to acquire theory on open channel flow

EAH 225 HYDRAULICSEAH 225 HYDRAULICS

Prof. Dr. Aminuddin Ab Ghani

Open Channel FlowOpen Channel Flow

OBE TOPIC OUTCOMES

To acquire theory on open channel flow To apply relevant equations to compute flow in open channelsin open channels To determine required size of channel

(Ch l D i )(Channel Design) To acquire theory on sediment transport in

rivers To apply relevant equations to computeTo apply relevant equations to compute

sediment discharge in rivers

ContentsContentsContentsContents

Introduction Existing Drainage System Channel Design Flow Modelling

References

SI Edition

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Introduction

O h l fl i th fl f t i d it

DEFINITIONS

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)

Menam Chao Praya, Bangkok Kulim River, Serdang

Artificial or Man made Channels (e g swales)OPEN CHANNEL CLASSIFICATION

Artificial or Man-made Channels (e.g. swales)vs. Natural Channels (e.g. rivers)

River

Swale

Rigid Boundary Channels: Channels withOPEN CHANNEL CLASSIFICATION

Rigid Boundary Channels: Channels with immovable bed and sides (e.g. concrete drains)

Irrigation channel

Stormwater drain

Mobile Boundary Channels: ChannelOPEN CHANNEL CLASSIFICATION

Mobile Boundary Channels: Channel boundary is composed of loose sedimentary particles moving under the action of flowing water (e.g. rivers) Bed Erosiong

Bank Erosion

Deposition

Water Level and Flow DischargeWater Level and Flow Discharge

Water Level and Flow Discharge

• Open channel flows are found in large and small

Water Level and Flow Discharge

p gscale.

• For example the flow depth can vary between ayfew cm in water treatment plants and over 10 min large rivers.

• The mean velocity of flow may range from lessthan 0.01 m/s in tranquil waters to above 50 m/si hi h h d illin high-head spillways.

• The range of total discharges may extend from0 001 l/ i h i l l t t t th0.001 l/s in chemical plants to greater than10000 m3/s in large rivers or spillways.

Sungai Muda

Jambatan Ladang Victoria

Peak Flood Discharge - Sungai Muda’s 2003 Flood

2003 Hydrograph @ Ldg Victoria

(6 October 2003)

y g p @ g

1200

1300

1400

Q = 1340m3/s

800

900

1000

1100

m3 /s

)

500

600

700

800

Dis

char

ge, Q

(m

200

300

400

500D

0

100

0 1000 2000 3000 4000 5000 6000 7000 8000

HourHour

Jan Feb Mac Apr May Jun Jul Aug Sep Oct Nov Dec

Maximum Water Level (06.10.2003 @ 1600Hrs)

Flood plain

Flood plain

Main Channel Inundation depths in theMain Channel Inundation depths in the flood plains = 1 – 2 m

Flood Inundation AreasSungai Muda’s 2003 FloodSungai Muda’s 2003 Flood

Ladang Victoria Station

Sungai Pahang

Temerloh

Peak Flood Discharge - Sungai Pahang’s 2007 Flood

6000

2007 Hydrograph @ Temerloh

(14 December 2007)

5000

5500

6000

14/12/2007 (6.00 pm)(Q = 5397 55 m3/s)

3500

4000

4500

(m3 /s

)

(Q = 5397.55 m /s)

2000

2500

3000

Dis

char

ge, Q

(

1000

1500

2000

0

500

0 1000 2000 3000 4000 5000 6000 7000 8000

Hour

Jan Feb Mac Apr May Jun Jul Aug Sep Oct Nov Dec

2007 Sungai Pahang FloodEsplanade TemerlohEsplanade, Temerloh

20072007

2010

Sungai Pahang

Pekan

2007 Sungai Pahang Flood2007 Sungai Pahang Floodg gg g

2007 Sungai Pahang Flood2007 Sungai Pahang Flood2007 Sungai Pahang Flood2007 Sungai Pahang Flood

2007 Sungai Pahang Flood2007 Sungai Pahang Floodg gg g

UNIFORM AND VARIED FLOWS

Uniform flow: If the flow depth (and thus the average velocity) remains constantremains constant.Uniform flow conditions are commonly encountered in practice in long straight sections of channels with constant slope, constant roughness, and constant cross section.The flow depth in uniform flow is called the normal depth yn,

hi h i i t t h t i ti t f h lwhich is an important characteristic parameter for open-channel flows.

