'The Transactions of the Bombay Geographical Society. From January 1865 to December 1867. (Edited by the Honorary Secretary.) Volume XVIII.' [‎102] (238/268)

102
GEOLOGICAL ACTION ON THE SOUTH COAST OF
The comparative velocity with which the tidal wave flows before it
is checked by the bank between Diu, Jaffrabad, and Goapanath, and
after it has to pass over the hank, is shown by the co-tidal lines, for it
flows from onposite Mool-Dwarka to Jaffrabad, a distance of about 50
nautical miles Originally one minute of arc measured along a meridian, but since 1929 redefined as 1,853.20 metres. in 1 hour and 5 minutes, as per Admiralty Tide Tables,
namely, from 10 hrs. 30 m. to ll hrs. 35 m., while from Jaffrabad to
Goapanath, a distance also of about 50 miles, it takes fiom 11 hrs.
35 m to 2 hrs. 15 m-, or two hours and forty minutes, or at little more
than one-third of the velocity it travelled over the former fifty miles.
The retarding effect of this bank is therefore very conspicuous and
rlpfifled.
On an inspection of Model Chart No. 2 (which was not in the
possession of the Author when the former Memorandum was written),
it will he readily seen that there is another very formidable bank which
helps to force np the tidal waters into the Itunn of Kutch, namely, the
hank to the Westward, formed by the sediment and detritus biougxit
down by the Indus. The area of this bank is between 4,000 and 5,000
square miles ; and its retarding influence is clearly indicated by its
taking two hours and a quarter for the tidal wave to travel 35 miles,
namely from Dwarka to Assar point.
The great tidal wave is thus influenced by the submarine groyne to
the Eastward, at the entrance of the Gulf of Cambay, between Diu,
Jaffrabad, and Goapanath, and by the enormous bank formed by the
detritus from the Indus, lying between the mouths o( that river and
the Gulf of Kutch, and thus the waters are forced up the Runn of
Kutch in greater quantity, and to a greater height, gradually merers-
ing from time to time, as the two Banks on either side increase in
extent, and the consequent increased effect in retarding the flow of
the tidal wave.
There are two submarine bays near the entrance to the Gulf of
Kutch, in 20 fathoms water; the one is opposite Yeerwarrah, and is 50
nautical miles Originally one minute of arc measured along a meridian, but since 1929 redefined as 1,853.20 metres. wide at its outer entrance, and runs 12 miles inwards
towards the land. The other is to the Westward of Lushington Shoal,
and is about 60 nautical miles Originally one minute of arc measured along a meridian, but since 1929 redefined as 1,853.20 metres. wide, and runs inwards for about 20
miles—these are shown by the purple colour—bordering the shallow
water (coloured red).