EAD 511 RIVER MANAGEMENT
Open Channel Hydraulics
IntroductionType of flowEnergy principlesUniform flowFlow modelingSediment transport
ContentsContents
References
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Introduction
Open channel flow is the flow of water in a conduit with a free surface at atmospheric pressure
The flow in an open channel is mainly governed by gravity (i.e. channel bed slope)
DEFINITIONS
Menam Chao Praya, Bangkok Kulim River, Serdang
Artificial or Man-made Channels (e.g. swales)vs. Natural Channels (e.g. rivers)
OPEN CHANNEL CLASSIFICATION
Rigid Boundary Channels: Channels with immovable bed and sides (e.g. concrete drains)
OPEN CHANNEL CLASSIFICATION
Mobile Boundary Channels: Channel boundary is composed of loose sedimentary particles moving under the action of flowing water (e.g. rivers)
OPEN CHANNEL CLASSIFICATION
Bank Erosion
Bed Erosion
Deposition
Types of Flow
GVF – Gradually Varying Flow
RVF – Rapidly Varying Flow
FLOW CLASSIFICATION BY DEPTH VARIATION
ReservoirIrrigation Canal
Sungai Kurau
FLOW CLASSIFICATION BY FROUDE NUMBER, Fr
For any type of channel :
Fr =
Fr <
Fr =
Fr >
Q2 Bg A3
1.0 Subcritical Flow
1.0 Critical Flow
1.0 Supercritical Flow
For rectangular channel :
Fr =V
gyo
For design purpose, Fr < 1.0
TYPICAL CROSS SECTIONS
Values showing isovelocity contours
Geometry and Notation for Open Channel FlowGeometry and Notation for Open Channel Flow
SIDE VIEW CROSS SECTION
V = Average Velocity y = Flow depth
S = Channel bed slope A = Flow area
P = Wetted Perimeter R = Hydraulic Radius
Energy Principles
ENERGY COMPONENTS
ENERGY GRADE LINE (EGL)
WATER SURFACE
CHANNEL BED
DATUM
H1
H2
hf
yo
Z
2gV2
H = + yo + 2gV2
Z
Velocity Head
Conservation of Energy : H1 = H2 + hf ; hf = Frictional loss
SPECIFIC ENERGYy0
yc
0
Constant Q Subcritical (Fr < 1)
Supercritical (Fr > 1)
Critical (Fr = 1)
Es min Es < E minEs
Specific Energy, Es = The height of the energy line (EGL) above the channel bottom
Es = Y0 +V2
2g
Critical flow occur at minimum energy, Es min
yc = Q2
gB2
1/3
= q2
g
1/3
Flow Classification:
yo > yc , V < Vc : Subcritical (Fr < 1)
yo = yc , V = Vc : Critical (Fr = 1)
yo < yc , V > Vc : Supercritical (Fr > 1)
GVF: Energy Balance
Water Surface Curves for GVF
Water Surface Profiles
Uniform Flow
UNIFORM FLOW- Uniform flow characteristics (a) Depth, discharge & velocity remains
constant along the length of the channel
(b) Constant – slope & constant – area channel
V1V2
Q
So
Sw
y1 = y2V1 = V2A1 = A2Sw = So
Prismatic Channel
y1y2
UNIFORM FLOW EQUATIONS
1) Manning : V = R2/3 So1/2n
1
Where n = Manning Coefficient
2) Chezy : V = C R So
Where C = Chēzy Coefficient
3) Darcy – Weisbach: V = 8g R Sof
Where f = Darcy – Weisbach coefficient
C = = R1/6
n8gf
MANUAL SALIRAN MESRA ALAM (MSMA) (DID, 2000)
21
321. SRnAQ =
Manning’s Equation
38
21
.
