application of remote sensing and gis fo

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Application of Remote Sensing and GIS in

Flash Flood Hazard Mapping andHydraulic Modeling(case study of Wadi Dahdah, Saudi Arabia)

ABSTRACTFlash floods are considered as catastrophic phenomena possessing majorhazardous threatto many of infrastructure facilities, especiallynew constructionprojectsin Saudi Arabia.Thisstudydealswiththeevaluationof flashfloodhazardin the ungauged Wadi Dahdah basin depending on its detailed morphometriccharacteristics, hydrological studies, meteorological Analysis, and hydraulicmodeling. For this study, ASTER data were used for preparing digital elevationmodel (DEM), geographical informationsystem(GIS)wasused in theevaluationof linear, areal and relief aspects of morphometric parameters,Remote sensingdata(Landsat8) toanalysisandpreparingDigitalLand Use/ Land covermapping,using some special software for rainfall analysis and estimating IDF curvesandfinallyusingWMSandHES-RASforHydrologicalanalysisandhydraulicmodeling.Thuscan predictthe probability occurrence of floodsatvariousfrequency timesand determinetheintensityoftheflood (depthandvelocityof flood water) insidethe streamof the Wadi,and incaseof importantconstructionexposedtotheriskof floods must to develop optimal solutions that control of flood waters andthroughtheestablishmentof differentprotectionworkssuchasdamsandstoragelakesanddrainagechannelsandculvert...andother.So itwasimportantto makesufficienthydrological studiesto safetythissites of the Probabilities dangersofflooding.

IntroductionFlashfloodsoftenoccurin aridregionsasa consequenceof excessiverainfallandoccasionallycausemajor lossesof propertyandlife(Subyani 2009).Floodhazard

mapping isa componentneededforappropriate land use inthe floodedareas.Itcreateseasily read, rapidlyaccessiblechartsand mapswhichmitigate theeffectsof floods (Bapalu and Sinha2005). Flood hazard mapping in arid regionsis anextremely important but difficult task; the main reason is the scarcity of data inaridregions.Flood hazardmappingisveryimportantforcatchmentmanagement(i.e.for sustainabledevelopment of thewater resourcesand forprotectionfromthe flood hazard and drought). Rainfall and runoff data are the essentialhydrological elements in the flood mapping of basin systems. So, because thestudyareaissufferingfromscarcityofdataandtheflood inundationmapsaredependenton thetopographicandgeomorphicfeaturesof theWadi ( etal.2012), thisstudyis basedontheintegrationbetweenphysiographicfeaturesof thestudyareaandGIStechniques.The integrationofGIStocreateflood hazard mapsand disasterdecisionsupporthas been continually upgraded and widespread since the beginning of thetwenty-first century, asa result of the increased availabilityof spatial databasesand GIS software(Zerger and Smith 2003). Several studies are cited in theliterature, relating to flood hazard mapping and zonation using GIS(Sui and

Maggio 1999;Merzi and Aktas2000;Guzzetti,and Tonelli 2004;Sanyal and Lu2006;Heetal.2003;Fernandezand Lutz2010).Drainagebasincharacteristicsinmanyareas of the world havebeen studied usingconventional geomorphologicapproaches(Horton 1945; Strahler 1964; Rudriaihetal.2008; Nageswararao etal. 2010; Al Saud 2009). Gardiner (1990)indicated that in some studies, themorphometric characteristics of basins have been used to predict and describeflood peaks and estimation of erosion rate, underlying the importance of suchstudies. The application of geomorphological principles to flood potential orfloodriskhasled toanoteworthyamountof researches,attemptingtoidentifytherelationships between basin morphometric and flooding impact(Patton 1988).Identification of drainage networks within basins or subbasins can be achievedusing traditional methods such as field observationsand topographic maps, oralternatively withadvanced methodsusing remotesensing and digital elevationmodel(Macka2001;Maidment2002).

Al Quassim

Al Madinah

Ar Riyad

Ash SharqiyahMakkah

Al Bahah

`Asir

Najran

Jizan

Ha'ilTabuk

Al Hudud ash ShamaliyahAl Jawf

`Asir

430'0"E

430'0"E

440'0"E

420'0"E

420'0"E

200'0"N 200'0"N

190'0"N 190'0"N

180'0"N 180'0"N

440'0"E

420'0"E

440'0"E

Degital Elevation Values

High : 961.765

Low : 288

!.

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour point

Watershed

!.

4

1

1

1

1

1

21

2

2

2

*The Digital Elevation Model Obtained fromAsterGDEM v2 30 m Resolution and Manupulatedby (IDW) Techniqu e to 15 m Resolution*.

0 0.5 1 2 3 4

Kilometers

DiGital EleVation MoDel of

the Study BaSin

Digital Elevation

Model of Saudi rabia

Digital Elevation

Model of ser

Location and geological characteristics of Wadi DahdahTheWadiDahdahislocated inthewesternpartof theKingdomofSaudiArabiaatAserRegion.Itliesbetween41.8and41.92longitudes

and 18.9 and 19 latitudes with an area about 104 km2and length about 14 km. Geologically, Wadi Dahdah is underlain by lateProterozoicplutonic,and volcanic rocksinthe northand eastof the Wadi withanareaabout 35.3% of the total area, byvolcanic andplutonicrocks,andbyTertiaryoceaniccrustof theRed Seaoffshore.Thecontactbetweencontinental andoceaniccrustisprobably10

15kmonshore.Thecoastal plainisblanketedbyQuaternarysedimentsof Aeoliansand,silt andpedimentdepositswithareaof about64.6% ofthetotalareawiththicknessthatrangesfrom2to10m.

K.Amin

Gis and Remote Sensing Sector,

Egyptian Mineral Resource andGeological Survey Authority.

Cairo, Egypt.e-mail: [email protected]


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Digital Elevation Modeling

Morphometric

Analysis

Relative SlopePosition

Terrain Ruggedness

Index

Hypsometric Curve

Aspect

Basic Terrain

Analysis

Relative Relief

PositionDownslope

Distance Gradient

Topographic

Position Index

Slope

Hydrological

Analysis

Stream Power

Index

Topographic

Wetness Index

Melton Ruggedness

Number

LS Factor

Hydro-Morphometric Parameters

Remote Sensing Data

Geometric

Correction &

Georeferencing

Digital image

processing

Image classification

NADVI

Land-use/Land

Cover Map

Meteorologic

Analysis

Rainfall

data

Hydrological Modeling

Soil data

SCS Curve

Number

Floodplain and Hydraulic

Model

Methodology

Drainage

Pattern Analysis

Stream Order


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!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

190'0"N

1858'30"N1858'30"N

1857'0"N

Aspect Map

Flat (-1)

North (0-22.5)

Northeast (22.5-67.5)

East (67.5-112.5)

Southeast (112.5-157.5)

South (157.5-202.5)

Southwest (202.5-247.5)

West (247.5-292.5)

Northwest (292.5-337.5)

North (337.5-360)

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour point

Watershed

!.

AspectGener

ally refersto the directionto which a mountain

slope faces. The aspect of a slope can make verysignificant influences on its local climate because thesuns raysare inthe westat the hottest time of day intheafternoon,andsoinmostcasesa west-facingslopewill be warmer than sheltered east-facing slope. Thiscanhavemajoreffectsonthedistributionof vegetationin thewatershedarea.Theaspectmap of W.Dahdahbasinis shown.It isclearlyseenthatwest-facingslopesmainlyoccurin thebasin.Therefore,theseslopeshavea lowermoisture contentand higher evaporation ratealthough and some parts are falling towards eastfacing which a higher moisture content and have alowerevaporationrate.

Slope-Drainage Basin Map

Slope

70

!.Project Site (Pour Point)

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Watershed

!

