CONTEMPORARY URBAN ENVIRONMENTS: Urban Drainage

Urban areas hold more precipitation than rural areas. This is because there is warmer air in cities that can hold more moisture. Dust and pollution make more condensation nuclei also. The humidity is decreased however because less vegetation in urban areas means less evapotranspiration occurs. The urban catchment is also dominated by surface runoff due to the tarmac, concrete and other hard surfaces. Drains are therefore needed to reduce surface water quickly.

Urbanisation is really signifcant in altering the storage of water. Urban rivers are primarily the exit for water transferred through the drainage basin. Reservoirs, lakes, ponds and swimming pools are permanent stores but vulnerable to evaporation. Depression storage, such as surface puddles, following rain is temporary. Interception storage is reduced owing to the replacement of vegetation by impermeable structure such as buildings, roads and pavements. Soil moisture storage will vary according to ground conditions.

We can also use flood hydrographs to look at the amount of precipitation and discharge in a certain amount of time. This is essential because of the increased risk of floods in urban areas caused by the higher proportion of urban precipitation making its way to urban river channels and the speed in which this happens.

Drainage management in urban catchment areas is controlled by hard and soft engineering. Hard-engineering projects invariably involve high costs of…