Analysis of Nearshore Profiles Off Paradip Port, East Coast of India

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Indian Journal of Marine Sciences Vol. 17, June 1988, pp. 94-98

Analysis of Nearshore Profiles Off Paradip Port, East Coast of India

KG S SARMA* &V SUNDAR

Ocean Engineering Centre, Indian Institute of Technology, Madras 600 036 Received 30 March 1987; revised received 9 September 1987

Sediment movement in the nearshore zone off Paradip has been studied in relation to sediment supply, harbour siltation and shore erosion. Estimates of erosion and deposition have been made at different cross sections along the coastline with the nearshore profiles. The effectiveness of the sand pumping and hoppering into the offshore area in safeguarding the beaches has been discussed. The nearshore profile data presented in this paper indicate that the active zone for initiation of sand movement by waves and bottom currents is even beyond 14 m depth. It has been·well supported by the rapid advance and retreat of the bottom contours starting from 3 to 14 m depths offParadip.

An understanding of the behaviour of sediment movement in the nearshore zone particularly in the vicinity of any port is highly essential for im- provement of navigationl. In this paper, nearshore profiles at different cross sections along the coast on either side of the Paradip Port have been ana- lysed to study the nearshore sediment movement.

Estimates of erosion and deposition quantities have been made at each of the cross sections.

Spatial and temporal variations of the bottom contours in the nearshore zone have also been presented.

Study Area

Paradip Port, situated at the northern end of Bay of Bengal, is one of the important shoreline harbours along east coast of India (Fig. 1). This port is located at about 6.7 km south of Mahana- di River confluence. This river mouth discharges about 28 x 106 tons of sediment annually into the

sea2•

The orientation of the coastline at Paradip is from WSW to ENE. Wave characteristics off Par- adip coast are subjected to changes depending on the seasonal reversal of monsoon winds over the Bay of Bengal. Wave direction is predominantly between SSW and S during the SW monsoon season (June to September) with a normal maximum height between 2.75 and 3 m and period of about 9 sec. During NE monsoon season (November to Febraury) the predominant wave direction is be-

*Present address: Asst. Manager (Hydrographic Survey), Rail India Technical & Economic Services Ltd., 97 Nehru Place, New Delhi 110019, India

94

tween E and SE with a maximum height varying from 2.5 to 3 m and predominant period of about 8 sec. Wave heights and periods are variable during transition months (October, March, April and May) but the predominant direction is from S due to the particular orientation of thecoastline2•

The direction of littoral drift along Paradip coast is from S to N during the' SW monsoon and transition periods while during the NE monsoon season it is from N to S depending on the local wave conditions. The net littoral drift is towards N and it is about 1 x 106m3 at Paradip.

Methods

The nearshore profile data used in the present investigation are based on continuous echosound- ings conducted by the Paradip Port authorities (the soundings charts are available in the marine department of the port). Profiles have been taken at different cross section points (CS 1 CS 30) on either side of the port covering a distance of about 6.5 km (Fig. 1). The distance between any 2 cross sections is about 200 m. The values of soundings have been reduced from a permanent chart datum.

Hydrographic surveys were conducted, before dredging the material, in 3 to 14 m depths regu- larly during January to March. The nearshore profile data run from 1967 to 1985 at irregular time intervals and the bathymetry charts for 1967, '69, '70, '73, '84 and '85 were available. In 1969, soundings were not conducted on the northern side of the harbour. In order to estimate the quantities of erosion and deposition across a

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SARMA &SUNDAR: NEARSHORE PROFILES OFF PARADIP PORT

16'

BAY OF BE NGAl

40' " 41'

Fig. I-Location map

42'

MAHANA I RIVi)R

J~

CONFLUENCE

MOUTH OF THE RI R

"

~'l

DUMPING GROUNDS

cross section, the successive nearshore profiles were drawn using the bathymetry and computations were made comparing each survey with the succeeding survey. Since the soundings were conducted at different cross sections along the entire coast, the errors accumulated by the quantity of dredged material in the immediate vicinity of the harbour do not affect the present computations.

The quantities of erosion and deposition are shown in Table 1. The shifting of 3, 5, 7, 10, 12 and 14 m depth contours have been plotted for the 'Years 1967, '73 and '85 to study the movement of sediment at different water depths with time.

Results and Discussion

Nearshore sediment movement-Quantities of

erosion or deposition vary in between the successive years (1967-'69, '69-'70, '70-'73, '73-'84 and '84-'85) as well as from cross section to cross section (CS 1 to CS 30) and the net erosion or deposition during any successive surveys at different cross sections along the coast is highly variable and does not follow any systematic pattern (Table

1)- Hence it is clear that the sediment movement in the nearshore zone off Paradip is highly compli-

cated and governed by various interrelated factors such as sediment supply, blockage of sediment due to harbour breakwaters, bottom configuration, wave characteristics and consequential wave refraction etc. About 4 x106m3 of sediment was deposited at each of the cross sections CS 17 and CS 18 during 1984-85 of which about 1.6 and 1.2 x106m3 of sand was silted up in the harbour approach channel at respective cross sections, ne- cessitating large scale maintenance dredging.