SlopeSlope analysis is an important parameter in geomor-phological studies for watershed development and

important for morphometric analysis. The slopeelements, in turn, are controlled by theclimatomorphogenicprocessesin areashavingrockofvarying resistance (Magesh et al. 2011; Gayen et al.2013). A slope map of the study area is calculatedbased on ASTER GDEMv2 data using the spatialanalysistool in ARC GIS-10.3.Slope grid is identifiedas the maximum rate of change in value from eachcell to itsneighbors (Burrough1986).Thedegree ofslope in

W.Dahdah watershed varies from 70.The slope map is shownin Fig.2b. Has higherslopedegree results in rapid runoff and increased erosionrate (potential soil loss) with less ground waterrechargepotential.Higherslopeis identifiedin North-easternpartofthebasinwhereit originates.

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

It affects where structures

or trails can be built,crops can be planted, the

speed of flowing waterand consequent erosion,landslide potential.

!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

190'0"N

1858'30"N1858'30"N

1857'0"N

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

Relative Relief Map

Legend

Stream Order 1

Stream Order 2

Stream Order 3Stream Order 4

Pour point

Watershed

!.

Relative Relief

VALUE

2 - 23

23 - 29

29 - 43

43 - 74

74 - 334

Relative reliefR

elative relief is difference between summit level, thehighest altitude fora givenarea,and base level,lowestaltitudefora givenarea(Dury,1962,p.174).Itplaysanimportant morphometric variable used for theassessment of morphological characteristics of anytopography (Gayen et al. 2013. The highest relativerelief is calculated as 334 m,while the lowest value isrecordedas2 mFig.3a.The lowreliefindicatesthatthenorthernand central Southern area under W.Dahdahbasin is flat to gentle slope type. Therefore, the areacouldbebasicallyused foragriculturalactivitiesaroundstreamsidesdue tobeing flatinnatureandalso awateraccessibility.

Relative Slope Position

landscapescan be classified into discrete slope positionclasses,Jones,K.Bruceetal2000.

Themajorof theBasinAreaIsmiddleslopeandupperSlopedelineatedatEastandWestofthebasin.Thererelationshipsbetweensoil moisture contentandarelative slope position (upslope, midslope, anddownslope) were qualitatively understandable even inthe early twentieth century (Zakharov, 1913).Quantitatively, the dependence of soil moisture contenton catchmentarea (which, in fact,describesthe relative

position of a point on the topographic surface) wasprobably first described byZakharov (1940, p. 384)asfollows: water amount per unit area increases fromupslope to downslope due to additional water supply.Thus, as CA increases, soil moisture content alsoincreases.

Zero, low slope

Slopeposition

Moderately positive

0

depression cliff

valley bottombase slope valleys

Very negative(valley)

Very positive

(ridge)

Zero, low slope(flat)

Zero, highslope(opencliff)

Negative

(cliff base)

Positive(cliffedge)

(flat)

(upper slope)

Zero, moderateslope(openslope)

Moderately negative(lower slope)

hill topridgetop

cliff

ridges slope edge

lower lateralconstantslopelateral upper

gentle plains

saddles

Morenegative Morepositive

gentle

1 ridge > + 1

2 upper slope > 0.5 =< 1

3 middle slope> -0.5, < 0.5, slope > 5 deg

4 flats slope >= -0.5, =< 0.5 , slope = -1.0, < 0.5

6 valleys < -1.0

!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

190'0"N

1858'30"N1858'30"N

1857'0"N

Relative Slope Position

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour point

Watershed

!.

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

VALUE

0 - 0.06

6. - 0.2

0.2 - 0.4

0.4 - 0.737. - 1

2

P

T

h

B

c

T

a

n

A

y

s


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Downslope Distance Gradient

]1[ This index has become widely used inhydrology,butitutilizesarelativelysmallportionofthe information contained in a digital elevationmodel (DEM). One potentially important featurenot considered in the implementation of theln(a/tan)indexis theenhancementor impedanceof local drainage by downslope topography. Thiseffect could be important in some terrain forcontrollinghydraulic gradients.Applied this index to our study Area shows highvaluesattheWesternand Easternpartof the basinand minorsitesin the Northernand Southern partswhich refer to high local drainage areas thatfeedingthemainstreamoftheBasin.

TRI (Nellemanns Terrain Roughness Index)is a somewhat antiquated contour density

(transect-and-contour map) approachwithapplications

toarcticwildlife.SeeNellemanetal.(2007),Nellemannand Fry(1995),Nelleman and Thomsen(1994) papersformethods. Nelleman etal.(2007), a paperon brownbears, classified TRI values fora studyon Scandinavianbrown bears into . They used a1:100,000scaleDEM with a 10mcontourinterval,4kmtransectswithin4kmx4kmgrid cells: =TRI >2.5, =TRI0(ridge)

Elevationat pointpt

Mean Elevationneighborhood

SlopeMeanElevationin

Neighborhood

Elevationatpointpt

MeanElevation inneighborhood

Elevation at pointpt

pt~ =tpi~ 0(constantslope,flatarea,orsaddle)Checkslopeof thepoint

Flat

scalefactor = outer radius in map units

irad = inner radius of annulus in cel ls

orad = outer radius of annu lus in cel ls

!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

190'0"N

1858'30"N1858'30"N

1857'0"N

Topographic Position Index

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4Pour point

Watershed

!.

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

Value

High : 4.8

Low : -4.8

0

0

10

20

30

40

50

60

70

0

20

40

60

80

100

120

1 3 5 7 9 111315171921232527293133353739414345474951

Hypsometric Curve

Relative Height 80.239521

Hypsometric CurveInterpretation

Elevation

00

max

Percentageofbasinpoints

aboveagivenelevaion

100

00

max

Percentageofbasinpointsaboveagiveneleva&on

100Young Basin Old Basin

Elevation

Hypsometr ic Integral =Maximum Elevation Minimum Elevation

Mean Elevation Minimum Elevation

3

P

T

h

M

o

p

m

c

A

y

s
http://onlinelibrary.wiley.com/doi/10.1029/2004WR003130/epdfhttp://onlinelibrary.wiley.com/doi/10.1029/2004WR003130/epdfhttp://onlinelibrary.wiley.com/doi/10.1029/2004WR003130/epdfhttp://onlinelibrary.wiley.com/doi/10.1029/2004WR003130/epdf


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The Topographic Wetness Index (TWI)

The topographic wetness index (TWI) was

developed by Beven and Kirkby (1979) within therunoff modelTOPMODEL.Itisdefinedasln(a/tan)whereaisthelocalupslopeareadrainingthroughacertainpointperunitcontourlengthandtan isthelocal slope. It Also called Compound TopographicIndex (CTI). Higher CTI values represent drainagedepressions, lower values represent crests andridges. And it is related with soil moisture. Itindicates the tendencyof a cell to produce runoff,since areas with high moisture are more prone tobecome saturated. The higher the value of thisindex ina cell,thehighersoilmoisture thatcanbefound in it. Compound Topographic Indexdescribes the tendency of terrain to accumulatewater. Stream Power and Sediment Transport

Indices describetendency of flowand can be usedtodepictlocationsof potentialerosion.

The stream power indexStreampower index (SI) takes into accountboth alocal slope geometry and site location in thelandscape combining data on slope gradient andcatchmentarea(SCA):

SPI = SCA * tan(Slope)Stream power index can be used to describepotential flow erosion at the given point of thetopographic surface.As catchmentarea and slopegradient increase,theamount of watercontributedby upslope areas and the velocity of water flowincrease, hence stream power index and erosionrisk increase. It controlspotential erosive power ofoverland flows, thickness of soil horizons, organicmatter, pH, silt and sand content, plant coverdistribution.Ref. I.V. Florinsky, Digital Terrain Analsis in Soil Scienceand Geology.

Slope Length and Steepness factor (LS-

factor)]2[The Universal Soil Loss Equation (USLE)model isthemostfrequentlyusedmodel forsoilerosion risk estimation. Among the six inputlayers, the combined slope length and slopeangle (LS-factor) has the greatest influence onsoil loss at the European scale. The S-factormeasurestheeffectof slopesteepness,and theL-factor defines the impactof slope length.Thecombined LS-factor describes the effect oftopographyon soilerosion.

