Indian Journal of Marine Sciences
Vol. 6, June 1977, pp. 39-48
Current Regime in the Gulf of Kutch
P. 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 of
Kutch and analysed.
Tides in the area are of mixed type and are predominantly semidiurnal
with a large diurnal inequality. The mean spring tidal range from mouth to the closed end of
the Gulf ranges between 2·1 and 6·2 m. A correlation between tidal ranges and tidal current
speeds has been established for Gurur and Bobby Shoals and off Narara Bet. The data reveal
that the major steady currents in the area are of tidal origin. However, during south-west
monsoon period, strong westerly winds would generate wind driven currents, with surface
speeds reaching about 0·5 mjsec. The width of the Gulf narrows down between long. 69°E and
69°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.
URRENT regime in an area is one of the important factors affecting navigation, fisheries,
offshore structures, harbour construction and
coastal climate. Systematic study of current regime
in the Gulf of Kutch (Fig. 1) has not been done
previously, though general knowledge of the surface
curren ts for a few localized places can be had by
referring to the west coast of India Pilot or Naval
Hydrographic office charts.
C
The currents prevailing in the Gulf are controlled
by the various parameters viz. wind, tide, bathymetry, coastal configuration and density distribution. A brief description of the above is presented
in this paper.
General Description
of the Area
There is no major river discharging into the
Gulf and the average annual rainfall in the area is
l
JAKHAU
.
.
13
I
r:
\.j '-'-,
\.
./_.rI
\ ,--._/
•
_JAMNAGAII
LEGEND
_.
---
3·66m
to·97m
18·26n'1
- .. - ..- 36'56m
Fig. 1 -
CONTOURS
CONTOURS
CONTOURS
CONTOURS
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 encountered
in a normal estuary is not expected in the area.
Mean spring tidal range- from the mouth to the
closed 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 from
open sea to the closed end is about 2t hr. Bathymetry, coastal configuration, wind pattern
and
tidal range in the Gulf are such that they can
create very complicated current regime; therefore,
a detailed current study has been planned.
liVinds - Wind pattern in the area is predominantly
seasonal with rare cyclonic disturbances.
In order to understand monthly wind distributions
in the area. nearly 4000 ship observations covering
the area 21° to 25°N lat. and 67°E long. to coastline
for the period 1961 to 1966 have been analysed.
Predominant
wind directions in the area are
west-southwesterly
and north-northeasterly
during
June to September and December to March respectively. Higher wind speeds are likely to occur
during June to September with winds up to 74 kmjhr
from west or west-southwest.
July is the windiest
month in the area with wind speed exceeding 20
km/hr for 81·5% of time with predominant direction
from west-southwest. The calmest month is February
with winds exceeding 20 kmjhr occurring for 13·3%
of time only, the predominant wind direction being
north -p orth westerly.
Tides - Tides in any area can be grouped under
3 broad classes: semi-diurnal, diurnal and mixed.
Tidal variations at Okha, Sikh,
Kandla and
Navalakhi are compared for April 1975 and presented
in Fig. 2. Tides in the area are of mixed type and
are predominantly semi-diurnal with a large diurnal
10
11
DATE AND
Fig. 2 -
40
Tidal variations
inequality.
Various tidal elevations viz. mean low
water springs, mean low water neaps, mean sea
level, mean lligh water neaps and mean high water
springs for 4 locations are presented in Table l.
From a study of the tidal variations at various
locations in the Gulf the following conclusions regarding the movement of tidal wave could be made:
Tidal wave approaches the Gulf from the west. On
entering the Gulf the speed of the wave is reduced
on the shallower waters near the coast while in
the deeper waters the speed is maintained until
long. 69°22'E. The time taken by the wave to
travel from long. 69°E to 69°22'E is about 1 hr 20
min. From long. 69°22'E onwards the speed is
considerably increased and the wave reaches the
closed end in about 1 hr, the direction of the tidal
wave being from west-southwest following the orientation of the Gulf.
Tidal range increases faster from long. 69°E to
69°30'E; the increase is of the order of about 80%.
