the Prevention + Amelioration of Floods

Question 1

What methods are used for the prevention + amelioration of river floods?

Answer 1

• forecasts + warnings
• hard engineering
• soft engineering

Question 2

How do forecasts + warnings ameliorate floods?

Answer 2

• pptn forecasts estimate lvl of flooding risk in an area
• streamflow data + models of streamflow routes can calculate areas most at risk when heavy pptn is forecasted, so warnings can be issued days before
• early warnings are vital so ppl can evacuate, move valuables + sandbag

Question 3

What are the methods of hard engineering?

Answer 3

• dams
• channel straightening
• levees
• diversion spillways

Question 4

• How do dams prevent floods?
• What are their purpose?
• How effective are they?
• What are the issues associated w them?

Answer 4

• obstruct river’s natural course, so reservoir builds up behind dam if channel flow is big enough
• purpose: flood control or water storage
• effective: river can’t flow but if dam fails or is opened up in controlled way water can get through
• issues: expensive to build, displacement of settlements, disruption of wildlife

Question 5

• What is channel straightening + how do they prevent floods?
• What are the issues associated w channel straightening?

Answer 5

• straightening: bends + irregularities removed from river channels using machinery
• so water flows faster through channel: water unlikely to overflow onto floodplain + moves quickly downstream
• issues: may cause flooding downstream + enhance erosion

Question 6

How do levees prevent floods?

Answer 6

• can be reinforced or constructed for flood prevention (as well as occurring naturally)
• provides a raised embankment so water in river channel must rise more before can spill out of channel onto floodplain

Question 7

• What is a diversion spillway + how does it prevent floods?
• What are the issues w diversion spillways?

Answer 7

• diversion spillway: constructed channel allowing excess water to flow into it when channel overflows
• may direct water downstream or to a diff. river + usually has floodgates: control when opened + closed
• issues: may direct water to areas that don’t flood naturally: envi. damage if spillway floods

Question 8

What are the methods of soft engineering?

Answer 8

• floodplain + drainage basin management
• wetland + river bank conservation
• river restoration

Question 9

How does floodplain + drainage basin management prevent floods?

Answer 9

• afforestation + tree management:
  
  • planting trees dec. surface runoff: dec. flooding
  • must be managed properly (e.g. pollarding) so trees sturdy + strong so don’t block rivers by falling
• floodplain land use management:
  
  • floodplains naturally block + divert flood water so damaging activities (urbanisation + agri. use) inc. risk of flooding so important to manage
  • urbanisation: inc. risk of homes + businesses flooding + dec. infiltration so limiting construction dec. risk
  • agri. land use: livestock trampling soil + unsustainable farming strategies (e.g. heavy machinery) dec. infiltration
• floodplain mapping:
  
  • used to decide where to build + land use by mapping areas at risk of flooding: limits damage to property + floodplain

Question 10

How does wetland + river bank conservation prevent floods?

Answer 10

• wetlands important: provide envi. floodwater can inundate (limits flooding elsewhere)
• wetland conservation strategies to dec. flood risk:
  
  • banning/limiting drainage of wetlands: protects ecosystems
  • monitoring changes so actions to counteract can take place
  • reintroduce species to restore natural balance
• damaged river banks: don’t hold water effectively inc. flood risk
• conserved by:
  
  • protecting + reintroducing veg.: limits erosion so dec. sediment in channels = more clear for water to flow through
  • ensure no waste: so doesn’t disrupt ecosystem + block river channel

Question 11

What is hard engineering?

Answer 11

• physically altering a river + its channel through building structures or using machinery

Question 12

What is soft engineering?

Answer 12

• use of natural, sustainable means to dec. flooding, rather than building structures

Question 13

What is river restoration?

Answer 13

• process of restoring a river back to its original state before it was altered

Question 14

How does river restoration prevent floods?

Answer 14

• restoring river to original state: e.g. reintroducing meanders to straightened channels
  
  • helps limit discharge downstream + often takes place where land no longer seen as valuable