You are forgetting something.
There were no "concrete jungles" in Noah's day.
If you want to know why water rushed around the way it does now, why not ask geologists?
Is it not because the water often has nowhere else to go, than where they are directed, by the obstacles that man has constructed. Not to mention the places that are blocked by man's bad habits.
Contractors are appointed by RIICO to clean the drains. But in many parts of the industrial area, drains have ceased to exist as they have been filled with polythene bags, leaves and other garbage. The fact that monsoon is around the corner , cleaning up drains is not a priority.
What causes a flood?
A flood, put simply, is the accumulation of water over normally dry land. It’s typically caused by the overflow of coastal or inland waters (like rivers and streams) or by an unusual accumulation of water from heavy or prolonged rains, storm surges, or sudden snowmelt. Often, the ways in which we manage our waterways (via dams, levees, and reservoirs) and the alterations we make to land also play a role in flooding. Increased urbanization, for example, adds impermeable surfaces (think roads and parking lots), altering natural drainage systems [and not keeping gutters and drains free of debris]. Areas can be especially prone to flooding when stormwater infrastructure isn’t maintained or homes are built in areas susceptible to flooding known as floodplains. More and more, flooding factors are also linked to climate change.
...low-lying areas with poor drainage are particularly vulnerable. Also caused by dam or levee breaks or the sudden overflow of water due to a debris or ice jam, flash floods combine the innate hazards of a flood with speed and unpredictability. That’s why they’re responsible for the greatest number of flood-related fatalities.
I see this mistake being repeated repeatedly - that of using today's situation, or features, and projecting these on to the account of the flood of Noah's day.
When we do this, we make assumptions that lead to faulty conclusions.