I agree to a large extent with the statement “Urbanisation within a drainage basin can affect flows to and within a river channel.” Urbanisation is the physical growth of urban areas as a result of rural migration. Some processes of urbanisation are cutting down of vegetation, removing earth and replacing it with manmade material and drains. Drainage basin refers to the land that drains into a river. Flows to a river channel are flows such as stem flow, infiltration and overland flow. Flows within a river channel are flows such as channel flow. These processes of urbanisation within a drainage basin affect flows to and within a river channel.
Urbanisation affects flows to a river channel such as stem flow, infiltration and overland flow. Processes of urbanisation such as cutting down of vegetation and replacing earth with manmade materials will affect these flows. The cutting down of vegetation will reduce interception by vegetation. This in turn reduces leaf drip, stem flow and infiltration. With less interception, water reaches the ground quickly and there would be less infiltration as water would run off over the surface as overland flow. In addition, the replacement of earth with manmade materials such as cement and tarmac etc will result in an increase in the Hortonian overland flow (HOF). In contrast, there would be a decrease in the amount and rate of infiltration. With less water being infiltrated into the soil, there would be a drop in the amount of saturated overland flow (SOF) and throughflow. This results to less groundwater being present and hence, a decrease in base flows. This leads to a higher and faster discharge after a storm as water would reach the river channel faster by HOF instead of infiltration, SOF or throughflow. An example is the Valley Stream in New York. Studies have shown that more water is being discharged to tide and not seeping into the ground, thus reducing base flow to the streams after urbanisation occurred. This has resulted in significant loss of ground water flow to streams in the area from 86% to 22%.Therefore, urbanisation processes within a drainage basin affects the amount and rate of flows. There would be a higher amount and rate of HOF while a decrease in amount of leaf drip and stem flow and SOF. The rate of infiltration, throughflow and baseflow will also decrease.
