Term
| What is a drainage basin? |
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Definition
| The catchment area from which a river system obtains it's water |
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Term
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Definition
| Area of high land which separates to drainage basin |
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Term
| What is the water balance and it's equation? |
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Definition
The balance between the river's inputs and outputs.
Precipitation = Streamflow + Evapotranspiration +/- changes in storage |
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Term
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Definition
| Volume passing a measuring point in a river at any given time |
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Term
| Equation for drainage basin discharge |
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Definition
| Precipitation - Evapotranspiration +/- Changes in storage |
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Term
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Definition
| The difference between peak rainfall and peak discharge |
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Term
| Name some factors that affect discharge |
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Definition
- Intensity and duration of a storm
- Precipitation
- Rain before storm
- Soil type
- Impermeable rock types
- Size and shape of drainage basin
- Slope angle
- Temperature
- Vegetation
- Land Use
- Urbanisation |
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Term
| Factors resulting in a flashy hydrograph (sharp points and jumps) |
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Definition
- Short lived but intense rainfall
- Impermeable underlying rock e.g. granite
- Urban area
- Small round drainage basin |
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Term
| Factors resulting in a long hydrograph |
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Definition
- Permeable rock e.g. limestone
- Dense woodland vegetation
- Elongated drainage basin
- High infiltration capacity of the soil |
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Term
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Definition
The process by which the bed and banks are worn down by the rivers load.
The river throws these particles against the bed and banks (sometimes at a high velocity) |
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Term
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Definition
| Material carried by the river bumps into each other and are smoothed/broken down into smaller partices |
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Term
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Definition
| The chemical action of river water, the acids slowly dissolve the beds and banks |
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Term
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Definition
| The process where air becomes trapped in joints and cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion. |
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Term
| Explain Vertical and Lateral Erosion |
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Definition
V = downwards, usually in upper reaches of land (high above sea level)
L = sideways, in middle/lower reaches due to lots of energy near sea level |
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Term
| Why does vertical erosion dominate? |
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Definition
| The river attempts to cut down to it's base level. High river level/velocity makes the river cut into it's valley by abrasion and hydraulic action |
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Term
| Why does lateral erosion occur more frequently than vertical? |
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Definition
| The river possesses a lot of energy which is used to widen the valley. The strongest current occurs on the outside of the bend and hydraulic action causes the bank to collapse. |
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Term
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Definition
| Boulders and pebbles are rolled along the river bed at times of high discharge |
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Term
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Definition
| Sand particles are bounced along the river bed by the flow of water |
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Term
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Definition
| Fine clay + sand particles are carried along within the water even at low discharges |
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Term
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Definition
| Some minerals dissolve in water such as calcium carbonate (this requires very little energy) |
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Term
| Factors that affect erosion |
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Definition
- Weight of water (more mass more energy)
- Height of river (higher = more energy)
- Steepness (controls speed and KE energy)
- Friction |
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Term
| Factors that effect deposition |
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Definition
- When gradient is reduced
- When discharge is reduced
- When in shallow water
- When size of load increases
- When there is reduced velocity on floodplain |
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Term
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Definition
| The quantity of sediment transported through a stream cross section at any given time |
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Term
| Factors affecting river load |
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Definition
- Extreme events (prolonged rainfall)
- Course of river
- Erosion
- Discharge + Velocity
- Size of drainage basin
- Rock type
- Precipitation
- Human Activity (deforestation, urbanisation) |
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Term
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Definition
| Total length of the river bed and bank sides that are in contact with the river |
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Term
| Define Cross Sectional Area |
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Definition
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Term
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Definition
| Cross sectional area / Wetted Perimeter |
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Term
| A higher wetted perimeter means.. |
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Definition