From long. 69°30'E to the closed end, the rate of
increase in tidal range is slower, being of the order
1-
TABLE
TIDAL
ELEVATIONS
AT VARIOUS
ST,\TIONS
Station
Mean
low
water
springs
(m)
Mean
low
water
neaps
(m)
Mean
sea
level
Mean
high
water
neaps
Mean
high
water
springs
Okha
Sikka
Kandla
Navalakhi
+0·41
+0'71
+0·78
+0·78
+1'20
+1·73
+1-81
+2·14
+2·04
+3·04
+3-88
+4·15
+2·96
+4'35
+5'71
+6·16
+3-47
+5'38
+6·66
+7·21
12
13
14
15
16
at different
J7
18
19
20 APR.':IS
TIME
stations
in April
1975
SRIVASTAVA
& JOHN:
CURRENT
of 30%. The total increase in tidal range from
the mouth to the closed end of the Gulf is about
150%.
Bathymetry and coastal configuration - The Gulf
of Kutch is an elongated gulf in the east-west
direction with an average depth of about 30 m. At
the mouth of the Gulf, Lushington
shoal with
depths nearly 5 m below chart datum is present.
On the south-east
side of Lushington,
a channel
with the depth of water varying between 30 and
50 m is present.
Besides Lushington,
there are
other shoals in the area, e.g. Gurur, Bobby, Ranwara,
etc. The presence of Ch anka reef and Ranwara
shoal narrows down the Gulf at about long. 69°20'E.
The coastal configuration of the Gulf is very irregular
with a number of islands, creeks and bays.
Density distribution - Data on the density distribution in the Gulf is not available except at the
mouth of Gulf and at station 5 (Fig. 1). Since the
tidal range and the tidal currents in the area are
quite significant, large scale mixing takes place in
the Gulf. There is no significan t fresh water influx
in the area and the average
annual
rainfall
is less than 52·5 ern, Hence a nearly uniform density
distribution
is expected in the Gulf.
Study of the density distribution at station 5 and
at eight locations in the outer Gulf of Kutch reveals
that the density is nearly uniform from surface to
bottom.
Therefore,
density currents in the Gulf
are expected to be negligible.
REGIME
IN THE
GULF
OF KUTCH
The locations where the current data have been
collected are presented in Fig. 1. Details of the
data collected for various stations
are given in
Table 2.
Tide data for Okha, Sikka, Kandla and Navalakhi
have been obtained
from the Survey of India.
Wind data for Okha, Jamnagar
and Kandla have
been obtained from the India Meteorological Departmer.t.
Detailed analysis for Gurur and Bobby shoals and
off N arara bet -- Long term current records- are
available only for locations Gurur shoal (station 2),
Bobby shoal (station 3) and off Narara bet (station 5).
Current records have been analysed to determine
half hourly current
speeds and directions.
The
$TILL
WAHl'.
LEVEL
J211t"'<p nSlfD
,
wlReSoM
i-O"G
'8l7t"'.p
po,-YPP.OPLENE
-80M
U:JfJG
Methods
The current meters used in the present study
are Bendix Q-15 self recording,
Hydroproducts
505-A self recording and Robert's direct reading
current meters.
Installation
of a typical current
meter is shown in Fig. 3.
TABLE
Station
No.
Location
Type of
current meter
used
2-
DETAILS
Float
observation
Surface
2
Gurur
About
3
4
Bobby shoal
Ranwara shoal
5
Proposed
H ydroproducts
self recording
model 505-A
do
Roberts
direct
reading
Bendex Q-15
self recording
One's direct
reading
6
7
8
9
10
11
12
13
SPM
do
do
Off Narara bet
do
do
do
do
do
Roberts
direct
reading
do
do
do
do
do
do
CURRENT
Depth of
measurement
below C.D. (m)
Lushington
shoal
shoal
OF
Fig.
3
About 3
At every meter
from surface
to bottom
7, 27
3-
Installation
DATA
of a typical
self-recording
meter (schematic)
current
COLLECTED
Horizontal
control
used
Theodolites
do
Theodolites
Period of
recording
Remarks
3.4 to 4.4.68
Collected by
chief hydrographer
Collected by
Engineers
India Ltd
do
do
8.3 to 2.4.75
do
6.4 to 9.4.74
1, 5, 10, 20, 30, 42
do
13.7 to 15.8.73
23.8 to 25.8.73
26.3 to 27.3.74
Surface, Mid
depth and near
bottom
do
do
do
Near bottom
do
do
do
21.4 to 23.4.74
do
do
do
do
do
do
26.4.74
18.4.74 and 24.4.74
25.4.74
22.4.74 and 23.4.74
21.4.74 and 22.4.74
22.4.74
do
Collected by
chief hydrographer
Collected by
Engineers
India Ltd
do
do
do
do
do
do
41
INDIAN
J. MAR.
SCI., VOL. 6, JUNE
speeds an d directions so obtained have been sorted
out to determine
the percentage
of occurrence of
different speed classes in different directions,
The
percen tage frequencies so obtained for stations 2,
3 and 5 are further analysed to determine predominant
speed,
maximum
speed and predominant
directions
(Table 3).
