The Water Cycle Flashcards
Hydrological Cycle
The continual movement of water between the rivers, oceans, atmosphere and land
How the water cycle works
1) evaporation
2) warm air rises
3) condensation
4) precipitation
5) interception
6) surface run off or through flow
7) percolates
Major stores of water
Ocean, ice caps, land and atmosphere
Transfers
Movement of water between stores
River or drainage basins
An area of land drained by a river and its tributaries
Edges of drainage basin
Watershed
Where the river meets the sea
Mouth of the river
Types of erosion
Abrasion
Attrition
Hydraulic Action
Corrosion/solution
Abrasion
Material carried by the river wears away the bed and banks
Hydraulic action
The power of the water forces air into gaps in the banks and weakens them so they eventually collapse
Attrition
The particles carried by the river are bashed against one another, making them smaller and rounder
Corrosion/solution
Particles are dissolved because of slightly acidic solution
Causes of vertical erosion
Swirling currents creating potholes in the river bed
Water falls creating plunge pools
Types of transportation
Traction
Saltation
Suspension
Solution
Traction
Rolling large stones along the bed of the river
Saltation
Bouncing smaller particles along the bed
Suspension
Sediment that floats within the river flow
Solution
Minerals dissolve in the water
Deposition
When the velocity of the river falls, it has less ability to carry its load. The river then starts to drop the material, starting with the largest particles. Loss of velocity can occur for many reasons
Reasons for the loss of velocity
River enters the sea or lake
There is less water entering the river
There is more sediment in the river
Competence
The maximum size of material the river is capable of carrying
Capacity
The total actual load transported
Levels of energy required to erode
Sands require the least energy as their particles do not coagulate
Silt/Clay requires a higher velocity as particles do coagulate
Pebbles are eroded at higher velocities
Boulders require the highest velocities to erode
Upper course vs lower course
Upper course: Steep gradients lead to rapid-flowing rivers
Middle course: River meanders through gentle gradients
Lower course: River braids over flat land
Upper course
- Vertical erosion
- Weathering
- Headward erosion
- Boulders create friction, slowing down the rate of flow
- Steep gradient
Characteristics commonly found in the upper course of rivers
- V-shaped valleys
- Potholes
- Interlocking spurs
- Waterfalls
- Rapids
- Gorges
- Large boulders
Middle course
Lateral erosion Transportation Asymmetrical channel Floodplain Truncated spurs Meanders
Lower course
Transportation
Deposition
Friction is reduced, so greater velocity
Characteristics commonly found in the lower course of rivers
Wide smooth channel Braiding Oxbow lakes Large floodplain Terraces Levees Deltas
V Shaped Valleys
Weathering breaks up material on slopes, which is then deposited into the river. Material is carried by riverbed through abrasion
Waterfalls
Soft rock erodes more quickly, undercutting the hard rock
Hard rock is left overhanging, because it isn’t supported it eventually collapses. Plunge pool is created by the erosion of rocks. Process repeats and waterfall moves upstream, forming a steep sided gorge on either side
Meanders
Meanders are formed by erosion and deposition. Centrifugal force causes the water to flow fastest around the outside of the river, creating erosion on the outside and deposition on the inside bend.
Oxbow Lakes
When the bends of a meandering river become so large that the water takes a more direct path, often cutting through the land of the bend. This may change the course of the river as more water runs through the alternate route. The old bend of the river eventually gets cut off, leaving an oxbow lake.
Braiding
River loses velocity, sediment is deposited and builds up to choke the main channel, causing the river to split in a braiding pattern.
Formation of a delta
- River carrying sediment reaches sea/lake
- Loses energy and deposited material
- Heaviest sediment first, more sediment is added
- if tides are strong then sediment will be washed away, if not then delta will form
Flocculation
When the fresh and salt water meet creating an electric charge causing the clay particles to coagulate
Types of delta
Birds foot: Many distributaries
Cuspate: Sediment spread evenly on either side
Arcuate: Rounded and convex structure
Physical causes of flooding
- Heavy rainfall
- Snowmelt
- Steep slopes
- Impermeable rock
- Very saturated soils
- Compacted or dry soils
Human factors that cause flooding
Urbanisation
Deforestation, removing trees reduces the amount of water intercepted and increases runoff
Storm Hydrographs
shows how rainfall events change the discharge of a river
Factors influencing storm hydrographs
Basin size Precipitation type Temperature Land use/ Urbanization Rock/Soil type Drainage density Tides/storm surges
Drainage density formula
Total length of all streams and rivers in a drainage basin, divided by the total area of the drainage basin
Factors affecting drainage density
Geology Land use Time Precipitation Relief
Bifurcation ratio meaning
a LOW bifurcation ratio means a HIGHER risk of flooding
Bifurcation ratio
Number of streams of one order in relation to the number of streams in the next order (1st order / 2nd order) then finding the average of all the ratios
Hydraulic radius
Ratio between the area of a cross section of a river channel, and the length of its wetted perimeter.
Purpose of the hydraulic radius
Determines the efficiency of a river. …
Drainage patterns
Trellised
Radial
Parallel
Dendritic
Radial
Streams radiate outwards from a central high point
Trellised
Tributaries enter the main river approximately 90 degree angles due to ridges of harder or impermeable rock, causing a trellis-like appearance of the drainage system
Parallel
Rivers flow uniformly down steep sloping surfaces
Dendritic
Streams join together to form tributaries into the main river. From overhead this makes a tree-like pattern with tributary “branches” and a river “trunk.”
