CHAPTER I

INTRODUCTION

1.1 Issue Background

The windings of rivers have long fascinated their human observers. For

example, Aboriginal legend explains the sinuous pattern of the modern Finke as the

creation of the immense and powerful Rainbow Serpentasheemerged

duringtheDreamtime from deep waterholes. Recently in PNAS, a new theory for the

general origin of such sinuous flow patterns was published, which follows from a long

tradition in seeking a scientific explanation for the winding patterns of rivers.

1.2 Problem Identification

1.2.1 Definition of The Sinuous Channel Pattern

1.2.2 Formula of The Sinuous Channel Pattern

1.2.3 Planform of The Sinuous Channel Pattern

1.2.4 Problem of The Sinuous Channel Pattern

1.2.5 Solution of The Sinuous Channel Pattern Problem

1.3 Purpose Identificatiom

1.3.1 To know definition of The Sinuous Channel Pattern

1.3.2 To konow formula of The Sinuous Channel Pattern

1.3.3 To know planform of The Sinuous Channel Pattern

1.3.4 To know problem of The Sinuous Channel Pattern

1.3.5 To know solution of The Sinuous Channel Pattern Problem

CHAPTER II

DISCUSSION

2.1 Definition and Theory of Sinuous Channel Pattern

As described in the classic 1955 book, An Introduction to Fluvial Hydraulics

by Serge Leliavsky (1891–1963), two general schools of practical engineering

research developed in regard to alluvial rivers. One school was empirical, using

quantitative measures of river properties. For example, an observation that da Vinci

had ade qualitatively was quantified in the 19th century: there is a regular downstream

decrease in the size of sedimentary particles on a streambed that closely follows the

downstream decrease in the slope of that stream. This relationship, known as

“Sternberg’s Law”, was used by Armin Schoklitsch (1888–1969) to infer an

explanation for river sinuosity.

Presuming from this “law” that a river’s slope must be adjusted to the

diameter of sediment transported, Schoklitsch reasoned that, if this slope of transport

is less than the average surface slope of the plain into which the river channel is

incised [i.e., the slope S used in Lazarus and Constantine’s theory], then it will be

necessary for the river to assume a winding path to make its channel slope equal to the

slope that is appropriate for the transported sediment size. Because the channel slope

is the ratio of vertical fall to the distance measured along the winding path of the

channel, dividing this number into the valley or surface slope, S, which is ratio of the

same vertical fall to the direct path down that valley, will yield a ratio of the distance

measured along the winding path of the channel to the distance along the more direct

path down the valley, which is by definition the sinuosity of the river.

Thus, like Lazarus and Constantine’s theory, the Schoklitsch theory places

emphasis on sinuosity in relation to surface slope, but unlike Lazarus and

Constantine’s theory, it does so in relation to the sediment size that the forces of the

river are transporting instead of the land-surface roughness R thatis opposing those

forces.The Schoklitsch explanation for meanderingaccords with the observation that

meandering generally takes place in the lower courses of rivers, where sediments are

relatively fine-grained and the corresponding slopes are relatively flat. However, as

noted by Leliavsky , the theory is not very useful to hydraulic engineers who need a

rational, mechanical formulation of the problem, which is the motivation for the

second school of alluvial river engineering.

Fig 1. Sinious Channel Pattern

2.2 Formula of The Sinuous Channel Pattern

Lazarus and Constantine’s theoryemploys a model of cellular topographyin

which flow finds a path of least resistanceacross a planar domain with a given slope

S.Furthermore, 40,000 model simulations revealthat, when the resistance R exceeds

S,both channel sinuosity and its variance increasewith increasing R/S. An

independent,corroborating test of this relationship isachieved by recognizing that R/S

can bethought of as a kind of Froude number,which is defined for channelized flows

asthe ratio of the mean flow velocity to a gravitationalwave velocity (square root of

flowdepth multiplied by gravitational acceleration).By substituting into this

expression thewell-known Gauckler–Manning formula thatrelatesmean flow velocity

to slope, flow depth,and the inverse of a roughness measure,Manning’s n, a floodplain

Froude number isgenerated that redefines both the slope and nas applicable to the

floodplain rather than toa river channel, which results in an expressionfor S/R that is

calculated for 20 rivers fromaround the world. When the original R/S valuesgenerated

by themodel are inverted to S/Rvalues, it is found that the channel sinuosityvalues

associated with floodplain S/R datasetobtained from this Froude number

conventionplot right along with themodel-generatedensemble minima for

sinuosity.Lazarus and Constantine emphasize thattheir approach generates a set of

simplestcaseexplanations as a means of insolating.