Melton Ruggedness NumberMelton ruggedness number (MNR) is a simpleflow accumulation related index, calculated asdifference between maximum and minimumelevation in catchment area divided by squareroot of catchment area size. The calculation isperformed for each grid cell, therefore minimumelevation is same as elevation at cell's position.Duetothediscretecharacterof asinglemaximumelevation, flow calculation is simply done with

Deterministic8. (Zmax-Zmin) / Sqrt(A)

References:Marchi,L.&Fontana,G.D. (2005):GISmorphometric indicatorsfor theanalysis of sediment dynamics in mountain basins. Environ. Geol.48:218-228,DOI 10.1007/s00254-005-1292-4.

I. hydrological indices

!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

1858'30"N1858'30"N

1857'0"N

Topographic Wetness

Index (TWI)

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour point

Watershed

0 0.450.9

190'0"N

!.

Value

High : 10

Low : 1!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

190'0"N

1858'30"N1858'30"N

1857'0"N

Stream Power Index

Value

High : 32000

Low : 00 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

190'0"N

1858'30"N1858'30"N

1857'0"N

LS Factor for the Basin

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour pointWatershed

!.

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

Value

High : 38.9349

Low : 0

!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

190'0"N

1858'30"N1858'30"N

1857'0"N

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

Melton Ruggedness Number

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour point

Watershed

!.

Value

2.8

Low : 0

4

P

T

h

H

o

o

c

A

y

s
https://www.msu.edu/~xuhui3/index_LS.htmlhttps://www.msu.edu/~xuhui3/index_LS.htmlhttps://www.msu.edu/~xuhui3/index_LS.htmlhttps://www.msu.edu/~xuhui3/index_LS.html


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Stream order (U)The ranking of streams has been carried out based on the methodproposed byStrahler (1964).streamorders are classified up to fourordersinthe W.DahdahBasin.The maximumstreamorderfrequencyis observed in case of first-order streams and thenfor second order.Hence,it isnoticed thatthere isadecrease instreamfrequencyasthestreamorderincreasesandviceversa.

Stream Length (Lu)According to Horton (1945),streams lengthsdelineatethetotal lengthsof streamsegment of eachof the successiveordersin a basin tend toapproximate a directgeometricseries inwhichthe firsttermis the averagelength of the streamof thefirstorder.Thestreamlengthisameasureof thehydrological characteristicsof thebedrock and the drainage extent. Wherever the bedrock and formation ispermeable,onlya smallnumberof relatively longerstreamsare formed in a well-drained watershed, a large number of streams of smaller length are developedwhere the bedrocks and formationsare lesspermeable(Sethupathi et al. 2011).The resultoforderstreamlengthin WadiDahdahbasin isshownintheTable. Itisclearly identified that thecumulativestreamlength is higher in first-orderstreamsanddecreasesasthestreamorderincreases.

Mean stream length (Lsm)Mean stream length (Lsm) reveals the characteristic size of components of adrainage network and its contributing surfaces(Strahler 1964).It has beencomputedbydividing the totalstreamlengthoforder u bythe numberof streaminthe sameorderu.It isnoted thatLsmvalueof any streamorderisgreaterthanthatof the lowerorderand lessthanthatof itsnexthigher orderinthe basin.TheLsmvaluesdifferwithrespecttodifferentbasins,asit isdirectlyproportional tothesizeandtopographyof thebasin.

II. Hydro Morphometric Paramters

1857'0"N

Low : 1!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

Catchment

190'0"N

1858'30"N1858'30"N

Catchment Drainage Map

Value

High : 241

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour point

Watershed

!.

40%

30%

20%10%

Stream Order/ Total Length

1

2

3

4

Stream number (Nu)Numberof streamsof differentordersandthetotal numberof streamsin the basin are counted and calculated in GIS platforms. Duringcalculation it is identified that the number of streams graduallydecreasesasthestream orderincreases;thevariation in streamorderand size of tributary basins is largely depends on physiographical,

geomorphological and geologicalconditionof the region.157streamline is recognized inthe whole basin, outof which 40 % (121) is 1storder,30% (29)2nd order,20% (6)3rdorder,10% (1)4thorder.

Stream

Order

Nu Stream

Order

StreamOrder

Length

Stream

Length Ratio

MeanStream

Lenght

bifurcation

ratio (Rb).

4 1 10.52 0.056 10.52 6

3 6 30.25 0.16 5.04 4.8

2 29 40.72 0.21 1.40 4.1

1 121 105.61 0.56 0.87

10 157 187.11553 Total

Bifurcation ratio (Rb)Horton(1945)consideredRbasanindexofreliefanddissectionwhileStrahler(1957)opinedthatRbshowsonlya smallvariationfor differentregionswithdifferentenvironmentsexceptwhere powerfulgeological controldominates.AccordingtoSchumn(1956),thetermbifurcationratio (Rb)maybedefined astheratioof the numberof the streamsegmentsof givenordertothe numberof segmentsof the nexthigherorders. It isa dimensionless

property and shows the degree of integration prevailing between streams of various orders in a drainage basin. 1st Order/2nd Order ..etc. Thebifurcation ratio was introducedby Horton (1945) and modified by Strahler (1952). It characteristically rangesbetween3 and 5inhomogeneousbedrock(Chorley1969andWaugh1996).Chorley(1969)had notedthatthelowerthebifurcationratio, thehighertheriskof flooding,particularlyofpartsand notthe entirebasin. The lower values of Rbare characteristics thatthe basin hassuffered less structural disturbances[1] andthedrainagepatternshasnotbeendistorted becauseof thestructural disturbances[6]..The highervalueof Rb indicated strong structural control on the drainagepatternandalso streamsthat have a higher average flood potential due to numerous tributary segments drainintorelatively fewtrunk transportingstreamsegments.Thebifurcationratiosof thestudyareavaryfrom4.1 to6,whichfallunderHighbasincategory[10].Themeanbifurcationratio(Rbm)maybedefinedastheaverageofbifurcationratiosof allorderandit s4.96incaseofW.dahdahBasin.

II.1 Thelinear network properties:

Relief ratio (Rh)Schumm (1956)states that the maximum relief to horizontal distance along thelongest dimension of the basin parallel to the principal drainage lineis termed asrelief ratio. The high value of relief ratio ischaracteristics of hilly areas withhighrunoff productionand soil erosion.Low value of relief ratios is mainly due to theresistantbasementrocksof thebasinandlowdegreeofslope(Mahadevaswamyetal.2011).The Rhnormally increases withdecreasing drainage areaand size of agivendrainagebasin(Gottschalk1964).Thereliefratioofthebasinis 0.042.

II.2 Aerial Aspects of theDrainageBasin: Elongation ratio (Re)Theelongationratio(Re)isthe ratiobetweenthe diameterof the circleof the sameareaasthe drainagebasinand the maximumlength of the basin[16].A circularbasinis moreefficient inthe dischargeof runoff thananelongated basin [20].Highervaluesof elongationratioshow high infiltrationcapacityandlowrunoff,whereas lower Revalueswhicharecharacterizedbyhighsusceptibilityto erosionand sedimentload (Reddyet al.2004).Thevaluesof Revary from0.6to 1.0over awidevarietyof climaticand geologictype.Valuesclose to1.0are typical of regionof verylow relief,whereasvalues in the range0.6 to 0.8 areusuallyassociated with highreliefand steep ground slope [1]. It can be grouped into three classnamelyCircular(>0.9),Oval(0.9-0.8),andLesselongated(


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The stream frequency (Fs)Streamfrequency(Fs)is thetotalnumberof streamsegmentsof allordersper unitarea(Horton1932).Reddyetal.(2004))statedthat low values of stream frequency (Fs) indicate presence of a permeable subsurface material and low relief. The channelsegmentnumbersforunit areasare difficulttobe enumerated(Singh 1980).Fsmainlydepend onthe lithologyof the basinandthe texture of the drainage network. The stream frequency value of theW.dahdah basinis1.51 km/ km2. The low streamfrequenciesvalue indicatessparse drainage network favoring groundwater recharge. Streamfrequencymainlydependson thelithologyof the basin and reflects the texture of the drainage network. The valueof streamfrequency(Fs)forthe basin exhibitspositive correlation with the drainage density value of the area indicating the increase in stream population with respect toincrease indrainagedensity.Channel frequencydensityservesasatool inestablishingtheerosionalprocessesoperatingoveranarea; tobemorespecific, the samein relation tothe streamordersand theircharacteristics provides datawhichcan throw lightevenonthesequencesofreliefdevelopmentsandthedegreeofruggednessinthearea(Singh1980).