Non niform or Varied flo : The flo depth aries ith distanceNonuniform or Varied flow: The flow depth varies with distance in the flow direction.

FLOW CLASSIFICATION BY DEPTH VARIATION

Reservoir

GVF – Gradually Varying Flow Sungai KurauGVF Gradually Varying Flow

RVF – Rapidly Varying Flow

TYPICAL CROSS SECTIONS

Values showing isovelocity contours

Parameters for Open Channel FlowParameters for Open Channel FlowParameters for Open Channel FlowParameters for Open Channel Flow

V = Average Velocity y = Flow depth

S = Channel bed slope A = Flow area

P = Wetted Perimeter R = Hydraulic Radius

SIDE VIEW CROSS SECTION

Geometric Properties Necessary For Analysisp y y

FLOW CLASSIFICATION BY FROUDE NUMBER, Fr

For any type of channel :For any type of channel :

Fr = Q2 Bg A3

Fr <g A

1.0 Subcritical Flow

Fr =

Fr >

1.0 Critical Flow

1.0 Supercritical Flowr p

For rectangular channel : VFr = gyo

Velocity Distribution In A ChannelVelocity Distribution In A Channel

Depth-averaged velocity is aboveDepth averaged velocity is above the bed at about 0.4 times the depth

Flow Velocity MeasurementFlow Velocity Measurement

Current Meter & Data Logger

Electromagnetic Current Meter

Flow MeasurementFlow MeasurementSungai Kulim SerdangSungai Kulim SerdangSungai Kulim, SerdangSungai Kulim, Serdang

Velocity = 0.18 m/s

Water Surface Slope, SoWater Surface Slope, So

Electronic Digital Measurement (EDM)

Distance = 100 Distance = 100 –– 250 m250 m

COMPOUND CHANNEL

Flood plainFl d l i

pFlood plain

Main ChannelMain Channel

Natural river during “normal” flow conditions

COMPOUND CHANNEL

Natural river during flood! (Floodplain Inundation)

COMPOUND CHANNEL

Flood Plain Flood PlainMain Channel

A1, n1 A3, n3

P P

A2, n2

P1 P3

• The roughness of the flood plains will be different (generally rougher) than

P2

that of the main channel

Q = A1

n1R1

2/3 +A2

n2R2

2/3 +A3

n3R3

2/3 So 1/2

1 2 3

Determination of Bankfull Width for Natural River

Flow Rating Curve

ENERGY COMPONENTS

ENERGY GRADEhf2gV2

ENERGY GRADE LINE (EGL)

WATER SURFACEH

f

yo

2g

WATER SURFACE

CHANNEL BED

H1

H2

yo

CHANNEL BED

DATUMZ

H = + yo + 2gV2

Z

Velocity Head

Conservation of Energy : H1 = H2 + hf ; hf = Frictional loss

SPECIFIC ENERGY

Specific Energy, Es = the height of the energy line (EGL) above the channel bottom: V2

Es = Y0 + 2g

Critical flow occur at minimum energy, Es min

yc = Q2

2

1/3

=q2 1/3

yc gB2 = g

Flow Classification:

> V < V S bcritical (F < 1)yo > yc , V < Vc : Subcritical (Fr < 1)

y = y , V = V : Critical (F = 1)yo yc , V Vc : Critical (Fr 1)

yo < yc , V > Vc : Supercritical (Fr > 1)

