Rivers, Floods and Management Key Terms

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Rivers, Floods and Management Key Terms Flash cards

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Abrasion Wearing of the shoreline by sediment carried by water flow. Erosion by scraping, scouring and rubbing of load in contact with banks and bed (Corrasion)
Afforestation Planting trees in the catchment area of a drainage basin to increase interception storage and evapotranspiration
Aquifer Porous and Permeable rocks that can store water
Antecedent Rainfall Rain that falls on already saturated soil. Soil cannot take any more water so it becomes surface runoff.
Attrition Reduction/rounding of particles of sediment carried in water by repeat collision with other sediment/banks
Bankfull The state of flow of a river when it completely fills its channel (at capacity)
Bedload Larger material, cobbles, pebbles and sand transported by saltation.
Braided stream Interconnected channels separated by deposited material
Capacity The total volume of sediment a river can carry
Calibre Measurement of the long axis of sediment in a river
Catchment Area The land that drains water into a particular river system
Channel Enlargement Deepening/Widening of the channel to accommodate larger discharge and transport it faster
Channel Flow Movement of water within the river channel
Competence The maximum size (calibre) of load a river is capable of transporting
Condensation Process that water vapour is converted into water
Corrasion Erosion by friction of load in contact with banks/bed (Abrasion)
Corrosion Dissolving of carbonate rocks (eg. Limestone) in water flow.
Cross sectional area Channel depth x Chanel width
Dams Barriers that hols back water and create a large reservoir behind them.
Defecit A Shortage eg. soil moisture
Deltas Formed when the amount of sediment delivered to the mouth of a river exceeds the amount taken away by waves, and so it is deposited.
Deposition When the rivers competence is not great enough to carry the sediment, so it is dropped.
Discharge Volume of water flowing in a river per second, measured in cumecs (Cubic metres per second)
Dissolved load (Solution load) When weak acids in water flow dissolve material in solution.
Distributary Small channel that leaves the main river on a delta (one of the braided channels)
Drainage Basin The area in which water will flow into one particular river
Dreding The removal of sediment from the river bed to increase channel depth
Eddies Fast-flowing circular currents of water in the rivers flow
Evaporation Transformation of water into water vapour by heat from the sun
Field capacity Amount of water that can be held by the soil before rainfall becomes antecedent.
Evapotranspiration Loss of water from a drainage basin into the atmosphere from the processes of evaporation and transpiration.
Flocculation River load particles joining together on contact with salt in sea water, increasing weight and causing them to be deposited
Flood A temporary excess of water that spills over onto the land
Flood Abatement Reducing possibility of flooding by managing land use upstream. Eg. afforestation
Flood embankments Building up of levees around river channel
Flood interception schemes Intercepting the channel, diverting part of the flow for town/agricultural use and to move water to flood retention areas.
Flood proofing Temporary protection against flooding. Eg. sandbags or Permanent Eg. Flood proof walls/flood gates
Flood relief channel Constructed to redirect excess water ahead of a settlement
Flood walls Increasing height of channel, preventing water spilling out over floodplain
Flood plain Flat and broad valley floor created by successive flooding events depositing alluvium (sediments)
Frequency How often flooding occurs
Gorge Narrow, rocky, steep-sided valley, created by recession of a waterfall
Graded profile Also called the long profile
Groundwater storage Storage of water in permeable rock under subsoil
Groundwater flow Movement of water through permeable rock under subsoil
Hard engineering Flood management strategies that involve structural measures offering protection through engineering.
Helicoidal flow Water flow pattern where the fastest current spirals across the channel in a corkscrew motion
Hjulstroms Curve Graph showing relationship between velocity, erosion and deposition.
Hydraulic action Force exerted by moving water on bed and banks of river
Hydraulic radius Ratio of the cross sectional area of the channel and the length of its wetted perimeter
Hydrograph Graph showing the discharge, depth and velocity of a given point of a stream at a particular time (normally during a storm)
Infiltration Downward movement of water into soil
Infiltration rate Speed (mm/s) at which water passes through ground into soil
Interception Prevention of precipitation reaching Earth's surface by trees and vegetation
Interception storage Total volume of water held on surface of vegetation
Knick point Break of slope in the long profile. Often upper limit which downcutting from rejuvination has reached. Marked by rapids/waterfalls
Lateral erosion Middle/lower sections where river has high energy especially if close to bankfull. Widens valley, especially strong on meanders, where hydraulic action undercuts river cliffs
Levees Natural ridge formed by deposition of coarse material along channel edge.
Lining the channel Lining river with concrete, making it smoother and reducing friction, allowing water to flow faster
Load Material carried by river
Magnitude Size of the food
Meanders Bends in a river formed by helicoidal flow, with erosion on the outside and deposition on the inside
Naturalisation Restoring rivers to a more natural state by removing hard engineering
Overland flow Movement of water over surface of land, usually when ground is saturated or frozen
Peak rainfall Time when maximum amount of rain was falling
Percolation Gravity flow of water seeping into soil or rock
Point bar Sediments laid down on the inside of a meander
Potholes Formed by abrasion, pebbles carried by flow get stuck in crack, an eddied is formed and the pebbles grinds down in circular motion to form pothole
Precipitation All moisture that reaches the Earth including rain, snow and dew
Profile Changing height of a river from source to mouth, also called long profile
Rapids Stretches of fast flowing water over rock and shallow riverbed
Realignment Straightening/shortening of river course by removing meanders, increases gradient making water move faster
Regime Annual pattern of river discharge
Rejuvination Renewal of energy permitting accelerated erosion and transport. Rivers adjusting to new base level
River cliff Outside of a meander, steep undercut bank
River restoration Returning uplands to peat bog increasing absorption in soil
Roundness Shape of sediment in a river, changes downstream as a result of attriction
Runoff Water flowing over land surface as channel flow/overland flow
Saltation Small stones bounce along channel bed
Sinuosity Curving nature of a meander. Actual channel length divided by straight line distance
Sluice gates Barriers that hold water back, some pump water in opposite direction
Soft engineering Flood management strategies that are non-structural, more 'natural'
Soil moisture Total amount of water, including water vapour in unsaturated soil
Solution load Dissolved minerals transported within mass of moving water
Stemflow Flow down plant trunks/stems following interception.
Stormflow Water that reaches the channel through runoff. Combination of overland flow and rapid throughflow
Strata Layers of rock
Surface storage Total volume of water on surface in lakes etc
Surplus More than is needed Eg. Soil moisture
Suspended load Bulk of sediment transported by river. Reason most rivers are brown in colour in bankfull
Throughflow Movement of water downslope within soil layer
Traction Large stones rolled along river bed
Urbanisation Increase in proportion of countries population living in urban areas
Velocity Speed and direction at which a body of water moves (m/s)
Verticle erosion Dominates upper reaches of river cutting into bed by abrasion and hydraulic action
Water budget Relationship between inputs and outputs in drainage basin, shown as graph
Washland restoration Wet lands allowed to flood at times of high discharge, to reduce impact elsewhere
Waterfalls Steep or verticle part of the river, occur when hard rock lies across the river with soft rock downstream which erodes faster
Watershed Boundary between two drainage basins, usually ridges of high land
Water table Surface of saturated layer of soil/rock
Wetted perimeter Portion of perimeter of a stream channel cross section that is in contact with the water
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