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2010-2011 TEAM
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  1. 2010-2011 TEAM Interest of distributed hydrological models (Mike SHE & HEC-HMS) 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia

  2. Different types of models Definition • 1) lumped = complete basin as single homogeneous • element with average rainfall input • 2) quasi-distributed = discretization of watershed into homogeneous sub-basins with single rainfall parameters based on topography • 3) distributed = physically based, division into elementary unit areas as grid cells, solving equations in each cell HEC-HMS comparison Rainfall distribution methods Mike-She comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 2

  3. Model type - lumped Definition • much simpler than deterministic models • obtained by aggregating or averaging the spatially variable processes • usually not done in a formal mathematical manner • rather, some simple assumptions are made which invariably start with continuity equation • can’t be used for longer simulation periods considering groundwater infiltration and flow HEC-HMS comparison Rainfall distribution methods Mike-She comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 3

  4. Model type - distributed Definition • hydrological phenomena vary spatially and temporally • in accordance with the conservation laws of mass, energy and momentum • models based on conservation laws are physically-based • laws expressed as partial differential equations (PDEs) • solutions of PDEs on finite differences or finite element grid computationally demanding HEC-HMS comparison Rainfall distribution methods Mike-She comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 4

  5. HEC-HMS Definition • mainlylumpedmodels • Example of method’scategorization: HEC-HMS comparison Rainfall distribution methods Mike-She comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 5

  6. HEC-HMS Definition • FullyLumped Model based on meanvalue • Quasi DistributedExample • Using new Rainfall distribution based on Krigingmethod for eachsub-catchments • Distributed Model • Inconvenient: Take time to build a model based on gridded file (.dss) • Advantage: Good for long time computation window HEC-HMS comparison Rainfall distribution methods Mike-She comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 6

  7. HEC-HMS Definition FullyLumped Model Vs Lumped Model Requiredparameters: HEC-HMS comparison Rainfall distribution methods Mike-She comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 7

  8. FullyLumpedVs Lumped Model Definition HEC-HMS comparison Rainfall distribution methods Mike-She comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 8

  9. Rainfall Distribution: ThiessenPolygons Definition HEC-HMS comparison Rainfall distribution methods Lumped : assign 1 rainfall value for 1 polygon. Mike-She comparison Conclusion Quasi distributed : Assign 2 rainfall values in 1 sub-basin. 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 9

  10. Interpolation method :Best Linear Estimator Unbiased Definition Lack of data to built a variogram. HEC-HMS comparison • Could be interesting to apply with : • More point of measurements, • Taking into account the altitude, • Taking into account the distance to the sea. Rainfall distribution methods Mike-She comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 10

  11. Comparison Definition HEC-HMS comparison Rainfall distribution methods Mike-She comparison Conclusion In our case of study, the rainfall distribution method= Thiessen polygons 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 11

  12. Mike SHE model Definition Fully distributed. The spatial and temporal variation of meteorological, hydrological, geological and hydrogeological data across the model area is described in gridded form for the input as well as the output from the model. HEC-HMS comparison Rainfall distribution methods Mike-SHE comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 12

  13. Modelling Process Domain Topography Manning M Definition HEC-HMS comparison Rainfall distribution methods Thiessen Polygons and precipitation rates Mike-SHE comparison very complex and time consuming Conclusion Network : 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 13

  14. Results Definition HEC-HMS comparison Rainfall distribution methods Mike-SHE comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 14

  15. Results Definition • Mike SHE hydrograph doesn’t match observed/estimated discharge rates and peak time at Napoleon III - bridge • although model is set up more precisely is doesn’t give more accurate results than lumped models • Manning coefficients M can be adjusted, however no big influence is expected • most likely destroyed sills/structures during the flood event responsible for “time-shifting” HEC-HMS comparison Rainfall distribution methods Mike-SHE comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 15

  16. CONCLUSION Definition HEC-HMS comparison Rainfall distribution methods Mike-SHE comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 16

  17. CONCLUSION Definition Are 5 rain gauges sufficient enough to distribute the rainfall well across the catchment? The observed/estimated discharge provided at Napoleon III Bridge is not accurate due to extrapolation of the rating curve. There is no justification in employing a complex, spatially distributed model when a simple one will suffice. Simpler models invariably have fewer parameters and are easy to calibrate. HEC-HMS comparison Rainfall distribution methods Mike-SHE comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 17

  18. Which model should we use? Definition • purpose (resolution of prediction) • available data (spatially and temporal varying data – soil, landuse, precipitation, temp. and other forcing variables) • time window (the more complex the more time needed) • scale of the project (small– homogeneous / • large– inhomogeneous catchment) • budget (computational and engineering time are expensive HEC-HMS comparison Rainfall distribution methods Mike-SHE comparison Conclusion 1stTopicPresentation, Friday 18th February 2011 Polytech’Nice - Sophia 18

  19. Thank you for your attention