Hydrological Systems Flashcards
Define source (of a river)
Start of a river - usually on high ground
Define a drainage basin
An area of land drained by a river and its tributaries
Define tributary
Smaller river that joins the main river
Define Confluence
Where two or more rivers meet
Define watershed
A ridge of high ground that forms the boundary between two drainage basins
Define mouth (of a river)
The end of the river where it meets a sea or a lake (usually quite wide)
Define precipitation
All forms of moisture that reach the Earths surface (e.g rain, snow, dew)
Define evaporation
The transformation of water droplets into water vapour by heating
Define (evapo)transpiration
Loss of water from a drainage basin into e atmosphere from the leaves of plants
Define channel storage
The water stored in a river
Define surface storage
Total volume of water held on the Eaths surface in lakes, ponds, puddles
Define groundwater storage
Storage of water underground in permeable rock strata
Define Interception storage
Total volume of water held on the surface of vegetation
Define Through fall
The water that drips off of the leaves of plants
Define Stem flow
Where precipitation flows through the arms of the plants to the ground
Define secondary interception
The movement of rain water from big plants to smaller plants
Define groundwater flow (base flow)
Deep movement of water through the underlying rock strata (horizontal)
Define through flow
The movement of water downslope within the soil layer
Define the water table
The level below which the ground is saturated with water
Define percolation
The gravity flow of water within the soil
Define infiltration
The downward movement of water into the soil surface
Define surface runoff (overland flow)
Movement of water over the surface of land
Define capillary action
Upward movement or water in soil (commonly through the roots of plants)
Define channel flow
The movement of water within the river channel
Define antecedent precipitation
Already existing precipitation that can cause additional saturation
Define zone of saturation
Ground below the water table that fractures and fills with water
Define infiltration capacity
The max rate at which a soil in a given condition will absorb water
What is the water balance?
Balance between inputs and outputs of moisture in the soil
What is soil moisture deficit?
When most of the water in the soil has been used up
Define soil moisture recharge
When the water in the soul is being replenished
Define soils moisture drawdown
When the stores of water in the soil are being used and their levels are lowering
What is soil moisture excess
When the soil stores are full (and overflowing)
Define Peak discharge
The point where there is the highest volume of discharge
Define peak rainfall
The highest amount of rainfall
Define falling/recession limb
When discharge slows down or decreases
Define base flow
Water that reaches the channel largely through slow through flow and from permeable rock below the water table
What is discharge?
The volume if water flowing in a river per second measured in cumecs
Define rising limb
When discharge increases or speeds up
What is lag time?
The time difference between peak rainfall and peak discharge
What is antecedent flow rate?
The discharge before the storm event
What is hydraulic action?
Movement of sediment by the frictional drag of the moving water
What is abrasion (corrasion)?
Rubbing or scouring of the bed and banks by the sedimentary material carried along by the rivers
Define attrition
Reduction in size of the sediment particles as they collide with each other the bed and the banks
Define Corrosion (solution)
Rocks dissolve into the water and are carried away
What are the 4 types of erosion?
Hydraulic action
Abrasion (corrasion)
Attrition
Corrosion (solution)
Why does deposition occur?
A river deposits when it is no longer competent or has the capacity to carry all of it’s load (no energy to carry sediment)
Name 5 causes of deposition
River enters a sea or lake Landslide - sudden increase in volume Shallow water - eg. Inside of meander Confluence - change of velocity Low flow - not enough energy to carry sediment
Name all the processes of transportation
Traction (bed load)
Solution (dissolve)
Saltation
Suspension
Define traction
Large rocks and material that are too heavy to be picked up by the current may roll along or slide along the river bed
Explain the transportation process of solution
Where rivers run through area of carbonate rocks and weak acids that act on more soluble rocks and gradually remove material in solution
Explain the process of saltation
Material ranging from pebbles to sand grains may be temporary lifted and bounced along the floor in a hopping motion
Explain the process of suspension
Usually comprises of very small particles (fine muds, clay, sand etc.) which are carried along by the water.
what is the long profile
It shows how from the source to mouth the balance between erosion transportation and deposition changes throughout the course of the the river
Why is the long profile concave?
Vertical erosion and downcutting dominates initial stages of rivers course and lateral erosion near the mouth causing a concave structure
Define river competence
Max size (calibre) a load of a river is capable to carry
Define river capacity
Total volume of sediment a river can transport
What is the Hjulstrom curve?
Relationship between the velocity of the river and competence
What influences the rivers 3 processes - transportation, erosion, deposition
Level of energy a river possesses
What 3 things contribute to a rivers energy?