Drainage Density (D)Drainage density(Dd) is a measure the total stream length in a givenbasin to the total area of the basin (Strahler 1964). Thedrainage density is affected by the factors that control characteristic length of the watershed. Drainage density is related tovarious features of landscape dissectionsuchasvalleydensity,channel head source area,relief,climate andvegetation(Moglenetal. 1998), soil and rockproperties(Kelsonand Wells 1989)and landscape evolutionprocesses. The significances of D as afactor determining the time of travel by water in a terrain and it also suggests that the D value vary between 0.55 and 2.09km/km2in ahumid regionwithanaverage of 1.03km/km2.(W.B.Langbein,1947),Thedrainagedensityof the W.dahdah basin

is1.79km/km2,which indicatesthatbasinareahasa highly resistantpermeablesubsurfacematerialwith intermediatedrainageand low tomoderaterelief.Higher drainage density isassociated with the basinof weak andimpermeable subsurface material,sparsevegetationandhighrelief.Lowdrainagedensityleadstocoarsedrainagetexturewhilehighdrainagedensityleadstofinedrainagetexture,highrunoffanderosionpotentialof thebasinarea.(Strahler1964).

Waterflow NetworkThe main streams flow directions ofW.dahdah basintakeNorth East South West direction which feeding the mainstream channel, and about 30% the rest directed from thewestbankofthemainstreamasshown.

Interpretation of Sf and DDThese low values of drainage density, stream frequency and drainage intensity also imply that surface runoff is not quicklyremovedfromthebasin,making itsusceptibletoflooding,gullyerosionand landslides,particularlyinthe lowerpartof thebasin.It is therefore recommended that human activities that could impact negatively on stream network in the basin should bediscouraged.DrainageTexture (T)Drainage texture is the total numberof streamsegments of allorders perperimeterof thatarea(R.E.Horton,1945).Thedrainagetexture dependsupona numberof natural factorssuch asrainfall,vegetation,climate, rock and soil type,infiltrationcapacity, reliefand stageof development(K.G.Smith,1950). Thedrainagetextureisclassified intofiveclasssuchasverycoarse(8).The basinhasa drainagetextureof2.89whichindicatesthemoderatedrainagetexture.Similarly,themoderatedrainagetextureandmediumvalueofdrainagedensityindicatesthepresenceof moderatelyresistantsemi-permeablematerialwithmoderaterelief.

Relief Basinrelief isthedifferenceinelevationbetweenthe highestand lowestpointsinthebasin.Itcontrolsthe streamgradientandtherefore influences flood patternsand theamount of sedimentthat canbe transported.Hadley and Schumm(1961) showedthat sediment load increases exponentially with basin relief. The high relief value indicates high gravity of water flow, lowpermeable and high runoff conditions.Thehighestpointof the studiedbasin is961and the lowest point is288metersabovesealevel (ASL).Thusthebasinreliefintervalforthestudiedareais673meters.

!.

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190'0"N

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1857'0"N

Terrain Surface Texture

Legend

Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour point

Watershed

!.

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

ValueHigh : 5.2

Low : 0

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Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Pour point

Watershed

Drainage Network Flow

Legend

0 0 .450 .9 1 .8 2 .7 3 .6

Kilometers

Flow Direction

Drainage Point

ConclusionThe morphometric parameters is an immense tools used inevaluating river basin and the watershed preference for soil,conservation of waterandresourcemanagementatmicro level.The

analysiscarried out for the W.dahdahcatchmentbasin depicts thatthe basin is tending towards elongated shape. The morphometricanalysis isof great importance in hydrological behaviorof basin forwaterqualityproject,engineering works,publicpoliciesapplicationsand flood forecasting, erosion control and environmentalmanagement,it isalsoessential foraccuratemodeling analysis.

The Evaluation of Flash Flood HazardEstimation of flooding and feeding probabilities for drainage sub-basinswithinthe presentareawere studied accordingtoEI-Shamy'smethod (1992a) established two relation graphs to classify the riskbasins assessment based on the relations between weighted meanbifurcation ratio and both of the drainage densityand the drainagefrequency.The locationof any basinon the two relationsdesignatesitsrunoff/infiltrationpotentiality.The most affecting factor in risk calculation is the density and

frequency of drainage segments. Increasing both density andfrequency lead to increasing total runoff and total infiltration. Sohazardisdirectlyproportionaltodensityandfrequency.Accordingto theseparameters, thesub-basins in thestudyareacanbeclassified into three classes.Class A: Basinsof high Rband lowFand D may represent ideal areas forfeeding the perviousunits withthe least chance for flash flooding; which may reflect appropriategeologic and geomorphologic setting with good chances ofdownward recharge to the existing shallow aquifers that mayformimportantwaterresourceinremoteareas.

0 1 2 3 4 5 6 7

1

10

B C

A

Frequency

Frequency

mRb

Basin

Rb: mBifurcation ratio,

F: Stream frequency,

A: Low flood possibilities,

B: High flood possibilities,C: Intermediate flood possibilities

0 1 2 3 4 5 6 7

1

10

B C

A

Frequency

Density

mRb

Basin

mRb: Mean Bifurcation ratio,

D: Stream density,

A: Low flood possibilities,

B: High flood possibilities,C: Intermediate flood possibilities

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0 0.75 1.5 3Kilometers

T M B a n d s

RGB

Red: Layer 4

Green: Layer 3

Blue: Layer 2

Legend

Dam Site

Watershed

TM Landsat 8 Natural Color

Interpreting The Landsat TM Color Composites

Tocreateatruecolorcomposite,thethreevisiblebandsavailableonLandsatarecoupledwiththeprimarycolorsinthecomputermonitor(R =visiblered,G =visiblegreen,andB=visibleblue).Othernamesforthiscompositeare normalor natural color. This composite image will have similar color to true or normal color aerial photos and the wayhumansseecolor.Healthyvegetationis green,darkbrownish-blue isHillsof basementrocks,Browntolightbrownclay

andsediments,grayline isarailroad,greenscatteredspotsarevegetation,darkgraynetwork isadrainagepatternandsmallwhite scattered areasareUrban. InTM Falsecolor7.6.4 Vegetationtypesare variationsof green;urbanfeaturesand bare field are lightgrey.Infrared composite image Thiscomposite simulatesthecolorof a color infrared aerialphotoandcanbeinterpretedusingthesamelogic.Vegetationtypesarevariationsofmagenta.

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Landsat 8 TM False Color

Urban

Legend

!.Dam Site

Watershed


TM Bands

RGB

Red: Layer 7

Green: Layer 6

Blue: Layer 4

Urban Areas

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RGB

Red: Layer 5

Green: Layer 4

Blue: Layer 3

Color Infrared (vegetation)


Legend

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Value

Normalized Difference

Vegetation Index (NDVI)


Legend

!.Dam Site

Watershed

High : 0.700028

Low : -0.0739723

Normalized difference vegetation index NDVINormalized Difference Vegetation Index (NDVI) was employed asthe basis forLand Use / Land Cover classification. Interpretation: NDVI values varydepending on the radiation absorption by chlorophyll in the red spectral

reflectance in the near infrared region. These values are between -1 and +1,expressing consistency of green vegetation. The closer to 1 (light colors) is ahigh consistencyof specificvegetationand hardwood.Values close to -1 (darktones) are barren land, with soil, or rock to date. A value of 0 (midtones) isassociated lands meadows. It is useful in areas with vegetation mapping,vegetationtypology,healthofvegetation,land usepatterns.Itisgivenby:NDVI=(NIR R)/(NIR+R )= (B5 B4) / (B5+B4)ResearchJournalof AgriculturalScience,45 (4),2013

Unsupervised classification provides more comprehensive information on

the spectral characteristicsof the area,presentsspectrallypure clusters forthe labellingstep,and givesthe opportunityto the analystto groupsimilarclusters into a smallernumberof landcover classes, (Hansen etal.,2000).The Basin has been classified for land use/land cover into six classes asshown.

