainfallPJmaxfrom1975to2013
Fig.6 CurvesIDF‘‘Intensity–
Duration–Frequency’’
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Model.EarthSyst.Environ.(2016)2:147 Page7of17 147
Overviewofthe flooding oftheOued M’zab:region after4 yearsofdryness.Thebadweathergraduallycontinued
Gharda¨ıa Tuesdaywithanaverageintensity.Wednesday,1ofOctober
wasthedayofAid(thefestivalwhichmarkstheendofthe
The growth of the population of Gharda¨ıa involved an fast among Moslems, it was the flood, with a pouring rain,
intense urbanization. This growth ran up against the con- addingupnearly150 mmin1 h.Theprincipalwadisofthe
straints of the relief, in particular with the narrowness of area (M’zab, Zeghir, NSA, Metlili) functioned with full
the valley. An uncontrolled extension of the habitat in the mode.Accordingtolocalsources,ithasbeenthefirsttimefor
palm plantation as in the minor bed of the Oued is 70 yearswhichthethreetributarywadisoftheOuedM’zab
observed. These phenomenon seriously modified the con- are inrising. Usually onlyone ofthethreewadis overflows
ditions of passage of risings and sucker in an inadmissible without endangering the surrounding populations. The
way the risks of destruction and major accidents related to authoritiesspeakaboutaflowabout1200 m3/s.TheNational
these events. Table 5 summarizes the most significant Agency of the Hydraulic Resources (Anonymous 4 2010)
floodsaswellastheprincipaldamage,inhumanlosses,of estimatedtheflowat900 m3/s.Thiscatastrophewhichtou-
woundedandwithoutshelters,causedbytherisingswhich chedthecityisbound,ontheonehand,withtheintensityof
the valley of M’zab knew in the last decade. the riskconcerned and onthe other hand, with the vulnera-
TheprotectionofthevalleyofM’zabagainstthefloods bility of the area to the floods (Medejerab 2009). The Geo-
requires knowledge, in addition to the flows of rising, the morphologic analysis after the rising of October 2008,
heights of water in the Oued M’zab for the different peri- indicatesavisiblechangeoftheriver(Fig. 8).
ods and more particularly for the periods of strong rising. The zone of El Atteuf represents the most exposed zone
Figure 7 illustrates the principal risings which touched the with the effects of the floods whose consequences are
zone of study during 107 years. For the period catastrophic. The known zone is located at the downstream
(1902–2008), it thus gives the monthly distribution of the of the Oued M’zab-region Gharda¨ıa. This zone is charac-
principal risings of the Oued M’zab. It is observed in terizedbyweakslopes,wheretheflowsofrisingsgather.It
particular that the extent of the risings is remarkably thus constitutes a vast zone of expansion of risings of the
repeated in the month of September. Oued M’zab. The Oued go along to El Atteuf, after filling
Thepouringrain,qualified‘‘tsunamiriver’’,accompanied the dams with upper waters. The Oued M’zab runs down-
withviolentstorms,beganonMondaySeptember29,2008, streamfromElAtteuf,bytherisingsofthelowerwadisand
Table5 MostimportantfloodsduringthelastdecadeintheM’zabValley
Date Typeof Descriptionofthedisaster
flooding
April24,1952 Verystrong Rainfallhasbeensignificantfromapoint15kmupstreamofGhardaiaandbeyondZelfana
TheupperbasinoftheM’zabWadihavelittleornoflows(WadiElKekakh,ElAbiod,Djaref)
inDayaGharda¨ıa,theflooddidfeelfromDaiabenDahlan;Itisshort,butviolentastheresultofanintense
runofftoZelfana,themaximumflowratecouldbeestimatedtobebetween500and1000m3/s.Theflood
carriedtents,drownedmorethan1200headofcattle
September23, Strongenough FloodoftheM’zabWadipoweredbywadisimmediatelyupstream;filleddams;Highwateroftheriver
1952 N’TissawhichfillsthedamofElAtteuf:lightspillofit.ThedamofBeni-Isguenhasbeenheavily
damaged.TheWadiflowsdownstreamofElAtteuf,thankstofloodingofwadislowerandespecially
Noumerate
November17, Important 98.9mmofprecipitationand4daysofflow
1980
October1984 ThedamupstreamofGhardaiaPalmGrovewasfilled.
