Date: 2 June 2012
Urbanization is the process that leads to an increase in the number and proportion of people living in urban settlements such as cities or towns. It also refers to the increase in the size of land area occupied by urban settlements. To cope with urbanization within a drainage basin, urban development and deforestation are carried out, which affect flows to and within a river channel. Other factors like drainage density, climate, area of drainage basin and gradient of slope can also affect flows to and within a river channel. Flows to and within a river channel also include overland flow, infiltration, through flow and base flow. Overland flow is the movement of rainwater over land. It occurs when either the storm is too heavy for water to infiltrate into the soil, where the soil is impermeable or when the soil has become saturated. Infiltration is the downward movement of water through tiny pores in the soil. Through flow is the water reaching the river through the soil and the underlying rock layers. Base flow is the water stored at a depth in rocks. I agree to a large extent that urbanization within a drainage basin can affect flows to and within a river channel. When urban development happens within a drainage basin, it means that more land is required for the development of housing and industries to meet the needs of the urban population, and as a result, built-up areas will increase. To have more land, parts of the drainage basin will be converted into concrete pavements and tarred roads. The concrete pavements and tarred roads prevent infiltration as most of the roads are made of granite and are impervious. As a result, there is an increase in the amount of overland flow into the rivers, which causes floods to occur. Also, when part of the river channel is being blocked, the river cannot flow as smoothly as before. The speed of the river flow will decrease.
For example, in London, the areas