L2-Open Channel Hydraulics.pdf

7/27/2019 L2-Open Channel Hydraulics.pdf

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EAD 511 RIVER MANAGEMENT

Open Channel Hydraulics


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Introduction

Type of flow Energy principles

Uniform flow

Flow modelingSediment transport

ContentsContents


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References


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


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Introduction


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9 Open channel flow is the flow of water in aconduit with a free surface at atmospheric pressure

9 The flow in an open channel is mainly governed

by gravity (i.e. channel bed slope)

DEFINITIONS

Menam Chao Praya, Bangkok Kulim River, Serdang


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9 Artificial or Man-made Channels (e.g. swales)

vs. Natural Channels (e.g. rivers)

OPEN CHANNEL CLASSIFICATION


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9Rigid Boundary Channels: Channels with

immovable bed and sides (e.g. concrete drains)



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9Mobile Boundary Channels: Channel boundary is

composed of loose sedimentary particles moving under

the action of flowing water (e.g. rivers)


Bank Erosion

Bed Erosion

Deposition


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Types of Flow


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GVF Gradually Varying Flow

RVF Rapidly Varying Flow

FLOW CLASSIFICATION BY DEPTH VARIATION

ReservoirIrrigationCan

al

Sungai Kurau


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FLOW CLASSIFICATION BY FROUDE NUMBER, Fr

For any type of channel :

Fr =

Fr

Q2 Bg A3

1.0 Subcritical Flow

1.0 Critical Flow

1.0 Supercritical Flow

For rectangular channel :Fr =

Vgyo

For design purpose, Fr< 1.0


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TYPICAL CROSS SECTIONS

Values showing isovelocity contours


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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


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Energy Principles


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ENERGY COMPONENTS

ENERGY GRADE

LINE (EGL)

WATER SURFACE

CHANNEL BED

DATUM

H1

H2

hf

yo

Z

2gV2

H = + yo

+2g

V2Z

Velocity Head

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


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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)


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GVF: Energy Balance


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Water Surface Curves for GVF


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Uniform Flow


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UNIFORM FLOW EQUATIONS

1) Manning : V = R2/3 So1/2

n1

Where n = Manning Coefficient

2) Chezy : V = C R So

Where C = Chzy Coefficient

3) Darcy Weisbach: V = 8g R Sof

Where f= Darcy Weisbach coefficient

C = =R1/6

n

8g

f


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Solution to Manning Equation for Lined Open Drains


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Suggested Values of ManningSuggested Values of Manningss

Roughness Coefficient,Roughness Coefficient,nn

Surface Cover

Suggested n values

Minimum Maximum

Grassed Floodways

Grass 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


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Critical Velocities, (m/s) forvarious conduit materials


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To prevent sedimentation and vegetative growth

Min 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 Channel

0.5 % - Grassed floodways and natural waterway


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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 So1/2


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Suggested Values of ManningSuggested Values of Manningss

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


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Flow Modelling

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


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HEC-RAS Modelling


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Cross Section at CH 41.2

(Ladang Victoria)


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Longitudinal Flood Profile for Sg Muda

(Q=1340m3/s)

MudaBarrage

Merdeka

Bridge

Exp

ressway

Bridge

Railway

Bridge B

ridge

Pipe

Bridge

Longitudinal Section for Sg. Muda Kedah (n = 0.025)


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n = 0.025

-10

-5

0

5

10

15

0 5 10 15 20 25 30 35 40

Chainage (km)

Elevation(m,

LSD)

Existing Bed Level Predicted Water Level (HEC-RAS) Observed


-10

-5

0

5

10

15

0 5 10 15 20 25 30 35 40

Chainage (km)

Elevation(m,

LSD)

Existing Bed Level Predicted Water Level (HEC-RAS) observed


n = 0.030

n = 0.035

-10

-5

0

5

10

15

0 5 10 15 20 25 30 35 40

Chainage (km)

Elevation(m,

LSD)

Existing Bed Level Predicted Water Level (HEC-RAS) observed


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Particle Size DistributionParticle Size Distribution


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Particle Size DistributionParticle Size Distribution

of River Bed Materialof 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 Purata

Saiz Partikel (mm)

Peratus Telus (%)

d90

d65

d10

d35

d50d60


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(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


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(b)(b) Bed Material :Bed Material :

Van Veen Sampler


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(c)(c) Bed Load :Bed Load :

Low Flow High Flow


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(d)(d) Suspended Load :Suspended Load :

Low Flow High Flow


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Suspended Load Sampling


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Suspended Load Sampling

@ Muda River

Ladang Victoria


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Sediment Databaseediment DatabasePari River @ ManjoiPari River @ Manjoi


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Channel cross sectionshannel 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)


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Observed FlowObserved Flow

ProfilesProfiles

Measured DataMeasured Data

flow profileslow profiles

Perbezaan Paras Air Sungai Pari

34.00

35.00

36.00

37.00

38.00

39.00

2000 2500 3000 3500 4000 4500 5000

Keratan Rentas, m

Pa

ras,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 Cera an Sun ai PariParas Air Cerapan


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Backwater DataBackwater Data

Hydrological dataydrological 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 50 100 150 200 250 300 350 400 450 500

Masa, jam

ParasAir,m

Puncak Hidrog raf Tahu n 2000 Sungai Pari

0

20

40

60

80

100

120

2390 2400 2410 2420 2430 2440 2450

M as a, jam

Kadaralir,m

3/s


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FluvialFluvial--12 Model12 Model

Predicted flow profilesredicted 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

34.50

35.00

35.50

36.00

36.50

37.00

37.5038.00

2000 2500 3000 3500 4000 4500 5000

Keratan Rentas, m

Paras,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

Paras,m

Paras air simulasi (FL-12) Paras air cerapan


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Cross section changesross section changes

Ch. 2475

Taman 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

Paras,m

P. Dasar Awal P. Air AwalP. Dasar Simulasi FL-12 P. Air Simulasi FL-12

P. Dasar Simulasi FL-14 P. Air Simulasi FL-14

35.00

36.00

37.0038.00

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


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Documents

L2-Open Channel Hydraulics.pdf