Indian Journal of Marine SciencesVol. 6, June 1977, pp. 39-48

Current Regime in the Gulf of KutchP. S. SRIVASTAVA& V. C. JOHN

Engineers India Ltd, New Delhi 110001

Received 10 June 1976; revised received 17 January 1977

Long term in situ current data have been collected for a number of locations in the Gulf ofKutch and analysed. Tides in the area are of mixed type and are predominantly semidiurnalwith a large diurnal inequality. The mean spring tidal range from mouth to the closed end ofthe Gulf ranges between 2·1 and 6·2 m. A correlation between tidal ranges and tidal currentspeeds has been established for Gurur and Bobby Shoals and off Narara Bet. The data revealthat the major steady currents in the area are of tidal origin. However, during south-westmonsoon period, strong westerly winds would generate wind driven currents, with surfacespeeds reaching about 0·5 mjsec. The width of the Gulf narrows down between long. 69°E and69°20'E causing an increase in the tidal current speeds, with speeds reaching up to 2·5 m/sec.The density currents in the Gulf are negligible.

CURRENT regime in an area is one of the im-portant factors affecting navigation, fisheries,offshore structures, harbour construction andcoastal climate. Systematic study of current regimein the Gulf of Kutch (Fig. 1) has not been donepreviously, though general knowledge of the surfacecurren ts for a few localized places can be had byreferring to the west coast of India Pilot or NavalHydrographic office charts.

The currents prevailing in the Gulf are controlledby the various parameters viz. wind, tide, bathy-metry, coastal configuration and density distribu-tion. A brief description of the above is presentedin this paper.

General Description of the AreaThere is no major river discharging into the

Gulf and the average annual rainfall in the area is

I r:\.j '-'-,

\. ./_.rI\ _/,--.

JAKHAU l. .13

• _JAMNAGAII

LEGEND- 3·66m CONTOURS

to·97m CONTOURS_. --- 18·26n'1 CONTOURS- .. - ..- 36'56m CONTOURS

Fig. 1 - Station locations in Gulf of Kutch

39

INDIAN J. MAR. SCI., VOL. 6, JUNE 1977

less than 52·5 cm ; hence 2 layer flow as encounteredin a normal estuary is not expected in the area.

Mean spring tidal range- from the mouth to theclosed end of the Gulf ranges between 2·1 and 6·2 rn,hence high speed tidal currents are expected.The time that a tidal wave takes to proceed fromopen sea to the closed end is about 2t hr. Bathy-metry, coastal configuration, wind pattern andtidal range in the Gulf are such that they cancreate very complicated current regime; therefore,a detailed current study has been planned.

liVinds - Wind pattern in the area is predomi-nantly seasonal with rare cyclonic disturbances.In order to understand monthly wind distributionsin the area. nearly 4000 ship observations coveringthe area 21° to 25°N lat. and 67°E long. to coastlinefor the period 1961 to 1966 have been analysed.Predominant wind directions in the area arewest-southwesterly and north-northeasterly duringJune to September and December to March respec-tively. Higher wind speeds are likely to occurduring June to September with winds up to 74 kmjhrfrom west or west-southwest. July is the windiestmonth in the area with wind speed exceeding 20km/hr for 81·5% of time with predominant directionfrom west-southwest. The calmest month is Februarywith winds exceeding 20 kmjhr occurring for 13·3%of time only, the predominant wind direction beingnorth -porth westerly.

Tides - Tides in any area can be grouped under3 broad classes: semi-diurnal, diurnal and mixed.

Tidal variations at Okha, Sikh, Kandla andNavalakhi are compared for April 1975 and presentedin Fig. 2. Tides in the area are of mixed type andare predominantly semi-diurnal with a large diurnal

10 11 12

DATE AND TIME

inequality. Various tidal elevations viz. mean lowwater springs, mean low water neaps, mean sealevel, mean lligh water neaps and mean high watersprings for 4 locations are presented in Table l.

From a study of the tidal variations at variouslocations in the Gulf the following conclusions re-garding the movement of tidal wave could be made:Tidal wave approaches the Gulf from the west. Onentering the Gulf the speed of the wave is reducedon the shallower waters near the coast while inthe deeper waters the speed is maintained untillong. 69°22'E. The time taken by the wave totravel from long. 69°E to 69°22'E is about 1 hr 20min. From long. 69°22'E onwards the speed isconsiderably increased and the wave reaches theclosed end in about 1 hr, the direction of the tidalwave being from west-southwest following the orien-tation of the Gulf.

