sediment transport in rivers

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EAH 225: HYDRAULICSSediment Transport in Rivers

ZORKEFLEE ABU HASAN

REDAC

CONTENTS • INTRODUCTION TO SEDIMENT TRANSPORT

• RIVER MORPHOLOGY AND QUALITATIVE

ANALYSIS

• SEDIMENT PROPERTIES

• INCIPIENT MOTION

• MODE OF TRANSPORT

• FLOW RESISTANCE

• BED LOAD

• TOTAL BED MATERIAL LOAD

• STABLE CHANNEL DESIGN

• REFERENCES

• ASSIGNMENTS

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1

EAH 225: HYDRAULICSSediment Transport in Rivers

ZORKEFLEE ABU HASANZORKEFLEE ABU HASAN

REDAC

INTRODUCTIONINTRODUCTION

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INTRODUCTIONINTRODUCTION

Fluvial sediment transport is the study of the interaction between channelized, unidirectional flows of relatively clear water and natural, generally non-cohesive, sediment.Sediment transport is an important in engineering b h l l k “hbecause it helps answer questions like “how can we keep sediment out of these turbines?”

INTRODUCTIONAN ALLUVIAL RIVER GENERALLY IS CONTINUALLY CHANGING ITS POSITION AND SHAPE AS A CONSEQUENCE OF HYDRAULIC FORCES ACTING ON ITS BED AND BANKS.THESE CHANGES MAY BE SLOW OR RAPID AND MAY RESULT FROM NATURAL AND MAY RESULT FROM NATURAL ENVIRONMENTAL CHANGES OR FROM CHANGES CUSED BY MAN’S ACTIVITIES

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INTRODUCTIONWHEN A RIVER CHANNEL IS MODIFIED LOCALLY, THE CHANGE FREQUENTLY CAUSES CHANGES IN CHANNEL CHARACTERISTICS BOTH UP AND DOWNSTREAMEXAMPLES OF HUMAN ACTIVITIES ARE CONSTRUCTION OF DAM AND RIVER STRAIGHTENINGSTRAIGHTENINGNATURAL CAUSES ARE EARTHQUAKES AND HEAVY RAINFALL

River System

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Figure 3.3 Typical Meandering River

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River Corridor

NATURAL RIVERSNATURAL RIVERS

Sungai Kampar @ Kg Jahang,

Gopeng

Sungai Ulu Paip, Kulim

Sungai Sedim, Kulim

Sungai Kulim, Kedah

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Nuki River (Kitakyushu City, Fukuoka Prefecture)

Example of River Rehabilitation in JapanExample of River Rehabilitation in Japan

Before construction( October 1991 )

23 months after construction (July 1995)Sediment was deposited on which vegetation grew,

Creating a natural water space. Immediately after construction

(August 1993)

Low Flow(22 Mei 2003)

Man made river at Kampus Kejuruteraan USMMan made river at Kampus Kejuruteraan USM

High Flow(19 Mei 2003)

(a) Completed works30 January 2003

(b) 4 months after construction

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River Equilibrium

SEDIMENT SEDIMENT TRANSPORT TRANSPORT CONCEPTCONCEPT

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MODE OF SEDIMENT TRANSPORT

WASH LOAD

BED

SUSPENDED LOAD

TOTAL LOAD

BED MATERIAL

BED MATERIAL

LOAD

TOTAL BED MATERIAL LOAD

Shields DiagramShields Diagram((Featherstone & Nalluri 1993Featherstone & Nalluri 1993))

No Sediment Transport

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Bed Form in Natural WaterwaysBed Form in Natural Waterways

RIVER WORKS RIVER WORKS DESIGNDESIGN

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21

321 SRV =

Manning’s n for River Design

SRnV

1.216/1

50dn= Uniform Sediment

(Cu = d60 / d10 ≤ 3)1.21

266/1

90dn= Non -Uniform Sediment

(Cu = d60 / d10 > 3)

Suggested Manning ‘s nSuggested Manning ‘s n

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River Reconstruction After 19River Reconstruction After 19thth

November 1997 Flood (Sungai Pari)November 1997 Flood (Sungai Pari)

Critical Shear StressCritical Shear Stress((Van Rijn, 1984Van Rijn, 1984))

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

Sediment Transport Sediment Transport EquationsEquations

Type of Equation Equation Data Rangeyp q q g

Bed Material Load

Shields 1.56 < d50(mm) < 2.47

Meyer-Peter-Muller 3.17 < d50(mm) < 28.6

Einstein – Brown ψ < 10

Einstein 0.785 < d50(mm) < 28.6

Graf 0 09 < d (mm) < 2 78

Total Bed Material Load

Graf 0.09 < d50(mm) < 2.78

Engelund & Hansen 0.19 < d50(mm) < 0.93

Yang0.137 < d50(mm) < 1.71yo(m) < 1.0 m

Ackers & White 0.04 < d50(mm) < 4.94

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River sediment River sediment River sediment River sediment data data

measurementmeasurementmeasurementmeasurement

Data MeasurementData Measurement(a)(a) Flow Discharge:Flow Discharge:

Current Meter Swoffer 2100 for wading Current Meter Model Neyrflux Type 80 for deep flow

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Data MeasurementData Measurement(b) Bed Material:

Van Veen Bed Material Sampler

Data MeasurementData Measurement(c) Bed load sampler:.

Low Flow High FlowHelley-Smith Bed Load Sampler

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Data MeasurementData Measurement(d) Suspended Load :

DH48 -Low Flow DH59 – High Flow

Data MeasurementData Measurement(d) Channel Slope:

(f) Water Temperature:

Survey Equipment

Thermometer

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Sediment Data MeasurementSediment Data Measurement

Data MeasurementSample Sediment Data

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Particle Size Distribution of River Bed Material

Stesen SP7 Sg. Pari

100 00Peratus Telus (%)

30 00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

d90

d65

d35

d50

d60

0.00

10.00

20.00

30.00

0.01 0.10 1.00 10.00 100.00

Sampel 1 Sampel 2 Sampel 3 PurataSaiz Partikel (mm)

d10

RELATIONSHIPS RELATIONSHIPS RELATIONSHIPS RELATIONSHIPS BETWEEN FLOW BETWEEN FLOW AND SEDIMENT AND SEDIMENT

LOADLOAD

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DATA ANALYSIS(a)(a) Relationship between flow discharge and total Relationship between flow discharge and total

sediment load discharge. sediment load discharge.

(b)(b) R l ti hi b t fl di h d t t l b dR l ti hi b t fl di h d t t l b d(b)(b) Relationship between flow discharge dan total bed Relationship between flow discharge dan total bed material load.material load.