May11,1990 Important Tracesoffloodinghavebeenobservedatanaltitudeof498.85matthedistanceof473.70mupstreamofthe
bridgeAdaoud
June2,1991 Veryimportant Manydamage
30September Veryimportant Veryimportantwithaprecipitationof151mm,Q=873m3/s
1994
October,1995 Strongenough Extensivedamage
October,1997 Important ThestationofNAHRGharda¨ıaregistered46.4mmofprecipitation
June2004 important Importantfloodcausedbyfallsoftinny,extensivematerialdamage
1October Veryimportant 6daysofflow,significantcasualties(43victims),causesthedestructionofinfrastructures,andvery
2008 extensivematerialdamage
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Fig.7 Monthlydistributionoffloodsduringaperiodof107years
Fig.8 Allureofriversbeforeandafterthefloodfrom1stofOctober2008
especially Noumerat. In the downstream zone, the rising is Generally, three principal methods can installed: his-
fed by the lower tributaries of M’zab like Hassi Chegga. torical and paleohydrologic methods (Baker et al. 1988;
Benito et al. 2004), hydrogeomorphologic methods and
the hydrological-hydraulics methods (Lastra et al.
Methods of investigation
2008).
Our choice was made on the last method. Thus, four
In the objective to analyze the whole of the results
stages are followed:
relating to the phenomena of risings of the area, sev-
eral methods can be used to chart the risks of flood. • Statistical analyze of rains in the studied period.
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Model.EarthSyst.Environ.(2016)2:147 Page9of17 147
• Hydrological modeling based on HECHMS, thus basin includes: Subbasin; Reach; Reservoir; Junction;
allowing the quantification of the flow of project. Diversion; Source; Outlet (Tramblay et al. 2011; Zhang
• HydraulicmodelingbasedontheHECRASallowingto et al. 2013; Andrzej 2013).
determine the hygrograms of rising.
• This modeling uses charts of the occupation of the Hydraulic modeling
ground and the DEM (digital elevation model) as well
as the flow calculated by the HECHMS. For hydrodynamic modeling the model HEC-RAS was
• The height of rising determined by HEC RAS and the considered.Thismodelsolvestheproblemsoftheflowson
digital model of ground (DEM) give the altitude of free surface permanent or non-permanent. It solves the
flood to the level of the zone of study, the intersection equation of unidimensional energy, the losses being eval-
oftheplanoffloodwiththeleveloftheoriginalground uatedbytheformulaoffrictionatthebottomofManning–
forms a horizontal plan which represents the flooded Strickler and by formulas of contraction/expansion of the
zone until to cartography of the vulnerable zones. The flow.Forthequicklyvariedsituationssuchasthehydraulic
various steps described are represented on the Fig. 9. projections, flows near the bridges, and the junctions of
river,theequationofenergyisreplacedbytheequationof
momentum. For the overflowing flows, the total section is
Hydrological modeling
divided into homogeneous sub-sections in terms of form
androughness(TateandMaidment1999).Eachpartialflow
The principle based on hydrological modeling called also
is calculated according to the ‘‘Divided Channel Method’’
model rain-flow. The latter make it possible to transform
using the formula of Manning–Strickler. The modeling
series describing the weather conditions of a catchment
basedonHEC-RASmakesitpossibletoevaluatetheflows
area (precipitations, moisture of the ground, etc.…) into a
and the heights of water on the whole of the sections of a
series of flows. This transformation of the rain into
river (Timbadiya et al. 2011;Prata et al. 2011).
