Rivers and Flood Management- Book 1 Key Terms Flashcards
Define drainage basin?
The catchment area, from which a river system gets its water
‘The area of land drained by a river and its tributaries’
Define the watershed
The point which separates drainage basins, generally following a high ridge of land, any rain falling within the watershed will flow into the drainage basin
Define an open system
A system consisting of inputs, outputs of energy and stores and transfers of water
Define the hydrological cycle
The cycle where water evaporates into the air then falls again as precipitation
Define an input
The input of water often via precipitation
Define an output
The process of water leaving the drainage basin
Define evapotranspiration
The joint process of evaporation and transpiration
Define precipitation
All ways in which moisture can leave the atmosphere, most commonly rain but it can also be snow, hail, dew and frost
Define interception
When precipitation is prevented from reaching the soil, either by plants or man made structures. It creates a significant store of water in wooded areas but is only a temporary store as collected water evaporates quickly
Define vegetation storage
All water contained in plants at any one time
What are surface stores of water
They include puddles, ponds and lakes
What is groundwater storage
Water stored either in the soil or rocks
What is the water table?
The top surface of the zone of saturation- zone of soil and rock were all the pores in the soil and rock are full of water.
What are aquifers?
Porous rocks that hold water within them
What is channel storage?
The water held within the river or stream channel
Define surface runoff (overland flow)
water flowing over the land either over the whole surface or through little channels, it’s common in arid areas where torrential rain falls on hard baked land
Define through fall
Water dripping from one part of a plant to another
Define stemflow
Water running down a plant stream or tree trunk
Define throughflow
Water moving slowly downhill through the soil, its faster through ‘pipes’ such as cracks in the soil, or animal burrows
Define infiltration
Water soaking into the soil, influenced by soil type, soil structure, and the level of water already in the soil, in a heavy storm where water can’t infiltrate into the soil fast enough, then it flows over the surface
Define percolation
Water seeping down into the water table
Define groundwater flow
Slow flowing water below the water table through permeable rock. Water flows slowly through most rocks, but rocks are highly permeable with lots of joints can have ground water flow e.g. Limestone
Define baseflow
Groundwater flow that feeds into rivers through river banks and beds
Define interflow
Water flowing downhill through permeable rock above the water table
Define channel flow
Water flowing in the stream itself (also called discharge)
Define evaporation
Water turning into water vapour- from a liquid to gas
Define transpiration
Evaporation from plant leaves- plants and trees take up water through their roots and transport it to their leaves wheee it evaporates into the atmosphere
Define river discharge
Also called river flow is another output
Define the water balance of a drainage basin
The balance between inputs and outputs together with changes in ground storages
Define a water surplus
The ground stores fill with water so there’s more surface runoff and higher discharge so river levels rise
Define ground water deficit
Ground water stores are depleted due to outputs being higher than inputs
Define ground water recharge
Refilling of ground water stores
Define river discharge
The amount of water in a river passing a given point at a given time, it’s measured in cumecs
Define the rising limb of a storm hydrograph
The increasing discharge of a river in response to water entering a river channel
Define peak discharge
The highest discharge a river reaches in a time of flood
Define the falling or receding limb of a storm hydrograph
When river discharge falls due to there being a less input going into the river
Define the baseflow of a river
The starting or finishing level of the river before and after a storm
Define the lag time for a drainage basin
The time delay between peak rainfall amount and the peak discharge
Define the river’s regime
The pattern of seasonal variation in the flow of a river, usually over a years period
Define the long profile of a river
It shows the changes in altitude along its course from the source to the mouth
Define hydraulic action
The force of air and water on the sides of rivers and in cracks
Define evorsion
The direct force of the water. Most effectiv in turbulent flow
Define cavitation
This is a process in which bubbles form in flowing water, these bubbles can implode next to it within cracks in the bank. They the. Evict tiny jets of water that can move up to 130m/sec. This can damage solid rock
Define abrasion
The wearing away of the bed bank by the load of the river. The effectiveness of this is determined by the type of load and type of bedrock and its rate increase as velocity does
Define solution
The removal of chemical ions in the rock, especially calcium. Key factors being the rate of erosion, geology of the bedrock, solute concentration of the water, discharge and velocity
Define attrition
The wearing away of the load of a river, it is commonly done by pebbles and rocks banging into each other and so knocking off any sharp corners as well as hitting the river bed
Define endogenic material
Material eroded from the bed and banks
Define exogenic material
Material that has arrived into the river channel by mass movement and weathering of the valley sides
Define traction
Where heavy load rolls and bounces along the river bed, in times of normal flow this is often sand but in times of flood it can be rocks and boulders
Define saltation
Where smaller particles or stones bounce along the river bed, as each stone lands it dislodges more, which are then moved along in the flowing water
Define suspension
Where finer particles are carried within the river without touching the beds and banks- this is the largest contribution to the rivers load
Define solution
When a river runs through a carbonate rock area, weak acids may act in these rocks and dissolve materials into solution
Define river capacity
The largest amount of material can be transported
Define competence
The size of the largest particle that can be transported
What is the Hjulström curve?
The relationship between the velocity of a river and the size of particles that can be eroded, transported and deposited
Define erosion velocity
The rate of flow at which the river is able to pick up particles of load
Define fall velocity
The rate of fall at which a river drops particles of load as they become too heavy to transport
Define deposition
It occurs when the river has reduced energy and it is no longer competent, nor has the capacity, to transport its entire load. When velocity and discharge decrease
Define a riffle
A shallow or rocky area of a stream where the water flows brokenly
Define flocculation
Where clay or silt particles coagulate due to electrical charges and sink more rapidly creating mudflats in river estuaries
Define mass movement
Movement of surface material caused by gravity. Landslides and rockfalls are examples of very sudden movements of this type, geological agents such as water, wind and ice all work with gravity to cause a leveling of the land
Define bedload
The material lying on the bed of the channel, this is only transported when river levels are high
Define dissolved load
This consists of soluble materials carried as chemical ions, so there are no measurable particles
Define total sediment load
The total load of sediment in the river channel, this tends to increase downstream
Define the valley cross profile
The view of the valley from one side to another. E.g. In the upper course this is the typical V-shape
Define the gravitational potential energy of a river
The energy it has due to its height above sea level
Define the kinetic energy of a river
The moving energy of water
Define the dynamic equilibrium of a river’s graded profile
Where the slope, width and other channel characteristics have adjusted to the volume of water and load carried by a river under prevailing conditions, here all factors are in balance
Define channel roughness
The amount of friction a river experiences as it moves downstream
Define Cross-sectional area
The width of a channel multiplied by the average depth of a river
Define velocity
Usually measured in metres per second