Energ Dissipator H dra lic J mpEnergy Dissipator: Hydraulic Jump

Energy Dissipator: Hydraulic JumpEnergy Dissipator: Hydraulic Jump

Classification of Hydraulic Jumps

Undular Jump

W k JWeak Jump

Oscillating Jump

Steady Jump

St JStrong Jump

GVF: Energy Balance

Water Surface Curves for GVF

Water Surface Profiles

Flow Modelling

http://www.hec.usace.army.mil/software/hec-ras/p y

Existing Drainage System

Rigid Boundary ChannelRigid Boundary Channel

Rigid Boundary ChannelRigid Boundary Channel(D P i d)(D P i d)(Dry Period)(Dry Period)

Rigid Boundary ChannelRigid Boundary ChannelTrunk Drain During Dry Period

Rigid Boundary ChannelRigid Boundary ChannelWet PeriodWet Period

Rigid Boundary ChannelRigid Boundary ChannelTrunk Drain - Wet Period

Feasibility Study On Drainage Improvement in Prai Industrial Complex Seberang Perai Tengah PenangIndustrial Complex, Seberang Perai Tengah, Penang

Study Area

Existing Primary Drains

Pump

Legend:P i D i

Pump House A

PumpPrimary DrainExisting Pump StationRailway

Pump House B

Existing Trunk Drains

Legend:

Pump House A

Legend:Primary DrainExisting Pump StationRailway

Pump House B

Existing Trunk Drains

B-2EL-6B Rubber Pitching :Rubber Pitching :T Width 30’ 46’Top Width = 30’ - 46’

Depth = 5’ – 13’

T-6E Rectangular :Rectangular :Width = 5’ – 8’

Legend:

Pump House A Depth = 16’

Legend:Primary DrainExisting Pump StationRailway

Pump House B J-2A

Feasibility Study and Detail Design of Flood Mitigation and Drainage Improvement in Taman Sentul Tamanand Drainage Improvement in Taman Sentul, Taman Sentul Jaya, Taman Pinang & Taman Mangga, Juru,

S.P.T, Penang, g

Utara

Tol Juru

ra

Study Area

Lebuhraya Utara-Selatan

Taman Sentul Jaya Area

Parit

Kawasan Perusaha

an

JayaTama

n Sentul

TNo. 5

Perkampungan Juru

Ringan

Taman

M

Taman

Pinang

Mangga

Precast Concrete Drain900mm

Precast Concrete Drain1200mm

Precast Concrete Covered Drain

1200mm1200mm

Precast ConcreteConcrete

Drain3000mm3000mm

Feasibility Study of Flood Mitigation and Drainage Improvement in Kampung Tersusun Juru SeberangImprovement in Kampung Tersusun, Juru, Seberang

Perai Tengah, PenangStudy AreaStudy Area

Secondary Drain

Primary Drain Trunk Drain

Flow sequence from

Natural WaterwaySungai Juru

sequence from drain to river

Parit No. 5

Sediment Transport in RiversSediment Transport in Rivers

Point Bar

Bed form

Sg Jelai, Batu Kurau


Bed formBed form

Sediment Rating Curve for Dengkil Reach,Sediment Rating Curve for Dengkil Reach,Sungai LangatSungai Langat

100

Sungai LangatSungai Langat

For Q = 50 m3/s, Tj = 20 kg/s

10

T j(K

g/s)

1teria

l Loa

d, T

DengkilJ d

Tota

l Bed

Mat Jemderam

Jalan Tangkas

Kg Dusun Nanding

Jambatan Bt 14 Cheras

Jambatan Kg Rinching, Semenyih

0.11 10 100 1000

T

Discharge, Q (m3/s)g ( )

Sediment Transporting Capacity for a River

Sediment Rating Curves for Sungai Muda, Sediment Rating Curves for Sungai Muda, Sungai Kurau and Sungai LangatSungai Kurau and Sungai Langat

10000

Sungai Kurau and Sungai LangatSungai Kurau and Sungai Langat

1000

10000

/s)

100

Load

, Tj

(Kg/

1

10

Bed

Mat

eria

l L

0.1

Tota

l B

Sungai MudaSungai langatSungai Kurau

0.011 10 100 1000 10000

Discharge, Q (m3/s)