LULC mapping!.

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Land Use / Land Cover

Unsupervised Classification


Legend

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Stream Order 1

Stream Order 2

Stream Order 3

Stream Order 4

Rai l road

!.

11 Residential

24Other agricultural land

62Nonforested wetland

73Sandy areas other than beaches

74Bare exposed rock

77Mixed barren land

Value

Residential

16%

Other

agricultural

land

16%

Nonforested

wetland

22%

Sandy areas

other than

beaches

15%

Bare exposed

rock

11%

Mixed barren

land

20%

Area km

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Rainfall isa crucialagroclimatological factor. It is importanttoanalyze therainfall data forestimating theprobability of flash flooding anditsdurationfrequency, in addition for cropping and agriculture. Rainfall intensities ofvariousfrequenciesanddurationsare thebasic inputsinhydrologicdesign,and theyarethemaineffectivefactoronfloodformation.Theyareused,forexample, in thedesignof stormsewers, culvertsandmanyotherstructuresaswell asinputstorainfall-runoff models.Precipitationfrequencyanalysisisused to estimate rainfall depth at a point for a specified exceedanceprobabilityandduration.

Inpoorly gauged regions,rainfall dataare oftenshort or evenabsent. Theavailabilityrainfall data are collectedfrom the nearestmetrological station(KhoshArea). Which the annual rain over the area for a period extendingfrom1966to2011.

FrequencyAnalysisof theMaximumAnnual DailyRainfallSixmethods of frequencydistributionwidely used in metrological analysishavebeenusedto representThemaximumannualseries.To choose between distributions, the visual fitting comparison, althoughnecessary,is highlysubjectiveandmisleading.Toovercomethissubjectivity,severalmethodsareavailableforthechoicebetweendistributions.Onecanusethemomentratiodiagramswhethertheordinaryorthelinearmoments.Anothermethodologyis theoneproposedby El-Adlounietal.

Rainfall Data Analysis

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Khosh Metrological

Station Location


Legend

!.Dam Site

Watershed

Khosh Metrological

Stat ion

0

10

20

30

40

50

60

70

80

90

1966

1971

1973

1975

1977

1979

1981

1983

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

2007

2009

2011

AnnualRain(mm)

Years

Annual Rainfall data record

Basic statistics

Number of observations 4MinimumMaximum 8Mean 33.Standard deviation 16.7Median 30.1Coefficient of variation (Cv) 0.501Skewness coefficient (Cs) 0.98Kurtosis coefficient (Ck) 4.2

To choose between tested distributions, the AkaikeInformation Criterion (AIC)([1] and [2])and BayesianInformationCriterion (BIC) [3] can be used.Both criteriaare based on the deviation between the fitteddistribution and the empirical probability with apenalizationthat isfunctionof thenumberof parametersof the distribution and the sample size. The distributionhaving the smallest BIC and AIC is the onethatbest fitsthe data. The Gumble distribution has shown to be thestrongestfittingdistributionasshownin thetable.

W.dahdah BasinNumber of observations: 43Return period : T=100Model Nbparam. XT P(Mi) P(Mi | x) BIC AICGumbel(MaximmLikelihood) 2 88.262 16.67 59.47 365.253 361.730Lognormal (MaximumLikelihood) 2 106.183 16.67 14.94 368.015 364.493Pearson type3 (MaximumLikelihood) 3 82.715 16.67 11.52 368.536 363.253Log-Pearson type3 =310) 82.618 16.67 10.10 368.799 363.515Normal (MaximumLikelihood) 2 72.167 16.67 3.93 370.688 367.165

Exponential (MaximumLikelihood) 2 134.086 16.67 0.04 379.953 376.431P(Mi) : A priori probabilityP(Mi | x) : A posteriori probability (Method of Schwartz) BIC : Bayesian information criterionAIC : Akaikeinformation criterion

[1] H. Akaike, Information Theory and Extension of the Maximum Likelihood Principle, In: B. N. Petrov and F. Csaki, Eds., 2nd

In ternational Symposium on In formation Theory, Akadmiai Kiado, Budapest, 1973, pp. 267-281.

[2] H. Akaike, Markovian Representation of Stochastic Pro- cesses and Its Application to the Analysis of Autore-gressive Moving Average

Processes, Annals of the Insti- tute of Statistical Mathematics, Vol. 26, 1974, pp. 363- 387. doi:10.1007/BF02479833

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Thepurposeof fittingdatatostatisticaldistributionsistobeableto estimatetheprobabilityof extreme precipitation intensities for a given return period (T). Firstly, the maximumamount of precipitationfora givenstormduration iscalculated (Pt), and isthenconvertedinto anintensity(commonlywithunitsof mm/hour).This intensityvalueisneededformanydesign calculations, most commonly for determining peak flow or peak runoff. Theestimated return values are needed to construct Intensity Duration Frequencycurves (IDFcurves), which are widely used in engineering applications. These curves show therelationship betweenthe intensity of the precipitationand the duration of the stormforagiven return period. The IDF curves are developed for a specific location,with a specificreturnperiod.

Intensity-Duration-Frequency (IDF) Curves

Return period Rainfall (mm) Standard deviation (mm) Confidence interval (95%) (mm)200 97.7 9.62 78.9 - 117

100 88.3 8.51 71.6 - 105

50 78.8 7.39 64.3 - 93.3

20 66.1 5.93 54.4 - 77.7

10 56.3 4.84 46.8 - 65.8

5 46 3.76 38.7 - 53.4

3 37.9 2.99 32.1 - 43.8

2 30.6 2.43 25.8 - 35.4

Frequency analysis results for the Gumble distribution.

Storm Durations

Determining precipitation intensities for various storm lengths is an important aspect forsafely designing structures and infrastructure to manage flooding. Often short stormdurationsaredesired astheycangivehighintensities(mm/hr).A theoretical ratioof 1.13to1.14 isadoptedtotransformthedailyrainfallvaluesand24-hrvalues[4]. Intheabsence ofshortduration recordsor anysimilarinformation, sub-daily rainfall duration ratioscouldbeassumed betweenrainfall intensities of 24-hrand those of the 12-, 6-,3-, 2-,1-hr, 30-,15-,and5-minratios.

(XTxB)XT = 1.14 (HYFRAN XT)

B = Bell Ratio as per below tableIt is well known that ratios for durations from 2 hours to 5 minutes are fairly constant indifferent climates because of the similarity of convective storms patterns [5,6].

(I)= (XT * B) / (T / 60)WhereI=RainFall Intensity(mm/hr)

XT=1.14(HYFRANXT)B=BellRatioasperbelowtableT=Duration(min).

Afterconstructingthe IDFCurvethentheestimationof rainfall depthvaluesfromthebelowequation.

