Stormwater in an urban environment

In a built-up urban environment there are less water-infiltrating earth surfaces than for example in suburban single-family housing areas or in parks. A densely built urban environment also often includes fewer trees evaporating water and other vegetation. The amount and discharge of stormwater in cities are higher than in areas which are in a more natural state. 

An area from which stormwater runs into a rill or water body is called a runoff or catchment area. The larger and more watertight the built-up part of the runoff area's surface is, the more and faster stormwater is generated. In this case, during heavy rainfall for example, an open trench where stormwater is being conveyed to can flood heavily. 

Picture: The impact of stormwater in the lower part of the runoff area

a) When the water infiltrates into the ground, stormwater remains under control in the environment. 

b) If, within a built-up environment, stormwater is conveyed quickly away, it might create floods elsewhere in the environment. 

If stormwater is conveyed quickly away from the property, it does not cause any harm on the property. However, stormwater can cause harm elsewhere in a built-up environment or in the recipient water body.

Urban compaction intensifies this phenomenon because along with it, the share of permeable earth surface decreases. This again increases the stormwater flows. Detention and infiltration of stormwater on properties and public areas even out the stormwater flow in the lower parts of the catchment area in which case the risk of damages caused by stormwater floods is reduced.

It is recommended to infiltrate and detain stormwater on the properties because it reduces the loading of the stormwater sewer network. The infiltration possibilities for stormwater depend on the soil of the area but detaining stormwater is possible everywhere. 

Read more about the stormwater management on a property  »