Southward movement of the sediment during the NE monsoon season and the migration of sand towards south from the dumping grounds (Fig. 1) may be the major causes for this siltation. There is an imbalance between erosion and accretion rates during the successive profile surveys for al- most all cross sections resulting in either net loss or gain of the sediment in the nearshore area.

Nearshore profiles- Nearshore profiles over different years which are highly important in the littoral processes, have been plotted for all the cross sections along the coast to study the varia- tion of their configuration with respect to time and space. Only representative profiles at cross sections 2, 14, 17 and 30 (Fig. 2) have been se- lected and presented for discussion such that CS 95

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\0 0\TableI-QuantitiesofErosion(-)andDeposition(+)intheNearshoreZoneoffParadip [Valuesin1x106m3] YEARCSICS2CS3CS4CS5CS6CS7CS8CS9CSIOCSIICSI2CSI3CSI4CSI5 1967 to69 Net

+0.15 -0.45 -0.30

+0.70 -0.60 +0.10

+0.00 -0.80 -0.80

+0.00 -0.45 -0.45

+0.10 -0.60 -0.50

+0.15+0.05 -0.35-1.30 -0.20-1.25

+0.30 -0.65 -0.35

+0.35+0.70 -0.20-0.02 +0.15+0.68

+1.05+1.30 -0.45-0.65 +0.60+0.65

+0.40+0.45+0.03 -0.60-0.25-0.85 -0.20+0.20-0.82 1969 to70 Net

+1.70 -0.00 +1.70

+0.00 -1.70 -1.70

+0.00 -1.05 -1.05

+0.00 -2.00 -2.00

+0.00 -1.65 -1.65

+0.01 -1.55 -1.54

0.05 -1.20 -1.15

+0.00 -1.75 -1.75

+0.00+0.00 -1.80-1.80 -1.80-1.80

+0.00+0.00 -2.25-2.75 -2.25-2.75

+0.00+0.00+0.00 -1.75-2.15-1.65 -1.75-2.15-1.65 1970 to73 Net 1973 to84 Net 1984 to85 Net YEAR 1967 to70 Net 1970 to73 Net 1973 to84 Net 1984 to85 Net

+0.20 -0.20 0.00 +0.45 -0.55 -0.10 +1.50 -0.40 +1.10 CSl6 +0.50 -0.30 +0.20 +0.45 -1.05 -0.60 +2.70 -0.10 +2.60 +0.50 -0.00 +0.50

+0.75 -0.00 +0.75 +1.00 -0.00 +1.00 +0.35 -0.60 -0.25 CS17 +0.25 -0.55 -0.30 +0.15 -1.00 -0.85 +1.75 -0.20 +1.55 +4.15 -0.00 +4.15

+0.05 -0.35 -0.30 +0.70 -0.40 +0.30 +0.25 -1.05 -0.80 CS18 +0.15 -0.80 -0.65 +0.50 -0.50 0.00 +0.00 -0.95 -0.95 +4.30 -0.00 +4.30

+0.30 -0.75 -0.45 +1.70 -0.25 +1.45 +1.35 -0.50 +0.85 CS19 +0.00 -0.95 -0.95 +1.60 -0.25 +1.35 +0.50 -0.90 -0.40 +0.85 -0.60 +0.25 *"

+0.10 -1.00 -0.90 +1.70 -0.00 +1.70 +1.30 -0.00 +1.30 CS20 +0.00 -0.85 -0.85 +2.75 -0.00 +2.75 +0.40 -1.10 -0.70 +0.50 -1.15 -0.65

+0.15+0.25 -0.55-0.75 -0.40-0.50 +1.20+2.80 -0.00-0.00 +1.20+2.80 +2.20+0.00 -0.00-0.85 +2.20-0.85 CS21CS22 +0.60+1.00 -0.30-0.05 +0.30+0.95 +0.05+0.02 -1.25-1.05 -1.20-1.03 +1.50+1.55 -0.40-0.01 +1.10+1.54 +1.55+0.40 -0.03-0.15 +1.52+0.25

+0.21 -0.40 -0.19 +1.70 -0.00 +1.70 +0.11 -0.40 -0.29 CS2 +0.85 -0.00 .D.85 +0.00 -1.30 -1.30 +1.00 -0.35 +0.65 +1.15 -0.20 +0.95

+0.45+0.33 -0.75-0.65 -0.30-0.32 +3.25+2.90 -0.00-0.00 +3.25+2.90 +0.00+0.00 -1.50-1.90 -1.50-1.90 CS24CS25 +1.20+0.00 -0.40-1.00 +0.80-1.00 +0.55+0.50 -0.35-0.35 +0.20+0.15 +1.00+2.00 -0.80-0.50 +.0.20+1.50 +0.80+1.15 -0.30-0.27 +0.50+0.88