D = (I*T)/60WhereD = Rain Fall Depth (mm)I = Rain Fall Intensity (mm/hr)T = Duration (min)

StormDuration (min) 5 10 15 20 30 60 120 180 360 720 1440

0.139 0.2 0.239 0.279 0.343 0.435 0.565 0.626 0.75 0.877 1

0

20

40

60

80

100

120

140

160

5 10 15 20 30 60 120 180 360 720 1440100y147.28 105.96 84.415 73.907 60.574 43.5 28.25 18.425 11.038 6.4533 3.6792

50y 131.44 94.56 75.333 65.956 54.057 34.278 22.261 16.443 9.85 5.759 3.2833

20y 110.25 79.32 63.192 55.326 45.345 28.754 18.673 13.793 8.2625 4.8308 2.7542

10y 93.908 67.56 53.823 47.123 38.622 24.491 15.905 11.748 7.0375 4.1146 2.3458

5y 76.728 55.2 43.976 38.502 31.556 20.01 12.995 9.5987 5.75 3.3618 1.9167

3y 63.217 45.48 36.232 31.722 25.999 16.487 10.707 7.9085 4.7375 2.7699 1.5792

2y 51.041 36.72 29.254 25.612 20.992 13.311 8.6445 6.3852 3.825 2.2364 1.275

Intensity(mm/hr)

Duration (min)

Intensity-Duration Frequency Curve

100y 50y 20y 10y 5y 3y 2y

Return

Period

(Year)

Distribution100 12.273 17.66 21.103 24.6357 30.286 43. 56.555.2758 66.22577.439 88.

50 10.953 15.76 18.833 21.9852 27.028 34.27 44.52249.3288 59.169.107 78.

20 9.187 13.22 15.797 18.4419 22.672 28.753 37.346541.3786 49.57557.969 66.

10 7.825 11.26 13.455 15.7077 19.310 24.490 31.809535.2438 42.22549.375 56.

5 6.39 9.2 10.99 12.83 15.77 20.0 25.99 28.796 34.5 40.34 4

3 5.268 7.58 9.058 10.5741 12.999 16.486 21.413523.725 28.42533.238 37.

2 4.253 6.12 7.313 8.537 10.495 13.31 17.28919.1556 22.9526.836 30.

[3] G. Schwarz, Estimating the Dimension of a Model,The Annals of Statistics, Vol. 6, No. 2, 1978, pp. 461-464. doi:10.1214/aos/1176344136

D. M. Hershfield, Rainfall Frequency Atlas of the United States for Durations from 30 Minutes to 24 Hours and Return Periods from 1 to

100 Years, Weather Bureau Technical Paper, No. 40, 1961, p. 115.[4]

F. C. Bell, Generalized Rainfall-Duration-Frequency Re- lationship, Journal of H ydraulic

Division, Vol. 95, No. 1, 1969, pp. 311-327.[5]

[6]Soil Conservation Service, Urban Hydrology for Small Watersheds, Technical Release 55,

United States Depart-ment of Agriculture, Washington DC, 1986.

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Hydrological Analysis and Mathematical Modeling Using WMS

A computer program called the Watershed Modeling System (WMS) is available tohydraulicengineerstoautomatically delineate drainage basinsanddeterminenearlyall of

thekeyparametersnecessary tocomputerapeak floworhydrograph.ByUsing theDigitalElevation Model (DEM) In addition, land use and soil type maps makes it possible todevelopthesupportingdataforvirtuallyall industrystandardhydrologicmodels.These data can be directly transferred to WMS where the hydrologic computations areperformedandtheresultsanalyzed.

Thereare two primaryclassesof hydrologicsimulationmodels:statisticalanddeterministic.Statisticalmodelsuseananalysisof historicalrecordssuchasstreamflow orprecipitationtoinfer designvalues fordifferent returnperiods(e.g. 10 yearor 100 year). A deterministicmodel ontheotherhand usesaseriesof inputparameterssuchasrainfall depth,watershedinfiltrationparametersandunithydrographsto determinerunoff fromphysicalprocesses.TheSCS methodologieswill be used here to illustrate thekinds of hydrologic parameterstypicallyrequired ofdeterministic models.Some of theseparametersinclude rainfall depth(and anincludedtemporal distribution),lossesfrom a runoffcoefficientor CN value, and atimeof concentrationorlagtimeusedinconjunctionwithaunithydrograph.

Land use

Soil

DEM

Runoff Curve Number Report for Basin W.dahdah

HSG Land Use Description CN Area Productkm 2 CN x A

D Other Agricultural Land 86 7.679 660.354D Residential 86 4.448 382.561D Mixed Barren Land 94 2.473 232.497D Bare Exposed Rock 98 10.447 1023.829D Nonforested Wetland 78 3.378 263.470D Sandy Areas other than Beaches 88 0.849 74.718B Residential 72 12.588 906.362

B Nonforested Wetland 58 19.584 1135.869B Other Agricultural Land 74 8.786 650.165B Sandy Areas other than Beaches 77 15.006 1155.490B Bare Exposed Rock 98 0.664 65.120B Mixed Barren Land 86 18.993 1633.423

CN (Weighted) = Total Product \ Total Area==========================================

78.0181

Database Processing for SCS Curve Number.

[1] The curve numbermethod was developed by theUSDA Natural ResourcesConservation Service, which wasformerlycalled theSoil Conservation Service or SCS the number isstill popularly known asa "SCS runoff curvenumber" in the literature. The runoff curve number was developed froman empirical analysis of runoff fromsmallcatchmentsandhillslopeplotsmonitoredbytheUSDA.It iswidelyusedandis anefficientmethod fordeterminingtheapproximateamountofdirectrunofffromarainfall eventin aparticulararea.Therunoff curvenumberisbased onthe area's hydrologic soil group, land use,treatment and hydrologic condition.References,suchasfromUSDA [1] indicate therunoffcurvenumbers forcharacteristic land cover descriptions andahydrologic soil group.CNhas a range from30 to 100; lower numbers indicate low runoff potential while largernumbers are for increasingrunoff potential.The lower the curve number, the morepermeable the soil is. As can beseen in the curve number equation, runoff cannot begin until the initial abstractionhas been met.It is importanttonote thatthe curve numbermethodology is anevent-based calculation, and should notbe used for a single annualrainfall value,asthiswill incorrectlymisstheeffects of antecedent moisture andthenecessityof aninitialabstractionthreshold.

[1] United States Department of Agriculture (1986). Urban hydrology for small watersheds(PDF). Technical Release 55 (TR-55) (Second ed.). Natural Resources Conservation Service, Conservation Engineering Division.

UsingArc-mapfor mapping the land use of the basin generated from the unsupervised classification method ofLandsat8 image according toaGIStableof Anderson land use codeswasusedalongwith the hydrologic soil groupforthemapunit,thenimportingandmapped inWMSforautomaticallycomputingtheCN fortheBasin.

Computation Travel Time, Lag time and Time of Concentration.

Rainclouds

loud formation

Precipitation

Evaporation

Ocean

Groundwater

Rock

Deeppercoaton

So

Percoaton

Infiltration

Travel time (Tt) is the time it takeswaterto travel fromone location to another.Travel time between two pointsis

determinedusingthefollowingrelationship:[2]Tt=l/3600Vwhere:Tt=traveltime,hl=distancebetweenthetwopointsunderconsideration,ftV=averagevelocityof flowbetweenthetwopoints,ft/s3,600=conversionfactor,stohTheTravelTimeautomaticallycomputedinWMSforthebasinequals3.530hrs.Lag timeand Time of Concentration.Lag time and time of concentrationare variablesoftenused when computingsurfacerunoffusingunithydrographmethodsavailable inthehydrologic modelssupportedinWMS.These variablesindicatetheresponsetimeattheoutletofawatershedforarainfall event,andareprimarilyafunctionof thegeometryof the watershed. WMS provides two powerful methods of computing travel times for lag time and time ofconcentrationfromthegeometricdatabeingusedforbasindelineationandparameterestimation.LagTimeComputationLag is the delay between the time runoff from a rainfall event over a watershed begins until runoff reaches itsmaximumpeak.

