Hydrological Systems Flashcards
Define Abrasion (corrasion) (erosion)
The rubbing or scouring of the bed and banks by the sedimentary material carried along by the river
Define Hydraulic action (erosion)
The movement of sediment by the frictional drag of moving water
Define Attrition (erosion)
Reduction in size of sediment particles as they collide with each other, the bed and banks
Define Corrosion (erosion)
Rocks dissolve in water and are carried away
Define Traction (transportation)
Large rocks and material that are too heavy to be picked up by the current. They can roll or slide along the river bed
Define Solution (transportation)
Rivers run through an area of carbonate rocks. Weak acids may act on more soluble rocks and gradually remove material in solution. This dissolves the material
Define Saltation (transportation)
Material ranging from pebbles to sand may be temporarily lifted and bounced along the floor in a hopping motion
Define Suspension (transportation)
This usually comprises of very small particles from fine clays and muds to sand. The particles are carried along by the water. This usually forms the bulk of sediment transported by rivers. More turbulent rivers can carry more suspended load
Why does deposition occur?
- there’s shallow water
- river enters a lake/sea
- doesn’t have the capacity or energy to carry it’s load
- reduction in gradient
What’s the long profile?
Balance between erosion, transportation and deposition changes throughout the course of the river
Why is the long profile concave?
Source is in the high mountains and river wants to get to sea level by vertical and lateral erosion
Define River competence
The maximum size of load it can carry
Define River capacity
The maximum volume of load it can carry
What is the Hjulstrom curve?
The relationship between velocity and competence
What influences erosion, transportation and deposition?
Energy of a river
3 things which contribute to a rivers energy
- Mass of water
- Height above sea level
- Gradient of the river
What influences a rivers energy?
- Altitude (potential energy)
- Steepness/gradient (kinetic energy)
- Gravity
What is Velocity?
The Speed and direction in which a body of water flows
Factors which influence velocity
Channel roughness Channel shape (hydraulic radius) Channel slope (gradient)
What is hydraulic radius?
The ratio of the cross-sectional area of the channel and the length of it’s wetted perimeter
=cross-sectional area / wetted perimeter
Factors which effect the shape of a v-shaped valley
- Climate
- Geology
- Vegetation
What is a waterfall?
A sudden fall of water that occurs where there are rapid changes nk gradient in the rivers course
What’s a pool? (Meanders)
A dip in the river bed
What is a riffle? (Meanders)
A mound of sediment/ an area of deposited sediment
What are braided rivers?
They have multiple channels and islands of sediment inbetween the channels
What causes braiding?
Fluctuation in discharge levels, low river velocity and by the river losing capacity and competence
What are levees?
Natural raised embankments made up of sand and mud deposits built up along either side of the flood plain of a river
What is a floodplain?
The area that would naturally be affected by flooding if a river rises above it’s banks
What is a delta?
Low-lying plain or landform that occurs at the mouth of a river near the ocean
What is rejuvenation?
An increase in the energy of a river cause by either a fall in it’s base level (sea level) or an uplift of the land
Define Isostatic change
(Ice melting)
Changes in uplift of land relative to the sea level as a result of crustal movements
Define Eustatic change
(Water freezing)
Change in relative height of the land and the sea may also result from a rise/fall in sea level
What is a knick point?
A sudden break in the gradient along the long profile of a river. They can be shown by waterfalls
What is a river terrace?
A remnant of a former floodplain which has been left at a higher level after rejuvenation
What is an incised meander?
Rivers have cut deeply into the landscape (Grand Canyon)
What is Flood frequency?
How often a flood occurs
What is Flood recurrence?
How often a flood of a certain magnitude occurs
How do you calculate flood recurrence?
T=n+1
M
What is flooding?
A river exceeds bankfall level