BS
nQBYv.s
Solution to Manning Equation for Lined Open Drains
Suggested Values of ManningSuggested Values of Manning’’s s Roughness Coefficient, Roughness Coefficient, nn
Surface CoverSuggested n values
Minimum Maximum
Lined Channels and Low Flow InvertsConcrete
Trowelled finish 0.011 0.015
Off form finish 0.013 0.018
Shotcrete
Trowelled, not wavy 0.016 0.023
Trowelled, wavy 0.018 0.025
Unfinished 0.020 0.025
Stone Pitching
Dressed stone in mortar 0.015 0.017
Random stones in mortar or rubble masonry 0.020 0.035
Rock Riprap 0.025 0.030
Suggested Values of ManningSuggested Values of Manning’’s s Roughness Coefficient, Roughness Coefficient, nn
Surface CoverSuggested n values
Minimum Maximum
Grassed FloodwaysGrass cover only
Short grass 0.030 0.035
Tall grass 0.035 0.050
Shrub cover
Scattered 0.050 0.070
Medium to dense 0.100 0.160
Tree cover
Scattered 0.040 0.050
Medium to dense 0.100 0.120
Critical Velocities, (m/s) for various conduit materials
To prevent sedimentation and vegetative growthMin Velocity = 0.6 m/s
To prevent Channel Surface Lining Erosion
Max Velocity = 4.0 m/s (Lined Channel / Low flow invert)
= 2.0 m/s (Floodways and Natural Waterway)
Minimum Longitudinal Slope
0.2 % - Lined Channel0.5 % - Grassed floodways and natural waterway
COMPOUND CHANNEL
Flood Plain Flood PlainMain Channel
A1 , n1
A2 , n2
A3 , n3
P1
P2
P3
• The roughness of the side channels will be different (generally rougher) than that of the main channel
Q = A1
n1R1
2/3 +A2
n2R2
2/3 +A3
n3R3
2/3 So 1/2
Suggested Values of ManningSuggested Values of Manning’’s s Roughness Coefficient, Roughness Coefficient, nn
Surface Cover Suggested n values
Minimum Maximum
Natural Channels
Small streams
Straight, uniform and clean 0.025 0.033
Clean, winding with some pools and shoals 0.035 0.045
Sluggish weedy reaches with deep pools 0.050 0.080
Steep mountain streams with gravel, cobbles, and boulders 0.030 0.070
Large streams
Regular cross-section with no boulders or brush 0.025 0.060
Irregular and rough cross-section 0.035 0.100
Overbank flow areas
Short pasture grass, no brush 0.025 0.035
Long pasture grass, no brush 0.030 0.050
Light brush and trees 0.040 0.080
Medium to dense brush 0.070 0.160
Dense growth of trees 0.110 0.200
Flow Modeling
Flow Modelling
http://www.hec.usace.army.mil/software/hec-ras/
HEC-RAS Modelling
Cross Section at CH 41.2 (Ladang Victoria)
Longitudinal Flood Profile for Sg Muda (Q=1340m3/s)
Mud
a B
arra
ge
Mer
deka
B
ridg
eE
xpre
ssw
ay
Bri
dge
Rai
lway
Bri
dge B
ridg
e
Pipe
Bri
dge
n = 0.025
-10
-5
0
5
10
15
0 5 10 15 20 25 30 35 40Chainage (km)
Ele
vatio
n (m
, LSD
)Existing Bed Level Predicted Water Level (HEC-RAS) Observed
Longitudinal Section for Sg. Muda Kedah (n = 0.03)
-10
-5
0
5