(c)(c) Relationship between flow discharge and bed load Relationship between flow discharge and bed load discharge. discharge.

(d)(d) Relationship between flow parameter and transport Relationship between flow parameter and transport parameterparameterparameter.parameter.

(e)(e) Sediment Rating Curve for sediment size distribution.Sediment Rating Curve for sediment size distribution.

(f)(f) Assessment of common sediment transport Assessment of common sediment transport equations.equations.

(g)(g) River ModellingRiver Modelling

Relationship between flow discharge dan total sediment load Relationship between flow discharge dan total sediment load (T(Tjj))

DATA ANALYSISDATA ANALYSIS

100

10

0.1

1

0.1 1 10 100Q (m 3 /s)Sungai Pari @ Manjoi

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Flow Parameter (Flow Parameter (ψψ) and Transport Parameter () and Transport Parameter (φφ))


1000

0.1

1

10

100

Para

met

er A

liran

, ψ

φ=0.5(ψ)-2.52

φ=10.39(ψ)-2.52

0.001

0.01

0.001 0.01 0.1 1 10 100Parameter Pengangkutan, φ

Sg Pari @ Tmn Merdeka Sg Pari @ Manjoi Sg Pari @ BuntongSg Kinta Sg Raia @ Kg Tanjung Sg Raia @ Bt GajahSg Kampar @ KM 34 Sg Kerayong Sg KulimSg Langat @ Kajang Sg Langat @ Dengkil Sg Lui @ Kg LuiSg Semenyih @ Kg Sg Rinching Persamaan Graf (1968) Persamaan Modified Graf (4.4)

Sediment Rating Curve


4.00

5.00

6.00

g/s)

Sungai Pari @ Manjoi

0.00

1.00

2.00

3.00

9.00 14.00 19.00 24.00 29.00 34.00 39.00 44.00 49.00 54.00Q (m3/s)

T i (k

g

> 10.00 mm 5.30 mm - 10.0 mm 4.00 mm - 5.30 mm 3.35 mm - 4.00 mm2.00 mm - 3.35 mm 1.18 mm - 2.00 mm 0.71 mm - 1.18 mm 0.60 mm - 0.71 mm0.43 mm -0.60 mm 0.30 mm - 0.43 mm 0.15 mm - 0.30 mm 0.08 mm - 0.15 mm< 0.08 mm

0 60

0.700.80

Sungai Pari @ Buntong

0.000.100.20

0.300.400.500.60

9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00 17.00 18.00Q (m3/s)

T i (k

g/s)

> 10.00 mm 5.30 mm - 10.0 mm 4.00 mm - 5.30 mm 3.35 mm - 4.00 mm2.00 mm - 3.35 mm 1.18 mm - 2.00 mm 0.71 mm - 1.18 mm 0.60 mm - 0.71 mm0.43 mm -0.60 mm 0.30 mm - 0.43 mm 0.15 mm - 0.30 mm 0.08 mm - 0.15 mm< 0.08 mm

g @ g

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RIVER RIVER MODELLINGMODELLINGMODELLINGMODELLING

EXAMPLEEXAMPLE

FLUVIALFLUVIAL--1212

FLOW CHARTFLUVIAL-12

mula

data input

t = t + Δt

penghalaan air

tempohmasa telah diliputi?tidak

ya

tamatpenghalaan endapan

penyesuaian geometri saluran

tamat

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STUDY REACHSungai Pari

RIVER MODELLING

g

STUDY REACHSungai Pari

Permodelan SungaiPermodelan Sungai

Taman Merdeka, Ch. 2475 ( 21 Oktober 2002)Alor Limpah Batu, Ch. 1220 ( 25 Julai 2001)

Ch. 3020 ( 21 Oktober 2002) Jambatan Manjoi, Ch. 3380 ( 21 Oktober 2002)

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Tokong Buddha, Ch. 4160 ( 21 Oktober 2002)Ch. 3600 ( 21 Oktober 2002)

Jambatan Silibin, Ch. 4540 ( 21 Oktober 2002) Kuala Sungai Pari ( 22 July 2001 )

WATER LEVELWATER LEVELParas AirParas Air


Perbezaan Paras Air Sungai Pari

37 00

38.00

39.00

m

Paras Air Cerapan Sungai PariParas Air Cerapan

WATER LEVELWATER LEVEL

34.00

35.00

36.00

37.00

2000 2500 3000 3500 4000 4500 5000Keratan Rentas, m

Para

s,

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)

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RIVER MODELLINGRIVER MODELLING

HYDROGRAPHHYDROGRAPH

Puncak Hidrograf Tahun 2000 Sungai Par i

60

80

100

120

ir, m

3 /s

Profil Aliran Berhayun Sungai Pari

39.0

40.0

0

20

40

60

2390 2400 2410 2420 2430 2440 2450M as a, jam

Kada

rali

OSCILATING FLOW OSCILATING FLOW

33.0

34.0

35.0

36.0

37.0

38.0

0 50 100 150 200 250 300 350 400 450 500Masa, jam

Para

s Ai

r, m

RIVER MODELLINGRIVER MODELLINGSEDIMENT RATING CURVESEDIMENT RATING CURVE

0 10

0.15

0.20

0.25

apan

, Qs

(m3 /s

)

Taburan Purata Saiz Endapan Bahan

Dasar Untuk Sungai Pari

80 00

90.00

100.00

d50 = 1.80 mm

0.00

0.05

0.10

0.00 10.00 20.00 30.00 40.00 50.00Masa (jam)

Out

put E

nda

0.00

10.00

20.00

30.0040.00

50.00

60.0070.00

80.00

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

BED BED MATERIALMATERIAL RIVER BANK MATERIALRIVER BANK MATERIAL

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RIVER MODELLINGRIVER MODELLING

Flood Hydrograph

35.5036.0036.5037.0037.5038.00

Par

as, m

Profil Paras Air Sungai Pari Bagi Kadaralir Q=15 m3/s

Flood Hydrograph Year 200034.50

35.00

2000 2500 3000 3500 4000 4500 5000Keratan Rentas, m

Paras air simulasi (FL-12) Paras air cerapan

37 50

38.00

38.50

mSimulation Simulation FluvialFluvial--1212

Profil Paras Air Sungai Pari Bagi Kadaralir Q=48 m3/s

35.50

36.00

36.50

37.00

37.50

2000 2500 3000 3500 4000 4500 5000Keratan Rentas, m

Para

s, m

Paras air simulasi (FL-12) Paras air cerapan

River modellingRiver modellingPerbandingan Penyelakuan Perbandingan Penyelakuan

FLUVIALFLUVIAL--12 dan FLUVIAL12 dan FLUVIAL--14 14

Bagi Sungai PariBagi Sungai Pari

Hidrograf Tahun 2000

38.00

40.00

42.00

, m Bagi Sungai Pari Bagi Sungai Pari

Perbandingan Penyelakuan Paras Dasar dan Air Sungai Pari

( Waktu Puncak )