In order to understand
the variation of current
at spring, neap an d transition period the cumulative
frequency tables of curren t speeds for various periods
and for different stations have been prepared.
Based
on these tables current speed exceedence graphs
have been drawn and are presented in Fig. 4.
In order to get an idea of the distribution
of currents in different directions the available data
on current speed and directions for each station
have been plotted on a polar diagram.
The scatter
diagrams
of curren t speeds and directions
so
obtained are presented in Figs. 5-7.
3-
TABLE
PREDOMINANT
SPEED
Station
No.
AND
AND
MAXIMUM
PREDOMINANT
No. of
observa-
Location
PreMa.x.
dorni- speed
nant
m/sec
speed
m/sec
tions
2
Gurur
shoal
376
0·95
1·59
3
Bobby
shoal
719
0·95
1-46
5
Off Narara Bet*
(proposed SP:'.I
site)
792
0·20
0·76
filtered
out.
*\Vave current
CURRENT
DIRECTION
Predominant
direction
Sou therlv
and So~thSou theasterl y
Westerly and
Easterly
Easterly and
Southwesterly
1977
Tidal currents in an area normally increase with
increase in the tidal range.
A comparison of flood
and ebb current speeds with different tidal ranges
recorded at the nearest port has been made.
These
data are presented
in Fig. 8.
General anaiysis for whole Gulf - Simultaneous
tidal data in the Gulf are available only for Okha,
Sikka, Karidla and Navalakhi.
For understanding
the variation of tides from the mouth to the closed
end of the Gulf, tide data for April for all the 4
stations have been plotted (Fig. 2).
Maximum surface currents recorded at each station
during the present study together with the data
presented in the Indian Hydrographic
charts have
been presented in Fig. 9.
Results and Discussion
Gurur shoal- Predominant and maximum surface
curren ts recorded are 0·95 and 1·59 m/sec respectively.
The recorded directions show considerable
variations
(Fig. 5). The probable reason for this
could be that the direction recording mechanism
of the current meter did not function properly.
Current speed exceedence diagram (Fig. 4) shows
that the spring currents are 60 to 65% stronger
than the neap currents.
Current speed exceeds
1 m/sec for 18, 50 and 60% of time in the case of
neap, transition and spring tides respectively.
In
order to understand
the variation in current speed
with the variation in tidal ranges, tidal data for
the nearest available port, i.e. Okha, were plotted
against the recorded current speeds (Fig. 8). From
this figure it can be seen that for the same tidal range
ebb currents are stronger than the flood current.
The probable reason for this can be that since the
recording is at an elevated place compared to the
surrounding
area the down ward run of the water
will 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
' «, \"
~
"."
\
~-'
ST. No. 2
'\
"
§
\
~ 7S
"
'
\
\
",
§
\
~
\
\
~
;
~
i
\
..•
\
~
~
- - - ... -
SPRING
TRANSIllUJ
NEAP
\
\
\
\
\
\
\
\
\
\
\
__
\
\
\.
25
-,
\.
\
IL
"
\
\
\
\
\
\
ST. No.6
"
.
,
W05Q
\
--I\~~-;N::-A;:;R:;-;A;-;:R;-;A~B:-;;E:-;T-'"
ST. No.3
"\
\
:
'."\.~,
\
",
~
.~"
\
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~ OL-~~~-L-L~~~~~~~''-~'~~''~'~:-~~~~~~~~~~~_~~\~~~~''~~~~~~~~~~~~
~
o
I
o.s
Fig. 4 -
42
i.s
1.0
Current
speed
CURRE~i5 SPEED
exceedence
curves
Im/sl
1.5
1,0
for different
stations
0
0,>
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 [Currents
were recorded
using Hydroproducts
model 505-A current meter.
Depth of measurement
5 m above sea bed.
Current
speed 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.
BOBBY
16 - 3 -75
Fig.