| more friction, more energy lost and a slower velocity |
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Term
| A higher hydraulic radius means.. |
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Definition
| less contact with banks for area of water, less energy lost, more efficient |
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Term
| Velocity is influenced by: |
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Definition
- Channel shape in cross section
- Roughness of bed/bank
- Channel Slope |
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Term
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Definition
| illustrates the changes in altitude of course of the river from source to mouth |
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Term
| What is the idealised long profile? |
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Definition
- Smoothly concave
- Graded profile, river is balanced between erosion and deposition |
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Term
| A river changes in these ways.. |
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Definition
- Erosion types and amounts
- Transportation types and amounts
- Deposition types and amounts
- Material sizes found in the river
- Landforms found on the river course
- Cross profile of the valley |
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Term
| Characteristics of the river's upper region: |
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Definition
(In order of travelling downwards)
- Source: soggy, messy land
- Releases water through drips
- High altitude
- V Shaped Valley
- Reservoirs
- High Energy
- Most powerful, a lot of erosion
- Steep Gradient
- Broad Curves
- Waterfalls |
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Term
| Characteristics of the river's middle region: |
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Definition
- Broadens out
- Lower altitude
- Energy declines
- Rocks are smaller/smoother
- Meanders are formed |
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Term
| Characteristics of the river's lower region: |
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Definition
- Marshland
- Meanders are bigger and wider
- Floodplain
- Estuary mud, everything deposited |
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Term
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Definition
| Abrasion occurs as turbulence swirls a rivers bedload in a circular motion causing it to rub and scrape out holes. These are then enlarged |
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Term
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Definition
| A sudden increase in channel slope. They are steep sections of river with turbulent flow where there are several sections of hard rock |
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Term
| How are waterfalls formed? |
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Definition
- Band of soft rock meets hard rock. Soft erodes more quickly making a step in bed.
- Water flowing over step speeds up (lack of friction) water has greater erosive power causing more s. rock erosion and undercutting of h. rock.
- H. rock can collapse. Deep plunge pool is created by abrasion at foot of waterfall from turbulence.
- Over time: more undercutting = more collapse, waterfall retreats leaving a steep sided gorge |
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Term
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Definition
River Tees:
- NE England, in the Pennines, flows east to North Sea
- H. rock = Whinstone. S. rock = Limestone
- 22 metres High
- 500m Gorge |
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Term
| How are meanders/ox bow lakes formed? |
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Definition
- Alternating pools and riffles
- River channel is deeper, more efficient and more erosive power (although energy is lost over riffles due to friction)
- Side to side flow due to spacing of pools and riffles
- Water speeds up and twists/coils
- Helicoildal flow causes more erosion and therefore more deposition on inside bend
- Combinatation exaggerates bends creating meander
- Neck of meander is broken through during flooding, deposition closes loop leaving lake |
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Term
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Definition
- Increase in river energy
- Caused by a change relative to sea level giving it more PE
- Making it higher above sea level so has to erode downwards
- River adjusts to new base level |
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Term
| Rejuvination: knick points |
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Definition
- Sudden break in gradient
- It marks the limit of how far inland the river has adjusted to new base level
- knick point moves upstream
- sharply defined creating waterfalls/rapids |
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Term
| Rejuvintation: River terraces |
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Definition
- Former floodplains that are left at a higher level after rejuvination
- Terraces are cut back as the new valley is widened by lateral erosion |
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Term
| Rejuvination: Incised Meanders |
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Definition
- Renewed energy means meanders are incised/deepened
- happens slowly: deep (ingrown meanders)
- happens quickly: gorge (entrenched meanders) |
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Term
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Definition
- Urbanisation (less vegetation)
- Decreased lag time
- More precipitation
- Impermeable rock types (more surface runoff)
- Small drainage basin
- Low lying ground |
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Term
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Definition
- River reaches sea, energy is absorbed
- River deposits load, builds up on sea bed
- Rises above sea level, partially blocks river mouth
- River braids into several distributaries to reach sea |
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Term
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Definition
- During a flood material deposits across whole flood plain (as river loses velocity + energy due to friction)
- Heaviest material is dropped first closest to channel
- Material builds up and formes levee (natural raised embankment) |
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Term
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Definition
- River carries vast amount of eroded sediment
- If velocity drops/load becomes too much it's deposited
- River divides into man small winding channels which will eventually open up to form one |
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