32.00

34.00

36.00

1000 1500 2000 2500 3000 3500 4000 4500 5000

Keratan Rentas, m

Para

s,

P Dasar Sim ulas i FL14 P. Dasar Sim ulas i FL12P Air Sim ulas i FL14 P. Air Sim ulas i FL12P. Dasar Mula

40 00

42.00

Perbandingan Penyelakuan Paras Dasar dan Air Sungai Pari

( Akhir Penyelakuan )

32.00

34.00

36.00

38.00

40.00

1000 1500 2000 2500 3000 3500 4000 4500 5000Keratan Rentas (m)

Para

s (m

)

P. Air FL-14 P. Air FL-12 P. Dasar FL-14P. Dasar FL-12 P. Air Pada Puncak

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River modellingRiver modelling

1 50

2.00

Hidrograf Puncak Tahun 2000Perbandingan Penyelakuan Perbandingan Penyelakuan



0.00

0.50

1.00

1.50

1000 1500 2000 2500 3000 3500 4000 4500 5000

Keratan Rentas, m

Hal

aju,

m/s

Halaju pd 2399 hr Halaju pd 2407 hr Halaju pd 2442 hr

1.00

Perbandingan Penyelakuan Halaju FLUVIAL-12

Bagi Sungai Pari Bagi Sungai Pari

0.00

0.20

0.40

0.60

0.80

1000 1500 2000 2500 3000 3500 4000 4500 5000Keratan Rentas, m

Hal

aju,

m/s

Halaju pd 2407 hr (Puncak) Halaju pd 2399 hr (Initial)Halaju pd 2444 hr (Akhir)Perbandingan Penyelakuan Halaju FLUVIAL-14


38.00

39.00

40.00

41.00

aras

, m

Perbandingan Penyelakuan Perbandingan Penyelakuan



Perbandingan Keratan Rentas Ch. 2475, Taman Merdeka

Hidrograf Tahun 2000 ( Waktu Puncak )

36.00

37.00

0.00 10.00 20.00 30.00 40.00 50.00Jarak Dari Tebing Kiri, m

Pa

P. Dasar Awal P. Air AwalP. Dasar Simulasi FL-12 P. Air Simulasi FL-12P. Dasar Simulasi FL-14 P. Air Simulasi FL-14

39 00

40.00

41.00


Perbandingan Keratan Rentas Ch. 3020


35.00

36.00

37.00

38.00

39.00


Par

as, m


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36 00

37.00

38.00

39.00

40.00

ras,

m

Perbandingan Penyelakuan Perbandingan Penyelakuan



Perbandingan Keratan Rentas Ch. 3380, Jambatan Manjoi


34.00

35.00

36.00


Pa


38 00

39.00

40.00

m


Perbandingan Keratan Rentas Ch. 3600


34.00

35.00

36.00

37.00

38.00


Para

s, m


USM_USM_REDAC_2003REDAC_2003

1

RIVER MORPHOLOGY ANDRIVER MORPHOLOGY AND QUALITATIVE ANALYSIS

1

ObjectivesStudents be able to

• understand basic concept of river morphology

• Predict qualitative response of river system

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2

Streamflow and Fluvial Processes (river morphology)

• Streams are powerful i ierosive agents moving

material from their bed and banks

• Streams also deposit vastamounts of sediment onthe terrestrial landscapethe terrestrial landscapeand within lakes andocean basins.

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The Long Profile of Streams

• At their headwaters: the grade is usually steep

• As streams get closer to sea level, the angle of the grade becomes more gently sloping.

• Near the mouth of the stream, the grade becomes almost flat.

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3

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Cross‐sections

• Stream channel near the h d theadwaters.

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4

Cross‐sections

• Stream channel near th iddl f t i lthe middle of a typical stream profile

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Cross‐sections

• Stream channel near the th f tmouth of a stream

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Historical problems

• Many channels are already clogged (due to erosion from previous generations)erosion from previous generations).

• Erosion control programs have reduced sediment loads to channels.

• Channels have been straightened.

• Riparian areas have been cleared.

• Roads and bridges constrain channels.

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Current problems

• Our channels are finding a new equilibrium.

• Some will get worse before they get better.

• Many are not stable.

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Reasons for instability

• Peak flows too high (urbanization)g ( )

• Sediment load too high (watershed sources)

• Removal of riparian vegetation

• Change of grade

S i h i f h l• Straightening of channels

• Widening of channels

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More reasons for channel instability

• Lack of flood plain

• Restriction of flow (bridge or culvert)

• Channelization

• Deposition in channel ‐ formation of point bars and islandsbars and islands

• Trash or debris

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STABILITY OF RIVER CHANNEL?

RIVER WILL BE IN THE STATE OF INEQUILBRIUM IFRIVER WILL BE IN THE STATE OF INEQUILBRIUM IF

THERE ARE CHANGES IN THE RIVER AND/OR ITS

SURROUNDINGS

THE RESULT: SCOUR AND DEPOSITION WHICH CHANGES THE CHARACTERISTIC OF THE RIVER.

EFFECT: LOSS OR GAIN OF LAND DUE TO NEWLY

FORMED MEANDERS, DAMAGE TO HYDRAULICS

STRUCTURES DUE TO SCOUR OR/AND DEPOSITION

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Effects of instability

• Head cutting

• Bank sloughing

• Meandering

• Formation of point bars and islands

• Braiding of stream• Braiding of stream

• Erosion of banks

• Loss of aquatic habitat17 of 53

EFFECTS OF SCOUR & DEPOSITION

EXAMPLES

• LOCALISED DAMAGE OF BANK PROTECTION

STRUCTURES

• SCOUR AT THE BRIDGE PIERS

• DEPOSITION AT THE CULVERTSDEPOSITION AT THE CULVERTS

• SCOUR UNDER THE HYDRAULICS STRUCTURES

• …...

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Head Cutting

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Grade change down stream and steep channel grade cause upstream migration of head cut.

Bars, Islands, and other obstructions

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Obstruction of the channel causes erosion of the banks.

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Definition of Stable Channel

• A stable channel carries all the water andsediment it receives without changingshape or pattern.

• This means:there should be neither erosion nordeposition.

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Transport capacity may be too high or too low

• Too high transport capacity–Channel too steep

–No flood plain

– Lack of riparian vegetation

• Too low transport capacity– Too much sediment load (from watershed)

–Obstructions in channel

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12

Channel must carry all the sediment and water completely through the

reach.

