Basincharacteristics
Fromhydrologicalprocessesatthepointscaletohydrologicalprocessesthroughoutthespacecontinuum:
⤷ pointscaleà riverbasin
Thewatershedcharacteristics(shape,length,topography,…)
– controltheresponseoftheriverbasin⤷ shapeofthehydrograph⤷ soilwaterdynamics
– canbeusedtoidentifysimilarityofresponseamongdifferentbasins⤷ extrapolationandregionalisation
ofmodels
NB
Riverbasin,drainagebasin,watershed,catchmentareusedassynonimous
Hydrology– Basincharacteristics– AutumnSemester2017 1
Lecturecontent
Quantitativecharacterizationof
– topographicfeatures
– rivernetworkcharacteristics
– soil
– landcover
– interrelationshipsbetweenwatershedfeatures
Skript:Ch.IV.1,IV.1.1,IV.1.3,IV.1.4
Basincharacteristics
2Hydrology– Basincharacteristics– AutumnSemester2017
Watersheddefinition
watershed:area oflanddrainingintoarivernetwork convergingtoanoutlet
theareaofthewatershedisdelimitedbythetopographic(=drainage)divideoutlinedonatopographicmap
3Hydrology– Basincharacteristics– AutumnSemester2017
Topographicvsphreaticdivide
• theareacontributingtowaterbalancecorrespondstothatdelimitedbythetopographic(=drainage)divide
• theareacontributingtowaterbalanceDOESNOTcorrespondtothatdelimitedbythetopographic(=drainage)divideêClosingthewaterbalancerequirestheknowledgeofthephreaticdivide
TOPOGRAPHIC DIVIDE ⋍ PHREATIC DIVIDE
TOPOGRAPHIC DIVIDE
PHREATIC DIVIDE
GROUNDWATER FLOW IMPERVIOUSLAYER
IMPERVIOUS LAYER4Hydrology– Basincharacteristics– AutumnSemester2017
Hypsometriccurveelevationrange[m]
ΔA[km2]
Atot[km2]
1685– 1500 3.4 3.4
1500– 1250 4.9 8.3
1250– 1000 7.6 15.9
1000– 750 4.1 20.0
750– 500 2.8 22.8
500– 443 1.3 24.1
2200
1900
1600
1300
1000
700
4002 40 6 8 10 12 14 16 18 20 22 24
H [masl]
A [km2]
1685masl
1500masl
1250masl
1000masl750masl
500masl
• cumulativefrequencydistributionofareaswithelevation⤷ watershedsteepness
• use⤷ watershedsimilarity⤷ hydropowerpotential (identifies
largecontributingareaswithhighelevationdifference)
H =hiAii∑Atot
= 1108 m
5Hydrology– Basincharacteristics– AutumnSemester2017
Watershedaverageslope(Alvard-Horton’s)
di = distancebetweentwosubsequentcontourlines
li = lengthoftheaverageelevationlinebetweentwosubsequentcontourlines
• localslope si = Δhi /di vsbasinslope,
• localslope forapproximatelyrectangularareasbetweentwosubsequentcontourlinesofdifferenceh:
⤷ whereai =areabetweentwocontourlines
• basinslope forregularlyspacedelevationranges(contourlinesdifference=h):
⤷
whereL =totallengthofaverageelevationlinesA =totalarea
s
si =hdi
= hlidili
= hliai
si =hl1a1a1A+ hl2a2
a2A+ ...+ hln
ananA
= hAl1 + l2 + ...+ ln( ) = hL
A
NB
thedegreeofaccuracydependsonthecontourlinespacingandontheaccuracyoftherectangularareasapproximation
6Hydrology– Basincharacteristics– AutumnSemester2017
Watershedaverageslope(gridmethod)
NB
theaccuracyofthemethoddependsonthenumberN oflocalslopeestimates
• localslope
si = Δhi /di
with Δh =contourlinesintervaldi =minimumdistancebetweentwo
contourlinesindifferentgridboxes
• basinslope
where N =numberofgridnodeswherelocalslopessi arecomputed
si =sii∑
N
7Hydrology– Basincharacteristics– AutumnSemester2017
• modernsurveyingtechniques(airbornelaseraltimetry,satelliteradaraltimetry,…)makeavailabledigitalterrainmodels(DTMs)
• mostcommonlyDTMsareavailableinrasterformatà gridofsquareswithelevationsassociatetoeachnode
Watershedcharacteristics(automaticmethods)
!
ShadedreliefrepresentationoftheDTMoftheMaggia
Riverbasin(gridsize25×25m)
DTMscanbemanipulatedbymeansofGeographicalInformationSystems(GIS) toextractbasincharacteristics:
⤷ watersheddelineation
⤷ localandbasinslope
⤷ digitalrivernetwork– flowdirection– flowaccumulation(drainagearea)
⤷ riverprofile
⤷ aspect
⤷ …à
8Hydrology– Basincharacteristics– AutumnSemester2017
ExampleofDRNextractedbyGISfromaDTM
DigitalRiverNetwork(DRN)
!
DigitalRiverNetwork
actualdrainagenetwork(“bluelines”)
}
9Hydrology– Basincharacteristics– AutumnSemester2017
ExampleofDigitalSoilMap(Maggiariverbasin,Tessin,CH)
Otherwatershedcharacteristics– Soil
soiltype soildepth
!!
• use⤷ delineationof
infiltrationandsoilstoragecharacteristics
⤷ parameterisationofinfiltrationmodels
• problems⤷ accuracyofinformation
⤷ differentclassification/resolutionusedbydifferentcountries
10Hydrology– Basincharacteristics– AutumnSemester2017
ExampleofDigitalLandUseMap(Maggiariverbasin,Tessin,CH)
Otherwatershedcharacteristics– Landuse
• use⤷ parameterisationof
models
– infiltration(e.g.SCS-CN)
– evapotranspiration
• problems⤷ representativenessof
mapdependsonrastersize
⤷ differentclassification/resolutionusedbydifferentcountries
! 11Hydrology– Basincharacteristics– AutumnSemester2017
Otherwatershedcharacteristics– DrainageDensity
• itmeasurestheefficiencyofthebasindrainage(i.e.ofhowwellorhowpoorlyawatershedisdrainedbyrivers)
• itdependsuponbothclimate(e.g.rainfallregime)andphysicalcharacteristics(e.g.geology,slope,soil,landcover)ofthedrainagebasin
• forequalclimaticcharacteristicscanbeusedasproxyinformationforpermeability⤷ highDà lowpermeability
⤷ lowDà highpermeability
D = total length of streamsarea
=Li∑ i
A
VERYHIGHà D>100km/km2HIGHà D18÷28km/km2
LOWà D<3km/km2 AVERAGEà D7÷10km/km2
12Hydrology– Basincharacteristics– AutumnSemester2017
Interrelationshipsofwatershedcharacteristics
!
!
13Hydrology– Basincharacteristics– AutumnSemester2017