+0.70+1.10 -0.40-0.20 +0.30+0.90 +2.90+0.85 -0.00-0.00 +2.90+0.85 +0.00+0.80 -1.50-0.25 -1.50+0.55 CS26CS27 +0.00+0.10 -1.00-1.50 -1.00-1.40 +0.50+0.80 -0.36-0.65 +0.20+0.15 +1.75+1.80 -0.10-0.42 +1.65+1.38 +1.10+0.45 -0.15-0.20 +0.95+0.25

+1.15'1-1.90+1.05 -0.10-0.00-0.00 +1.05+1.90+1.05 +0.55+0.0I+0.55 -0.75-1.05-0.00 -0.20-1.04+0.55 +0.80+0.35+0.00 -0.55-0.55-0.70 +0.25-0.20-0.70 CS28CS29CS30 +0.15+0.55+0.00 -1.50-1.30-2.35 -1.35-0.75-2.35 +0.95+6.75+2.30 -0.20-0.25-0.05 +0.75+0.50+2.25 +1.60 -0.20 +1.40 +0.35+1.60+2.50 -0.80-1.05-0.85 -0.45+0.55+1.65 ~

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SARMA &SUNDAR: NEARSHORE PROFILES OFF PARADIP PORT

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-2 -4-6-8 -10-12-14

-5 -7 -11-9

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Distance Seaward from the reference point (m)__

400 800 1200 1600 2000 2400 2800 3200 3600 4000

-0--1967

---6--¹⁹⁶⁹

--- 1970 --1973

--<:>-- 1984

-,-,- 1985

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Fig. 2- Nearshore profiles off Paradip

since the area is away from the source. But at CS 14, which is located adjacent to the southern side of the harbour breakwaters, a reverse trend has been noticed. The inshore area has been subjected to erosion from 1973 to 1985 due to the blockage of southward movement of the sediment into the inner nearshore zone by harbour breakwaters and approach channel while deposition has been noticed in the offshore zone from 1984 to '85. A large scale shoaling of the entire area has been noticed at CS 17 from 1973 onwards which must be due to the total effect of interception of the southward littoral drift by the breakwaters, migration of sediment from the Mahanadi river and from dumping grounds during the NE monsoon season. The latter two reasons would have led to significant amount of the material being deposited in the offshore zone at CS 30 (Fig. 2d).

But the sediment does not drift towards the shore at CS 30 since this nearshore portion is sheltered to some extent by the dumping grounds and the river mouth, as a result of which the inshore area is subjected to erosion.

Shifting of bottom contours in nearshore zone- A prominent feature observed from Fig. 3 is that the bottom contours are shifting more while prog- ressing towards the sea. The 3 and 5 m isobaths clearly indicate the nonlinear flows giving rise to the asymmetric pattern of material accumulations and are probably controlled by near symmetric circulating cells with variable spatial scales along the coast. The 7 m isobath, immediately north of breakwater shows significant deposition during the period of general southerly drift. Further offshore, a large shoal is noticed on the northern side of the harbour particularly at 10 and 12 m depths. The shoal must have been caused due to the drifting of the sediment from the dumping grounds or from the Mahanadi river. Deepening of the 3 m isobath on northern side of the harbour reveals that the sand from the dumping grounds does not drift towards the shore to safe- guard the northern beaches. Besides, the littoral supply may be cut off by the Mahanadi river mouth as discussed earlier.

14 and CS 17 are adjacent to the harbour breakwaters while CS 2 and CS 30 are away from the breakwaters. At CS 2 the inshore portion of the profiles builds up from 1970 to 1985 may be due to the supply of littoral sediment to the inner nearshore zone, whereas the offshore portion is deepening from 1967 to 1985. The erosion in the offshore region indicates that the sediment from the dumping grounds is not reaching the CS 2

On the whole the above study reveals that the entire nearshore area off Paradip even beyond 14 m depth is an active zone for sediment movement. The study also reveals that the method of dumping material offshore, on the assumption that the material would be moved onshore by wave action does not prove successful to safe- guard the beaches as observed earlier3.4,

97

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INDIAN J MAR SCI, VOL. 17, JUNE 1988

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500 400 4300

700 4100

900 700 500 900 800

300 ]600

200 400

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SCALE 300 (101014mOEPTH

CONTOUR)

200 ]300 200

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---1973

--- 1985

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-5

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r.::.=."-:...---1 0

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

CROSS SECTIONS (NORTH)

Fig. 3-Shifting of bottom contours off Paradip

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Acknowledgement

The authors thank the Paradip Port authorities for providing the necessary data. This work is a part of the project sponsored by the Central Board of Irrigation and Power, Government of In- dia and the auffiors greatfully acknowledge this support.

References

1 Anon, Shore protection manua~ U S Army corps of Engrs, Washington D C, 1 (1977).

2 Render!, Palmer &Triton, Report on the development of a deep water Port at Paradip, [Commerce (Ports) Department, Govt. of Orissa] 1962.

3 Hall J V (Jr)&Watts G M, Trans ASCE, 122(1957) 155.

4 Sarma K G S, Nearshore dynamics along Visakhapatnam coast, Ph.D. thesis, Andhra university, 1986.

98

Analysis of Nearshore Profiles Off Paradip Port, East Coast of India