Annalysis of Sediments of Mahaoya

8/7/2019 Annalysis of Sediments of Mahaoya

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Analysis of stream

sedimentsof Mahaoya

GL-317

ABSTRACT[Analysis of stream sediments gives lots of importantinformation about process of the stream. The sedimentationprocesses of Structurally controlled stream in headwaterregions are somewhat different from existing sedimentationmodels of rivers channels. Because turbulence currents aremaking different conditions place to place. Generalization of pattern of sedimentation of Maha-Oya headwater regionsomewhat difficult by considering small number of databecause Sedimentation process (velocity of stream flow) mainlygoverned by underlying structure.]

A.N.P.W.M.R.B.M.B Athurupane (S/07/004)G.G.M.S.Wickramasinghe (S/07/180)M.A.K.Kumari (S/07/357)N.A.U.S.Nishshanka (S/07/388)


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Analysis of stream sediments of Mahaoya GL-317

2 Department Of Geology, University Of Peradeniya.

Introduction

A method for determining the grain size distribution of clastic particles typically between 1.0

mm and 0.062 mm (from coarse silt to coarse sand) a relatively accurate method fordetermining depositional hydrology and for refining sedimentary environments

To study of the different sedimentation process along the stream, Cross section is done bymechanical analysis of three different sediment samples along three different places of thestream cross section.

The location that sediments collected is situated close to the University Christian church and it is10m downstream from the bridge. S R, S M & S L samples were collected at the right side, middleand left side of the stream respectively.

Locations details given below.

SL SM SR

Fig 01. Sampling locations


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Photographs of samples

METHODOLOGY AND APPARATUS

APPARATUS

Equipment Required

1. Balance - sensitive to 0.1 g.

2. Sieves - Canadian Metric Standard square mesh sieves of size as required for the type of gradation for the material being tested.

3. Mechanical sieve shaker.

4. Containers - pans suitable for washing the sample.

5. Drying apparatus - suitable pans and stove for drying the samples

Fig 02. Sieving Instrument Fig 06. Analytical Balance

Fig 02. SL Fig 03. SM Fig 04. SR


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PROCEDURE

1. Collecting samples.Representative samples were collected using instruments that are shown bellow.

2. Drying samples.Samples were dried by using electric ovens and drying under solar radiation.

3. Selecting representative sample.Selecting representative samples using sample separation and then 500g of sampleweighted using triple bean balance (fig 04.).

4. Sieving.Using following order sieving sample were stand in 10 minutes. Then the retained masson the each sewed were measured using Analytical balance.

Fig 07. Selecting representative sample.


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DATA AND CALCULATIONS

SL-Left Sample

sieve size retaining weight retaining percentage cumulative %pan 0.5 0.100 0.100

0.063 3.35 0.672 0.7730.125 3.63 0.729 1.501

0.15 7.38 1.481 2.9830.18 3.62 0.727 3.709

0.212 20.34 4.083 7.7920.25 167.35 33.591 41.383

0.5 228.98 45.961 87.3441 58.53 11.748 99.0932 6.14 1.232 100.325

499.82 100.325

Table 01. Cumulative percentage of retaining weight of S L

Graph 01. Grain size distribution curve of S L


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CURVE SIGNATURE:

D10 0.22

D60 0.31

C cL 1.41

Remarks:- Uniformlygraded sediment

Graph 02. Retaining weight percentage of S L

Table 02. Calculation of S L


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SM-Middle sample

sieve size retaining weight retaining % cumulative %pan 0.12 0.024 0.024

0.063 0.47 0.094 0.118

0.125 0.81 0.163 0.2810.15 2.08 0.418 0.6990.18 1.49 0.299 0.998

0.212 9.05 1.817 2.8140.25 47.38 9.510 12.324

0.5 122.97 24.683 37.0071 164.96 33.111 70.1182 148.87 29.882 100.000

498.2 100.000

Table 03. Cumulative percentage of retaining weight of S M

Graph 03. Grain size distribution curve of S M


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CURVE SIGNATURE:

D10 0.25

D60 0.80

C cM 3.20

Remarks:- Uniformlygraded sediment

Graph 04. Retaining weight percentage of S M

Table 04. Calculation of S M


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SR- Right sample

sieve size retaining weight retaining percentage cumulative %pan 0.31 0.062 0.062

0.063 0.56 0.112 0.175

0.125 0.78 0.157 0.3310.15 2.15 0.432 0.7630.18 2.36 0.474 1.236

0.212 7.96 1.598 2.8340.25 39.71 7.971 10.805

0.5 72.15 14.482 25.2871 95.37 19.143 44.4302 275.11 55.221 99.651

496.46 99.651

Table 05. Cumulative percentage of retaining weight of S R

Graph 05. Grain size distribution curve of S R


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INTERPRITATION

Three samples are collected from three different places of the stream (along cross-section of stream) namely Right sample (S R), Middle sample (S M) and Left sample (S L).

A A

B B

AA

AB

AA

AB

SR SM

SL

Fig 08. Cross section along A -A

SL

SM

SR

Fig 08. Cross section traces

Fig 09. Cross section along B -B

SM

Flow

Bed rock

Sediments


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W E

Q

This area is rich in sediments. This part of the stream act as pool (according to BB cross -section). Just above the upstream side flow velocity is much higher they carry most of the sediments as

suspend. Just below the B point flow velocity decreases due to underlying morph ology. Thereforeterminal velocity of particles in suspended load is decreasing and they are starts to settle down.

According to the graphs 02, 04 and 06 retaining grain size range is 0.25-02 mm. Therefore sand-gravel fraction is significant in the location. But sedimentation (velocity decreasing) is different in thethree sampling locations. Therefore three samples showing different distribution and some fractions havehigh percentages.

Coefficient of uniformity

Left bank sediment and middle sediments are showing sorted nature. And right sample (point bar)showing well graded nature.

According to fig 10 Place where left sample taken has vertex currents with both side rotatingnature because of that temporary calm area has formed. That area will facilitate to sedimentation.Normally erosive bank away from point bar sedimentation is very less (only large grain) but in this case itis somewhat different.

All of the samples do not have much amount of fine particles because velocity of stream in thispart comparably high than lower parts. this part of the stream is highly structurally controlled andprocesses are different from normal sedimentation.

CcL 1.41 Uniformly graded sediment

CcM 3.20 Uniformly graded sedimentCcR 5.20 Well graded sediments

Turbulence currentsBarrier (Rock Boulder)

Vertex currents with differentdirectional movement

Sediment bar

Left bankRight bankpoint bar

Fig 10. Schematic flow pattern of location

Calm region


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CONCLUSION

o Right (point bar) sample has well graded nature. Middle and left samples have uniformlygraded nature that means sorted nature is there.

o Left sample has well sorted nature than other two samples but presences of fine particlesare greater than other two samples.

o All the samples containing lesser amount of fine particles.

o Stream with turbulence currents sedimentation process vary with the current pattern.

o Expressing general sedimentation processes of Structurally controlled streams inheadwater region is difficult with few number of data

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Annalysis of Sediments of Mahaoya