Rivers, Floods and Management Key Terms

Frage	Antworten
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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Rivers, Floods and Management Key Terms

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