BASIN W.dahdah AREA 104.897 km 2Equations: SCS Method

Lag Time L 0.8 * ((((1000/CN)-10) +1) 0.7)/(1900*sqrt(Y)) = 5.896 hrsVariables:L Watershed length 78153.3 ftCN SCS curve number 78.0181Y Watershed slope in percent9.76906 %

Time of Concentration (Tc)Time of concentration is the time required for runoff to travel fromthe hydraulically mostdistant point in thewatershed to the outlet. The hydraulically most distant point is the point with the longest travel time to thewatershed outlet, and not necessarily the point with the longest flow distance to the outlet. Time ofconcentration is generally applied only to surfacerunoff and maybe computed using many different methods.Timeof concentrationwill varydependinguponslopeandcharacterof thewatershedandtheflow path.[2]

Equations:KirpichMethod for overland flowon bareearth

Timeof Concentration m* 0.00013 * (L 0.77/S 0.385) =3.47613 hrsVariables:mEarth typecoefficient 1L Length of overland flow78153.3 ftS averageoverland slope 0.0193552

Conceptual watershed i ll us trat ing

traveltimefromthecentroid(graydot)

ofeachbandof areato thewatershed

outlet (NationalEngineering Handbook2010)

[2]National Engineering Handbook 2010 Chapter 15 Part 630.

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HEC-1 Hydrologic Simulation Model

[3]Hydrologicalsimulationincludesstudyof thereturnperiod estimationof rainfall of givenprecipitation,i.e.the100yearstormorthe100yearflood,50 year,30..3yearsetc.100yearflood,50 yearstorm,or200yearflood,asadescriptionofthemagnitudeofastormor

flood.We understand thatthelargerthenumberbefore 'yearflood',thegreaterwill bethe effectonriverlevelsandonanything outontheriver's floodplain.ReturnPeriod (T)- Theaverage lengthoftimein yearsforanevent(e.g.floodor river level)of givenmagnitudetobeequaledor exceeded.Thedesignstormwasoftendevelopedfromfrequency-duration-intensitycurvesbasedonrainfall records.EarlydiscussedinPartVandestimatedfor thebasin.TheHEC seriesof software isproduced bytheU.S.ArmyCorpsof EngineersHydrologic EngineeringCenter.KeepingtheCurve Numberandthetimeofconcentrationconstant,7 differentdesignstormswereruninthemodel.

[3] written by: Harlan Bengtson edited by: Lamar Stonecypher updated: 10/18/2013

Unite Time (min) Distribution (100y)Distribution (50y) Distribution (20y)Distribution (10y) Distribution (5y) Distribution (3y) Distribution (2y)

5 12.2737 10.9532 9.18 7.82 6.39 5.26 4.25

10 17.66 15.76 13.22 11.26 9.2 7.58 6.12

15 21.1037 18.83 15.79 13.45 11 9.05 7.31

20 24.6357 21.98 18.44 15.7 12.83 10.57 8.54

30 30.2869 27.02 22.67 19.31 15.77 12.99 10.49

60 43.5 34.27 28.75 24.49 20.01 16.48 13.31

120 56.5 44.52 37.34 31.8 25.99 21.41 17.28

180 55.2758 49.32 41.37 35.24 28.79 23.72 19.15

360 66.225 59.16 49.57 42.22 34.5 28.42 22.95

720 77.4391 69.1 57.96 49.37 40.34 33.23 26.83

1440 88.3 78.8 66.1 56.3 46 37.9 30.6

WMS result

Parameters

HEC-1 Hydrographs

A range of curve numbers were run in HEC1 using a 7 Return distributiondesign storm of 24 hour duration. The following hydrographs resulted. Thehigher curve numbers result in a larger amount of runoff and therefore ahigherpeakflowandflowvolume.

TheAnalysisof Hydrographcurves, indicatedthatthefood volumethrough2-

100 yearReturn Duration range from3968844.3m3 to 310951.9m3 while

thepeakflowoffloodrangesfrom234.31Cmsto18.43Cms.

[4]Thistypeof hydrograph isknownasa stormor flood hydrographand it isgenerally drawn with two vertical axes. One is used to plot a line graphshowing the discharge of a river in cumecs (cubic meters per second) at agivenpointover a period of time.Thesecond isusedtoplota bar graph oftherainfalleventwhichprecedesthechangesindischarge.The scale onthe horizontal axis is usually inhours/days and thisallowsboththe rainevent tobe recordedand the subsequent changesin riverdischargetobe plotted.The shape of the hydrograph varies according toa numberofcontrolling factors in the drainage basin but it will generally include thefollowing features.

The baseflowof the riverrepresentsthenormal day today discharge of the riverand isthe consequence of groundwaterseeping into the riverchannel.The risinglimb of the hydrograph represents the rapid increase in resulting from rainfall

causingsurfacerunoffandthenlaterthroughflow.Peakdischargeoccurswhentheriver reachesits highest level. The time difference between the peak of the raineventandthepeakdischargeisknownasthe lagtimeorbasinlag.Thefalling limb(orrecessionlimb asit issometimesknown) iswhendischarge decreasesand theriverslevel falls.Ithasa gentlergradientthantherisinglimbasmostoverlandflowhasnowbeendischargedandit ismainlythroughflowwhichis makinguptheriverwater.A numberof factors(knownasdrainage basincontrols) influence the wayinwhich a river responds to precipitation and have an effect on the shape of thehydrograph. The size, shapeand relief of the basin are importantcontrols. Watertakes longer to reach the trunk streamin a large, round basin than in does in asmall, narrow one. Where gradients are steep, water runs off faster, reaches theriver more quickly and causes a steep rising limb. Prolonged heavy rain causesmoreoverland flow thanlightdrizzlyrain.Areasof permeable rocksand soil allowmoreinfiltration and solesssurface run off.The way inwhichthe land isusedwillalso have aninfluence onthe hydrograph vegetation interceptsprecipitationand

allows evaporation to take place directly into the atmosphere so reducing theamount of water available for overland flow while the large number ofimpermeable surfaces in urban areasencourages run off into gutters and drainscarryingwaterquicklytothenearestriver.

Hydrograph interpretation

[4] http://www.bbc.co.uk/scotland/education/int/geog/rivers/hydrographs/

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Type of catchment soil Value of C

Rocky and impermeable soil 1-0.8

Slightly permeable , bare soil 0.8-0.6

Cultivated soil covered with vegetation 0.6-0.4

Cultivated absorbent soil 0.4-0.3

Sandy soil 0.3-0.2

Heavy forest 0.2-0.1

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Flow

(cms)

Time

HEC-HMS Simulation Model of W.dahdah Basin

flow 100yDR (M3/S) flow 50yDR (M3/S) flow 20yDR (M3/S)

flow 10yDR (M3/S) flow 5yDR (M3/S) flow 2yDR (M3/S)

Duration Return Peak Discharge (M3/S) Volume (mm) Duration Return Peak Discharge (M3/S) Volume (mm)

100yDR 229.6 36.96 10yDR 94.9 15.3

50yDR 186.6 30.03 5yDR 59.5 9.55

20yDR 132.8 21.36 2yDR 18.5 2.97

HEC-HMS Hydrologic Simulation Model

TheHydrologicModelingSystem(HEC-HMS)is designedtosimulatethecompletehydrologic processesof dendriticwatershedsystems.The software includes many traditional hydrologic analysis procedures such as event infiltration, unit hydrographs, and hydrologicrouting.Geometric attributessuchasareas,lengths,andslopesarecomputedautomatically fromthedigitalwatershed.Parameterssuchas lossrates, base flow, unithydrograph method, and routing data are entered through a seriesof interactive dialog boxes.Once theparameters needed to define an HMS model have been entered, an input file with the proper format for HMS can be writtenautomatically.Theresultsand hydrographsobtainedbyusingHyetographprecipitationmethod.

Computed Results at W.dahdah BasinPeak Discharge: 229.6 (M3/S)Precipitation Volume: 88.30 (MM) Direct Runoff Volume: 36.96 (MM)Loss Volume: 50.67 (MM) Baseflow Volume: 0.00 (MM)Excess Volume: 37.63 (MM) Discharge Volume: 36.96 (MM)

Subbasin Used for rainfall-

runoff computation on a

watershed.

