River Processes and Pressures Flashcards
what is hydraulic action?
the force of the water on the bed and banks of the river removes material
what is attrition?
the load that is carried by the river bumps together and wears down into smaller smoother pieces
what is abrasion?
material carried by the river rubs against the bed and banks and wears them away
what is corrosion/solution?
some rock minerals dissolve in the river water
what are the four main types of transportation?
traction
saltation
suspension
solution
what is traction?
large boulders roll along the river bed
what is saltation?
smaller pebbles are bounced along the river bed, picked up and then dropped as the flow of the river changes
what is suspension?
finer sand particles are carried along the river giving a brown appearance
what is solution?
minerals from rocks such as limestone and chalk are dissolved in water and carried along the river
what is transportation?
the way in which the river carries eroded materials
what is deposition?
the river slowing down and dropping some of its load
what is a waterfall?
a steep drop ion a river’s course
how are waterfalls formed?
- a band of resistant rock lays over less resistant rock
- less resistant rock underneath erodes forming an undercut and an overhang
- the overhang can no longer be supported so rocks fall
- the powerful fall of water erodes a plunge pool
what are interlocking spurs?
water flows naturally from side to side of a valley around ridges called spurs which interlock at the other side of the valley
what are meanders?
bends in the river course
how are meanders formed?
the river swings one way and the other causing erosion on the outside bends
how are floodplains formed?
the river deposits sediment on the outside bends after flooding as heavier particles cannot be carried back into river by water
how is an oxbow lake formed?
the neck of a meander narrows cutting it off from the rest of the lake
what are levees?
the build up of floodplains
what are deltas?
a flat area of land created by a build up of sediment
how are deltas formed?
the speed of a river decreases as it approaches the sea so it deposits some of the material it is carrying
how does climate impact transportation rate?
rivers in wet climates transport more material than those in dry climates
how does climate impact weathering processes?
freeze thaw weathering more likely to occur in cold climates
how does climate impact average amount of discharge?
wetter climates mean more discharge than hotter climates where discharge evaporates
how does climate impact erosion rate?
rivers in wet climates have a greater erosion rate
what is soil creep?
particles of soil move slowly down the sides of valleys under the influence of gravity
what is slumping?
valley sides are eroded by the river making the sides steeper and increasing the downward movement of material
what is the lag time on a storm hydrograph?
the difference in time between peak rainfall and peak river discharge
what does a storm hydrograph show?
how a river responds to a rainstorm
what does the line on a storm hydrograph show?
the discharge in metres cubed per second
what do the bars show on a storm hydrograph?
the amount of rainfall measured in millimetres
how does geology make lag time short, the rising and falling limbs steep and discharge high on a storm hydrograph?
more resistant rock will will absorb less water than less resistant rock so run off will be greater and faster
how does soil type make lag time short, the rising and falling limbs steep and discharge high on a storm hydrograph?
more impermeable soils will absorb less water than permeable soils so surface run off will be greater and faster
how does vegetation make lag time short, the rising and falling limbs steep and discharge high on a storm hydrograph?
plants use water so run off will be greater and faster on the ground where there is less vegetation
how does slope make lag time short, the rising and falling limbs steep and discharge high on a storm hydrograph?
steeper slopes cause faster surface run off so more water reaches the river quicker
how does drainage basin shape make lag time short, the rising and falling limbs steep and discharge high on a storm hydrograph?
a wide basin with a lot of tributaries close together means water enters the river faster
how do antecedent conditions make lag time short, the rising and falling limbs steep and discharge high on a storm hydrograph?
when the ground is already saturated further water will run off into the river quicker
what is the water shed in the river basin?
the area of high land forming the edge of a river basin
what is the source in the river basin?
where the river begins
what is the mouth in the river basin?
where a river meets the sea
what is the confluence in the river basin?
the point at which two rivers meet
what is the tributary in the river basin?
a small rivers or stream that joins a larger river
what is the main river channel in the river basin?
the main area through which the river flows
what is the drainage basin in the river basin?
the area of land drained by a river
what is interception?
water being prevented from reaching the surface by trees of grass
what is the watertable?
current upper level of saturated rock/soil where no more water can be absorbed
what is infiltration?
water sinking into the rock/soil from the ground surface
what is groundwater flow?
water flowing on top of the ground
what is percolation?
water seeping deeper below the surface
what is throughflow?
water flowing through the rock layer parallel to the surface
what is transpiration?
water lost through pores in vegetation
what is surface run off?
water flowing through the soil layer parallel to the surface
what is evaporation?
water lost through round/vegetation surface
how does deforestation increase flooding?
prevents interception so there is more surface run off
how does land use change increase flooding
rates of transpiration, erosion and deposition will slow
no trees to stop interception
how does urbanisation increase flooding?
more impermeable surfaces like concrete prevent infiltration
what are flood walls?
artificial barriers built along a river to raise height or river channel to increase capacity
what are embankments?
artificial levees to raise height of river channel and increase rivers capacity
what are flood barriers?
gates built near the river mouth which close during storm surges
what is floodplain retention?
maintaining the rivers original landscape by lowering the level of floodplains or planting grass and trees
what is river restoration?
restoring a rivers original features like meanders to slow water velocity
