Gulf of Cambay Cradle of Ancient Civilization (cont.)
By Badrinaryan Badrinaryan
The term SONAR stands for Sound Navigation and Ranging. Sonar is a sensing stratergy which measures features of an environment (or medium) by the way in which that environment transmits, reflects and/or absorbs acoustic (sound) waves. The seabed is a little understood environment due to its inaccessibility and resistance to large scale detailed analysis. Sonar represents a clear approach of looking at the seafloor. Side Scan
Sonar uses sound waves to produce images of the seafloor. The hard areas reflect more energy and are seen as dark shades, whereas softer areas do not reflect energy as well and are represented by lighter shades. This “Backscatter” is absent behind objects or features that rise above the seafloor, and are represented as white shadows in the sonar image. The dimensions of shadows are used to infer the size of the objects. The system used was a digital one which provides high resolution sonar images of the seafloor through advanced digital technology in 100 and 400 kHz frequency. The unit is connected to a Differencial Global Positioning System (DGPS) for the accurate position of the survey vessel and in turn that of the objects.
Figure – 5
In these surveys it was the SideScan Sonar which gave excellent results supported by other systems. Initially two major palaeo channels of rivers were recognized. One over a length of 9.2km and another over 9.0km. When these were sampled, it was seen that just below a thin marine sediment cover of few centimeters, river alluvium and pebbles typical of terrestrial river sediments, below which typical river conglomerates were observed at depth. Such evidence clearly indicated that the area presently under sea, was originally dry land over which rivers were flowing. Due to different factors, they got submerged and now lie beneath the sea. The sonar images showed regular geometric patterns in one palaeo channel over a length of 9km in the sea about 20km west of Hazira coastal area. Associated with this on either side of the palaeo channel , basement like features in a grid pattern were observed at a water depth of 20-40m. These resemble an urban habitation site wherein, in the basement now at the bottom of the sea, pit like structures are seen. Another palaeo channel over 9.2km was detected off Suvali coastal area. Here also similar features were observed. In general the basement like features were located in a linear east-west direction on either side of the palaeo channel. It is seen that these features are 5x4m size on the eastern side whereas the westernmost part had dimensions of 16 x 15m. The habitation sites are all seen to be laid in a strict grid like pattern (Fig.5) indicating a good sense of town planning by the ancients.
Figure – 6
There were also evidences of water conducting system like canals, etc. All these point to a properly planned township, with a high level of knowledge and practice by the ancients. The area in general is seen to be covered by sand waves which occur above the seabed. Often these cover the dwelling but even then the shapes could be made out (Fig.6). Apart from the regular sites of habitation, the Side Scan Sonar picked up images of several big structures. Some of these structures are as follows :
There is a rectangular (41m x25m) shaped depression, wherein one can sea steps gradually going down to reach a depth of about 7m (Fig.7). Surrounding this depression there is a wall like projection on all sites. One could observe an inlet and outlet and also a separate enclosure. This looks like a tank or bathing facility now occurring below 40m of sea water. It occurs near the western periphery of the town. It resembles the “Great Bath” that is found in the ruins of “Mohonjadaro” and “Harappa”, where also these occur on the western side of the township. There are two divisions in the tank, which may represent separate enclosures for men and women or for socially higher and lower categories of people. There are two openings probably for inlet and exit of water to keep the water in the tank fresh and clean.
Figure – 7
In Fig.8 one could observe a long linear prominent and well made basement of a major structure measuring 200m x 45m. It nestles on high ground and one can see steps on the right corner approaching the structure. Inside the structure there are many 18m and above square shaped room like features with fortifications surrounding it. This type of huge structures resembles the “CITADAL” found in Mohanjodaro, Harrappa, Dholavira wherein these occur at the western extremity again on the high ground. Probably it is an administrative building supervising the entire civic activities of the township or could be a place of worship. Some pieces of fossilized human bones, natural teeth and
some fossilized animal bones were recovered during sampling on the eastern side of the citadel
Figure – 8
Sonar image in Fig.9 picked up a major dilapidated structure measuring 190m x 85m with spaces separated by what looks like collapsed walls. In front of it, on the bottom side there are several basements of rectangular shaped 2.5 to 3.5m x 6m structures, resembling minor dwellings. It could be an ancient granary for the township probably with dwelling place nearby, for the workers. In the nearby areas some fossilized food grains have been collected. In many of the Harappan sites the granary is a regular feature.
The image in Fig.10 is that of a basement of a buried settlement and it measures 74m x 48m. It has regular square, rectangular and arch shapes. The darker portions are the elevated or standout features. These indicate that there are still some constructed portions standing up partly. To the north of the structure also, a few square and rectangular shaped basements are visible.
A buried structural basement is depicted in Fig.11. The main structure measures 40m x 19m with wall-like dark features rising to 2-3m above the seabed. A series of step-like features are seen approaching the structure from the right side. To one corner of the main structure a 11m x 7m rectangular depression looking like a small tank or pond is observed.
Figure – 9
Sub-bottom profiler surveys, instead of reflecting sound waves from the seabed like side scan sonar, penetrate the seabed. The waves travel beneath the seabed in different formations in different speeds and the instrument collects the reflection data over selected frequencies. It provides good depth information on geological features apart from delineating any suspected buried anthropogenic structures.
The sub-bottom profiler image in Fig.12 is below the 200m x 45m Citadel like structure. The standout features were picked up at regular intervals and appear to be the basement and foundations of the structure. It is observed that the foundations have been dug up to 5-6m in the soil over which broad column like features have been constructed, probably to take the load of the huge structure above.
The sub-bottom profiler image in Fig.13 is below the buried settlement of 74 x 48m structure. Here also man made foundations like column can be clearly seen emerging from below the seabed and occur as standout features. Here, the foundations have been dug up to 3-4 m deep in the soil. These types of planning and method of construction by ancients clearly reveal that they had a very good knowledge of civil and structural engineering, wherein broader and deeper foundations were provided for bigger and heavier structures and thinner and shallow foundations for comparatively smaller structures. Likewise almost all the structures including the dwelling sites indicate a good amount of planning and design, taking into consideration the structural aspects.
Figure – 10
Figure – 11
Figure – 12
Figure – 13