Junction Used to combine

flows from upstream reaches

and sub-basins.

Watershed Modeling By Rational Method

The RationalMethodisoneof the simplestand bestknownmethodsroutinelyappliedinurbanhydrology.Peakflowsarecomputedfromthesimpleequation:Q =kCiA

where:Q -Peakflowk-ConversionfactorC -Runoff coefficienti -Rainfall intensityA-Area

Runoff coefficient for different soil types-Richard 1988

1- Rainfall Intensity (i) and Basin Peak Flows

Aspartof the WMSinterface tothe Rational Method,youcan computeIDFcurvesusingeither HYDRO-35,NOAA,or userdefineddata.ByUsingtheestimatedIDFcurveearlyinPartVresultedfromtherainfall frequencyanalysis.

Time min./y 100y 50y 20y 10y 5y 2y

5 147.2844 131.4384 110.2548 93.9084 76.728 51.0408

10 105.96 94.56 79.32 67.56 55.2 36.72

15 84.4148 75.3328 63.1916 53.8228 43.976 29.2536

30 60.5738 54.0568 45.3446 38.6218 31.556 20.9916

60 43.5 34.278 28.7535 24.4905 20.01 13.311

18.66 12.084 10.155 8.639 7.011 4.695 Intensity

Asthe dataentryfor eachbasin iscompleted, a peakflow (Q)iscomputed and listed in theFlowrate (Q) row. The Rational Method equation does not produce a hydrograph.However,oneofseveral unit-dimensionlesshydrographscanbeusedtodistributethepeakflowthroughtimetocreatearunoffhydrograph.TheresultedFlowrate(Q)=8286.348cfs.=234.64cms.FlowVelocity(V)=Q/A =2.23m/s.

2- Rational Method Traditional Basin Hydrograph

ApplicationOfMathematicalModel hydrology:Specialized the applicationof the modeltofollowthe movementof flood watersfromthedifferent drainagebasins, Where the study take the link between the results of geological, morphological and metrological

analyzestogainaccesstohigh-accuracycalculationsinfloodwatervolumes,flowratesandthe timeof runoffinto force and the time of arrival the floodsto the maximumvalueatreturnperiod.These studiesuseful forproposethenecessary actionsforthe protectionof industrial designhydraulically, structurallyanddeterminetheextentof efficiencytoface the floodwater.Accordinglyupon hasbeenselected aadvancedhydrologicalprograms which model (WMS). Where this model helpsto checking accounthydrograph curve in multipleways according to drainage basins easy and complex, with natural or artificial methods through theapplicationofHEC-HMSprogramandHEC-I.

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River = W.dahdah Reach = Main RS = 99 BR

Station (m)

Elevation(m)

Legend

EG100y

WS100y

Crit100y

0.0 m/s

0.2 m/s

0.4 m/s

0.6 m/s

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1.0 m/s

Ground

Ineff

BankSta

.03

0 20 40 60 80 100 120 140290

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The profile displays the water surface level ovar W.dahdah from the outlet

Main Channel Distance (m)

Elevation(m)

Legend

EG 100y

WS 100y

Crit 100y

Ground

W.dahdah Main

0 50 100 150 200

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0


VelLeft(m/s),

VelChnl(m/s),

VelRight(m/s)

Legend

Vel Chnl 100y

W.dahdah Main

0 50 100 150 2001.0

1.5

2.0

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3.0

3.5


HydrDepthL(m),HydrDe

pthC(m),HydrDepthR(m)

Legend

Hydr Depth C 100y

W.dahdah Main

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River = W.dahdah Reach = Main RS = 99 BR

Station (m)

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Crit100y

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Floodplain delineation and hydraulic model

Usingthe RASMappingtool togenerate botha raster(gridof pixelsor "cells")and polygon of the flooding extents, by intersecting the water-surfaceelevationsateach cross-sectionwith thedigital terrain surface.Post-processingin the form of creating Flood Extent, Flood Depth, and Flood Impact mapsimprovesdefiningthehydraulicmodelandthedeterminationofthebridgesite.

!.

4152'30"E

4151'0"E 4154'0"E

4149'30"E

193'0"N

190'0"N

1858'30"N1858'30"N

1857'0"N

Flood depth at the

outlet of Wadi

dahdah


Legend

!.Out let

Watershed

Khosh Metrological

Stat ion

Geomorphologistsdefinethe floodplainasa flat valley flooradjacent a stream or river made by alluvial unconsolidatedsedimentstransportedanddepositedbytheriverandusuallyexperiences flooding when the river floods (Demek, 1988).Hydrologists and engineers define the floodplain as thesurface next to the channel that is inundated once during agiven return period regardless of whether this surface isalluvialornot(Ward,1978).

Geographical representations of floodplain depths, velocities, and extentsprovide great insight into the model response,and ideally the behaviorof thenatural systemunderanalysis.

Floodplain depth gridTheoutputFlooddepthgridof100yprobabilityfloodingperiodattheoutletof WadiDahdahBasinrepresentsthewatersurfaceelevationlevel grid(WSEL)Minus thegridrepresentingtheground elevationand the floodplainextent.The Flood Coverage dividethe floodedareaintozones,eachwithadepthrange.Rangesfrom0 -1.15representtheFloodStage.Rangesfrom1.15 2.3representtheminorflooding.Rangesfrom2.3 3.46representmoderateflooding.Rangesfrom3.46 4.61representmajorflooding.

HEC-RAS Hydraulic Model and Bridge Design

34 Cross-sections were plotted along 172m on the mainstreamof Wadi dahdah starting attheoutlet with averagedistance 5 mbetweenthem. According tothe topographic

areaandthecross-sectionsthebridge site wasdeterminedatthe station 99 with length 150m to crossthe wadi. TheHEC-RASmodel included inputting a bridge deckof 15mwidth, and the contraction/expansion coefficients for theboundingcross-sectionssetto0.1/0.3, respectively.6 pierswith 2.5 m widthweredesigned.The 100y Flood durationreturnedof 234.8 cmsflowrateusedtoestimatethesteadyflowrateandhydraulicdesignanalysis.

Up Stream Bridge Down Stream Bridge

Cross Sections, Profiles and Rating Curves

Afterthe modelhas finished the steadyflowcomputations. The output is available in agraphical and tabular format. Graphicaldisplaysare often the most effectivemethodof presenting input data and computed

results.Graphicsallowtheusertoeasilyspoterrorsin the inputdata, aswell asprovidingan overview of the results in a way thattables of numbers cannot. The profile plotshowsthat the water surface of 100y flooddistributionreturnat297.1melevation.

The flood severity grid represents the combined effect of depth and velocity, most oftencommunicatedincategoriesof Low,Medium,High,VeryHighandExtreme Hazard.Studieshavebeen performed inmultiplecountries tocategorizethe depthx velocityresult into variousfloodhazard or flood severity classifications. Based on studies in Australiaand published in the2006Designing Safer Subdivisions - Guidance on Subdivision Design in Flood Prone Areas(http://www.ses.nsw.gov.au/content/documents/pdf/ resources/Subdivision_Guidelines.pdf)manual,whichwasderived fromearlierworkfromtheNew SouthWalesFloodplainDevelopmentManual (2005).

Flood Severity Category Depth * Velocity Range (m2/sec)Low < 0.2

Medium 0.20.5

High 0.51.5Very High 1.52.5

Extreme > 2.50

0.5

1

1.5

2

2.5

0 20 40 60 80 100 120 140 160 180 200

Depth*VelocityRange(m2/sec)

Distance

Wadi Dahdah flood severity

Combined Scour Depths =

Pier Scour(2.12) + Contraction Scour(m) (0.25): = 2.37 m.

Critical Velocity (m/s): 0.74

Equation: Live

The Peak flow rate of 100y Duration Return (Q): 235 cms.

The peak water level : 297.1m

The Peak flow velocity inside the brid ge: 0.9 m/s

The Bridge top width : 104 m

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