Tidal range increases faster from long. 69°E to69°30'E; the increase is of the order of about 80%.From long. 69°30'E to the closed end, the rate ofincrease in tidal range is slower, being of the order

TABLE 1 - TIDAL ELEVATIONS AT VARIOUS ST,\TIONS

Station Mean Mean Mean Mean Meanlow low sea high high

water water level water watersprings neaps neaps springs

(m) (m)

+0·41 +1'20 +2·04 +2·96 +3-47+0'71 +1·73 +3·04 +4'35 +5'38+0·78 +1-81 +3-88 +5'71 +6·66+0·78 +2·14 +4·15 +6·16 +7·21

OkhaSikkaKandlaNavalakhi

13 16 J7 18 1920 APR.':IS

Fig. 2 - Tidal variations at different stations in April 1975

14 15

40

SRIVASTAVA & JOHN: CURRENT REGIME IN THE GULF OF KUTCH

of 30%. The total increase in tidal range fromthe mouth to the closed end of the Gulf is about150%.

Bathymetry and coastal configuration - The Gulfof Kutch is an elongated gulf in the east-westdirection with an average depth of about 30 m. Atthe mouth of the Gulf, Lushington shoal withdepths nearly 5 m below chart datum is present.On the south-east side of Lushington, a channelwith the depth of water varying between 30 and50 m is present. Besides Lushington, there areother shoals in the area, e.g. Gurur, Bobby, Ranwara,etc. The presence of Ch anka reef and Ranwarashoal narrows down the Gulf at about long. 69°20'E.The coastal configuration of the Gulf is very irregularwith a number of islands, creeks and bays.

Density distribution - Data on the density distri-bution in the Gulf is not available except at themouth of Gulf and at station 5 (Fig. 1). Since thetidal range and the tidal currents in the area arequite significant, large scale mixing takes place inthe Gulf. There is no significan t fresh water influxin the area and the average annual rainfallis less than 52·5 ern, Hence a nearly uniform densitydistribution is expected in the Gulf.

Study of the density distribution at station 5 andat eight locations in the outer Gulf of Kutch revealsthat the density is nearly uniform from surface tobottom. Therefore, density currents in the Gulfare expected to be negligible.

MethodsThe current meters used in the present study

are Bendix Q-15 self recording, Hydroproducts505-A self recording and Robert's direct readingcurrent meters. Installation of a typical currentmeter is shown in Fig. 3.

The locations where the current data have beencollected are presented in Fig. 1. Details of thedata collected for various stations are given inTable 2.

Tide data for Okha, Sikka, Kandla and Navalakhihave been obtained from the Survey of India.Wind data for Okha, Jamnagar and Kandla havebeen obtained from the India Meteorological Depart-mer.t.

Detailed analysis for Gurur and Bobby shoals andoff N arara bet -- Long term current records- areavailable only for locations Gurur shoal (station 2),Bobby shoal (station 3) and off Narara bet (station 5).Current records have been analysed to determinehalf hourly current speeds and directions. The

$TILL WAHl'. LEVEL

'8l7t"'.p po,-YPP.OPLENE -80M U:JfJG

J211t"'

INDIAN J. MAR. SCI., VOL. 6, JUNE 1977

speeds an d directions so obtained have been sortedout to determine the percentage of occurrence ofdifferent speed classes in different directions, Thepercen tage frequencies so obtained for stations 2,3 and 5 are further analysed to determine predomi-nant speed, maximum speed and predominantdirections (Table 3).

In order to understand the variation of currentat spring, neap an d transition period the cumulativefrequency tables of curren t speeds for various periodsand for different stations have been prepared. Basedon these tables current speed exceedence graphshave been drawn and are presented in Fig. 4.

In order to get an idea of the distributionof currents in different directions the available dataon current speed and directions for each stationhave been plotted on a polar diagram. The scatterdiagrams of curren t speeds and directions soobtained are presented in Figs. 5-7.

TABLE 3 - PREDOMINANT AND MAXIMUM CURRENTSPEED AND PREDOMINANT DIRECTION

StationNo.

Location No. of Pre- Ma.x. Predominantobserva- dorni- speed direction

tions nant m/secspeedm/sec

2 Gurur shoal 376 0·95 1·59 Sou therlvand So~th-

Sou theasterl y3 Bobby shoal 719 0·95 1-46 Westerly and

Easterly5 Off Narara Bet* 792 0·20 0·76 Easterly and

(proposed SP:'.I Southwesterlysite)

*\Vave current filtered out.

