Urban drainage:

Question 1

Urban precipitation, surfaces and catchment characteristics;

Answer 1

• Urban areas have 5-15% more precipitation than rural areas mainly because of warmer temps due to UHE and more condensation nuclei.
• Less vegetation means reduced evapotranspiration and more runoff as there is less interception.
• Low infiltration as there are many impermeable surfaces, short lag time increased risks of flooding.

Question 2

impacts on drainage basin storage areas;

Answer 2

• Urban rivers are primarily the exit transferred through the drainage basin. Management of river channels by dredging (sediment removed from river channels so they can hold more water) and channelisation will increase their storage capacity.
• Interception storage is reduced due to lower levels of vegetation
• lakes, ponds and swimming pools are vulnerable to evaporation.

Question 3

Urban water cycle: water movement through urban catchments as measured by hydrographs:

Answer 3

• A flood hydrograph shows how river discharge responds to storm events.
• Urban hydrographs tend to be flashy due to impermeable surfaces.

Stages of hydrograph:
- Precipitation causes the discharge in the river to rise.
- Short lag time
- High peak discharge
- Baseflow reduces as throughflow reduces.

Question 4

Issues associated with catchment management in urban areas.

Answer 4

• Catchment management is a way if managing rivers and improving drainage systems by looking at the whole river catchment.

Aims to minimise issues such as flooding, droughts and water pollution.

2 main methods that can be used:
- Soft and Hard engineering.

Soft:
- Afforestation, river bank conservation and flood plane zoning

Hard:
- River straightening
- Raised embankments

Issues with hard: high costs, require lots of planning and have negative environmental and social impacts.

Soft is more sustainable.

Question 5

The development of SUDS:

Answer 5

Are natural drainage systems, designed to manage the flow of urban water sustainably. They slow surface runoff from any development and allow natural processes to break down pollutants.

examples of SUDS.

• Swales
• Permeable road or pavement services
• Infiltration trenches
• Green roofs

Benefits of SUDS:
- Slow down surface run off and reduce the risks of floods
- prevent water pollution
- Provide valuable habitats
- Create green spaces.