Cu06997 lecture 12_sediment transport and back water


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Cu06997 lecture 12_sediment transport and back water

  1. 1. Open channel, with bed slope >02211 AuAuQ Head lossReference line𝑦1 + 𝑧1 +𝑢122𝑔= 𝑦2 + 𝑧2 +𝑢222𝑔+ ∆𝐻1−24
  2. 2. u1Reference [m]Surfacelevel y +z [m]Total Head H [m]P1z1y1u12/2gP2z2y2u22/2gu2212222211122 HguzyguzyHead loss [m]ΔHVelocity Head [m]Open channel, with bed slope <= 04
  3. 3. ebylSl ezz303222beSCBQyz1= Rise water level at distance l [m]z0= Rise water level at weir [m]l= Distance from weir [m]Sb= Bed slope [1]ye=equillibrium depth [m]Back water profile [Stuwkrommen]yeEstimation!!!4
  4. 4. A critical depth B equilibrium depth322bgqy vcBack water profile [Stuwkrommen]3222beSCBQy4
  5. 5. CU06997 Fluid DynamicsSediment transport9.1 Introduction (page 282)9.2 The threshold of movement (page 282-287)9.3 A general description of the mechanics of sediment transport (p282-292)9.4 Sediment transport equations (page 292-304)9.5 Concluding notes on sediment transport (page 304-307)Just read the book, in this presentation just some general principles1
  6. 6. Sediment transport• Erosion or scour• Deposition / SedimentationSediment transport• By rolling or sliding along the bed (biggerparticles)• By suspension in the moving fluid (smallerparticles)Sediment transport is very complex1
  7. 7. Sediment transport turbulent flowRolling [rollen]Sliding [glijden]Saltation [Saltatie]Suspend [Suspensie]Dissolved [Opgelost]2
  8. 8. A schematic diagram of where the different types of sediment loadare carried in the flow. Dissolved load is not sediment: it iscomposed of disassociated ions moving along with the flow. Itmay, however, constitute a significant proportion (often severalpercent, but occasionally greater than half) of the total amount ofmaterial being transported by the stream.
  9. 9. Sediment transport 3 stepsStep 1: Particles start to move (erosion / scour)[Deeltjes komen los van bodem]Step 2: Particles move horizontal (transport)[Deeltjes worden (horizontaal) verplaatstStep 3: Deposition of particles (sedimentation)[ Deeltjes ‘vallen’ weer op de bodem]1 2 32
  10. 10. Parameters which influence erosionDensity DichtheidGrain size Korrel diameterShape VormCohesion CohesieTurbulence TurbulentieBed slope Talud helling (bodem)Hydraulic Radius Hydraulische straal2
  11. 11. Erosion𝜏 = 𝜌 ∙ 𝑔 ∙ 𝑅 ∙ Sτ = shear stress fluid [N/m2]R = Hydraulic Radius [m]S = Slope of channel bed [1]Relation with mean boundary shear stressErosion, no relation with velocity???Of course there is a relation with velocity, inthis case velocity is in the bed slope. Asteeper bed slope will give a higher velocityErosion will start to occur when the shearstress caused by the flowing water is higherthan the critical shear stress of the material2 vementMocr  movementnocr 
  12. 12. Hulström diagram indicating erosion, transport or depositionof sediment according to flow velocity and grain sizeErosion, Transport, Deposotion2
  13. 13. Table indication critical velocitySoil type Critical velocity (m/s)Clay[klei, leem, löss]0,60 …. 0,80Clay and sand (Silt)[zavel grond]0,30 …. 0,60Fine sand[fijn zand]0,15 …. 0,30Coarse sand[grof sand]0,20 …. 0,50Peat (fixed)[vast veen]0,30 …. 0,60Peat[slap veen]0,15 …. 0,302
  14. 14. Waves can make particles move (a bit) (back and forth)Waves can’t make particles transport!!!Combination current [stroming] and waves can makeparticles transport easer!!Effect of waves on erosion2
  15. 15. Transport capacity• A river has a sediment transport capacityor load. Transport capacity has a limit.Important parameters are discharge, velocityand turbulence.• When the limit of transport capacity isreached, new erosion will not occur• When velocity decrease, transport capacitywill decrease. Sedimentation will occur• When velocity increase, transport capacitywill increase. Erosion will occur3
  16. 16. sedimentationDam / weir3Transport