Tidal currents in an area normally increase withincrease in the tidal range. A comparison of floodand ebb current speeds with different tidal rangesrecorded at the nearest port has been made. Thesedata are presented in Fig. 8.

General anaiysis for whole Gulf - Simultaneoustidal data in the Gulf are available only for Okha,Sikka, Karidla and Navalakhi. For understandingthe variation of tides from the mouth to the closedend of the Gulf, tide data for April for all the 4stations have been plotted (Fig. 2).

Maximum surface currents recorded at each stationduring the present study together with the datapresented in the Indian Hydrographic charts havebeen presented in Fig. 9.

Results and DiscussionGurur shoal- Predominant and maximum surface

curren ts recorded are 0·95 and 1·59 m/sec respec-tively. The recorded directions show considerablevariations (Fig. 5). The probable reason for thiscould be that the direction recording mechanismof the current meter did not function properly.

Current speed exceedence diagram (Fig. 4) showsthat the spring currents are 60 to 65% strongerthan the neap currents. Current speed exceeds1 m/sec for 18, 50 and 60% of time in the case ofneap, transition and spring tides respectively. Inorder to understand the variation in current speedwith the variation in tidal ranges, tidal data forthe nearest available port, i.e. Okha, were plottedagainst the recorded current speeds (Fig. 8). Fromthis figure it can be seen that for the same tidal rangeebb currents are stronger than the flood current.The probable reason for this can be that since therecording is at an elevated place compared to thesurrounding area the down ward run of the waterwill add to the ebb flow, A study of the wind

100 """'~"'=-------~G:-:-U::R-:-:U':'R-S::-:H::O:-:A-:-L--t~':;;:"S:=---------;;-B:::;OB~B:V:;-;:S~H:-;:;O~A-;-L --I\~~-;N::-A;:;R:;-;A;-;:R;-;A~B:-;;E:-;T-'"' «, \" ST. No. 2 .~" ST. No.3 ST.No.6

~ "." '."~-' \ '\ \.~,

" " ' "§ \ \ \ "~ 7S ", \ "\ -,

~ \ \ \: ", \ . \§ \ \ \. \~ , \ \ \W05Q \ \ \~ ..• \ \ \; \ \ \~ \. \ \i25 \ \ \ \IL __ SPRING \ \ \~ - - - TRANSIllUJ \ \ \~ - ... - NEAP \ \ \

~ \ \ \~ OL-~~~-L-L~~~~~~~''-~'~~''~'~:-~~~~~~~~~~~_~~\~~~~''~~~~~~~~~~~~

o I o.s 1.0 i.s CURRE~i5 SPEED Im/sl 1,0

\

\

1.5 0 0,>

42

Fig. 4 - Current speed exceedence curves for different stations

SRIVASTAVA & JOHN: CURRENT REGIME IN THE GULF OF KUTCH

GURUR SHOAL (STATION NO.-2)1e-3-75 TO 3-4-75

Fig. 5 ~ Scatter diagram of currenl speeds and directions at station 2 (Gurur shoal) from 18.3.75 to 3.4.75 [Currentswere recorded using Hydroproducts model 505-A current meter. Depth of measurement 5 m above sea bed. Currentspeed measured in m/sec and direction in degrees from North. Current speed values averaged over 5 min recording

period. Spring (X), neap (e) and transition (A)]

43

INDIAN J. MAR. SCI., VOL. 6, JUNE 1977

BOBBY SHOAL (STATION NO.- 3)16 - 3 -75 TO 3 - 4 . "IS

Fig. 6 - Scatter diagram of current speeds and directions at station 3 (Bobby shoal) from 18.3.75 to 3.4.75 [Detailssame as in Fig. 5. Depth measurement 6 m above sea bed)

44

SRIVASTAVA & JOHN: CURRENT REGIME IN THE GULF OF KUTCH

NO·

180"sNARARA BETcSTATION NO.-S)13-7-73 TOI5-8-73

Fig. 7 - Scatter diagram of current speeds and directions at station 5 (Narara bet) from'13.7.73 to 15.8.73 [Detailssame as in Fig. 5. Scatter plotting are not shown separately for spring, neap and transition periods]

