# Lecture 9: River Sediment Transport - PowerPoint PPT Presentation

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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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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

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

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

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

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

b

y

Using

Area

Perimeter

From

6

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

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

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

b

y

Dimensionless Grain Diameter

Since

then

Mobility Number

10

b

y

Parameters

Mobility Number

Sediment discharge

11

3. Total Sediment Transport Load – Engelund/Hansen’s (1967) Formula

Friction factor

Shields Parameter

N/s/m

12

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

b

y