10
15
0 5 10 15 20 25 30 35 40Chainage (km)
Ele
vatio
n (m
, LSD
)
Existing Bed Level Predicted Water Level (HEC-RAS) observed
Longitudinal Section for Sg. Muda Kedah (n = 0.035)
n = 0.030
n = 0.035
-10
-5
0
5
10
15
0 5 10 15 20 25 30 35 40Chainage (km)
Ele
vatio
n (m
, LSD
)
Existing Bed Level Predicted Water Level (HEC-RAS) observed
Longitudinal Section for Sg. Muda Kedah (n = 0.025)
Cross Section at Ch 41.2 (Ladang Victoria) during Maximum Water Level
(06.10.2003 @ 1600Hrs)
n = 0.025 n = 0.03
n = 0.035
Sediment Transport
SEDIMENT TRANSPORT MODES
BED MATERIAL
BED LOAD
SUSPENDED LOAD
WASH LOAD
TOTAL BED MATERIAL LOAD
TOTAL LOAD
Shields DiagramShields Diagram((Nalluri & Featherstone 1995Nalluri & Featherstone 1995))
No Sediment Transport
Bed Form in Natural WaterwaysBed Form in Natural Waterways
Particle Size Distribution Particle Size Distribution of River Bed Material of River Bed Material
Stesen SP7 Sg. Pari
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0.01 0.10 1.00 10.00 100.00
Sampel 1 Sampel 2 Sampel 3 PurataSaiz Partikel (mm)
Peratus Telus (%)
d90
d65
d10
d35
d50
d60
Sediment Transport Sediment Transport EquationsEquations
Mode of Transport Equations Rujukan Persamaan Range of Data
Bed Load
Shields 2.2 1.56 < d50 (mm) < 2.47
Meyer-Peter-Muller 2.3 3.17 < d50 (mm) < 28.6
Einstein – Brown 2.4 ψ < 10
Einstein Rajah 2.29 0.785 < d50 (mm) < 28.6
Total Bed Material Load
Graf 2.5 0.09 < d50 (mm) < 2.78
Engelund & Hansen 2.6 0.19 < d50 (mm) < 0.93
Yang 2.70.137 < d50 (mm) < 1.71yo (m) < 1.0 m
Ackers & White 2.8 0.04 < d50 (mm) < 4.94
Data CollectionData Collection
(a)(a) Flow DischargeFlow Discharge
• Hydrological Procedure No. 15 “River Discharge Measurement by Current Meter” (DID, 1976).
Swoffer 2100 Current Meter Model Neyrflux Type 80 Current Meter
(b) (b) Bed Material :Bed Material :
Van Veen Sampler
(c) (c) Bed Load :Bed Load :
Low Flow High Flow
(d) (d) Suspended Load :Suspended Load :
Low Flow High Flow
Bed Load Sampling @ River Muda
Ladang Victoria
Suspended Load Sampling @ Muda River
Ladang Victoria
Sediment DatabaseSediment DatabasePari River @ ManjoiPari River @ Manjoi
Fluvial Fluvial ModelingModeling
Pari River
Pari River
Channel geometryChannel geometry
Channel cross sectionsChannel cross sections
Ch. 3020 ( 21 Oktober 2002) Jambatan Manjoi, Ch. 3380 ( 21 Oktober 2002)
Taman Merdeka, Ch. 2475 ( 21 Oktober 2002)Alor Limpah Batu, Ch. 1220 ( 25 Julai 2001)
Channel cross sectionsChannel cross sections
Jambatan Silibin, Ch. 4540 ( 21 Oktober 2002)
Tokong Buddha, Ch. 4160 ( 21 Oktober 2002)Ch. 3600 ( 21 Oktober 2002)
Kuala Sungai Pari ( 22 Julai 2001 )
Observed Flow Observed Flow ProfilesProfiles
Measured DataMeasured Data
flow profilesflow profiles
