The opulence of water, silt and heat have made Bengal one of the most ecologically productive regions on earth. The key signatures of the region are extensive alluvial plain, intricate network of dynamic river system and intense seasonality of monsoon rain causing annual inundation of floodplain. The changing hydrology of Bengal has had immense impact on the human settlements. The Society has been struggling continuously to cope with the dynamic river system of Bengal. This coping mechanism is best understood when one looks at the changing locations of capital towns and ports of Bengal since 300 ac till date. The colonial rulers had lack of understanding of holistic eco-hydrology of the delta. The structural interventions (embankments, weirs and barrages) were not successful to alter hydrology. rather they invited many an adverse impact. There have been number of technical advances in recent decades that have enabled new research into the behaviour of the delta rivers. The aim of this text is to throw new light on the complex history of society and water in Bengal combining extant historiography with other new sources.

Graham Chapman, Emeritus Professor, Lancaster University, UK, who passed away on 31 August 2014, had been a champion for the holistic study of South Asia, writing prolifi-cally about the region as a whole, its history, environment, agriculture, urbanisation and geopolitics. He was a renowned authority on the geography of the Ganges and Brahmaputra systems and the conflicts and politics involved in them.

Kalyan Rudra is presently the Chairman of West Bengal Pollution Control Board and a member of the Central Pollution Control Board as well. He is also the Advisor to the International Union for Conservation of Nature in its project called 'Ecosystem for Life'. Dr Rudra did intensive research on the rivers of the Ganga-Brahmaputra delta and on the water resource management of West Bengal. He has been working on the history of mapping Bengal and engaged in editing A Bengal Atlas by James Rennell (1780).

It was a great shock to receive the news of Professor Graham Chapman's sudden death in London a year ago at the age of 70. He had contributed much to Indian Geography, particularly to the geography of West Bengal as the contents of this publication clearly testify. My academic comradeship with Graham started in September 2000, when a devastating flood marooned large part of Southern Bengal and he was stranded in Berhampur (Murshidabad district, West Bengal). We investigated the causes and effects of that deluge and the result was a paper titled 'Water as Foe, Water as Friend: Lessons from Bengal's Millenium Flood', which was published in Journal of South Asian Development. His specific contribution was focussing on the history of changes in the Ganga and its distributaries in Bengal. He had keen interest in the complex history of society and water in West Bengal combining extant historiography with the new knowledge.

In 2006-07, Professor Chapman collaborated with Mrs Pat Saunders, an independent historical geographer, in the first phase of a project then entitled Human Intervention and Dynamic Environmental Change in Bengal funded by the British Academy and based in Lancaster University. Phase two of the project, now termed as the Bengal Maps Project, continues at the University of Cambridge, with additional inputs from Professor Keith Richards, Dr Maminul Haque Sarkar of Bangladesh, Mr Hugh Brammer and myself. It was Professor Chapman's enthusiasm and skill which enabled the important research on the history of river changes in greater Bengal to take place.

The rivers flowing through Bengal are its cultural and economic backbone. The rivers have contributed generously to the rise and prosperity of the earliest civilisations in history. The river system of Bengal has so changed that it is often difficult for the historians to find linkage between the archaeological sites and the rivers which once helped to flourish them. The present occasional paper is expected to bridge the knowledge gap in the history of Bengal.

It is not quite often, especially in this era of effortless communication, that a person becomes synonymous with his area of research. Prof. Kalyan Rudra has achieved that distinction. Thus, it is little wonder that his is the name that comes to the mind of the highest echelon of the government officials and common man alike when one deals with the nature of the riverscape of Bengal.

Prof. Rudra was awarded the PhD degree by the University of Calcutta for his work on the Evolution of the Bhagirathi-Hugli river system. He had been teaching in a degree college affiliated to the University of Calcutta, and took a break from the teaching career in 2007. He then conducted two research projects under the aegis of the West Bengal Pollution Control Board. One is on the water resources and its quality in West Bengal and the other is on the rivers of West Bengal. He has published many research papers in reputed journals of India and abroad. He has held the posts of the Advisor to the Department of Environment, Government of West Bengal, and the Chairman, West Bengal Wasteland Development Corporation. Presently he is the Chairman, West Bengal Pollution Control Board.