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Which channel is more efficient?

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“C” Channel “E” ChannelStraight Channel

13

The “C” Channel is most efficient

• “C” channel carries water and sediment most ffi i tlefficiently.

• Straight channel has no flood plain.– Deposition occurs under low flow.

– Erosion occurs under high flow.

• “E” channel has too tight curves• E channel has too tight curves.

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Sinuosity reduces grade.

100’

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Medium grade Steep grade Low grade

90’

14

Stream Bank Stabilization ‐ Armoring

• Armoring a stream bank is expensive.

• Armoring one place causes another to blow out.

• Armoring gives poor aesthetics.

• Armoring gives poor aquaticArmoring gives poor aquatic (and terrestrial) habitat.

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Stream Bank Stabilization ‐Bio‐Engineering

• protecting banks with vegetation– preferred if it will work

– may not stand the highest flows

– may be self‐healing

• may incorporate some structural support

• Less expensive than all structures

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Stream Restoration

• Re‐establish meander pattern

• Re‐establish profile

• Re‐establish riffle and pool structure

• Slope back high banks

• Establish bank egetation

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• Establish bank vegetation

• Establish riparian vegetation

How much is worth doing?

• Before investing large budget, determineif the stream is stable.– If not stable, will it recover by itself? or

– Is restoration needed?

• Riparian area value may be its own

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justification.

16

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QUALITATIVE RESPONSE OF RIVER SYSTEM

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Qualitative Response of River System

• Nearly all channels are formed, maintained, d lt d b t d di t thand altered by water and sediment they carry

• Channels are in equilibrium when hydraulics and sediment variables are in balance

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• Many rivers have achieved a state of approximate equilibrium throughout long reaches.

• Regardless of the degree of channel stability, man’s local activities may produce changes in river characteristics both locally and throughout an entire reach.

• All too frequently the net result of riverAll too frequently the net result of river improvement is a greater departure from equilibrium than that which originally prevail.

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An extreme example of habitat simplification. On theleft is the original urban stream in an Eastern Europeancity. Note the good riparian vegetation, and the variedwater velocities in the channel. On the right is thechannel after it has been ‘channelised’ for flood control.Note the simplification of the stream with uniform flow,and a single reed species at the water’s edge.

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• Good engineering design must invariably seek to h th t l t d f th tenhance the natural tendency of the stream

towards poised condition.

• Predicting the response to channel development is a very complex task.

• There are a large number of variables involved inThere are a large number of variables involved in the analysis.

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• Studies to investigate channel response to t l d i d h b L (1955)natural and imposed changes by Lane (1955),

Leopold and Maddock (1953), Schumm (1971), Santos and Simon (1972), Simon, Li and Associates (1982) support the following general relationship

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Depth of flow (y)Depth of flow (y) αα Water discharge (Q)Water discharge (Q)

Channel width (W)Channel width (W) αα Water discharge (Q) and Water discharge (Q) and Sediment Discharge (Qs)Sediment Discharge (Qs)

Channel shape, Channel shape, expressed as W/yexpressed as W/y

αα Sediment Discharge (Qs)Sediment Discharge (Qs)

Channel slope (S)Channel slope (S) 1/1/αα Water discharge (Q)Water discharge (Q)

Si it ( )Si it ( ) V ll lV ll lSinuosity (s)Sinuosity (s)[sinuosity: stream channel [sinuosity: stream channel length divided by length of length divided by length of meander belt axis or by meander belt axis or by valley length]valley length]

αα Valley slopeValley slope

1/1/αα Sediment Discharge (Qs)Sediment Discharge (Qs)

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Transport of bed Transport of bed material (Qs)material (Qs)

αα Stream Power (Stream Power (ττoV)V)

αα Concentration of fine materialConcentration of fine materialαα Concentration of fine material Concentration of fine material (C(Cf))

1/α1/α Bed material diameter (dBed material diameter (d5050))

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Adopted from Simon and Senturk (1992)

Application of Qualitative Analysis

• Geomorphic principles are useful for qualitative analysis of river response withoutqualitative analysis of river response without describing transient behaviour

• A well known geomorphic relationship proposed by Lane (1955), depicting concept of equilibrium

Q d QSQsd50 α QS• This principle as illustrated as a relationship of balance

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Application of QualitativeApplication of Qualitative Analysis

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Dam Construction

aggradation degradation

Aggradation (deposition) upstream of dam will reduce Qs downstream Assuming fallreduce Qs downstream. Assuming fall diameter and water discharge remain constant, slope must decrease downstream of dam

24

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Lowering of main river bedFrom QsdFrom Qsd5050 αα QSQS, , it it can be seen that the can be seen that the increase in slope Sincrease in slope Sincrease in slope S increase in slope S must be balance by must be balance by increase in sediment increase in sediment transport Qs. Thus transport Qs. Thus under the new under the new imposed condition, imposed condition, local gradient of the local gradient of the

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tributary stream tributary stream significantly significantly increased increased →→headcuttingheadcutting..

25

Channel Straightening

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Channel Straightening

• The initial shortening of channel increase its l d th t l it hi h islope and thus stream velocity, which increase the stream’s capacity to transport sediment

• Sedimentation occurs at the downstream end due to reduction of velocity

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Channel Widening

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Channel Widening

• The enlarged cross‐section at the upstream d f th id d h d b tend of the widened reached causes an abrupt

decrease in stream velocity → induces sedimentation in the reach with greatest deposition occuring near the upstream end.

• Gradually, the stream develops a narrow, y, p ,meandering channel through the deposits

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Channel Widening

• The enlarged cross‐section produces drawdown ff t hi h b i t th t d f theffect which begins at the upstream end of the widened reach and extend upstream.

• Resulting increased velocities cause erosion of the upsteam natural channel, and the erosion progresses upstreamp g p

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01‐Mar‐09

1

APPLICATION OF QUALITATIVE ANALYSIS

Extracted from:SEDIMENT TRANSPORT TECHNOLOGY, WATER AND SEDIMENT DYNAMICDaryl B.Simons and Fuat Senturk

1

SEDIMENT PROPERTIESSEDIMENT PROPERTIES

DIFFERENCES BETWEEN RIGID BOUNDARY DIFFERENCES BETWEEN RIGID BOUNDARY AND LOOSE BOUNDARIES FLOWAND LOOSE BOUNDARIES FLOW

RIGID BOUNDARY CHANNELRIGID BOUNDARY CHANNELNo movement at the boundaries of flow.No movement at the boundaries of flow.

LOOSE BOUNDARY CHANNELLOOSE BOUNDARY CHANNELThe sediment grains moves after a The sediment grains moves after a Threshold Condition [Incipient Motion].Threshold Condition [Incipient Motion].The sediment movement is influenced by The sediment movement is influenced by the hydraulic and sediment characteristics. the hydraulic and sediment characteristics.

2

DIFFERENCES BETWEEN RIGID BOUNDARY DIFFERENCES BETWEEN RIGID BOUNDARY AND LOOSE BOUNDARIES FLOWAND LOOSE BOUNDARIES FLOW

RIGID BOUNDARY CHANNELRIGID BOUNDARY CHANNELChannel boundary does not changeChannel boundary does not changeWetted perimeter is impermeableWetted perimeter is impermeable

LOOSE BOUNDARY CHANNELLOOSE BOUNDARY CHANNELChannel eometry changes Channel eometry changes Wetted perimeter is not impermeable. Wetted perimeter is not impermeable. Hence, the flow does not stop at the flow Hence, the flow does not stop at the flow boundaryboundary

Channel boundary Flow in loose boundary channel

goes beyond the boundary. Flow in loose boundary channel

goes beyond the boundary.

3

CHANNEL GEOMETRY CHANGES

4

Channel xChannel x--section chanes with channel section chanes with channel dischargesdischarges

P e r b a n d i n g a n B e n t u k K e r a t a nA n d a i a n P a r a s T i d a k B e r u b a h d i T i t i k 3 . 9

mm

0 . 3 0

0 . 4 0

0 . 5 0

0 . 6 0

0 . 7 0

as D

asar

[m]

Y q 1 . 5 9 Y q 0 . 6 0

Y q 0 . 5 1 Y q 0 . 3 0

0 . 0 0

0 . 1 0

0 . 2 0

0 2 4 6

L e b a r [ m ]

Ara

Sediment PropertiesSediment PropertiesTermsTerms Sign / Sign /

SymbolSymbolDesctiptionsDesctiptions UnitUnit

aa DensityDensity ρρ Mass per unit volumeMass per unit volume Kg/mKg/m33

bb Specific Specific weightweight

γγ = = ρgρg

Weight per unit volume. Where g is Weight per unit volume. Where g is the gravitional accelarationthe gravitional accelaration

Kg/mKg/m33,,N/mN/m33

cc Specific Specific gravitygravity

γγss//γγ Ratio of specific weight of a given Ratio of specific weight of a given material (material (γγss) to the specific weight of ) to the specific weight of

t (t ( ) t 4) t 4ooC A ifiC A ifiwater (water (γγ) at 4) at 4ooC. Average specific C. Average specific weight of sediment is 2.65weight of sediment is 2.65

dd Fall velocityFall velocity ωω The average terminal fall velocity of a The average terminal fall velocity of a particle falling alone in quiescent, particle falling alone in quiescent, distilled water of infinite extent.distilled water of infinite extent.

m/sec , cm/sm/sec , cm/s

ee Kinematic Kinematic ViscosityViscosity

υυ The ratio of dynamic of dynamic The ratio of dynamic of dynamic viscosity to mass densityviscosity to mass density

mm22/s/s

5

Water PropertiesWater Properties

Yang (1996)

19-Feb-09

1

Incipient motionIncipient motionConsider a plain stationary bed consisting of loosecohesionless (mobile) solid particles of uniform sizeflowing over it.As soon as liquid starts flowing, hydrodynamicforces are exerted upon the solid particles of thebed at the wetted perimeter of the conveyancesystem.A further increase in the flow in flow intensity causesan increase in the magnitude of these forces.For a particular stationary bed, a condition isFor a particular stationary bed, a condition iseventually reach at which particles in the movablebed are unable to resist the hydrodynamic forcesand, thus, get first dislodge and eventually stars tomove.

Graf (1984)

τo = ρgRSShear stress

τo < τc

CHANNEL BED

τc

Critical Shear stress

19-Feb-09

2

τo < τc

CHANNEL BED

Critical condition, or initial scour, or Critical condition, or initial scour, or incipient motion [threshold condition]incipient motion [threshold condition]

τo ≅τc

CHANNEL BED

19-Feb-09

3

Incipient motionIncipient motion

IncipientIncipient motionmotion cancan bebe determineddetermined bybyusingusing criticalcritical velocityvelocity andand Shield’sShield’sDiagramDiagram

Critical Velocity / Permissible VelocityCritical Velocity / Permissible Velocity

Defined as the maximum mean velocity of a channel that will not cause erosion of thechannel that will not cause erosion of the channel boundary [Chang, 1988]Hjulstrom and ASCE Studies: Hjulstorm prepare the curves based on the data of several investigators. ACSE Task Committee presented a graphical relationship showing the criticala graphical relationship showing the critical water velocities fro quartz sediment as a function of mean grain size.

19-Feb-09

4



19-Feb-09

5



Frontier and Scobey’s Study (1926): They d t i fi ld fmade an extensive field survey of

maximum permissible value of mean velocities in canal.The permissible velocities for canals of different materials are as summerizeddifferent materials are as summerized

19-Feb-09

6

ShieldsShields DiagramDiagramShields introduce the concept of the dimensionless entrainment function

as function of shear Reynold number υ/dU=R

[nalluri, pg353]

Reynold number υ/dU** =eR

19-Feb-09

7

ShieldsShields DiagramDiagramImportant factors areshear stress τ, sediment dU( / ) /τ ρ 1 2shear stress τ, sedimentdiameter d, kinematicviscosity ν, density ρ, andaccelaration due togravity g. These factorsare group into twodimensionless functions:

ddUc f( / ) *τ ρ

ν ν=

τρ ρ

τγ ρ ρ

c

s f

c

s fd g d( ) [( / ) ]−=

− 1

dimensionless functions:

ρs and ρf sediment density and fluid density, γ specificweight of water, U* shear velocity [√(τo/ρ)] , and τccritical shear stress.

ShieldsShields DiagramDiagramWhen flow is fully turbulent around the bed material (Re* > 400 and d > ≈ 4 mm ) the ( e )Shield criterion can be written as

19-Feb-09

8

ShieldsShields DiagramDiagramRelationship between these parameters is derived from researches by Shields and other yresearchers:

Example of Application : determine armour size to p ppprotect river bank and bed erosion

Shields DiagramShields DiagramThe Shields diagram contains the critical value for τ*c as an implicit th t t b bt i d di tl T

2/1

110 ⎥⎤

⎢⎡

⎟⎟⎞

⎜⎜⎛

− gdd sγthat cannot be obtained directly. To overcome this difficulty, the ASCE Sediment Manual (1975) utilize a third dimensionless parameterWhich appears as a family of parallel lines in the diagram From the value of the third parameter the

11.0 ⎥⎦

⎢⎣

⎟⎟⎠

⎜⎜⎝

− gdv γ

Chang [pg83]:

diagram. From the value of the third parameter, the value of critical Shields stress is obtained at the intersection with the Shields curve which can be calculated.