Manning’s equation:

However, Lazarus and Constantinenote that their simple formulation has a

potential for great applicability because R and Scan be determined from remote

sensing data,digital terrain maps, light detection andranging surveys, and other studies

that bypasstime-consuming and expensive in-channeldata collection.Finally, it is

relevant to observe that theGaukler–Manning formula used in Lazarusand

Constantine’s theory has the samephysical basis as an equation published in1776 by

Antoine de Chezy (1718–1798),who had been engaged to design a canal tosupply

water to the city of Paris.

Chezy recognizedthat because the gravitational forceacting on water moving

through a channel(proportional to depth × slope) would haveto be opposed by an

equal but opposite resistingforce (proportional to velocity squared ×a measure of

resistance), velocity can beequated to the square root of the product ofslopemultiplied

by depth divided by the measureof resistance. Chezy Equation:

However, because this approachis based on Newton’s third law, thisequation

can only apply at one instant in time. Thus, in covering both quasistatic channelsand

mobile channels, Lazarus and Constantine’stheory definitely applies to theformer

because they do not change, but it canonly apply to the latter at a particular instantin

time relative to the overall evolution of theriver. This issue is similar to one raised

bygeologist J. Hoover Mackin (1905–1968) in his criticism of an explanation for

meanderingvery similar to that proposed by Schoklitsch. According to Mackin,

anyaccount of winding rivers in terms of theslope of a valley floor or other surface

leavesout a factor that would be very important toa geologist: the origin of that valley

floor orsurface. Evolving,mobile rivers, as opposed toquasistatic channelized flows,

create the valleyfloors and surfaces upon which they flow atany moment in time.

From this geologicalviewpoint, an explanation for the pattern of any evolving river

must include somethingabout the historical development of that river.

The meander ratio or sinuosity index is a means of quantifying how much a

river or stream meanders (how much its course deviates from the shortest possible

path). It is calculated as the length of the stream divided by the length of the valley. A

perfectly straight river would have a meander ratio of 1 (it would be the same length

as its valley), while the higher this ratio is above 1, the more the river meanders.

The sinuosity index has been used to separate single channel rivers into three

general classes: straight (SI < 1.05), sinuous (SI 1.05-1.5), and meandering (SI > 1.5)

Fig 2. Channel Pattern

2.3 Sinuous Channel Form

Beside on the form, Sinuous Channel devided in to there:

a. Sinuous Canal Form

The slope is ramp

Have the same relative width

Didn’t braide

The channel is narrow and deep

Example :

Fig 3. Rio Cauto at Guamo Embarcadero River, Cuba

b. Sinuous Point Bar

The slope more steep

The straight part is more stable than the wider part

Fig 4. Point bar at the “Gosong Sungai”

Example :

Fig. 5. Bone River, Gorontalo

c. Sinuous Braided

Have the steepest slope

River’s flow shifts radially

Have big bed load

Example :

Fig 6. Braided Stream

2.4 Problem of The Sinuous Channel Pattern

All the rivers flow tended to meander pattern forming (sinuous pattern). The

water that flows tend to be turbulent so arch and unevenness in the canals divert water

flow to the other side of the riverbank. Style water that hit the banks of the river,

causing erosion and weakening and make a small indentation in the river channel.

Due to continuously hit by the current, the curve becomes a great form bends

(meanders) were great. On the inside of the bend, so that the minimum speed to be

deposited sediment load. The precipitate which occurred at the height of the bend is

referred to as point bar. Two main processes around the bend in the river is the

erosion on the outer side of the bend and precipitation (depositional) on the inside of

the bend in the river, causing a round a bend (Meader loops) migrate laterally. Erosion

effectively run on the bending curve of the river so that the bend will be migrated.

The development curve of the bend and then become more circular and eventually

will cut round the river bend and be straight back. Turn that is truncated (cut off) in a

circle left bend into crescent-shaped lake that is better known as the oxbow lake.

2.5 Solution of The Sinuous Channel Patter Problem

How to cope precipitate on sinuous pattern is made of mangrove forests.

because the mangrove forests have ecological functions that are important, such as

damper waves and wind, coastal protection from abrasion, mudguard and trapping

sediments transported by water flow, as the breeding and feeding sites and is

spawning an assortment of aquatic biota, as fertilizer waters because it produces

detritus from leaf litter are broken down by bacteria into nutrients.

2.6 Sinuous Tubidite Channel

Isolated sinuous turbidite channels are usually identified by their characteristic

pattern on amplitude slices of volumes of 3D seismic. In some cases, they are

reasonably well imaged on 2D surveys, where one single line can image the same

channel several times due to the sinous nature of the channel.

Thick sinuous complexes appear to develop when slope equilibrium is re-

established in an area previously starved and oversteepened by tectonic activity

during the period of starvation, or oversteepened simply as a result of

hemipelagite deposition during a period of starvation (oversteepening does not

imply a precise angle, it corresponds to the contrast between the actual slope and

the equilibrium slope of the system at issue).

