River presentation
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Rivers, floods and management
Rivers, floods and management
Rivers, floods and management
The drainage basin hydrological cycle
Rivers, floods and management
The storm hydrograph
River discharge
Rivers, floods and management
What factors might result in a ‘flashy’
hydrograph?• short-lived but intense
rainfall
• impermeable underlying rock
such as granite
• steep relief
• urban area, where water is
channelled through drains to
the stream
• small round drainage basin
River discharge
Rivers, floods and management
• dense woodland vegetation
• high infiltration capacity of
soil
• permeable underlying rock,
such as limestone
• elongated drainage basin
What factors might create a hydrograph like
this?
River discharge
Rivers, floods and management
The long profile
Rivers, floods and management
The Hjülstrom curve
Rivers, floods and management
Amanda Barker
An upper course channel
Rivers, floods and management
Amanda Barker
A middle course channel
Rivers, floods and management
A lowland channel in flood
Amanda Barker
Rivers, floods and management
• vertical erosion
(by hydraulic
action and
corrasion) below
the waterfall
deepens the
plunge pool
• undercutting of
the softer rock
leads to eventual
collapse of the
resistant Whin
Sill and results
in headward
erosion
John
Pallister
High Force waterfall
Rivers, floods and management
The development of an oxbow lake
Rivers, floods and management
• the sediment load carried by the river is substantial
• the river has a large drainage basin
• the mouth of the river is located on a coastline where ocean
currents and tides are weak so the rate of deposition exceeds
the rate of sediment removal
Reasons for formation of a delta
Rivers, floods and management
• knick points, rapids
and waterfalls
• river terraces
• incised meanders, both
entrenched and ingrown
Features related to rejuvenation
Aerofilms
The city of Durham is built inside
an entrenched meander
Rivers, floods and management
• excessive precipitation
over a long period of
time
• intensive precipitation
over a short period of
time
• snowmelt
• climatic hazards such
as hurricanes
Flooding
• the nature of the
drainage basin
• relief
• rock and soil type
• natural vegetation
Physical causes of flooding
Rivers, floods and management
• Urbanisation creates impermeable surfaces so reducing
infiltration. Surface water is therefore transported more
rapidly through drains to the river.
• Deforestation reduces interception and increases runoff.
• Some methods of river management, such as channelisation,
increase flood risk downstream.
• Global warming leads to more extreme rainfall events.
Flooding
Influence of human activities on flooding
Rivers, floods and management
Flooding
Areas of high flood risk in England and Wales
Rivers, floods and management
Flooding
Short-term responses:
• media broadcasts of
information
• emergency relief, rescue,
shelter, food
• armed services for evacuation
and building emergency
defences
Long-term responses:
• government and/or foreign aid
• disaster planning for the
future
• flood management programmes
Responses to flooding
Rivers, floods and management
Flooding
• channelisation, to raise, straighten or strengthen banks
• dams and weirs
• diversion channels
• dredging
• retention basins and balancing lakes
• artificially raising the height of the floodplain
Examples of hard engineering
Rivers, floods and management
• afforestation
• floodplain zoning
• land-use management, e.g. contour ploughing
• wetland and riverbank conservation
• river restoration
• improved forecasting and warning
Flooding
Examples of soft engineering