19-Feb-09

9

Shields DiagramShields Diagram

Shields DiagramShields Diagram

19-Feb-09

10

Computation Computation ExampleExample

A wide channel having a slope of 0.001 d fl i t 0 3 d th E i thand flowing at 0.3 m depth. Examine the

stability of the bed material if the mean diameter is 1.0 mm.

Computation ExampleComputation Example

19-Feb-09

1

Mode of TransportMode of TransportWhen the flow characteristics (velocity, average shear stress etc.) in an alluvial channel exceed )the threshold condition for the bed material the particles moves in different modes along the flow direction. Some particle roll or slide along the bed inermittently and some others saltate (hopping and bouncing along the bed). Fi ti l ( ith l f ll l iti )Finer particles (with low fall velocities) are entrained in suspension by the fluid turbulence and transported along the channel in suspension.

[nalluri, pg357]

transport determinantstransport determinants

particle sizeparticle shapeparticle specific gravityvelocitysediment dischargeg

19-Feb-09

2

Mode of Sediment TransportMode of Sediment Transport

There are two common classifications of th l d i th t [ h 131]the load in the stream [chang, pg 131] First: divide the load into bed load and suspended loadSecond: separates the load into bed material load and wash loadmaterial load and wash load

bedloadbedload

“sediment that moves by sliding, rolling, or saltating (bouncing) on or very near the bed.”

Leopold et al (1992) – Fluvial Processes in GeomorphologyLeopold et al (1992) – Fluvial Processes in Geomorphology

19-Feb-09

3

types of suspended loadtypes of suspended loadsuspended load –

wash load “sediment load of a stream whichwash load – sediment load of a stream which is composed of particles sizes smaller than those found in appreciable quantities in the shifting portions of the stream bed” – TOO SMALL TO DEPOSITsuspended load – “particles which are moved b d d d i th t l b tby and suspended in the water column, but can settle in locations where the travel velocity is low or settling depth is small.” CAN DEPOSIT UNDER SOME CONDITIONS.

Garde and Raju (2000) – Mechanics of Sediment Transport and Alluvial Stream Problems.Garde and Raju (2000) – Mechanics of Sediment Transport and Alluvial Stream Problems.

washloadwashload

generated from caving of streambanks of a tributary and washes through a reach withouttributary and washes through a reach without appreciable deposition.simplification - these particles pass through the river system relatively unrelated to the hydraulic condition in a given reach – the wash load is independent of the discharge; i t d d d i / il bilit finstead, depends on erosion/availability of fine materials from upstream.Einstein recommended that washload include the particle size for which 10 % of the bed material is finer. (Einstein H.A. 1950)

19-Feb-09

4

Federal Interagency Stream Restoration Working Group (FISRWG). (1998).

(ASCE, 1997)

19-Feb-09

5


WASH LOAD

BED LOAD

SUSPENDED LOAD

TOTAL LOAD

BED MATERIAL

BED LOAD


(Nalluri & Featherstone, 2001)

19-Feb-09

6

Classification of alluvial channels. Schumm’s classification system relates channel stability to kind of sediment load and channel type.[Figure 7.10, (FISRWG,1998).

1

SEDIMENT TRANSPORTSEDIMENT TRANSPORT

FLOW RESISTANCEFLOW RESISTANCE

11

RESISTANCE OF FLOW IN RESISTANCE OF FLOW IN ALLUVIAL CHANNELALLUVIAL CHANNEL

Resistance of an alluvial channel varies considerably with flow velocitiesconsiderably with flow velocitiesThe bed forms are flow induced and directly affect the roughness or flow resistanceVariation of bed form roughness has i t t ff t th t di h

22

important effects on the stage-discharge relationship during the passage of flood in the short term.

2


Stage-discharge predictor is a flow-resistance relationship used to determineresistance relationship used to determine the depth or hydraulic radius of flow for a given discharge, channel shape, channel slope, bed material properties, and temperatureThe relationship between mean velocity (V) the depth (y ) or hydraulic radius (R)

33

(V), the depth (yo) or hydraulic radius (R), slope (S) and sediment size (d), can be divided into 2 categories

a) Total Resistance approachb) Grain and form resistance approach


Total Resistance approachLacey Equation (Lacey, 1930)One of the earliest resistance relationship for alluvial channel flow based on the regime canal data from India

44

India.

V = 10.8 R2/3 So1/3 (SI unit)

3


Total Resistance approachJ E ti (S i 1974)2) Japanese Equation (Sugio, 1974)The equation developed using data from Japan.

V = K R0.54 So0.27 (SI unit)

K values for different bed form are

55

K values for different bed form areK = 6.51 for rippleK = 9.64 for dunesK = 11.28 for transition regime

66Bed forms of sand bed channels (Simons and Richardson, 1966) [source Yang, 1996)

4


Total Resistance approachG d R R j (1966)3) Garde – Ranga Raju (1966)Garde and Ranga Raju analysed data from flume, canals and natural streams.A graphical relationship between parameter

77

K1 V/√(ΔgR) versus K2(R/d)1/3S/ΔK1 and K2 are functions of sediment size

Total Resistance approach

3) Garde – Ranga Raju (1966)j ( )

KK11 V/V/√√((ΔΔgRgR) versus K) versus K22(R/d)(R/d)1/31/3S/S/Δ Δ [Fig 14.2, Featherstone and [Fig 14.2, Featherstone and NalluriNalluri, 1995], 1995]

88

[Fig 14.3, Featherstone and Nalluri, [Fig 14.3, Featherstone and Nalluri, 1995]1995]

5


Grain and form resistance approachThi ti i t d th t fThis equation introduces the concept of splitting the overall resistance into grain resistance and form resistanceGrain resistance: resistence contributed by the surface drag (tangential force)

99

Form resistance: cause by pressure different between the front and back surfaces of the bed form

(Chang, 1988)

1010Bed forms of sand bed channels (Simons and Richardson, 1966) [source Yang, 1996)

6

Grain and form resistance approachThe divided resistence approach can be expressed in terms of the energy gradient asas

S = S’ + S”or for hydraulic radius

R = R’ + R”Th th d f t

1111

There are many methods for stage-dischare prediction. Only Einstein and Barbarossa (1952) is explained

Grain and form resistance approachEinstein and Barbarossa’s Method (1952)Under fully rough condition, R’ is obtained ffrom