Comparison of Sediment Transporting Capacity Curves


Meandering River: Sg Pahang atTemerloh

M d i A RiMeandering Amazon River

Deposited Sands at Sg Pahang River MouthDeposited Sands at Sg Pahang River Mouth

Obstructed river mouthObstructed river mouth

Sg Pahang, Pekan

Sand Depositionp

Sand Dredging

Scour at Bridge Piers

Kuala Muda BridgeKuala Muda Bridge

Channel Design

Design Objectives

The hydraulic design of anh l i fopen channel consists of

determining the dimensions ofdetermining the dimensions ofa channel section to carry thedesign discharge under thecontrolling conditionscontrolling conditions

UNIFORM FLOWFlow in a channel is called uniform flow if the flow depth (and thus theaverage flow velocity remains constant. Uniform flow conditions arecommonly encountered in practice in long straight runs of channels withy p g gconstant slope, constant cross section, and constant surface lining.

yThe flow depth in uniform flow is called the normal depth yn, and theaverage flow velocity is called the uniform-flow velocity V0.

Computations In Uniform FlowComputations In Uniform Flow

Two calculations are usually performed to l if fl blsolve uniform flow problems:

- Discharge from a given depth

- Depth for a given discharge- Depth for a given discharge

Manning’s EquationManning’s EquationManning's formula is normally used for steadyuniform flow:

21

321 SRV 231 SRnV

M i ’ h ffi in = Manning’s roughness coefficient


• It is desirable to limit the design flow• It is desirable to limit the design flow Froude number (Fr) such that it is less h 0 86 h 1 13 dthan 0.86 or greater than 1.13 due to

the formation of the undular surface waves near critical depth (Fr = 1.0)


• Specification of freeboard is needed to• Specification of freeboard is needed to allow for uncertainties in estimation of h l h (M i ’ ) dchannel roughness (Manning’s n) due

to accumulation of debris and aquatic qgrowth in the channel.


Values of Freeboard for EngineeredValues of Freeboard for Engineered Waterway (Channel width > 1m):

Rectangular Channel = 0.3 - 0.6 m Trapezoidal Channel = 0 3 0 8 m Trapezoidal Channel = 0.3 – 0.8 m Earth Channel = 0.3 – 0.9 m

V l f F b d f ll d iValues of Freeboard for small open drain (Channel width ≤ 1m): 50 mm

MANUAL SALIRANMANUAL SALIRAN MESRA ALAM (MSMA)MESRA ALAM (MSMA) (JPS, 2000)( , )

Open Drains Volume 10 (Chapter 26)

Cross Section for Open Drain

0.5 m

Drainage Reserve

0.5 m Design flow width + freeboardgmin min

(a) Grassed Swale

Drainage Reserve

1.5 m minimum 1.0 m

Drainage Reserve

(b) Lined Open Drain

Manning’s Roughness Coefficient, nManning s Roughness Coefficient, n (Design Chart 26.1)

Surface Cover or Finish Suggested n values

Minimum Maximum

ConcreteConcrete

Trowelled finish 0.011 0.015

Off form finish 0.013 0.018Off form finish 0.013 0.018

Stone Pitching

Dressed stone in mortar 0 015 0 017Dressed stone in mortar 0.015 0.017

Random stones in mortar or rubble masonry 0.020 0.035

Rock Riprap 0.025 0.030

Brickwork 0 012 0 018Brickwork 0.012 0.018

Precast Masonry Blockwork 0.012 0.015

Solution to Manning Equation for Lined Open Drains

10

0.9

8

9

501 1

504

14

1

Swale reserve width, R (m)( including required freeboard )

y

0.8

0.7

5

6

7 Base width, B (m)

3

0.6

4

, QD

(m3 /s

)

Base width, B (m)

Flow depth, y (m)

