Floods occur when the river flows higher then its regular base. They bring disaster to humans, and fertile soil, making crops grow better.
Tectonic shifts caused a major river, the Sarasvati/Ghaggar river, to dry up. There were also changes in the monsoon rains which caused floods followed by droughts, so that most of the people left.
The indus river
The soil in the Indus River valley receives its rich silt from the annual flooding of the river. The Indus River carries sediment and nutrients downstream, depositing them on the surrounding land during floods. This process replenishes the soil and makes it fertile for agriculture.
The Aryans (Vedic people) overthrew the stone forts of the Dasyu. If you refer to the Indus Valley Civilization people, no one conquered them, they left Sindh because of floods and drought.
Indus River Valley.
The Indus River Valley is the longest river in Pakistan.
There were monsoon rains that caused floods which damaged houses and other buildings. During the dry season, people and animals went hungry and thirsty, and crops dried up.
It flows through it.
Indus River Valley, India.
The Harappan or Indus Valley civilization was located in the Indus Valley of Pakistan and the Sarasvati river valley in north India, from about 2600 to 1900 BC.
In The River Indus