V = average flow velocity

1212

U*’ = √(gR’So ) [U*’ = Shear velocity related to grain size]

7

Grain and form resistance approachEinstein and Barbarossa’s Method (1952)For cases where grain roughness does not produce fully rough condition, R’ is computed from Manning equationcomputed from Manning equation

The form roughness is assumed to be related to

1313

the sediment transport rate along the channel bed because flow resisance due to bed forms is a function of flow to which the sediment rate may be related

Cont…

Einstein and Barbarossa’s Method (1952)…contA functional relationship suggested for the lower flow regimeg

1414

The functional relationship between V/U*” was determined from field data as shown in next slide

8

Einstein and Barbarossa’s Method (1952)Einstein and Barbarossa’s Method (1952)

1515

Yang, 1996)

Sample CalculationSample Calculation

16160.56 m

9


1717


1818

10

Sample Calculation Sample Calculation [E[E--B: Yang, pg 73]B: Yang, pg 73]

1919


2020

11


2121

2222

12

2323

2424

13

2525

2626

1

SEDIMENT TRANSPORTSEDIMENT TRANSPORTSEDIMENT TRANSPORTSEDIMENT TRANSPORTBED LOADBED LOAD


11


WASH LOAD

BED LOAD

SUSPENDED LOAD

TOTAL LOAD

BED MATERIAL

BED LOAD


2

SEDIMENT TRANSPORTSEDIMENT TRANSPORTBEDLOADBEDLOAD

Several empirical equations from laboratory have been proposed with basic assumptionshave been proposed with basic assumptions that the sediment is homogenous and non cohesive.The results differ appreciably and it is dangerous to transfer the information to outside the limit of the experiment

33

outside the limit of the experiment.The following are the most commonly used equations


a1. Shields Equation (1936):q = bed load per unit widthqb = bed load per unit widthq = unit discharge in channelΔ = (γs/γ) – 1τo = ρgRSoτc = from Shields Diagram

44

[ranges 0.06 < Δ < 3.2; 1.56mm < d50 < 2.47 mm]

3

SEDIMENT TRANSPORT BEDLOADSEDIMENT TRANSPORT BEDLOAD

a2.Shields EquationCritical Shear Stress [Van Rijn 1984]

Category Dgr τc/(ρgΔd50) Category

1 Dgr <4 0.24xDgr-1.0 1

2 4< Dgr <10 0.14xDgr-0.64 2

3/1

250

1

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−

=ν

γγ gs

dDgr

55

3 10< Dgr <20 0.04xDgr-0.1 3

4 20< Dgr <150 0.013xDgr0.29 4

5 Dgr >150 0.059 5


b.b. MeyerMeyer--PeterPeter--Muller Equation (1948) [MPM]:Muller Equation (1948) [MPM]:

66

4


c. Einstein’s Equation/Approach:Einstein introduce probability concepts of sediment ste t oduce p obab ty co cepts o sed e tmovement and developed an emphirical relationship

φ = f(ψ)The relationship is expressed in the plot of φ versus ψfunctions Einstein defined the transport function as

⎤⎡

77

( ) ⎥⎦

⎤⎢⎣

⎡−

=Φ 3ss

bw

dγγgγ

γq

qbw = bed load discharge by weight per unit channel width

Relationship between Relationship between φφ versusversus ψψ for Einstein bed load for Einstein bed load functions functions

88

[Yang, [Yang, 1996]1996]

5


d. Einstein - Brown Equation;B (1950) d l d b d l d t tBrown (1950) developed a bed-load transport function based on Einstein’s (1942) equation:

3140 ⎟⎠⎞

⎜⎝⎛Ψ

=Φ

99

For ψ < 10, The relationship is expressed in the plot of φ versus functions

Relationship between Relationship between φφ = f(1/= f(1/ψψ) for ) for EinsteinEinstein--Brown equationBrown equation

1010Yang, 1996Yang, 1996

6

DISCREPANCY RATIODISCREPANCY RATIO

Discrepancy Ratio is one of the methods to l t th it bl di t t tselect the suitable sediment transport

equation for a particular river reach.DISCREPANCY RATIO (DR) is the ratio between computed sediment load against measured load. Acceptable range is:measured load. Acceptable range is:

½ ≤ DR ≤ 2

1111

Sample ComputationSample ComputationFlow Discharge, Q = 0.6 m3/sFlow velocity, V = 0.42 m/sy,Surface width, B = 5.70 mFlow Area, A = 1.43 m2

Hydraulic radius, R = 0.24 m2

Bed Gradient, So = 0.001

1212

Water Temperature, T = 25 oCBed load, Qb = 9.48 x 10-6 m3/sSuspended load, Qs = 9.60 x 10-6 m3/sMean diameter, d50 = 1.1 mm

7

Sample ComputationSample ComputationAssumptions

Sediment specific gravity γs = 2 65Sediment specific gravity, γs = 2.65

Water specific gravity, γ = 1.0Water Density ρ = 1000 kg/m3

Gravity g = 9.81 m/s2

Kinematic viscosity ν = 1 x 10-6 m2/s

1313

Kinematic viscosity ν 1 x 10 m /s

DISCREPANCY RATIO (DR)½ ≤ DR ≤ 2

Transport Parameter,

Sample Sample Computation: Computation: EinsteinEinstein--Brown EquationBrown Equation

3140 ⎟⎠⎞

⎜⎝⎛Ψ

=Φ

Flow Parameter,

⎠⎝ Ψ

Volumetric concentration, Cv = Qb/Q

1414

8

Sample Computation: Sample Computation: EinsteinEinstein--Brown EquationBrown Equation

1515

Sample Computation: Sample Computation: Shield EquationShield Equation

1616

9

Sample Computation: Sample Computation: Shield EquationShield Equation

1717

Sample Computation: Sample Computation: Meyer Meyer -- Peter Peter -- MullerMuller

1818

1

EAH 225: HYDRAULICS EAH 225: HYDRAULICS (2008/09)(2008/09)(2008/09)(2008/09)

SEDIMENT TRANSPORTSEDIMENT TRANSPORTTOTAL BED MATERIAL LOADTOTAL BED MATERIAL LOAD

11


TOTAL BED MATERIAL LOADTOTAL BED MATERIAL LOAD

Based on the mode of transport, total load i th f b d l d d d dis the sum of bed-load and suspended load.The following approaches describe some of the available direct methods of estimating total bed material load

