Lecture 9: River Sediment Transport
-
Upload
lavinia-vincent -
Category
Documents
-
view
234 -
download
23
description
Transcript of Lecture 9: River Sediment Transport
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
Lecture 9: River Sediment Transport
CEM001 Hydraulic Structures, Coastal and River Engineering
River Engineering Section
Dr Md Rowshon Kamal
H/P: 0126627589
1
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
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?
Development of Sediment Transport Formulae
2
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
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.
Development of Sediment Transport Formulae con’t
3
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
1. Bedload Formula – Meyer-Peter & Müller (1948)
2/3*cS
*b )FF(8q
Critical Shields Parameter = 0.047)1( sgD
o
1sgDD
qsbWhere D is average sand diameter
2/3)047.0(81 ssb FsgDDq
Valid for D > 3.0mm
Sediment Flow Ratem3/s/m
4
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.
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
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
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
Answer
Using 2/3)047.0(81 ssb FsgDDq
y
b
Area 20.1600.40.40 mbyA
Perimeter mbyP 0.480.400.422
)1()1()1(00
sD
RS
sgD
gRS
sgDF os
From
0566.0)65.1(01.0
00028.0333.3
sF
2/3047.00566.08165.201.081.901.0 sbq
mPAR 333.3/
msmqsb //100.3 356
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
2. Total Sediment Transport Load – Ackers & White’s Formula (1973)
Dimensionless Grain Diameter
3/1
2
1)(
sgr
gDD
Mobility Number
n
ms
n
grDD
V
gD
uF
1
*
10log321)(
Flow velocity
Hydraulic mean depth
n
m
m
gr
grs u
V
D
qD
A
FCq
*
1Sediment Flow Ratem3/s/m
Flow discharge
7
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
Total Sediment Transport Load – Ackers & White’s Formula (1973) con’t
60grDIf
025.0
17.0
78.1
0
C
A
m
n
gr
then
601 grDIf then
46.3)(log98.0log79.2log
/23.014.0
/83.667.1
log56.01
2
grgr
grgr
gr
gr
DDC
DA
Dm
Dn
If then1grD Cohesive forces are dominant
1.
2.
3.
8
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
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
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
Answery
b
8.231
)1014.1(
165.281.901.0
1)(3/1
26
31
2
s
gr
gDDDimensionless Grain
Diameter
Since 60grD
025.0
17.0
78.1
0
C
A
m
n
gr
then
Mobility Number
n
ms
n
grDD
V
gD
uF
1
*
10log321)(
010*
10log321)(
DD
V
gD
uF
ms
gr
10
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
Answer con’ty
b
mR
mP
mA
333.3
0.48
0.160 2
smgRSu
mbAD
smAQV
m
/0957.0
0.4/
/5.2/
0*
305.0
01.0
410log32
5.2
65.101.081.9
1
grFMobility Number
Parameters
n
m
m
gr
grs u
V
D
Dq
A
FCq
*
1Sediment discharge
msmqs //102.44
01.0)40/400(1
17.0
3050.0025.0 34
78.1
11
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
3. Total Sediment Transport Load – Engelund/Hansen’s (1967) Formula
2/5/ 1.0 f
2/ 2
V
gSyf Friction factor
2/1
3
gDq s
s
t
Ds )(
Shields Parameter
350/
2/5
)1(1.0
Dsgf
q st Sediment transport load
N/s/m
12
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
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
School of Civil Engineering/Linton School of Computing, Information Technology & Engineering
Answery
b
350
2/5
1'
1.0Dsg
fq st
32
/ 1052.35.2
0.400028.081.92
f
056.0 sF
33
2/5
01.065.181.981.9265010516.3
056.01.0
tq
msNqt //21.2
14