Perbezaan Paras Air Sungai Pari
34.00
35.00
36.00
37.00
38.00
39.00
2000 2500 3000 3500 4000 4500 5000Keratan Rentas, m
Para
s, m
P. Air 7/10/2002 (35.00 Cumecs) P. Air 8/10/2002 (34.70 Cumecs)P. Air 9/10/2002 (47.80 Cumecs) P. Air 10/10/2002 (14.15 Cumecs)P. Air 21/10/2002 (7.05 Cumecs)
Paras Air Cerapan Sungai PariParas Air Cerapan
Backwater DataBackwater Data
Hydrological dataHydrological data
2000 Flood Hydrograph2000 Flood Hydrograph
Profil Aliran Berhayun Sungai Pari
33.0
34.0
35.0
36.0
37.0
38.0
39.0
40.0
0 50 100 150 200 250 300 350 400 450 500Masa, jam
Para
s Ai
r, m
Puncak Hidrograf Tahun 2000 Sungai Par i
0
20
40
60
80
100
120
2390 2400 2410 2420 2430 2440 2450M as a, jam
Kada
ralir
, m3 /s
River dataRiver data
Taburan Purata Saiz Endapan Bahan
Dasar Untuk Sungai Pari
0.00
10.00
20.00
30.0040.00
50.00
60.0070.00
80.00
90.00
100.00
0.01 0.10 1.00 10.00 100.00
Saiz Partikel, mm
Pera
tus
Telu
s, %
Cerapan Dasar Hil ir Cerapan Dasar Hulu
d50 = 2.50 mm
d50 = 1.80 mm
Bed materialBed material Bank materialBank material
Sediment rating curveSediment rating curve
0.00
0.05
0.10
0.15
0.20
0.25
0.00 10.00 20.00 30.00 40.00 50.00Masa (jam)
Out
put E
ndap
an, Q
s (m
3 /s)
FluvialFluvial--12 Model12 Model
Predicted flow profilesPredicted flow profiles
Profil Paras Air Sungai Pari Bagi Kadaralir Q=48 m3/s
Profil Paras Air Sungai Pari Bagi Kadaralir Q=15 m3/s
2000 Flood
34.5035.0035.5036.0036.5037.0037.5038.00
2000 2500 3000 3500 4000 4500 5000Keratan Rentas, m
Par
as, m
Paras air simulasi (FL-12) Paras air cerapan
35.50
36.00
36.50
37.00
37.50
38.00
38.50
2000 2500 3000 3500 4000 4500 5000Keratan Rentas, m
Par
as, m
Paras air simulasi (FL-12) Paras air cerapan
Cross section changesCross section changes
Ch. 2475Taman Merdeka
Ch. 3020
36.00
37.00
38.00
39.00
40.00
41.00
0.00 10.00 20.00 30.00 40.00 50.00Jarak Dari Tebing Kiri, m
Par
as, m
P. Dasar Awal P. Air AwalP. Dasar Simulasi FL-12 P. Air Simulasi FL-12P. Dasar Simulasi FL-14 P. Air Simulasi FL-14
35.00
36.00
37.00
38.00
39.00
40.00
41.00
0.00 10.00 20.00 30.00 40.00 50.00Jarak Dari Tebing Kiri, m
Para
s, m
P. Dasar Awal P. Air AwalP. Dasar Simulasi FL-12 P. Air Simulasi FL-12P. Dasar Simulasi FL-14 P. Air Simulasi FL-14
Cross section changesCross section changes
Ch. 3380Jambatan Manjoi
Ch. 3600
34.00
35.00
36.00
37.00
38.00
39.00
40.00
0.00 10.00 20.00 30.00 40.00 50.00Jarak Dari Tebing Kiri, m
Par
as, m
P. Dasar Awal P. Air AwalP. Dasar Simulasi FL-12 P. Air Simulasi FL-12P. Dasar Simulasi FL-14 P. Air Simulasi FL-14
34.00
35.00
36.00
37.00
38.00
39.00
40.00
0.00 10.00 20.00 30.00 40.00 50.00Jarak Dari Tebing Kiri, m
Para
s, m
P. Dasar Awal P. Air AwalP. Dasar Simulasi FL-12 P. Air Simulasi FL-12P. Dasar Simulasi FL-14 P. Air Simulasi FL-14