45

INDIAN J. MAR. SCI., VOL. 6, JUNE 1977

1·5 ..GURUR SHOAL BOBBY SHOAL OFF NARARA BET "/ST. No.2 ST. No.3 ST. No.5 .r

I. :.. / ):1../ .. , .'j' a "......./.~IJI~ I . ,/. .'>!. .. . • . . . .. ...s I- a/.' .

0"25.. ;. I ." ". :&. .:lJJ • 1 , 'j / ......lJJ

" . . .". . .c, /oJ> : //: .I- / .. a ..Z ./lJJ (.a: /" ./a::l 'I: .I. /us J ~'/ /. . '.~ "0 /. •...~ /~

x FLOOD• EBB

- ---FITTED RELATION--FITTED RELATION

FOR FLOODFOR EBB

2'5 5'0 7·52·5TIDAL RANGE AT OKHA (m)

Fig. 8 - Comparison of flood and ebb current speeds with different tidal ranges recorded at different stations [Totalranges for Okha and Kandla are taken from tide tables. Current speed values are averaged over 5 min recording

period. Recording period for Gurur and Bobby shoals is 18.3.75 to 2.4.75 and Narara bet is 13.7.73 to 15.8.73]

pattern at Okha during March reveals that thepredominan t and the next predominant directionsof wind are north-westerly and westerly respec-tively. These wind pattern can create north-easterly a-id easterly surface currents in the areaand hence cannot add to the ebb flow in thearea.

Bobby shoal- Predominant an d maximum surfacecurrents recorded are 0·95 and 1·46 m/sec respec-tively. The 2 predominant directions of recordingsare 80° + 10° and 260° + 10°, which is also theorientation of the Gulf, ~howing thereby that thetidal currents are predominant in the area (Fig. 6).Curren t directions are bimodal with flood current andebb current flowing for 47 and 41% of the timerespectively. During the remaining 12% of the time,current direction is variable between 90° to 250° butspeed remains generally below 0·4 m/sec. Currentspeed exceedence diagrams (Fig. 4) show that surfacespeed exceeding 1 m/sec occurs 5, 45 a-id 56% ofthe time in the case of neap, transition and springtides respectively. These percentages are lowerthan those recorded at Gurur shoal. The springtidal currents are nearly 45 % stronger than neapcurrents.

A comparative study of the tidal range andmaximum recorded current speed (Fig. 8) showthat ebb current is in general higher than the floodcurrent. The probable reason for this is the sameas discussed for the Gurur shoal.

Off N arara bet - Surface current: - The currentdirections off Narara bets are bimodal, with pre-dominant directions and peak speeds nearly parallelto the bottom contour. Predominant and maximum

46

surface currents recorded are 0·20 and 0·76 m/secrespectively. The 2 predominant directions ot're-cording are 78° ± 10° during flood and 2l3° ± 10°during ebb period. These 2 predominant directionsare separated by l35° rather than UlO°. This maybe due to the concave nature (Fig. 1) of the southerncoast of the Gulf of Kutch which causes an additionalsoutherly component thus changing current direc-tion.

Curren ts are dorninan tly tidal with a semi-diurnalperiodicity. For 5% time, speed remains less than0·05 m/sec which represents slack period betweenflood and ebb tides. Current speeds during springexceeded 0·5 m/sec for 37% of time with the peakspeed of 0·76 nt/see towards 75°. Current speedexceeden ce diagrams (Fig. 4) show that surfacecurrents exceed 0·5 m/sec for 4'5, 27 and 37% oftime in the case of neap, transition, and spring tidesrespectively, which are lower than those recordedat Bobby and Gurur shoal. Spring tidal currentsare about 82% stronger than neap currents.

From Fig. 8 it is seen that in general floodcurrents are stronger than the ebb currents unlikein the case of currents at Bobby and Gurur shoals.During the months of June to September (south-west monsoon) winds exceeding 20 kmjhr occur for58% of time (Fig. 2) with predominant directionsranging between west to west-southwest. The wind-driven currents generated during this period rangefrom easterly to east-northeasterly and hence thesecurren ts will superimpose over th e flood tidalcurrents. This may be the probable reason forflood currents being stronger than ebb currents offNarara bet.

SRIVASTAVA & JOHN: CURRENT REGIME IN THE GULF OF KUTCH

) r,\)-...

