Water Cycle - Rivers Flashcards
(34 cards)
How are floodplains formed?
Due to the same process of levees forming, ground closer to river is higher up than ground further away from river channel.
How are gorges formed?
As waterfalls retreat over time (cap rock falling process), a steep sided valley is left where waterfall was, which is the gorge.
How are interlocking spurs formed?
In the upper course, vertical erosion is prevalent, so in areas of hard rock, the river bends around it as lateral erosion isn’t powerful enough.
How are levees formed?
During high energy events river overflows. Friction from bank causes overflowed water to lose energy, so heavier sediment is deposited closer to bank, and finer silts (alluvium) deposited further from bank. Multiple of these events form levees.
How are waterfalls formed?
River flows over hard rock overlaying soft rock, causing faster erosion in soft rock, forming a notch. Soft rock erodes more leaving hard rock sticking out and this drop increases until waterfall is formed. Keeps eroding backwards until a plunge pool is formed as undercutting and collapsing occurs.
How can laminar flow change?
Water can come in through the mouth disturbing laminar flow.
How is turbulent flow caused?
Obstacles in channel or on channel floor throw off the thalweg.
State 6 river landforms.
V and U shaped valleys
Interlocking spurs
Meanders and oxbow lakes
Waterfalls and gorges
Levees and floodplains
Estuaries and deltas.
State one advantage and one disadvantage of afforestation.
Advantage - new ecological habitats and acts as carbon sink.
Disadvantage - May reduce farmland and impact existing food webs and ecosystems.
State one advantage and one disadvantage of channel straightening.
Advantage - velocity increases, reducing chances of it flooding at the straight part.
Disadvantage - Straight path might have geographical or urban obstacles needing to be removed.
What is one advantage of dams?
Holds water preventing flooding and generates hydroelectric power.
What is one disadvantage of dams?
Traps sediment, leading to more erosion downstream.
What is one advantage of doing nothing regarding river management?
Over longer periods, biodiversity can increase as new habitats are created.
What is one disadvantage of doing nothing regarding river management?
Unmanaged rivers can damage infrastructure on river banks via erosion.
What is one advantage of dredging?
Deepens river allowing larger vessels through.
What is one disadvantage of dredging?
May disrupt aquatic ecosystems.
What is one advantage of floodplain zoning?
Reduces flood damage by minimizing impact on more important property.
What is one disadvantage of floodplain zoning?
Limits urban growth as building restrictions are imposed.
What are some examples of hard engineering?
Dams, reservoirs, channel straightening, flood gates, levees.
What are some examples of soft engineering?
Do nothing, preparation, afforestation, floodplain zoning, dredging.
What factors increase the chances of deposition?
Reduction in gradient, shallow water, decrease in river discharge, increase in calibre of load.
What does energy in a river depend on?
Height that the water has to descend and mass of water available.
What does the Hjulstrom curve show?
The relationship between the size of sediment and the velocity required to erode, transport, and deposit it.
What increases river velocity?
Steeper gradient, larger channel width and depth, more discharge.
