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Analysis of the relative contributions -( hydrographs ) of the sub-catchments during the flood. Contents. Interpolated Rainfall :« simple to complexe » methods Hydrographs calculation SCS Method Calibration of MIKE SHE for the VAR catchments Parameters , values , graphs

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analysis of the relative contributions hydrographs of the sub catchments during the flood

Analysis of therelativecontributions -(hydrographs) ofthesub-catchmentsduringtheflood

contents
Contents
  • InterpolatedRainfall :« simple to complexe » methods
  • Hydrographscalculation
    • SCS Method
  • Calibration of MIKE SHE for the VAR catchments
      • Parameters, values, graphs
  • Contribution analysis during theflood
  • Calibration???
  • Conclusions
rainfall interpolation methods simple to complexe
Rainfall Interpolation Methods :« simple to complexe »
  • Homogeneous Rainfall on the sub-catchment

Hypothesis : Spatial distribution of the rainfall are the same on the all catchment

=> mean of the six rain gauges station

rainfall interpolation methods simple to complexe1
Rainfall Interpolation Methods :« simple to complexe »
  • Thiessen Method
  • Estimating rainfall weighted taking into account each station.
  • Thiessen Polygon (ARCGIS)
  • Assigning to each station an influence area (%) thatrepresentsweighting factor.
  • To calculate the interpolatedrain :
  • ∑ rainfall for each station xweighting factor
  • ----------------------------------------------------
  • Total area conerning
rainfall interpolation methods simple to complex
Rainfall Interpolation Methods :« simple to complex »
  • Kriging Method

Interpolation by kriging for eachsub-catchment and for eachhour

hydrographs calculation
Hydrographscalculation

SCS Method (Soil Conservation Service)

Hypothesis 1: Infiltration capacity tends to zero as time increases.

Hypothesis 2: Runoff appear after it dropped some rainfall.

Hypothesis 3: R (t) = [ si Pu (t) > 0 ]

Cumulated Water

  • SCS Parameters:

Finish Time

  • S: Maximum infiltration capacity, depend on Soil characteristics, cover,
  • condition of initial wetting.
  • Tm: Time of the peakdischarge, base on Concentration Time ( Tm = 3/8 Tc).
  • Tc: Concentration Time, calculatewith PASSINI Method (take in account: Surface, Slope and Longest Flow Path).
  • Area (km²) : Surface of eachsub-catchment.

Time

hydrographs calculation1
Hydrographscalculation

SCS Result:

  • Almost no big differences appear between the rainfall distribution results from the Thiessen and the homogeneous method
  • The discharge value are globally in accord with calculate value in the Napoleon Bridge
  • Except for Surfer method. Doesn’t take in account the different landuse, the slope or the topography. With more than we could obtain better result including topography in Surfer.
  • Homogeneous discharge is more important than the Thiessen value. Due to Thiessen method take in account spatial reference of the station.
hydrographs calculation2
Hydrographscalculation

Tinee hydrograph

SCS Result:

calibration of mike she
Calibration of MIKE SHE

Firstcalibration-usingonly MIKE SHE

Using: 300 m gridsize

Experiences : verylittlepeak of runoff

thewidth of theimaginedriverbed is 1500 m

Reasons:biggridsizetoobigwidth of

riverbed, bighydraulicradius and littlewaterdepth

littlevelocity and discharge

Conclusion:

wehavetouserivernetworkfor modelling couplingwith MIKE11

calibration of mike she and coupling with mike 11
Calibration of MIKE SHE and couplingwith MIKE 11

Parameters:

  • IWD - InitialWaterdepth0,00-0,005
  • DS – Detentionstorage0,00-0,05
  • Manningnumber (overland)10,0-40,0
  • Net Rainfall Fraction 0,90-0,95
calibration of mike she and coupling with mike 111
Calibration of MIKE SHE and couplingwith MIKE 11

Parameters of the best calibration: M=24 m1/3/s

NRF=0.93

IWD = 0.000 m

DS= 0.00 mm

Results of calibration: PeakofdischargeQc= 3701 m3/s Qm= 3680m3/s

Wrongtime of thepeak 2.5 hoursdifferences

sensitivityanalysisnotsensitive M,IWD,NRF littlesensitive DS

Conclusions: Wecan’tcalibrate more accuratelyundertheseconditions (300 gridsize) and It’snotnecesserybecausetherearenotobserveddata!

contributions analysis
Contributionsanalysis

The runoff’speak and timingdependsonthefollowingparameters:

Shape of thecatchment

Landusesurfaceroughness

Topography

Rainfall, Area

Var sub-catchments:

same Landuse more than 90% forest and natural areaexcept Down Var sub-catchmentsimilar topography

Differences: rainfall, area, shape of thesub-catchments

contributions analysis1
Contributionsanalysis

Similarrunoffcharacteristiconeverysub-catchment

Relativecontributions of runoff: Q%=∑Q/QiA%=∑A/Ai

Esteron:20% c= Q%/A%=128%

Vesubie:8% c=57%

Tineé: 32% c=120%

Upper Var: 36% c=93%

Down Var: 4% c=74%

calibration
Calibration ???

Similarrunoffcharacteristiconeverysub-catchment

Relativecontributions of runoff: Esteron:21%

Vesubie:5%

Tineé: 36%

Upper Var: 36,5%

Down Var: 1,5%

conclusions
Conclusions

The relative contribution of sub-catchments only depends on the distribution of rainfall.

The Tinee, Upper Var, Esterongave more than 90% of thewholerunoff.

CONCLUSIONS OF MIKE PART:

Ifwecalculatetherelativecontributions of thesub-catchments (duringtheflood), wedon’tneedtousecalibrated modell, becausetherelativecontribution is notsensitiveforthecalibratedparameters.