18.104.22.168 Force of water breaks down rock particles from the river channel
22.214.171.124 Eroded rocks picked up by the river scrape and rub against the
channel, wearing it away. Most erosion happens by abrasion
126.96.36.199 Eroded rocks picked up by the river smash into each other and break into
smaller fragments. Their edges also get rounded off as they rub together.
188.8.131.52 River water dissolves some type of rock, e.g. chalk or limestone.
184.108.40.206 Large particles , like boulders, are pushed along the river bed by the force of water.
220.127.116.11 Pebble-sized particles are bounced along the river bed by the force of water.
18.104.22.168 Small particles, like silt and clay, are carried along by the river.
22.214.171.124 Soluble materials dissolve in the water and are carried along.
2.3.1 When a river drops the eroded material.
126.96.36.199 Happens when the river slows down (loses velocity).
188.8.131.52.1 4 reasons as to why a river loses velocity.
184.108.40.206.1.1 Volume of water decreases.
220.127.116.11.1.2 Amount of eroded material increases.
18.104.22.168.1.3 The water is shallower.
22.214.171.124.1.4 The river reaches its mouth.
3 River Landforms
3.1.1 Middle or lower course
3.1.2 1. The current is faster on the outside of the bend because the water is deeper.
3.1.3 2. More erosion takes place on the outside of the bend, forming river cliffs.
3.1.4 3. The current is slower on the inside of the bend because its shallower.
3.1.5 4. So eroded material is deposited on the inside of the bend, forming slip-off slopes.
3.2 Ox-Bow Lakes
3.2.1 Formed form large meanders.
3.2.2 1. Erosion causes the outside bends to get closer..
3.2.3 2...until there's only a small bit of land left between the bends (called the neck).
3.2.4 3. The river breaks through this land, usually during a flood..
3.2.5 4..and the river flows along the shortest course.
3.2.6 5. Deposition eventually cuts off the meander...
3.2.7 6..forming an ox-bow lake.
3.3 Waterfalls and Gorges
3.3.1 1. Waterfalls form where a river flows over an area of hard rock followed by an area of softer rock.
3.3.2 2. The softer rock is eroded more than the hard rock, creating a 'step' in the river.
3.3.3 3. As water goes over the step it erodes more and more of the softer rock.
3.3.4 4. A steep drop is eventually created, which is called a waterfall.
3.3.5 5. The hard rock is eventually undercut by erosion. It becomes
unsupported and collapses.
3.3.6 6. The collapsed rocks are swirled around at the foot of the waterfall where
they erode the softer rock by ABRASION. This creates a deep plunge pool.
3.3.7 7. Over time, more undercutting causes collapses. The
waterfall will retreat, leaving behind a steep-sided gorge.
3.4 Flood Plains and Levees.
3.4.1 Flood plain
126.96.36.199 1. This is the wide valley floor on either side of a river which sometimes floods.
188.8.131.52 2. When a river floods onto the flood plain, the water slows down and
deposits the eroded material. This makes the flood plain higher.
184.108.40.206 3. Meanders migrate across the flood plain, making it wider.
220.127.116.11 4. The deposition that happens on the slip-off slopes of meanders also builds
up the flood plain.
18.104.22.168 1.These are natural embankments (raised bits) along the edges of a river channel.
22.214.171.124 2. During a flood, eroded material is deposited over the whole flood plain.
126.96.36.199 3. The heaviest material is deposited closest to the river channel, because it gets dropped first when the river slows
188.8.131.52 4. Over time, the deposited material builds up, creating levees along the edges of the channel, e.g. along the Yellow
River in China.
4 Rivers on maps
4.1 Contour lines
4.1.1 Orange lines on maps.
4.1.2 Height = number marked on.
4.1.3 Steepness = how close together they are.
4.2 Evidence for a waterfall
4.2.1 They are marked on a map, but the symbol for a cliff is black, blocky
5 River Discharge
5.1 Volume of water that flows in a river per second.
Measured in CUMECS (m^3/s)
5.2 Peak discharge = The highest
discharge in the period of time you're
5.3 Lag time = The delay between peak
rainfall and peak discharge.
