Which practice is closely associated with most ancient river valley civilizations

I believe the answer is: irrigation systems

The indus valley civilizaitons was the first civilization to create a system that connect their rivers to their agricultural field.

This concept was studied and adopted by many other civilization after them s (such as european and African civilizations) due to its efficiency

Due to access to water, and thus the ability to create irrigation systems, ancient river valley civilization were among the first to dabble in agriculture. During the Indus Valley Civilization's time farming practices were common, and by the Aryan's settlement times formal agricultural systems were set in place.