1

2

Swale reserve width, R (m)( including required freeboard )

y

z1

z1

'Vee' shaped Section

3

4

5

1 2

0.5

3

Des

ign

Flow

,

Use 'vee' shaped section

0.5

Q n

S 01/

2

Z = 5.5

Z = 6

0.42

1.5 0.1

Valu

e of

Q S

Z = 5

Z = 4.5

Z = 4

1

1 5

0.3

2 3 41.5

0.05

Longitudinal Grade, S0 (%)

0.01

0.1 0.90.5

Flow Depth, y (m)

0.2 0.3 0.4 0.6 0.7 0.8

0.005

0.15

Lined Drains Volume 10 (Chapter 26.3)

Uncovered Open Lined DrainUncovered Open Lined Drain (Minor System – Chap. 26)( y p )

Drainage Reserve Width

B = 0.5 – 1.0 m 1.5 m minimum1.0 m

g

H max = 0.5 m50 mm

C d O Li d D iCovered Open Lined Drain (Minor System – Chap. 26)(Minor System Chap. 26)


B = 0.5 – 1.0 m 1.5 m minimum1.0 m

g

H = 0.5 m – 1.0 m

Cover 50 mm

V l it Li it tiVelocity Limitation (Minor System – Chap. 26.3.6)

T t di t ti d t ti th

(Minor System Chap. 26.3.6)

To prevent sedimentation and vegetative growth

Min Average Flow Velocity = 0 6 m/sMin Average Flow Velocity 0.6 m/s

To prevent Channel Surface ErosionTo prevent Channel Surface Erosion

Max Average Flow Velocity = 4.0 m/sMax Average Flow Velocity 4.0 m/s

Note: Average Flow Velocity > 2.0 m/s, drain provided with a handrail fence, or covered with solid or grated cover

Composite Drains Volume 10 (Chapter 26.4)

G d S ti

Recommended Composite Drain

C

Q50 mm freeboard

Grassed Section

14 i

Qminor

4 i1

4 min4 min

Lined drain

Design flow width + freeboard

Lined drain

Design flow width + freeboard

• Provided in locations subject to dry-weather base flows which wouldotherwise damage the invert of a grassed swale, or in areas with highlyerodible soils.

•The lined drain section is provided at the drain invert to carry dry-weatherbase flows and minor flows up to a recommended limit of 50% of the 1 monthARI.

Grassed Swale Volume 10 (Chapter 26.2)

Constructed Swale

gluttons

Filter layer

storagegeotextiile

drain

Bio-Ecological Drainage System(BIOECODS)

Perimeter SwalePerimeter Swale

Type Type AA

Type BType B Type CType C

Recommended Swale Cross-Sections

Freeboard (Mi S t Ch 26 2 4)(Minor System – Chap. 26.2.4)

Min freeboard of 50 mm above the design stormwater level

Velocity Limitation (Mi S Ch 26 2 5)(Minor System – Chap. 26.2.5)

Max Average Flow Velocity < 2.0 m/sg y

Manning’s Roughness Coefficient, n Design Chart 26.1

Surface Cover or Finish Suggested n valuesSurface Cover or Finish Suggested n values

Minimum Maximum

Grassed Swales

Short grass cover 0.030 0.035

Tall grass cover 0.035 0.050

Engineered WaterwaysVolume 11 (Chapter 28)

(Major System)(Major System)

Engineered WaterwaysEngineered Waterways


W VariesVaries

g

H300 mm

Minimum Longitudinal Slopeg p

0.2 % - Lined Channel0.5 % - Grassed floodways and natural waterway

To prevent sedimentation and vegetative growth

Min Velocity = 0.8 m/s

T t Ch l S f Li i E iTo prevent Channel Surface Lining Erosion

Max Velocity = 4 0 m/s (Li d Ch l / L fl i t)Max Velocity = 4.0 m/s (Lined Channel / Low flow invert)

= 2.0 m/s (Floodways and Natural Waterway)

Suggested Values of Manning’s Suggested Values of Manning’s Roughness Coefficient, Roughness Coefficient, nn

Surface CoverSuggested n values

Minimum Maximum

Grassed FloodwaysGrass cover only

Short grass 0.030 0.035Short 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