5.4 Rising limb = The increase in river
discharge as rainwater flows into the river
5.5 Falling limb = The decrease in river
discharge as the river returns to its
5.6 What affects river discharge?
5.6.1 Amount and type of rainfall
184.108.40.206 Lots of rain and short, heavy periods of rainfall means there's
more RUNOFF. Lag time is decreased, so discharge increases.
220.127.116.11 Hot, dry conditions and cold, freezing conditions both result in hard ground -
this increases RUNOFF. Lag time is decreased, so discharge increases.
5.6.3 Previous weather conditions
18.104.22.168 After lots of rain, soil can become saturated (absorbs more water). More rainwater wont be able to
INFILTRATE into the soil so RUNOFF will increase. Lag time is decreased and discharge increases.
5.6.4 Land use
22.214.171.124 Urban areas have drainage systems and they're covered with impermeable materials like
concrete - these increase RUNOFF. Lag time is decreased and discharge is increased.
5.6.5 Rock type
126.96.36.199 Water INFILTRATES through pore spaces in permeable rock and flows along cracks in previous
rock - this means there isn't much RUNOFF. Lag time is increased, so discharge decreases.
188.8.131.52 Water can't INFILTRATE into impermeable rock - this means there's a
lot of RUNOFF. Lag time is decreased, so discharge increases.
184.108.40.206 Lots of RUNOFF occurs on steep slopes. Lag time is decreased, so discharge
5.7 Lag time happens because most rainwater doesn't land directly in the river channel -
there's a delay as rainwater gets to the channel. it gets there by flowing quickly overland
(called SURFACE RUNOFF or just RUNOFF), or by soaking into the ground (called
INFILTRATION) and flowing slowly underground.
6.1 Physical Factors
6.1.1 Prolonged rainfall
220.127.116.11 After a long period of rain, the soil becomes SATURATED.
Any further rainfall can't INFILTRATE, which increases
RUNOFF. This increases discharge quickly, which can
cause a flood.
6.1.2 Heavy rainfall
18.104.22.168 Heavy rainfall means there's a lot of RUNOFF. This
increases discharge quickly, which can cause a
22.214.171.124 When a lot of snow or ice melts it means that a
lot of water goes into a river in a short period of
time. This increases discharge quickly, which
can cause a flood.
126.96.36.199 If a river is in a steep-sided valley, water will
reach the river channel much faster because
water flows more quickly on steep slopes. This
increases discharge, which can cause a flood.
6.2 Human factors
188.8.131.52 Trees intercept rainwater in their leaves, which then evaporates.
Trees also take up water from the ground and stores it. This means
cutting down trees increases the volume of water that reaches the
river channel, which increases discharge and makes a flood more
6.2.2 Building construction
184.108.40.206 Buildings are often made from impermeable
materials, e.g. concrete, and they're surrounded
by roads made from tarmac (also impermeable).
Impermeable surfaces increase RUNOFF and
drains quickly runoff to rivers. This increases
discharge, which can cause a flood.
6.3 Case studies
6.3.1 Carlisle, England. 8th January 2005. River Eden
220.127.116.11.1 200mm of rain in 36 hours.
18.104.22.168.2 Impermeable materials increased RUNOFF.
22.214.171.124.3 Discharge reached 1520 CUMECS.
126.96.36.199 Primary effects
188.8.131.52.1 3 deaths.
184.108.40.206.2 3000 people left homeless.
220.127.116.11.3 4 schools flooded.
18.104.22.168.4 350 businesses shut down.
22.214.171.124.5 70000 addresses lost power.
126.96.36.199.6 Roads and bridges damaged.
188.8.131.52.7 Rivers polluted.
184.108.40.206 Secondary Effects
220.127.116.11.1 Children lost out on education.
18.104.22.168.2 Stress-related illnesses.
22.214.171.124.3 3000 jobs at risk.
126.96.36.199 Immediate responses
188.8.131.52.1 People evacuated.
184.108.40.206.2 Reception centres - food and water.
220.127.116.11.3 Temporary Accomodation.
18.104.22.168 Long-term responses
22.214.171.124.1 Emotional support.
126.96.36.199.2 Flood defence scheme.
6.3.2 Bangladesh, India.
July-August 2007. River
Brahmaputra and Ganges.