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Why does it flood?

House Flooding along Briar Creek
Flooding is caused by too much rain
in too little time

Flooding is a natural occurrence caused by heavy rain.

If it rains hard enough or long enough, low-lying areas are at risk of flooding.

Flooding does not necessarily mean problems with the storm drainage system. Drainage systems, including storm drains, pipes, ditches and creeks, are designed to hold a specific amount of storm water.  
A flash flood occurs when the amount of rainfall overwhelms our natural and man-made drainage systems or low-lying areas. Generally, one inch of rain per hour will cause flash flooding.

Extra water has to go somewhereHouses and cars surrounded by floodwater
There is a limit to how much water our creeks can hold. If enough rain falls in a short amount of time, creeks naturally overflow onto the floodplain.

Floodplains are designed by nature to flood. For that reason, floodplains are part of a healthy creek system.
                                                                            Rain-swollen creeks naturally overflow
                                                                                         onto the floodplain

Development doesn't cause flooding but can make flooding worse
Although flooding is a natural occurrence, man-made changes to the land can also be a factor. In cities and suburbs, pavement and rooftops prevent some rainfall from being absorbed by the soil. This can increase the amount of runoff flowing into low-lying areas or the storm drain system. And eventually, that excess runoff flows into our creeks.
While flooding cannot always be prevented, the risks can sometimes be reduced. Storm Water Services:

Heavy downpours can overwhelm our storm drain system
Heavy downpours can overwhelm
our storm drain system