"KHAMBHALIA

5 tAL E •... 1:665,1 SO

-JAMNAGAR

LEGEND:-3·66 m CONTOURS

10 97 m CONTOURS-·-·-18·28m CONTOURS- .. - .. - 3656 m CONTOURS

(b)

Fig. 9 - (a) Maximum surface currents recorded at each station during the present study and (b) surface currentsrecorded at area marked [A] in the top figure

47

INDIAN J. MAR. SCI., VOL. 6, JUNE 1977

Season

TABLE 4 - NORMAL WIND-DRIVEN SURFACE CURRENTS

Max. wind Max. current Predominant

Speed Dir. Speedwind

Dir.(kmjhr) (rnjsec) Speed Dir.

(kmjhr)

49 3300 0·34 191 16 300

49 2400 0·34 101 16 300074 2700 0·49 116 24 2400

61 600 0·42 275 9 3300

December-MarchApril-MayJune-SeptemberOctober-November

Predominantcurrent

Speed Dir.(mjsec)

0·090·090·150·08

225165105195

Bottom currents _. An analysis of the data onbottom currents reveals that the curren ts are stronglyperiodic with bimodal current directions. The pre-dominant directions are 1l00± 10° during floodand 169° ± 10° during ebb. The predominantdirections differed from the surface current directionswith the flood current turned more onshore. Theebb curren ts instead of following the directions2900± 10° as expected, flow towards 169°+ 10°.The bottom currents are normally 70% of the surfacecurrents.

Surface currents in the Gulf of Kutch - The widthof th e gulf narrows down between long. 69°10'Eand 69°26'E due to the presence of Chanka Reefand Ranwara shoal. This causes an increase inthe tidal current speeds with speeds reaching upto 2·5 m/sec. The current speeds at the mouth ofGulf and east of 69°26'E are comparatively lower,with speeds reaching up to 1·5 m/sec. The generaldirection of curren ts in the area are parallel to thebottom con tour suggesting thereby the dominanceof tidal currents.

The wind-driven current will play an importantpart in modifying the tidal circulation in the areawhen the wind speed exceeds 20 krnrhr. Thenormal wind currents for different seasons in thearea have been computed using the Ekmansrelationsv" and the wind data. The analysed datais presented in Table 4. Maximum wind-drivencurrents in the Gulf are expected to occur duringJune-September. In order to know the maximumsurface current the wind-driven currents should becombined vectorially to the tidal currents presentedin Table 4. Very high wind speeds are expectedduring cyclonic period. A very severe cyclone hitthe Gulf of Kutch during October 1975. Themaximum wind speed recorded during the abovecyclone at various shore stations are given inTable 5.

The maximum wind speeds (167 km/hr) wererecorded at J amnagar. The over water wind speedsare expected to be 10% higher and hence wind speedof the order of 184 km/hr can be expected off

48

TABLE 5 - MAXIMUM WIND RECORDED DURING THECYCLONE ON 22 O(T 1975

Windrecording

station

Maximum windrecorded

Timehrs

VeravalDwarkaOkhaJamnagar

08001100

t1500

Speed Direction*(krnjhr] (degrees)

90 18067 360

100 110167 90

*Variation in direction of wind is due to the location ofstation lying in different quadrants of the cyclone.

+Exact time not known.

Jamnagar. Hence the maximum wind currentwhich could have occurred during the pre ientcyclone may be 0·57 m/sec towards 275°.

As explained in the section on general descriptionof the area, the density currents in the area areexpected to be negligible.

AcknowledgementThe authors wish to express their thanks to Dr

A. K. Malhotra, for his keen interest in the work. Theauthors are grateful to their colleagues Dr A. K.Lyal.l, Mcsse~s P. Vijay Kumar, V. Gopalan and J. S.Nagi for then valuable field work. The basic datausc~ in ~hi.s paper ~avc b.een collected by EngineersIn~Ia Limited for ItS clients, Indian Oil Corpo-ration and Department of Lighthouses and Light-ships.

References1. Survey of India, Indian tide tables, 1975.2. Engineers India Ltd, Draft report on the marine surveys in

G.ulf of Kutc.h for the construction of lighthouses, 1975.3. Engmeers India Ltd, Draft project report - offshore

terminal in Gulf of Kutch. 1974.4. EKMAN, V. W., Astronomi Fysik, 2 (1905), 11.5. NEUMA~N, G. & PIERSON, W. J. Ull. Principles of

phys1Cal oceanography (Prentice Hall Inc., Engle WoodCliffs, New Jersey), 1966.