Flooding The process of urban development carries with it a variety of hydrological consequences. In particular, urbanisation increases the magnitude of floods and reduces the average interval between serious flood- ing. The major mechanisms that cause this include: the greater proportion of i surfaces, which tends to increase the total volume of storm run-off and reduce the amount of water which infiltrates into the ground; 2. the artificial 'improvement' (e.g. paving and straightening) of stream channels, which reduces the time lag between rainfall and chan- nelled run-off; 3. landscaping and subdivision of the land into building sites, which usually shortens the dis- tance over which water flows before reaching a drainage way, which reduces 4. human settlement of flood plains,