44
6-
Scatter
diagram
6, JUNE
SHOAL
1977
(STATION
NO. - 3)
TO 3 - 4 . "IS
of current speeds and directions
at station
same as in Fig. 5. Depth measurement
3 (Bobby shoal) from
6 m above sea bed)
18.3.75
to 3.4.75
[Details
SRIVASTAVA & JOHN: CURRENT REGIME IN THE GULF OF KUTCH
N
O·
180"
s
NARARA
BETcSTATION
13-7-73 TOI5-8-73
Fig. 7 -
Scatter diagram of current speeds
same as in Fig. 5. Scatter plotting
NO.-S)
and directions at station 5 (Narara bet) from'13.7.73
to 15.8.73 [Details
are not shown separately for spring, neap and transition periods]
45
INDIAN
J. MAR. SCI., VOL. 6, JUNE
1977
1·5
GURUR
SHOAL
ST. No.2
ST. No.3
.. . I-'j'•
.. ;.
~
.s
>!.
0"25
"
:
IZ
lJJ
a:
a:
:l
u
~ "0
~
~
I.
.
. . .. I
a
..
/:
..
.
." / ......
. . .". . .
".
.
a
/.
/.
x
2·5
RANGE
,/. .'
/
./
:&.
.:
..
./
/
TIDAL
.. . .
/.'
.I.
2'5
.r
):1
.
.
a
~'/
J
..
,
".......
/.~IJI
/
(.
'I:
"/
ST. No.5
I
'j
//
/"
oJ>
s
:.. /
• 1,
lJJ
lJJ
c,
BET
OFF NARARA
BOBBY SHOAL
/
•...
. '.
FLOOD
•
EBB
- ---FITTED
RELATION
--FITTED
RELATION
5'0
AT
OKHA
FOR FLOOD
FOR EBB
7·5
(m)
Fig. 8 - Comparison of flood and ebb current speeds with different tidal ranges recorded at different stations
[Total
ranges 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 the
predominan t and the next predominant directions
of wind are north-westerly
and westerly respectively. These wind pattern
can create northeasterly a-id easterly surface currents in the area
and hence cannot add to the ebb flow in the
area.
Bobby shoalPredominant an d maximum surface
currents recorded are 0·95 and 1·46 m/sec respectively. The 2 predominant directions of recordings
are 80° + 10° and 260° + 10°, which is also the
orientation of the Gulf, ~howing thereby that the
tidal currents are predominant in the area (Fig. 6).
Curren t directions are bimodal with flood current and
ebb current flowing for 47 and 41 % of the time
respectively. During the remaining 12% of the time,
current direction is variable between 90° to 250° but
speed remains generally below 0·4 m/sec. Current
speed exceedence diagrams (Fig. 4) show that surface
speed exceeding 1 m/sec occurs 5, 45 a-id 56% of
the time in the case of neap, transition and spring
tides respectively.
These percentages
are lower
than those recorded at Gurur shoal. The spring
tidal currents are nearly 45 % stronger than neap
currents.
A comparative
study of the tidal range and
maximum recorded current speed (Fig. 8) show
that ebb current is in general higher than the flood
current.
The probable reason for this is the same
as discussed for the Gurur shoal.
Off N arara bet - Surface current: - The current
directions off Narara bets are bimodal, with predominant directions and peak speeds nearly parallel
to the bottom contour.
Predominant and maximum
46
surface currents recorded are 0·20 and 0·76 m/sec
respectively.
The 2 predominant
directions ot'recording are 78° ± 10° during flood and 2l3° ± 10°
during ebb period. These 2 predominant directions
are separated by l35° rather than UlO°. This may
be due to the concave nature (Fig. 1) of the southern
coast of the Gulf of Kutch which causes an additional
southerly component thus changing current direction.
Curren ts are dorninan tly tidal with a semi-diurnal
periodicity.
For 5% time, speed remains less than
0·05 m/sec which represents slack period between
flood and ebb tides. Current speeds during spring
exceeded 0·5 m/sec for 37% of time with the peak
speed of 0·76 nt/see towards 75°. Current speed
exceeden ce diagrams (Fig. 4) show that surface
currents exceed 0·5 m/sec for 4'5, 27 and 37% of
time in the case of neap, transition, and spring tides
respectively, which are lower than those recorded
at Bobby and Gurur shoal. Spring tidal currents
are about 82% stronger than neap currents.
From Fig. 8 it is seen that in general flood
currents are stronger than the ebb currents unlike
in the case of currents at Bobby and Gurur shoals.
During the months of June to September (southwest monsoon) winds exceeding 20 kmjhr occur for
58% of time (Fig. 2) with predominant
directions
ranging between west to west-southwest.
