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Analysis of the relative contributions -( hydrographs ) of the sub-catchments during the flood

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

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  1. Analysis of therelativecontributions -(hydrographs) ofthesub-catchmentsduringtheflood

  2. 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

  3. 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

  4. 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

  5. Rainfall Interpolation Methods :« simple to complex » • Kriging Method Interpolation by kriging for eachsub-catchment and for eachhour

  6. 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

  7. 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.

  8. Hydrographscalculation Tinee hydrograph SCS Result:

  9. 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

  10. 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

  11. 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!

  12. 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

  13. 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%

  14. Calibration ??? Similarrunoffcharacteristiconeverysub-catchment Relativecontributions of runoff: Esteron:21% Vesubie:5% Tineé: 36% Upper Var: 36,5% Down Var: 1,5%

  15. Calibration ???

  16. 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.

  17. Thank for your attention Team Six...

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