Rivers key terms Flashcards
Evaporation
The process which liquid water is transformed into water vapour
Transpiration
The process by which water is lost from a plant through stomata in its leaves
Evapotranspiration
The total amount of moisture removed by evaporation and transpiration from a vegetated land surface
Groundwater flow
The slowest transfer of water within the drainage basin. Provides the main input of water during drought or dry seasons. Flows through bands of sedimentary rock.
Infiltration
The passage of water into the soil. Takes place quickly at the beginning of a storm, but as the soil becomes more saturated, infiltration rates drop. sandy soils infiltrate more than clay.
Interception
The process by which raindrops are prevented from directly reaching the soil surface. Leaves and stems intercept water.
Percolation
The downward movement of water within the rock under the soil surface. The rate of percolation depends on the nature of the rock.
Precipitation
Water in any form that falls from the atmosphere to the surface of the earth. Includes rain, snow, sleet and hail.
Runoff
All the water that enters a river and eventually flows out of the drainage basin.
Stemflow
The water that runs down the stems and branches of plants and trees during and after rain to reach the ground
Throughfall
The water that drips off leaves during a rainstorm. It occurs when more water falls onto the interception layer of the tree canopy than can remain on the leaves.
Throughflow
The water that moves down-slope through subsoil, pulled by gravity
Soil moisture surplus
Soil water store is full which gives a surplus of soil moisture for plant use and runoff into streams
Soil moisture use
Plants must rely on stored water which is gradually used up
Soil moisture deficiency
Plants must have adaptations to survive for long periods or land must be irrigated
Soil moisture recharge
The soil water store starts to be recharged
Return period
An estimate of the likelihood of an event
Abrasion
Rocks hitting the river bed and bank
Hydraulic action
The power of moving water erodes the river
Solution (erosion)
Rocks dissolved by acids and erode the river
Attrition
Rocks hitting each other which make them smaller and rounder
Suspension
Fine, light material carried along in the river
Solution (transportation)
Dissolved rock carried along in the river
Saltation
Small pebbles and stones bouncing along river bed
Traction
Large rocks rolling along river bed
Example of a waterfall and gorge
High force on River Tees, Northern England
Example of a meander and oxbow lake
River cuckmere
MEDC flood case study
Cumbria Floods - Cockermouth, Cumbria
LEDC flood case study
Pakistan - Indus River
Hard engineering case studies
- Mississippi River, USA
- Three Gorges Dam, China - Yangtze River
Soft engineering case studies
- Yellow River, China - Afforestation
- Rhine River, Germany - floodplain zoning
- Met Office/ The EA - forecasting floods and warning
Causes of high velocity?
- High discharge
- High hydraulic radius
- Increase of gradient
- Low wetted perimeter
What is velocity determined by?
- Channel shape in cross section
- Roughness of channel beds and banks
- Channel gradient
What is hydraulic radius?
Shows channel efficiency
Hydraulic Radius calculation
Cross sectional area - channel width X depth
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Wetted perimeter
What is the Hjultsrom curve?
Shows the relationship between river velocity and size of particles that can be eroded, transported and deposited.
What are the key points on the Hjultsrom curve?
1) silt/sand are picked up at lowest velocities
2) clays are difficult to erode as pebbles, although small, they are cohesive and clay bed is smooth.
3) large boulders are dropped easily
4) clay particles can be transported in suspension at low velocities
What is the Bradshaw model?
Illustrates the main changes expected down the long profile of a river
Can make hypotheses on expected changes in the channel characteristics down the long profile
Formation of deltas
Deltas form only when the rate of deposition exceeds the rate of sediment removal.
Formation of braided streams
Braiding occurs when the river is forced to split into several channels separated by islands.
Formation of potholes
Potholes are formed where there are depressions, fine particles and large boulders may become trapped and swirled around by the current
Why does river rejuvenation occur?
Occurs when there is a rise of fall in sea level. The river adjusts to this change and creates landforms
What are river rejuvenation land forms?
- Knick points
- River Terraces
- Incised Meanders
Formation of a Knick Point
Formed due to sudden increase in gradient. Rejuvenation always starts closest to the sea and migrates upstream. A knick point marks each period of rejuvenation which resulted in an incised valley floor.
Formation of a River Terrace
They are the remains of a former floodplain which has been left at a higher level after rejuvenation. The down cutting of a renewed river leaves old flood plain above the level of the present river at a suspended level.
Formation of a Incised Meander
Renewed energy from rejuvenation results in an increase of vertical erosion and incised meanders. Ingrown meanders are also found in this process which incision is less rapid and lateral erosion is dominant.