22

estimating total bed material load

2


a.a. Graf’s EquationGraf’s Equations d1γ

⎟⎟⎞

⎜⎜⎛

( ) 52.239.10 −Ψ=Φ o

50s

RS

d1γγ

⎟⎟⎠

⎜⎜⎝

−=Ψ

vVRCΦ

33Range: 10-2 < φ <103

350

s

v

d1γγ

g ⎟⎟⎠

⎞⎜⎜⎝

⎛−

=Φ


b.b. Ackers Ackers -- White EquationWhite Equation n10.1

gr dR11.3A

⎥⎥⎤

⎢⎢⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛−

( )/m1v

50s

JC1K

d1γγg

V+=

⎟⎟⎠

⎞⎜⎜⎝

⎛−

2n/s

50g

8λ

dK

⎟⎠⎞

⎜⎝⎛

⎥⎦⎢⎣⎟⎠

⎜⎝

=

/m12n/

s

n1gr λAR ⎥

⎤⎢⎡

⎟⎞

⎜⎛

⎟⎟⎞

⎜⎜⎛⎟⎟⎞

⎜⎜⎛

−

44

50

C8BRd

J

⎥⎥⎥⎥⎥

⎦⎢⎢⎢⎢⎢

⎣

⎟⎠

⎜⎝⎟⎟

⎠⎜⎜⎝⎟⎟⎠

⎜⎜⎝=

2VgRSo8λs =

3


b.b. Ackers Ackers -- White EquationWhite Equation (…cont)(…cont)3/1

s 1γγg

dD ⎥⎥⎤

⎢⎢⎡

⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

ν = kinematic velocity

Coefficient Fine Transitional Coarse

Dgr <1.0 1.0 < Dgr ≤ 60 Dgr > 60

n 1 0 n = 1 00 0 56 log D 0 00

250gr dD

⎥⎥⎥

⎦⎢⎢⎢

⎣

=ν

55Range: 0.04 <d (mm) < 4.0 ; Fr ≤ 0.8

n 1.0 n = 1.00 – 0.56 log Dgr 0.00

Agr − Agr = 0.14 + 0.23/ √( Dgr ) 0.17

m − m = 1.34 + 9.66/ Dgr 1.50

C log C = 2.86 log Dgr - (log Dgr)2 -3.53 0.025

Source: Pg.155, Yang, 1996


c.c. Yang’s EquationYang’s Equation

S

S

WW *50

TUlog0.457

νdlog0.2865.435logC −−=

⎞⎛⎞⎛⎟⎟⎠

⎞⎜⎜⎝

⎛−⎟⎟

⎠

⎞⎜⎜⎝

⎛−−+

SSS

S

WWWW oc*50 SVVSlogUlog0.314

νdlog0.4091.799

0.660.06

νdUlog

2.5V50*

c +−⎟

⎠⎞

⎜⎝⎛

=SW

70νdU

1.2 50* <<for

V dUf

66

05.2Vc =SW ν

dU70 50*≤for

where ( ) ( )

γγ

ppmCppmCs

Tv =

4

77

Sample ComputationSample Computation

88

5


99

ANSWERANSWERYANG EQUATIONYANG EQUATION

1010

6


0.660 06dUlog

2.5V50*

c +−⎟

⎞⎜⎛

=SW 0.06

νlog ⎟

⎠⎜⎝

1111

1212

7


1313

ANSWERANSWERACKERSACKERS--WHITE EQUATIONWHITE EQUATION

1414

8


1515


1616

9


1717

ANSWERANSWERGRAF EQUATIONGRAF EQUATION

1818

1

STABLE CHANNELSTABLE CHANNELSTABLE CHANNEL STABLE CHANNEL DESIGNDESIGN


11

Application of Beginning of Motion Application of Beginning of Motion to Practical Problemsto Practical Problems

The initiation of motion is involved in many The initiation of motion is involved in many hydrauics problem such as local scour slopehydrauics problem such as local scour slopehydrauics problem such as local scour, slope hydrauics problem such as local scour, slope stability, stable channel design, etc.stability, stable channel design, etc.The design of stable channels is very important.The design of stable channels is very important.Incipient motion criteria presented earlier Incipient motion criteria presented earlier (Incipient Motion) apply to the channel bottom. (Incipient Motion) apply to the channel bottom. Certain modifications of incipient motion criteriaCertain modifications of incipient motion criteriaCertain modifications of incipient motion criteria Certain modifications of incipient motion criteria are needed before they can be applied to stable are needed before they can be applied to stable channel design.channel design.

22

2

Stability of a particle on a sloping surface

Source: Chang,

33

1988

Stability of a particle on a sloping surfaceStability of a particle on a sloping surface

For particle on a side slope, there is a gravitional forcegravitional force component acting parallel to the slope which tends to roll the particle down.Forces acting on a Lane (1953) developed

t bl h l d iForces acting on a particle at point A;FD → tractive forceW → submerged weight

44

stable channel design curve for trapezoids with different typical slope.[Fig 2.14, Yang (1996)]

3


Source: Yang, 1996

55


Figure 2.14 (Yang, 1996) are based on maximum allowable tractive forceFig 2.14a: for the channel sidesFig 2.14b: for the channel bottomFig 2.14 indicates that h t tshear stress at:

channel bottom = γd50Schannel slope = 0.75 γd50S

66Source: Yang, 1996

4


The shear stress on channel side at incipient motion

2/1

2

2

sw tanθtan1tancosθWτ ⎟⎟⎠

⎞⎜⎜⎝

⎛−=

φφ

incipient motion

φtanWτ sb =At channel bottom, θ = 0,

Ratio of limiting forces acting on the channel side and channel bottom

77

φφ 2

22/1

2

2

b

w

sinθsin1

tanθtan1cos θ

ττK −=⎟⎟

⎠

⎞⎜⎜⎝

⎛−==


Value of τb can be obtained from Shield Diagram or US Bureau

f R l tiof Reclamationφ - Angle of repose as Fig 2.13, Yang (1996)Value K can be estimated from Fig 5.7, Chang (1988)

88

Chang (1988)

Source: Yang, 1996

5


99

Source: Chang, 1988


1010

6

1111

1212

7

1313

1414

8

1515

REFERENCES

1. CIVIL ENGINEERING HYDRAULICS, C. NALLURI AND R.E. FEATHERSTONE

2. SEDIMENT TRANSPORT TECHNOLOGY, WATER AND SEDIMENT

DYNAMICS, DARYL B. SIMONS AND FUAT SENTURK

3. FLUVIAL PROCESSES IN RIVER ENGINEERING, HOWARD H. CHANG

4. SEDIMENT TRANSPORT, THEORY AND PRACTICE, CHIH TED YANG

5. KAJIAN PENGUMPULAN DATA DAN ANALISIS ENDAPAN SUNGAI,

LAPORAN AKHIR, REDAC

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