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