To be frank..its less bcz in general for the level of rainfall it happened in chennai and flood water will cause more damage to the flow what they have,as we are experienced near my home town.... water even flowed over tha barrage as the inflow is hgh and outflow is unable to reach and what happened if the floods come from high level to low level example is kurnool City floods.
But as MAS is just 5mts above sea level so water is more stagnated than flow