We use here the term “sinuous channel” for turbidite systems in order to

avoid confusion with meandering fluvial channels. Sinuous channels develop in

turbidite environments, when the density of turbidity currents is just slightly

higher than the density of seawater, i.e. the currents carry a very small amount

of sand. Sinuous channel fills are often shaly. Meandering (fluvial) channels

typically develop in low-grade fluvial plains and high amounts of sand are

deposited as point bars in the inner bends of the channels while the outer bank is

excavated. Notice that in classic sedimentology, a flow is sinuous when the ratio

of sinuosity, (distance between two points following the flow versus the shortest

distance between them), ranges between 1.5 and 2 and is meander-form when it

is higher than 2.

Seismic amplitude responses sometimes suggest that some sinuous

(turbidite) channels can be filled by sand. These would result from more complex

histories, where the sand infill is not associated with the process that built the

meanders, but by the passive infill in a later stage of meanders created during

episodes of low activity.

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Fig. 7 The avulsion mechanism, that is to say, a sudden cutting off or separation of land by an abrupt change in the course of the stream, in turbidite systems has been treated by Flood et al. 1991. Avulsion typically leads to a steepening in slope, with

the new channel less sinuous than the old abandoned one. As the new channel progressively re-establishes equilibrium, its sinuosity increases to reach a maximum

after which it essentially aggrades vertically.

Such complexes typically show the growth of a single channel over several hundreds of ms (t.w.t.). The channel over that period of time usually shows a progressive increase from lower to higher sinuosity. Most of the time, a maximum sinuosity is reached after a while and pure aggradation occurs afterwards with progressive migration downslope (sweep).

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Fig. 8 Contrary to fluvial meanders, which essentially get filled by progressive lateral accretion, turbidite sinuous channels typically get filled by successive

episodes of cut and fill. Downcutting is interpreted to result from higher energy flows and produces sinuous lows, which are further filled up by retrogradational

packages of turbidites. Like in fluvial meanders however, successive episodes of cut and fill migrate laterally towards the concave bank due to the curvature of the

channel. Hence the similarity in the final geometry at seismic scale.

The main differences between fluvial and turbidite sinuous channels result

from the difference in accommodation (fig. 8). Accommodation in fluvial systems is

usually low, its rate of creation corresponding roughly to the subsidence of the area.

On the other hand, accommodation in turbidite systems is best defined as the

difference between the actual profile of the system and the “equilibrium profile”

corresponding to the sediment supplied to the system (flow volume and sand / mud

ratio). In many cases, accommodation for turbidite systems is very high, allowing for

high aggradation, whereas fluvial systems essentially migrate laterally. In other terms,

the ratio between lateral migration and aggradation is high to very high in fluvial

systems, and low in turbidite systems.

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Fig. 9 Sinuous turbidite channels are created by low-density currents, slumps or small high-density sand-rich turbidite flows. The bend evolution is characterized by

an increase in amplitude and decline of wavelength with a lack of sweep and standstill of swing to attainment of channel stability. The channel evolution is

characterized by strong aggradation, progressive reduction of length and depth, frequent avulsion, rare cut-off ridges and absence of swale topography. Fluvial

meandering channels are created by bed load, suspensions and hyperconcentrated flow during flood events. Their bend evolution is characterized by an increase in amplitude and decline in wavelength, bend translation downstream (sweep) and

laterally (swing) with repetition of bend sequence. The channel evolution is marked by a quick lateral migration, length and depth stability, frequent cut-offs, and

development of ridge and swale topography.

Equilibrium profile is probably the main quantitative difference between

fluvial and turbiditic “meander belts”. For comparison, the equilibrium slope of

meandering rivers is in on the order of 1:10,000, that of turbidite “meanders” more

commonly ranges between 1:100 (Rhone) and 1:1000 (Indus) (see Clark and

Pickering, 1996, for a compete review).

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Fig. 10 Two well-expressed channel-levee complexes in the deep Gulf of Mexico are shown above. The lower channel displays very clearly a succession of downcutting

events followed by rather aggradational dominated fill. Both channels can easily be mapped, and are clearly highly sinuous in map view. Note that the migration is

unidirectional for each channel complex, indicating that the lateral component of migration is predominant with respect to the downstream component.

BIBLIOGRAPHY

Baker, Victor R. 2013. Sinuous Rivers. Tucson: University of Arizona. Accessed: March 3,

2016.

Sukarno, Indratmo. 2014. Rekayasa Rekayasa Sungai. Malang. Accessed: March 6, 2016.

http://KamuTakPernahJalanSendiri/MorfologiSungai.html

Geochaching. 2009. Menomonee Rivers: Straight, Sinous, or Mandering. Accessed: March 6,

2016.

Tempo, Bella. 2013. Delta Sungai Batui Sulawesi Tengah. Sulawesi Tengah. Accesse :

March 6, 2016. http://karinamelias.blogspot.co.id/2013/05/delta-batui-sulteng.html

sinouos channel pattern

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