Contemporary Urban Environments 7

Urban areas are covered in impermeable materials. Many urban structures are designed to shed water quickly.

This means that infiltration is low in urban areas, so replenishment of groundwater stores is slow. Groundwater feeds rivers, so during drier periods, river discharge in urban areas is low.

Precipitation is higher in urban areas than in rural areas, and storms are more intense - this increases surface runoff.

Runoff is channelled through man-made pipes, which transports water to rivers and streams.

Low infiltration rate, high surface runoff and channelling of water means that water enters rivers quickly. This gives a short lag time and high peak discharge, with a fast return to base flow.

Catchment management is a way of managing rivers and improving drainage systems by looking at the whole river catchment, and the interactions between water and land.

It aims to minimise issues, such as flooding, drought, water pollution and erosion in sensitive areas, and to improve river ecosystems.

There are two main methods that can be used to manage river catchments:

• Hard engineering - this involves man-made structures, such as dams, floodwalls and reservoirs, which are often used to prevent flooding and ensure a constant water supply. However, hard engineering schemes are often expensive and can disrupt natural systems and they can also alter wildlife habitats.
• Soft engineering - this uses knowledge of the river basin and its processes to try to work with nature. It involves land use management. It can also involve river restoration and conservation. It is gnerally cheaper than hard engineering, and it can improve the local environment. However, planning restrictions can limit the construction of new homes and businesses, and land use management is hard in areas that are alredy urbanised.

Decisions about what methods to use are made by experts in water management rather than residents - what is best for the catchment as a whole may not be best for all individuals, so some residents and communities may feel ignored.

Catchment management schemes can also be disruptive.

Sustainable…