Mass of water
Height above sea level
Gradient
Define velocity
Speed and direction at which the body of water flows
State 3 factors that influence velocity
Channel shape (hydraulic radius)
Roughness
Slope (gradient)
Define hydraulic radius
Ratio of cross-sectional area of the channel and the length of it’s wetted perimeter
What 3 things effect the shape of a V-shaped valley?
Climate
Geology
Vegetation
Define a pothole
Circular depression on the river bed carved out of solid rock
Define a waterfall
Sudden fall of water where there is a rapid change in gradient in the rivers course
What is a pool
Dip in river bed
What is a riffle
Mound or area of deposited sediment
What is rejuvenation
Increase in energy of a river caused by either a fall in its base level or an uplift in land
Define isostatic change
Land rising relative to the sea as a result of crustal movements
Define eustatic change
Global changes in the sea levels
Define a knick point
Sudden bread or irregularity in the gradient along the long profile of a river
Define a river terrace
Remnant of a former floodplain which has been left at a higher level after rejuvenation of the river
How do interlocking spurs form?
Rivers take the easiest and quickest route by eroding through soft rock and leaving hard rock protrusions called interlocking spurs
Abrasion and hydraulic action are able to erode the channel vertically but not the lateral banks so the river meanders around the hard rock
What are levees?
Natural raised embankments made up of sand and mud deposits built up along either side of the floodplain of a river or stream
How do levees form?
As a river overflows it’s bank during a flood, the velocity of the water falls.
Competence of river suddenly reduced
The thickest and coarsest sediments are deposited at channel edges
Thin and fine sediments deposited over outer floodplain
Over time deposited sediment builds up
What are deltas?
When a river reaches a lake or the sea the water slows down and loses the power to carry sediment, this sediment is dropped and forms a delta
What are the 3 types of delta?
Arcuate/fan-shaped: land around river mouth arches out into sea and river splits many times on way to sea, creating a fan effect
Cuspate: land around mouth of river just out arrow-like into the sea
Bird’s foot: river splits on way to sea, each part juts out, like a birds foot
Explain formation of deltas
Rivers energy and efficiency is reduced as it joins a larger body of water (sea) which decreases the hydraulic radius.
River loses power to carry sediment and drops it at the mouth of the river
Areas of sediment continue to grow creating landforms that rise above water surface
Factors influencing formation of deltas
- Amount and type of sediment available
- Variations in volume of water discharged from river
- Geometry of Coast
- Coastal processes
What is a floodplain
Area that would naturally be affected by flooding if a river rides above it’s banks
Low flat lands used to hold floodwater temporarily
Formation of floodplains
Lateral erosion (hydraulic action and abrasion) due to fast velocity River erodes valley sides, widening valley floor to create a floodplain
Define incised meanders
Rivers that have cut deeply into the landscape because they have been deepened by rejuvenation
what do we mean by flood frequency?
How often does a flood occur?
What is flood recurrence?
How often does a flood of a certain magnitude (size) occur?
what is magnitude-frequency analysis of flood risk
Calculating the recurrence interval which shows the no. of years within a flood of a a certain size can be expected
How reliable are flood recurrence intervals?
Relies on natural events and processes
only based on previous events
only a prediction
Name all 6 types of hard engineering flood management techniques
Dams ans reservoirs, Straightening channels, Levees and embankments, Relief channels, Dredging, Flood walls
Name all 7 types of soft engineering flood management techniques
Permeable surfaces, Basins and ponds, floodplain zoning, naturalisation of channels, wetland conservation, swales, filter strips
What are filter strips?
Gently sloping areas of vegetation that allow water to infiltrate into the soil
define hard engineering
building artificial structures such as dams aimed at controlling natural processes
define soft engineering
A sustainable approach to managing the coast without using artificial structures but using the natural processes of the river
What happened at River Tay,Scotland?
Major flood in Feb 1990
Flooded again mid-Jan 1993 with record of 2200m3/s
Both floods greater in magnitude than previous high record 52
What is a flood
When a river exceeds bankfull level and bursts its banks
What are the 5 natural causes of flooding?
Vegetation - interception, storage, transpiration
Slope - steeper angled means less absorption
Rock Type - infiltration in permeable rock, groundstorage
Drainage density - streams divided by area, lag time
Soil depth - deeper soil absorbs more, less runoff
State 5 human causes of flooding
Impermeable areas of tarmac - more runoff
Deforestation - less interception etc.
Ploughing - compacts soil so less infiltration
Sewers - directs into river, short lag time
Urbanisation - remove grasslands, less infiltration