Surface Cover Suggested n values

Minimum Maximum

Natural Channels

S ll tSmall 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 080Light brush and trees 0.040 0.080

Medium to dense brush 0.070 0.160

Dense growth of trees 0.110 0.200


S f CSuggested n values

Surface CoverMinimum 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

T ll d 0 018 0 025Trowelled, 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 030Rock Riprap 0.025 0.030


Surface CoverSuggested n values

Minimum MaximumMinimum Maximum

RoadwaysKerb & Gutter 0.011 0.015

Hotmix Pavement

Smooth 0.012 0.014

Rough 0 015 0 017Rough 0.015 0.017

Flush Seal Pavement

7 mm stone 0.017 0.019

14 mm stone 0.020 0.024

I. Composite WaterwaysI. Composite Waterways(With Increased Capacity - Chap 28)

Estimate the Overall Roughness Coefficient

m An 3/5

Coefficient

m

i

i i

ii

*

AP

An

n3/5

13/2

/

(28.1)

i i

i

PA

13/2

where,n* = equivalent Manning’s roughness coefficient for the whole

cross-sectionni = Manning's roughness coefficient for segment iAi = flow area of segment i (m2)P = wetted perimeter of segment i (m)m = total number of segments

II. Natural WaterwaysII. Natural Waterways

Minimum Longitudinal Slope0.5 %

To prevent Channel Erosion

M V l i 2 0 /Max Velocity = 2.0 m/s

oror

Critical Velocity y

V l it Li it tiVelocity Limitation (Major System - Chap 28)(Major System Chap 28)

Minimum Longitudinal SlopeMinimum Longitudinal Slope0.5 %

To prevent Channel Erosion

M V l i 2 0 /Max Velocity = 2.0 m/s

oror

Critical Velocity y

Critical Velocities, (m/s) for various conduit materialsvarious conduit materials

III. Grassed FloodwaysIII. Grassed Floodways

6

1

6

1

C Low FlowProvision

6 61

50501

Batter BatterBase

Figure 28.3 Typical Grassed Floodway Cross-SectionC Terracing

Qmajor

Qminor

C Terracing

161

5050

BatterTerrace Base

Figure 28.4 Typical Grassed Floodway Terracing

Low Flow Provision:Low Flow Provision:Minimum capacity of 50% of the 1 month ARI flow.

1.2

1.3

Design ChartDesign Chart

1.1

1.0

0.9Design Chart Design Chart 28.228.2 0.8

7

Flow

, (m

3 /s)

5055

60

4045

1.4

1.5

1.6

0.7

Floodway Base Width –Preliminary Estimate(Manning's n = 0.035,

A i 2 / )

Des

ign

F

2025

3035

4

Average Velocity = 2 m/s)15

10

5

Flow Modelling

HEC-RAS Modellingg

Sungai Muda Model Set-up

Cross Section at CH 41.2 (Ladang Victoria)(Ladang Victoria)

Longitudinal Flood Profile for Sg Muda (Q=1340m3/s) (Q=1340m3/s)

dge

Mud

a B

arra

ge

Mer

deka

B

ridg

eE

xpre

ssw

ay

Bri

dge

Rai

lway

Bri

dge B

rid

Pipe

Bri

dge

M M B E B

What Is a Bund?What Is a Bund?• The U.S. Federal Emergency Management Agency (FEMA)

defines a bund or levee as a “man-made structure, usually anearthen embankment, designed and constructed in accordancewith sound engineering practices to contain, control, or divert theflow of water so as to provide protection from temporaryflooding.”

Determination of Bund Height from Inundation Depth

Flood plainFlood plain

Main ChannelMain Channel

BUND DESIGN AND CONSTRUCTION

Bund Height = 3 m (Freeboard = 1 m)

BUND CONSTRUCTION AT LAHAR TIANG 2B (HULU)

BUND CONSTRUCTION AT PANTAI KAMLOON 2B (HULU)

to acquire theory on open channel flow

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