The Indus Valley Civilization did not flourish by the Saraswati...

Analysis of the sediments on the river bed and satellite imagery showed recently that the majority of the Indus civilizational sites were grouped around the Ghaggar-Hakra rivers which are monsoonal rivers and not perennial ones. Via checkdams and storage sites, the cities stored water for use in the non-monsoon seasons. By not being near perennial rivers, these settlements avoided the destructive floods and change of channels that the mighty rivers are capable of.

Tall well, Mohenjo Daro / Nikesh Chawla / CC-BY-SA 4.0

A recent study showed that Indus urban settlements developed along an abandoned river valley rather than an active Himalayan river. This remnant of the inactive river is a former course of the Sutlej River. The flow of the Sutlej in this course terminated considerably earlier than the Indus occupation, with diversion to its present course completed 8000 years ago. This enabled long-term stability for Indus settlements sited along the inactive river.

Alluvial landscapes built by large perennial rivers form the environmental templates on which the earliest urban societies nucleated. On long time scales, rivers migrate by relatively abrupt changes in their course called avulsions. River avulsions have long been considered important in the development of early complex society. It is commonly accepted that settlements are clustered near active rivers and that river avulsion leads to settlement abandonment. 4500 years ago, the Indus Civilisation developed one of the most extensive urban cultures in the Old World (much more extensive than either the Egyptian or the Mesopotamian civilization). This civilisation was established on the alluvial plains of the Indo–Gangetic basin in northwestern India and Pakistan.

Lothal Dockyard / Raveesh Vyas / CC-BY-SA 2.0

The Indus Civilisation has long been considered river-based, with two of its largest and best-known cities, Harappa and Mohenjo-Daro, located adjacent to large perennial Himalayan rivers – the Ravi and the Indus, respectively. However, the largest concentration of Indus settlements is located near the divide between the Ganges–Yamuna and Indus river systems in India and Pakistan, far from major active rivers. There is an inactive river course around which these settlements are grouped which was thought to be the mythical river Saraswati. The drying up of the river that formed the Ghaggar–Hakra channel has been suggested as a major factor in the decline and abandonment of Indus urban centres in the region.

Analysis of the sediments on the river bed and satellite imagery showed that a major Himalayan river was not contemporaneous with Indus settlements in the Ghaggar–Hakra region and did not sustain the Indus Civilisation in this region. The locus for the abundant Indus Civilisation urban settlements along the Ghaggar–Hakra channel was the relict, underfilled topography of a recently abandoned valley of the Himalayan Sutlej River rather than an active Himalayan river. This abandoned incised valley was an ideal site for urban development because of its relative stability compared to Himalayan river channel belts that regularly experience devastating floods and lateral channel migration.

Water canal for the Great Bath,
Mohenjo Daro / Quratulain
CC-BY-SA 3.0

The abandoned river channel became fed by sedminents from ephemeral monsoon-fed rivers derived from the Himalayan foothills, likely the equivalent of the modern Ghaggar River and its tributaries. Indus urban settlements in the region were thus likely sustained by monsoons. This and the potential to pond flood waters in the topographic depression formed by the valley likely offered favourable conditions that led Indus populations to preferentially settle along the incised palaeovalley. A study suggested that decline in monsoonal rivers due to weakening of the Indian summer monsoon was responsible for the decline in the civilization.

River dynamics controlled the distribution of Indus sites in the region, but in the opposite sense to that usually assumed: it was the departure of the river, rather than its arrival, that triggered the growth of Indus urban settlements here. A stable abandoned valley, still able to serve as a water source but without the risk of devastating floods, is a viable alternative model for how rivers can nucleate the development of ancient urban settlements.

Acknowledgment : This post is entirely based on and edited from the article : 

Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements.