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Lecture 9: River Sediment Transport

Lecture 9: River Sediment Transport CEM001 Hydraulic Structures, Coastal and River Engineering River Engineering Section. Dr Md Rowshon Kamal rowshon@legendagroup.edu.my H/P: 0126627589. 1. Development of Sediment Transport Formulae.

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Lecture 9: River Sediment Transport

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  1. Lecture 9: River Sediment Transport CEM001 Hydraulic Structures, Coastal and River EngineeringRiver Engineering Section Dr Md Rowshon Kamal rowshon@legendagroup.edu.my H/P: 0126627589 1

  2. Development of Sediment Transport Formulae • Empirical formulae developed for bedload, suspended load and total sediment transport rate using laboratory and field data. • They are based on hydraulic and sediment conditions – Water depth, velocity, slope and average sand diameter etc. • There can be significant differences between predicted and measured sediment transport rates, WHY? 2

  3. Development of Sediment Transport Formulae con’t • These differences are due to change in: • - Water temperature, • - Effect of fine sediment, • - Bed roughness, • - Armouring, and • - Inherent difficulties in measuring total sediment discharge. • Use of most appropriate formula based on the availability of conditions, experience and knowledge of the engineer. 3

  4. 1. Bedload Formula – Meyer-Peter & Müller (1948) Valid for D > 3.0mm Where D is average sand diameter Critical Shields Parameter = 0.047 Sediment Flow Rate m3/s/m The Shields diagram empirically shows how the dimensionless critical shear stress required for the initiation of motion is a function of a particular form of the particle Reynolds number, Rep or Reynolds number related to the particle. 4

  5. Application of Meyer-Peter & Müller Formula (1948) A river of width 40.0m, depth 4.0m and bed slope 0.00028 carries a discharge of 400m3/s. If the river boundary has a typical grain diameter, D50=10.0mm (s= 2650kg/m3), assuming a rectangular cross-section, estimate the sediment transport rate using Meyer-Peter and Műller formula. 5

  6. b y Answer Using Area Perimeter From 6

  7. 2. Total Sediment Transport Load – Ackers & White’s Formula (1973) Dimensionless Grain Diameter Flow velocity Mobility Number Hydraulic mean depth Sediment Flow Rate m3/s/m Flow discharge 7

  8. Total Sediment Transport Load – Ackers & White’s Formula (1973) con’t 1. If then 2. then If 3. If then Cohesive forces are dominant 8

  9. Application of Ackers & White’s Formula (1973) A river of width 40.0m, depth 4.0m and bed slope 0.00028 carries a discharge of 400m3/s. If the river boundary has a typical grain diameter, D50=10.0mm (s= 2650kg/m3), assuming a rectangular cross-section, estimate the sediment transport rate using Ackers and White’s formula. 9

  10. b y Answer Dimensionless Grain Diameter Since then Mobility Number 10

  11. b y Answer con’t Parameters Mobility Number Sediment discharge 11

  12. 3. Total Sediment Transport Load – Engelund/Hansen’s (1967) Formula Friction factor Shields Parameter N/s/m Sediment transport load 12

  13. Application of Engelund/Hansen’s Formula (1967) A river of width 40.0m, depth 4.0m and bed slope 0.00028 carries a discharge of 400m3/s. If the river boundary has a typical grain diameter, D50=10.0mm (s= 2650kg/m3), assuming a rectangular cross-section, estimate the sediment transport rate using Engelund/Hansen’s formula. 13

  14. b y Answer 14

  15. Thank You 15

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