The winddriven currents generated during this period range
from easterly to east-northeasterly
and hence these
curren ts will superimpose
over th e flood tidal
currents.
This may be the probable
reason for
flood currents being stronger than ebb currents off
Narara bet.
SRIVASTAVA & JOHN: CURRENT REGIME IN THE GULF OF KUTCH
) r,
\)
-...
-JAMNAGAR
LEGEND:-
m
m
3·66
10 97
-·-·-18·28m
- .. - .. - 3656 m
CONTOURS
CONTOURS
CONTOURS
CONTOURS
"KHAMBHALIA
5 tAL
E •... 1 :665,1 SO
(b)
Fig.
9-
(a) Maximum
surface
currents
recorded at each station during the present
recorded at area marked [A] in the top figure
study
and
(b) surface
currents
47
INDIAN
TABLE
Max.
Season
December-March
April-May
June-September
October-November
4-
wind
Speed
(kmjhr)
Dir.
49
49
74
61
3300
2400
2700
600
J.
MAR.
SCI.,
6, JUNE
1977
NORMAL WIND-DRIVEN SURFACE CURRENTS
Max.
current
Predominant
wind
Speed
(rnjsec)
Dir.
0·34
0·34
0·49
0·42
191
101
116
275
Bottom currents _. An analysis of the data on
bottom currents reveals that the curren ts are strongly
periodic with bimodal current directions.
The predominant
directions
are 1l00± 10° during flood
and
169° ± 10° during
ebb. The predominant
directions differed from the surface current directions
with the flood current turned more onshore.
The
ebb curren ts instead of following the directions
2900± 10° as expected, flow towards
169°+ 10°.
The bottom currents are normally 70% of the surface
currents.
Surface currents in the Gulf of Kutch - The width
of th e gulf narrows down between long. 69°10'E
and 69°26'E due to the presence of Chanka Reef
and Ranwara shoal. This causes an increase in
the tidal current speeds with speeds reaching up
to 2·5 m/sec. The current speeds at the mouth of
Gulf and east of 69°26'E are comparatively lower,
with speeds reaching up to 1·5 m/sec. The general
direction of curren ts in the area are parallel to the
bottom con tour suggesting thereby the dominance
of tidal currents.
The wind-driven current will play an important
part in modifying the tidal circulation in the area
when the wind speed exceeds 20 krnrhr.
The
normal wind currents for different seasons in the
area have been computed
using the Ekmans
relationsv" and the wind data. The analysed data
is presented in Table 4. Maximum wind-driven
currents in the Gulf are expected to occur during
June-September.
In order to know the maximum
surface current the wind-driven currents should be
combined vectorially to the tidal currents presented
in Table 4. Very high wind speeds are expected
during cyclonic period. A very severe cyclone hit
the Gulf of Kutch during October 1975. The
maximum wind speed recorded during the above
cyclone at various shore stations are given in
Table 5.
The maximum wind speeds (167 km/hr) were
recorded at J amnagar.
The over water wind speeds
are expected to be 10% higher and hence wind speed
of the order of 184 km/hr can be expected off
48
VOL.
TABLE
5-
Predominant
current
Speed
(kmjhr)
Dir.
Speed
(mjsec)
Dir.
16
16
24
9
300
3000
2400
3300
0·09
0·09
0·15
0·08
225
165
105
195
MAXIMUM WIND RECORDED DURING THE
CYCLONE ON 22 O(T 1975
Wind
recording
station
Time
hrs
Maximum wind
recorded
Speed
(krnjhr]
Veraval
Dwarka
Okha
Jamnagar
0800
1100
t
1500
90
67
100
167
Direction*
(degrees)
180
360
110
90
*Variation
in direction
of wind is due to the location
station lying in different quadrants
of the cyclone.
+Exact time not known.
of
Jamnagar.
Hence the maximum
wind current
which could have occurred during the pre ient
cyclone may be 0·57 m/sec towards 275°.
As explained in the section on general description
of the area, the density currents in the area are
expected to be negligible.
Acknowledgement
The authors wish to express their thanks to Dr
A. K. Malhotra, for his keen interest in the work. The
authors 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 data
usc~ in ~hi.s paper ~avc b.een collected by Engineers
In~Ia Limited for ItS clients, Indian Oil Corporation and Department of Lighthouses and Lightships.
References
1. 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 Wood
Cliffs, New Jersey), 1966.