Hydrology Flashcards
What is evaporation?
water that is heated by the sun from liquid to gas and rises into the atmosphere
What is evapotranspiration?
evaporation and transpiration happening at the same time
what is percolation?
water flowing down from the soil into the bedrock
what is abrasion?
wearing away of the bed and bank by the load carried by the river
what is attrition?
wearing away of the load carried by a river, creates smaller and rounder objects
what is hydraulic action?
force of air and water on the sides of river and in cracks
what is cavitation?
force of air exploding; as fluids accelerate, pressure may drop causing bubbles to form which will implode in cracks and event mini jets of water
What is corrosion?
removal of chemical ions, especially calcium
How are different loads transported?
-smallest particles are carried in suspension as the suspended load
-salted load are bigger particles transported in a series of hops
-tracted load are pebbles shunted along the bed
-material is carried in solution as the dissolved load
what is laminar flow?
-the flow will develop into layers in an efficient river, with the top and bottom slower than the middle
-some friction with air and friction with bank and bed
what is turbulent flow?
-the flow will be turbulent with verticals and horizontal eddies in rivers with a less smooth base
- causes more erosion
what is helicoidal flow?
-high pressure on the outside of a meander creates low pressure on the inside which creates a flow from one to the other
-spiral flow
How is meander formed?
-alternating areas of fast and slow flow will develop, faster areas will have more erosive power and create deeper areas called pools and slower areas will be shallower riffles
-thalweg will be deflected by the riffles onto the bank and start to create erosion on the bank
-deeper pools become the outside of the meander with riffles between
-helicoidal flow will lead to deposition on the inside of the bend creating in a slip off slope with erosion creating a river cliff on the outside
How is a arcuate delta formed?
weak currents, long shore drift and lots of material gives a gently shaped delta
e.g. Nile
How is a cuspate delta formed?
stronger, opposing currents - pointy tooth like shape created
e.g. Ebro, Spain
How is a birds foot delta formed?
Huge quantities of material creates a birds foot shape
e.g. mississippi
How is a delta formed?
-where rivers meet the sea, deposition occurs
-if the currents are not strong enough to wash it away a delta will for,
-deposition is increased by flocculation - these are the particles that would otherwise not be deposited on the Hjölstrom curve, clay deposits make deltas very fertile
How is a levee formed?
-when a river floods it suddenly loses efficiency, loses velocity and drops load heaviest first
- past flood the water cannot get back into the river so sinks into the flood plain, depositing alll of its lighter load (including clay)
-As the channel deepens, deposition occurs on the bed and raises it
What are braised channels and how do they form?
-channel is divided by islands often vegetated and long lived
-occur on steep channel gradient, large proportion of course material, easily eroded bank material, highly variable discharge
- island of alluvial deposits forming shingle deposits
CS: what are the causes of flooding in Bangladesh?
- deforestation in Nepal for fuel wool increases overland flow and soil erosion
-snowmelt in himalaya meaning discharge is seasonal and affected by climate change
-urbanisation of Ganges valley means more overland flow due to impermeable surfaces, less infiltration and shorter lag time (over 650mil population)
-floodplains and delta, land is very flat and prone to flooding (75% is 5m of sea level)
-cyclones in bay if bengal bring in storm surges which cause costal flooding
-monsoon climate so seasonal heavy rainfall causes annual flooding
-poor river management of dams in india and levees in bangladesh
