Flashcards
River Discharge
Cards in this deck (50)
- 1What is river discharge?This is the volume of water (in cubic centimetres) that flows in a river per second
- 2What is river discharge affected by?Precipitation (the more precipitation, the higher the discharge)
How weather (the higher the temperature, the lower the discharge as the rate of evaporation is higher)
Removal of water from the river (abstraction) - this reduces discharge - 3What are hydrograph?These are graphs of river discharge over time.
- 4`What do hydrographs show?They show how the volume of water flowing at a certain point in a river changes over a period of time.
- 5What do storm hydrographs show?They show river discharge around the time of a storm event.
- 6What is peak discharge?This is the highest point on the graph, when the river discharge is at its greatest
- 7What is lag time?This is the delay between peak rainfall and peak discharge
- 8Why does lag time occur?The delay happens because it takes time for the rainwater to flow into the river
- 9What can a shorter lag time lead to?This can increase peak discharge because more water reaches the river during a shorter period of time
- 10What is a rising limb?This is the part of the graph up to peak discharge. The river discharge increases as rainwater flows into the river
- 11What is the falling limb?This is the part of the graph after peak discharge. Discharge is decreasing as less water is flowing into the river. A shallow falling limb shows water is flowing in from stores long after it's stopped raining
- 12What sort of hydrograph would be made for a river with rapid runoff and not much storage capacity?This gives a hydrograph with a short lag time and high peak discharge. This is called a 'flashy' hydrograph (the graph has steep, roughly symmetrical
- 13What drainage basin characteristics affect a storm hydrograph?Larger drainage basins can catch more precipitation, so they have a higher peak discharge compared to smaller basins.
On the other hand, smaller basins generally have shorter lag times as precipitation has less distance to travel.
Steep sided drainage basins have shorter lag times then shallower basins - water flows more quickly downhill into the river on steep slopes. This can also increase peak discharge.
Circular basins are more likely to have a flashy hydrograph than long, narrow basins as lots of water will reach the measuring point at the same time, increasing peak discharge.
Basins with a high drainage density (lots of streams) drain quickly, so have shorter lag times - 14How can the amount of water present in the drainage basin affect a storm hydrograph?If the ground's already waterlogged, then infiltration is reduced and surface runoff increases.
Surface runoff is much faster than through flow or base flow, so rainwater reaches the river faster, reducing lag time. - 15How can rock type affect a storm hydrograph?Impermeable rocks don't store water. This reduces infiltration increases runoff, reducing lag time.
Peak discharge also increases as more water reaches reaches the river in a shorter period. - 16How can the soil type affect a storm hydrograph?Sandy soils allow a lot of infiltration, but clay soils have very low infiltration rates.
Low infiltration rates increase surface runoff, reducing lag time and increasing peak discharge - 17How can vegetation affect a storm hydrograph?Vegetation intercepts precipitation and slows its movement to the river channel, increasing lag time. Interception is highest when there are lots of vegetation and deciduous trees have their leaves
The more vegetation there is, the more water is lost (through evapotranspiration) reducing peak discharge - 18How can precipitation affect a storm hydrograph?Intense storms means greater peak discharges than light rain showers
The type of precipitation also affects lag time e.g. the snow that has fallen in a winter storm can melt and flow into the river in spring thus giving a very long lag time - 19How can temperature affect a storm hydrograph?Both hot, dry and freezing conditions result in hard ground. This reduces infiltration and increases run off, reducing lag time and increasing peak discharge. High temperatures increase evapotranspiration so less water reaches the channel reducing peak discharge and run off.
- 20How can human activity affect a storm hydrograph?In urban areas, there are large amount of impermeable surfaces. This reduces infiltration which increases run off, reducing lag time and increasing peak discharge.
Man made drainage systems affects the hydrograph in a similar way. Water flows down drains and into the river before it can evaporate and infiltrate into the soil causing a shorter lag time and increase peak discharge. - 21What does headward erosion do to a river?It makes it longer.
- 22Where does headward erosion occur?Near the river source as through flow and surface run off cause erosion at the point the water enters the river channel (the valley head)
- 23What does vertical erosion do to a river?It deepens the river.
- 24Where does vertical erosion occur?In the upper stages of a river.
- 25What does lateral erosion do to a river?It makes the river wider.
- 26Where does lateral erosion occur?In the middle and lower stages of a river.
- 27What are the 5 main ways that river erosion occurs?Hydraulic action
Abrasion (corrasion)
Attrition
Cavitation
Solution or corrosion - 28What is hydraulic action?The pressure of the water breaks rock particles away from the bed and banks.
- 29When is hydraulic action strongest?In rapids, waterfalls and during floods.
- 30What is abrasion?Eroded pieces of rock in the water rub and scrape against the bed and banks removing material.
- 31What is attrition?Eroded rocks smash into each other and break into smaller fragments. The edges also get round off as they smash into each other.
- 32What is cavitation?Air bubbles in turbulent stretches of water implode causing shock waves that break pieces of rock off the banks and bed.
- 33What is solution?The dissolving of rock through chemical processes
Carbon dioxide dissolves in water to form a weak carbonic acid which reacts with rocks such as limestone and chalk. - 34Which type of erosion is most common in rivers?Abrasion
- 35What are the 4 main ways of transportation in rivers?Traction
Saltation
Solution
Suspension - 36What is traction?Large articles e.g. boulders push along a river bed by force of water.
- 37Why is saltation?Small particles like pebbles or gravel bounce along the river bed as they are too heavy to be carried in suspension
- 38What is suspension?very fine material e.g. salt and clay are whipped up by turbulence and carried along the water.
- 39What is solution?Substances that can dissolve are carried along in the water e.g. limestone is dissolved into river water that is slightly acidic.
- 40What is the most common form of transportation?Suspension
- 41What is a river's bedload?This is material transported by traction or saltation.
- 42What is deposition?This is the process of dropping eroded material
It happens when the river loses energy. When it slows down, it drops some of its load. - 43How can the speed and energy of the river be reduced?Reduced rainfall which causes lower discharge
Increased evaporation or abstraction causes lower discharge
Friction e.g. in shallow areas of the river and close to the banks reduces the speed of the river, reducing its energy.
When the river is forced to slow down, e.g. before a narrow section of the river, it loses its energy.
When the river meets the sea, the river loses its energy as the sea absorbs it. - 44What is the capacity of a river?This is the total load (measured in volume, weight or mass) that a river can transport at a given point.
- 45In rivers, what does the particle size range from?It can range from silt and clay (less than 0.1mmin diameter, to big boulders
- 46What does the competence describe?The maximum particle size that a river is capable of transporting at a given point.
- 47What is the competence of a river affected by?The amount of energy it has which is related to its velocity. Generally the greater the velocity the greater the energy.
- 48What does the hjulstorm curve show?It shows the relationship between velocity and competence.
It also shows how the processes of erosion, deposition and transportation vary with river velocity.
It also shows that particles of sand (between 0.1 and 1 mm in diameter) can be eroded at lower velocities than finer particles. This is because silt and clay stick together more than sand which means they are harder to dislodge so more energy is required (greater velocity required). - 49What does the critical erosion velocity curve in the graph show?It shows the minimum velocity needed for the river to pick up (erode) and transport particles of different sizes. It takes higher velocity to erode material than it does to transport material.
- 50What does the mean settling velocity show?It shows the velocities at which particles of different sizes are deposited i.e. it shows the competence of the river at different velocities.
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- AS - Level Geography (Rivers) Flashcards on River Discharge, created by Tom Baker on 06/04/2016.
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- Tom Baker
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