Rivers,floods And Management Flashcards
Abrasion
The scraping,scouring,rubbing,grinding and drilling action of materials being moved by a river
Attrition
The collision of one piece of a rivers load with another breaking off bits of rock in the proces. Makes rocks rounder and smaller
Base level flow
The lowest limit to which erosion can take place, usually sea level
Braiding
Occurs when a heavily loaded river rapidly loses energy and rocks are deposited mid channel
Channel cross profile
The view of a river channel from one side of the channel to the other
Cumec
The unit of discharge measured in m3 s-1
Deforestation
The deliberated clearance of forrest by cutting or burning
Deposition
The laying down of solid material such as silt on the river bed or floodplain
Drainage basin
The area of land drained by a river and its tributaries
Drainage basin hydrological cycle
An open system with inputs, outputs, transfers and stores that maps the movement of water through a drainage basin
Drilling
A form of abrasion where a pebble trapped trapped in a hollow on a stream bed is rotated by the moving water so that it wears away by the moving water so that it wears away the bedrock in a circular fashion
Efficiency
The ratio of the cross sectional area of a river and its wetted perimeter.It is expressed as the hydraulic radius
Erosion
The wearing away of the lands surface by rocks carried in a river
Evapotranspiration
The total amount of water leaving a vegetated surface by the joint process of evaporation and transpiration
Groundwater
Water which collects underground in pore spaces in rock
Groundwater flow
The movement of ground water, provides water for a river during drought
Hard engineering management strategies
A series of management strategies where there is controlled disruption of natural processes by using man made structures
Hjulstrom curve
A graph to show the relationship between the velocity of a river and the size of particles that can be eroded,transported and deposited
Hydraulic action
An erosion process where the banks and bed of the river are eroded by the moving water alone
Hydraulic radius
A measurement of the efficiency of a river; the ratio of the cross sectional area of a river and its wetted perimeter
Infiltration
The movement of water from its surface downwards into the soil
Interception
When precipitation is prevented from reaching the soil by leaves and branches(vegetation)
Kinetic energy
The energy of a moving mass. Function of mass and velocity
Overland flow
The rapid movement of water over saturated or impermeable land
Percolation
The downward movement of water from soil to the rock below or within rock
Potential energy
The energy stored in a mass as a result of its position in a force field ( gravity)
Recurrence interval
The frequency with which a flood of given magnitude is likely to occur
Rejuvenation
An increase in the energy of the river as a result of a fall in base level or uplift of land.
Roughness
A measurement of the frictional drag on a river bed on the moving water.calculated using mannings N formula
Runoff
All the water that flows out of a drainage basin
Saltation
A form of transportation where river particles bounce along the river bed.
Soft engineering management strategies
Ecologically sensitive management solutions to river erosion and flooding eg afforestation or land use zoning
Solution
A form of erosion where the river water dissolves soluble bed rock
Suspension
The transportation process whereby small material is carried in the body of the river
Thalweg
The part of a river that has maximum velocity and depth
Throughfall/stemflow
The water that drips off leaves or travels down the trunk of a tree during rainfall
Throughflow
The water that moves down slope through soil
Traction
The rolling of river bed load along a river channel
Transportation
The movement of eroded particles from their origin to the place they are deposited
Wetted perimeter
The total length of a river channel In cross section which is in contact with the water
Confluence
Where two river or steams meet
Types of water storage
Interception, Vegetation storage, Surface storage, Groundwater storage, Channel storage
What is the water balance
Shows the balance between the inputs and outputs
Affects how much water is stored in basin
What is lag time
Delay between peak rainfall and peak discharge -takes time for water to flow into river.
Shorter lag time increases peak discharge
River erosion methods
Hydraulic action Abrasion (corrasion) Attrition Cavitation - air bubbles imploding that cause shockwaves to break off pieces of Rock of banks and beds Corrosion ( solution)
Competence
Maximum particle size that a river is capable of carrying at a certain point
Capacity
The total load that a river can transport at a given time
What is helicoidal flow
Corkscrew like currents that spiral from bank to bank between pools (deepest water) causes more erosion and deepening of pools.
Also causes deposition in inside bend
Physical factors that increase the risk of flooding
- Sparse vegetation and deciduous trees- little interception
- Impermeable ground - no infiltration
- Circular drainage basins - all water arrive at same time as all points a similar distance away
- High drainage density - drain quickly so short lag time, increase discharge
- Steep slopes - water reach Channel faster , increase discharge
Human factors that increase flood risk
- Urbanisation - impermeable surfaces, gutters reduce lag time increase discharge
- Deforestation - reduced interception
- Flood management strategies eg if dams fail
- Agriculture - over grazing , less interception, soil erosion
- Climate change - increase rainfall
Social impacts of flooding
People and animals killed Floodwater contaminated - lack of clean drinking water Contaminated water - diseases Possessions can be damaged People made homeless
Economic impacts of flooding
Businesses shut down Rescue work and repairs costly Unemployment levels rise Infrastructure destroyed Crops destroyed
Environmental impacts of flooding
Floodwater contaminated so can pollute rivers
River banks eroded
Positive :
River sediment deposited so land more fertile
Wetlands can be created eg marshes, ponds and are habitats for many
