6.3.3 Drainage systems
Minimising the risk of flooding by designing effective drainage systems is another important aspect of urban plans. This is partly a matter of designing and building drains that are large enough to cope with high volumes of water. Rainwater from roofs can be collected and put to good use rather than just allowed to run into the drains. There are also ways of reducing the area of impermeable hard-surfacing so that more water can infiltrate into the ground and the speed and volume of surface run-off is reduced. These sustainable drainage systems (SuDS) include a range of techniques such as using gravel or cobblestones, which are permeable, rather than solid concrete, leaving grass or bare earth areas where possible so that water can infiltrate into the ground, and building ponds or water-holding areas into the drainage system so that rainwater is temporarily contained and the speed of flow is reduced.