Urban drainage

• what falls in greater amounts in urban areas?

  precipitation
• what are the urban drainage systems designed to deal with?

  surface runoff generated from impermeable surfaces
• how are urban drainage systems designed to deal with surface runoff from impermeable surfaces?

  through a system of underground pipes and sloping roofs
• what is low in urban areas?

  infiltration
• as infiltration is low in urban areas, what is slow?

  replenishment of groundwater stores
• what feeds rivers in urban areas?

  groundwater
• what happens to the rivers during drier periods?

  river discharge in urban areas is low
• what increases runoff in urban areas?

  the increase in precipitation and storms
• what is runoff channeled through?

  man-made pipes which transports water to rivers and streams
• what causes water to enter rivers quickly?

  low infiltration rates, high surface runoff and channeling of water
• describe the hydrograph of an urban river

  a short lag time and high peak discharge with a fast return to base flow
• what does catchment management do?

  it manages the river and improves drainage systems by looking at the whole river catchment and the interactions between water and land
• what does catchment management aim to do?

  minimise the issues such as flooding, trough, water pollution and erosion in sensitive areas and to improve river ecoystems
• what are the two main methods that can be used to manage river catchments?

  soft and hard engineering
• MANAGING RIVER CATCHMENTS (HARD ENGINEERING) - what does it involve?

  man made structures such as dams, flood walls and reservoirs
• MANAGING RIVER CATCHMENTS (HARD ENGINEERING) - what are the man made structures used for?

  they are often used to prevent flooding and ensure a constant water supply
• MANAGING RIVER CATCHMENTS (HARD ENGINEERING) - what are the problems with hard engineering?

  it is expensive, can disrupt natural systems and alter wildlife habitats
• MANAGING RIVER CATCHMENTS (SOFT ENGINEERING) - what does this use knowledge of?

  uses knowledge of the river basin and its processes to try to work with nature
• MANAGING RIVER CATCHMENTS (SOFT ENGINEERING) - what does it involve?

  land use management, river restoration and conservation
• MANAGING RIVER CATCHMENTS (SOFT ENGINEERING) - pros of soft engineering

  its cheaper than hard engineering and it can improve the local environment
• MANAGING RIVER CATCHMENTS (SOFT ENGINEERING) - problems with soft engineering

  planning restrictions can limit the construction of new homes and businesses and land use management is hard in areas that are already urbanised
• MANAGING RIVER CATCHMENTS - who makes decisions about what methods to use?

  experts in water management rather than residents
• MANAGING RIVER CATCHMENTS - why do residents feel ignored as water experts make decisions about what method to use?

  as what is best for the catchment may not be the best for all individuals
• SUDS - what does it stand for?

  sustainable urban drainage systems
• SUDS - what do they aim?

  imitate natural drainage systems rather than channeling water through pipes and drains
• SUDS - what do they attempt to do?

  manage surface water in urban areas
• SUDS - what do they try to decrease?

  flooding, water pollution and drought
• SUDS (VEGETATED TRENCHES) - what are they?

  trenches which increase interception of rainfall and retention basins which store water
• SUDS (VEGETATED TRENCHES) - what do they help to increase?

  infiltration and water storage
• SUDS (VEGETATED TRENCHES) - what does it decrease?

  it decreases runoff and channel flow which lowers flood risk
• SUDS (VEGETATED TRENCHES) - what does increased infiltration decrease?

  decreases pollutants which enter watercourses
• SUDS (VEGETATED ROOFS) - what do they do?

  intercept rainfall and increase evapotranspiration which reduced flood risk
• SUDS (CONTAINERS) - what do they do?

  they're on roofs which catch and store rainwater for reuse, they lower drought risk
• SUDS (SWALES) - what do they do?

  direct water to storage areas in grass basins
• SUDS (WATER DETENTION AND RAIN GARDEN) - what do they do?

  reduces runoff but increases infiltration and storage
• SUDS - why are SUDS more sustainable than traditional urban drainage methods?

  they work with the natural environment to improve drainage and air quality
• SUDS (VEGETATED TRENCHES and VEGETATED ROOFS) - what are pros?

  they provide new habitats and increase biodiversity
• Characteristics of urban drainage in urban areas

  UHI means more precipitation and more run off

  short lag time

  impermeable surfaces - low infiltration

  less vegetation to intercept rianfall

  drainage is needed to remove water quickly

  water stores are decreased
• characteristics of the urban water cycle

  ‘flashy’ regime

  high peak discharge

  fast return to base flow
• what is catchment management

  managing rivers and improving drainage systems - looking at the whole catchment - holistic approach

  aim: to minimise flooding, drought, water pollution and erosion

  hard engineering: dams, levees, channels

  soft engineering: land use management, flood plain zoning, river restoration

  issues with catchment management:

  • decisions are made by local authorities without consulting locals - conflict
  • expensive and disruptive
  • ecological balance is disturbed