Human Causes of Flooding - Urbanisation

More people are living in towns and cities

Population growth and urbanisation has led to demand for land to build on - floodplains are flat and are food for housing

Concrete and tarmac, used for roads and pavements as they are impermeable, preciptation cannot infiltrate so gets into the river much more quickly

Less interception as trees and plant matter is removed so precipitation gets into the river much more quickly.
Often surface water is channelled directly into drains and sewers, so precipitation reaches the river much more quickly.

Bridges over rivers can constrict rivers, slow discharge and reduce the carrying capacity of the river.

Reference: http://www.acegeography.com/causes-of-flooding.html