Techniques de l’eau et calcul des réseaux le calcul hydrologique proprement dit Michel Verbanck 2012.

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1 Techniques de l’eau et calcul des réseaux le calcul hydrologique proprement dit Michel Verbanck mikeverb@ulb.ac.be 2012

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3 Stream ordering Quantitative way of studying streams. Developed by Horton and then modified by Strahler. Each headwater stream is designated as first order stream When two first order stream combine, they produce second order stream Only when two streams of the same order combine, the stream order increases by one When a lower order stream combines with a higher order stream, the higher order is retained in the combined stream

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13 0 50000 100000 150000 JanFebMarAvrMaiJunJulAugSepOctNovDec 0 40 80 Débits Q d, m 3 j -1 Précipitations, mm j -1 Répartition des volumes à écouler pendant l´année

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16 Hydrogramme observé

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19 Rainfall and Conversion to Runoff Use either design rainfalls or historical events Spread uniformly over a given basin area Use Unit hydrograph to compute response for relatively large basins - 10 to 100 km² The unit hydrograph is defined as the hydrograph of direct runoff that results from 1 inch ( 25.4mm ) of excess rainfall generated uniformly over the watershed at a constant rate during a specified time.

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21 Loss Rate Method: Initial and Uniform Loss Rate Method Initial Amount Lost to Infiltration (in) Uniform Loss at a Constant Rate (in/hr) Example: Initial Loss = 0.5 in, Uniform Loss = 0.05 in/hr Inches/Hour

22 The unit hydrograph is defined as the hydrograph of direct runoff that results from 1 inch ( 25.4mm ) of excess rainfall generated uniformly over the watershed at a constant rate during a specified time. In practice, a large number of actual watersheds are evaluated and then made dimensionless by dividing all discharge ordinates by the peak discharge and the time values by the time to peak.

23 0 100 200 300 400 0510152025 intensité de pluie, s -1 ha -1 Durée de pluie, minutes pluie cumulée sur 10 min Traitement d´un événement de pluie pluie mesurée

24 Routing a hillslope hydrograph through the network 1: Rainfall is transformed by the hillslopes into a hydrograph which is delivered throughout the network. 2: Hydrographs from A take longer to travel to the outlet than those from B, and those from C arrive sooner still. 3. When these are combined, the outlet hydrograph is more drawn out, and the peaks from A, B, C do not coincide

25 Rainfall and Conversion to Runoff Use either design rainfalls or historical events Spread uniformly over a given basin area Use Unit hydrograph to compute response for larger basins - 10 to 100 km² Use Rational Method to compute peak flow for small basin area – a few hectares

26 Rainfall and Conversion to Runoff Use either design rainfalls or historical events Spread uniformly over a given basin area Use Rational Method to compute peak flow for small basin area – a few hectares Use Unit hydrograph to compute response for larger basins - 10 to 100 km²

27 The unit hydrograph is defined as the hydrograph of direct runoff that results from 1 inch ( 25.4mm ) of excess rainfall generated uniformly over the watershed at a constant rate during a specified time. In practice, a large number of actual watersheds are evaluated and then made dimensionless by dividing all discharge ordinates by the peak discharge and the time values by the time to peak.

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30 calcul des réseaux Q av

31 0 100 200 300 400 0510152025 intensité de pluie, s -1 ha -1 Durée de pluie, minutes pluie cumulée sur 10 min Traitement d´un événement de pluie pluie mesurée

32 isohyètes 24-Jul-1969 étude des inondations dans le bassin de la Woluwe, Min.Trav.Publics

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35 Storm event 16 June 2011 Rainfall 16.3 mm / 15 min Maximal intensity at 16:05

36 inégale répartition spatiale des pluies

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38  = coefficient de ruissellement Aire A intensité i QiA av  Méthode rationnelle Débit à l´exutoire

39 intensité des précipitations et des flux instantanés Durée de pluie & d´écoulement 0 0 Coeff de ruissellement moyen: = Probabilité de récupération d´eaux  m produit V précipité V  AidtV précipité   QdtV avproduit  

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41 averse de référence d’orage pour la région bruxelloise période de retour décennale L’intensité i (l / ha. s) de l’averse d’orage de durée ≤ 120 min est donnée par Cette expression, sous sa forme la plus générale, est appelée formule de Talbot. Il s’agit de l’intensité moyenne pendant l’épisode, appliquée au centre du bassin technique considéré. NB. Au delà d’une durée de 120 minutes, on considère qu’il s’agit d’une pluie de longue durée (dans ce cas le coefficient 6000 est porté à 8000). t p : durée de la pluie (minutes)

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43 Texture du sol

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45 toiture verte en intérieur d’ilôt

46 Time of Concentration Different areas of a watershed contribute to runoff at different times after precipitation begins Time of concentration –Time at which all parts of the watershed begin contributing to the runoff from the basin –Time of flow from the farthest point in the watershed Isochrones: boundaries of contributing areas with equal time of flow to the watershed outlet

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49 modèle du réservoir linéaire

50 Le modèle du réservoir linéaire

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53 linear reservoir cascade

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