hydrogramofrisingresultsinthesuccessiveapplicationof
two functions. A first function of production which deter-
mines the hye´togram of clear rain starting from the rough Cartography of the flooded zones
rain.Asecondfunctionoftransfermakesitpossible,asfor
it, to determine the hydrogram of rising resulting from the The results obtained by HECRAS are used to chart the
clear rain (Gharbi and Soualmia 2013). vulnerable zones to the flood in the Oued M’zab-region
The Model HEC-HMS, is a deterministic hydrological Gharda¨ıa. The triangulation of the digital model of the
model and conceptual HEC-HMS (Hydrologic Modeling ground is necessary for the cartography of the flooded
System). This hydrological model was developed by zones. By using the DEM, the height of rising determined
‘‘Hydrologic Engineering Center (HEC)’’ of the US Army by HEC RAS give the altitude of flood to the level of the
BodyofEngineers(USACE2010).Itinparticularmakesit oued M’zab. The intersection of the plan of flood with the
possible to make leave the flow project. The module of level of the original ground forms a horizontal plan which
Fig.9 RepresentationoftheapproachusedforthemappingoffloodareasinOuedM’zab-regionGharda¨ıa
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Fig.10 TriangulationoftheDEMofthestudyarea
represents the flooded zone. The flooded surface increases the recorded wave (of about less than a 1 h. The software
according to the height of rising. The followed step led to underestimates the speed of infiltration.
thecartographyofthefloodedzones.Forthisstagewehad Forhydraulicmodeling,theboundaryconditionscanbe
the recourse to several software such as: ARCGIS, GEO defined by a height of water or a constant or variable flow
RAS (Fig. 10). in the course of time. The definition of the boundary
conditions in the software HEC-RAS with a dimension is
verysimple.Itissimplyenoughtoinformatthesametime
Results and discussions the first profile across the section by a condition limits
upstream and the last profile by the condition limits
The results of the simulations carried out by HEC-HMS downstream. The hydraulic parameter used to define the
represent the result of a combination of several models limitingconditionisregardedasconstantoverallthewidth
brought into play (a model for the quantification of pre- of the profile transversely. With the upstream ends and
cipitations, a model for the calculation of the infiltration downstream of the section considered of the Oued M’zab,
and the streamed water blade…). These results made it the normal height of the flows is considered( (Fig. 13).
possible to inform about precipitations of entry and the The maximum flow obtained by simulation as well as
basicflowwhichrepresentsthequantityofclearraintaking the geometrical data of the wadi are considered for the
part in the appearance of the hydrogram of rising. The software HEC-RAS. The injection of this constant flow
application of HEC-HMS for the catchment area of the willmakeitpossibletosimulatethepointofrisingandthus
OuedM’ zab-region Gharda¨ıamadeitpossibletoquantify producechartsofflood.InthemodelHEC-RAS,theuseof
the flow for each sub basin (Fig. 11). steady operation is very simple and especially very fast
The simulation of the flow to the discharge system of a since the software provides only one result to each point.
catchment area is significant for many applications of Hydraulic modeling makes it possible to visualize the
engineering and stock management of water, such as the profile along the watermark and critical depth line
forecast of the risings. The results obtained by HECHMS (Fig. 14). It is noted that the watermark exceeds the
make it possible to build the hydrogram risings of each dimensionoftheoriginalgroundwhatgeneratesafloodof
under basin as well as total area catchment. Figure 12 the banks. The digital simulations are carried out for one
presents the hyetogram and the hydrogram at the entry of periodof100 yearsreturn.ThemodelHEC-RASshowsits
the catchment area, following the rising of October 2008. capacity as representation of extended of the flood and the
Simulationconsideredtakesagaintheconditionsofrawof geographical information system will make it possible to
October 2008. specialize well the elements exposed at this risk and by
The flow obtained by simulation HEC-HMS is consequencetoleadtoatoolofdecision-makingintegrated
Q = 888.5 m3/s. By comparison with other work well.
max
(Table 6), the value of the maximum capacity obtained by The parametric results of simulation are given in
our simulation is comparable in particular with that of Table 7.Itcomes outfromtheseresultsthattheheightsof
Benaouedj(2011).ItisnoticedthatHEC-HMSreproduced water vary from 2.50 to 5.00 m above the roof. An over-
wellthevalueofthepeakoutputBenaouedj(2011),NAHR estimateofthewaterlevelisdueprimarilytothereduction
(Anonymous 4 2010). A shift of (26 %) is observed com- inthewidthoftheOued.Inallthepointsofthesection,the
pared to the value of Bensaha (2009). It can be explained valueofthenumberofFroudeislowerthan1.Thecritical
by the fact that the simulated wave arrives slightly before mode is not reached.
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