The Atlas of Changing River Courses in West Bengal, 1767-2010 published by the Sea Explorers' Institute in 2012 is a path-breaking work by Prof. Rudra.

We, at the Centre for Archaeological Studies & Training (Eastern India), are immensely grateful to Prof. Rudra for delivering an occasional lecture on 'Time Streams: History and Rivers of Bengal' on 18 August 2015, delivered to a full house of students, professors and knowledge enthusiasts. I am confident that a printed version of the lecture will be of great use to everybody engaged in similar areas of research.

The Ganga-Brahmaputra delta is the largest and fastest changing on earth, as a result of the large monsoon discharges and silt loads of these two rivers, and of the many major tributaries that debouch straight from the Himalaya and the northeast Deccan into the delta zone. The delta almost coincides with the cultural and linguistic region known as Bengal, whose history has generated an extensive literature, much of it sensitive to the dynamic ecology (e.g. Eaton, 1996; Iqbal, 2010).

There have been many technical advances in recent decades that have enabled new research into the behaviour of the delta rivers. Old maps can be scanned and digitised, making them more easily available; GIS systems can be used to geo-rectify old maps and to split information into different layers; and satellite imagery can be matched with this evidence. Recent examples of work in this direction include Saunders and Chapman (2006), who provided a bibliographic guide to map sources available, and Rudra (2012a), who used this material to provide an Atlas of the Changing River Courses in West Bengal, in his case using maps from the time of Rennell's surveys (from 1764 to 1777), later map sources, and satellite imagery. In addition, soil surveys (e.g. FAO, 1988) have thrown new light on river history.

The aim of this monograph is to see if any new light can be thrown on the aspects of the complex history of society and water in West Bengal combining extant historiography with these new sources.

BENGAL

The Bengal delta straddles the tropic of Cancer. Hence, the combination of water, silt and heat creates one of the most ecologically productive regions on earth. In prehistoric times, the vast majority of the region was forested, interspersed with many great rivers, swamps, marshes and new char land, and also inhabited by a variety of fauna which included several top carnivores (Imperial Gazetteer of India, 1909: 217). However, it was and is differentiated. In general the area to the north of the current Ganga and west of the current Brahmaputra, known as the Barind (see Fig. 1), is higher (a fault bounded uplifted block of sedimentary strata) and drier than the southern part of the delta. The natural vegetation there includes thornier trees, as opposed to the sal of other areas. The coastal fringe of the delta is different again, including the mangroves and sundri trees of the Sundarban. A detailed account of the many forest types is given in Champion and Seth (1968). Significantly, Bengal delta has superb biological resources, but no stone, virtually no iron, and no accessible fossil fuels (save recent discoveries of gas). The nearest source on the Ganga to provide stone is the outcrop of basalt in the Rajmahal Hills at the head of the delta.

The delta is, in contemporary times, split politically between West Bengal in India and Bangladesh (erstwhile East Pakistan), but Bengali is spoken in both parts. Bengali is a Sanskritic language, whose provenance is from Aryan settlers in the upper Ganga valley. But Bengali contains grammatical features and words from proto-Munda, a language within the Tibeto-Chinese family. Modern Munda is spoken by the adivasis in the hilly country of the northeast Deccan. Genetically, modern Bengalis seem to be a relatively homogeneous group, though the product of many different groups, including Indo-Aryan (probably the most recent admixture), Dravidian, Mongoloid, and Austro-Asiatic. Combined, this evidence suggests that there has been a long history of human settlement within the delta, presumably at low density by hunter-gatherers. Given that the rivers erode their banks, deposit new land and periodically change course, it is hardly surprising that there is little physical evidence of this early occupation.