Evidence for a tsunami hitting Dholavira at some point in the past was recently presented by scientists from the Indian National Institute of Oceanography (NIO). While some of the details and implications remain unclear, there is mounting evidence that the management of water at Indus sites like Dholavira, both storage and perhaps protection from too much water, was a critical part of this settlement's construction.

http://www.thehindu.com/news/cities/mumbai/news/harappans-built-barriers...