Hydrology and fluvial geomorphology:
With reference to a recent river flood, explain the causes of the flood and evaluate attempts to reduce
its impact:
The Pakistani Floods (2010)
• Heavy rainfall
o July 2010, excess of 200mm in a 4-day period (and above average rainfall in August)
o Increase in overland flow (fastest flow) due to saturation of soil= inc. Rate and discharge
(water table reaches the ground surface)
• Deforestation
o 2-2.4% annually (worsened by endemic culture of illegal logging and implicant support
of officials through corrupt backhand payments
o Reduces the ability of drainage basins to intercept precipitation, therefore, run-off rates
and discharge are increased
• Levees
o Indus Valley Civilization used levees since 2500BCE
o Contained river sediment and reduced river capacity
• Estimated 6 million at risk of cholera
o Instillation of latrines and water storage tanks to prevent water borne diseases
o Effective= (during flood) 10 million people were forced to drink unsafe water
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With the aid of examples, examine the extent to which hard engineering prevents river floods:
• Levees-
o As early as 2500BCE, Indus Valley Civilization used levees
o Contained river sediment and reduced river capacity
o Short term=effective, Long term= exacerbates flooding
• Damns-
o (Three Gorges Dam, China) Area behind is flooded: 13 cities and hundreds of villages
• Dams-
o Three Georges Dam reduced the recurrence interval for large floods from 1 in 10 year to
1 in 100 years
o Recurrence interval is an average therefore contains anomalies/collapse= widespread
death and damage downstream
----------------------------------------------------------------------------------------------------------------------------- -------------
With the aid of examples, examine the extent to which soft engineering prevents river floods:
River Quaggy, Lewisham
• River restoration
o Concreate channel replaced by sinuous channel (re-meander channelized section)
o Downstream flooding becomes less likely since the river flows slower
With reference to a recent river flood, explain the causes of the flood and evaluate attempts to reduce
its impact:
The Pakistani Floods (2010)
• Heavy rainfall
o July 2010, excess of 200mm in a 4-day period (and above average rainfall in August)
o Increase in overland flow (fastest flow) due to saturation of soil= inc. Rate and discharge
(water table reaches the ground surface)
• Deforestation
o 2-2.4% annually (worsened by endemic culture of illegal logging and implicant support
of officials through corrupt backhand payments
o Reduces the ability of drainage basins to intercept precipitation, therefore, run-off rates
and discharge are increased
• Levees
o Indus Valley Civilization used levees since 2500BCE
o Contained river sediment and reduced river capacity
• Estimated 6 million at risk of cholera
o Instillation of latrines and water storage tanks to prevent water borne diseases
o Effective= (during flood) 10 million people were forced to drink unsafe water
----------------------------------------------------------------------------------------------------------------------------- -------------
With the aid of examples, examine the extent to which hard engineering prevents river floods:
• Levees-
o As early as 2500BCE, Indus Valley Civilization used levees
o Contained river sediment and reduced river capacity
o Short term=effective, Long term= exacerbates flooding
• Damns-
o (Three Gorges Dam, China) Area behind is flooded: 13 cities and hundreds of villages
• Dams-
o Three Georges Dam reduced the recurrence interval for large floods from 1 in 10 year to
1 in 100 years
o Recurrence interval is an average therefore contains anomalies/collapse= widespread
death and damage downstream
----------------------------------------------------------------------------------------------------------------------------- -------------
With the aid of examples, examine the extent to which soft engineering prevents river floods:
River Quaggy, Lewisham
• River restoration
o Concreate channel replaced by sinuous channel (re-meander channelized section)
o Downstream flooding becomes less likely since the river flows slower
