IB Geography HL - Freshwater - Terminology

Precipitation

All forms of moisture that reach the Earth's surface in different forms such as snow or rain

Interception

When precipitation lands on buildings, vegetation and concrete before it reaches the soil

Interception storage

Water storage on leaves and branches. It is is only stored temporary as it is often quickly evaporated

Stemflow

When water is intercepted by leaves and branches and flows down tree trunks or stems

Surface storage

When water is held in lakes or puddles and cannot infiltrate into the soil

Infiltration

When water moves downwards through the soil through tiny pores

Soil moisture storage

Water is stored in the pores of the soil

Percolation

When the water moves vertically down through the rock

Groundwater storage

When water from percolation is stored at depth in the rock

Evapotranspiration

The loss of water directly from rivers or lakes or from vegetation

Transpiration

When water is removed from leaves into the atmosphere

Surface run off

When water does not infiltrate into the land, and water flows over land

Throughflow

When water moves sideways through the soil

Baseflow

The part of the river's discharge that is provided by groundwater seeping into the bed of the river

Cryosphere

The snow and ice environment where freshwater is stored

What is the hydrological cycle?

The constant recycling of water between the sea, air and land

Why is the hydrological cycle a closed system?

Because no water is added or lost

Upper course of a river

V shaped valley, shallow, steep sides, interlocking spurs

Lower course of a river

Flat valley, deep, levees, oxbow lakes, meanders, floodplains

What are floodplains

flat areas found in the lower parts of a river, comprising of clay, silt or alluvium deposited when the river is in flood.

Why are drainage basins an open cycle?

They have inputs (where water enters the system as rain, snow etc) and outputs (where water leaves through the sea or evaporation)

What is a water budget

The annual balance between precipitation, evapotranspiration and runoff

Watershed/drainage divide

The boundary between two drainage basins

Drainage basin

The area drained by a river and its tributaries

Discharge

The volume of water flowing over a certain point in a certain time, measure in cumecs

How to calculate discharge?

Velocity x cross sectional area

Channel efficiency

The ability of a channel to move water and sediment

Wetted perimeter

The part of the CSA that is in contact with the banks and bed of the river

Which types of channels are more effective at moving water?

Narrow, smooth and deep channels

Why are most rivers wide and shallow?

During a flood most of the river's energy is devoted to erosion and transport, so the channel becomes wider, and when the flow decreases, sediment is deposited on the bottom of the river

Which kind of rivers are best at at moving sediment?

Wide, shallow and rough channels

When are channels most efficient?

When the channels are at their "bankfull" discharge

What is a process?

A series of actions, changes or functions bringing about a result

What types of processes are there?

Erosion, deposition and transportation

Abrasion

When rocks hit against the bed and the banks of the river, wearing it down

Attrition

When rocks hit against each other and wear each other down

Solution (erosion)

Chemicals dissolved in the water corrode the bed, banks and sediment

Hydraulic power

Water smashing into the banks cause air to get trapped, and widens cracked

Vertical erosion

Deepens the valley, commonly found in the upper course

Lateral erosion

Widens the valley, found in the lower course, uses most of its energy for transportation

What factors affect the rate of erosion?

Load, velocity+ discharge, gradient, geology, pH and humans

How does load affect the rate of erosion?

Heavier and sharper load means a greater potential for erosion

How does velocity affect the rate of erosion?

Greater velocity means more erosion

How does gradient affect the rate of erosion?

The higher, the more GPE, so the faster velocity and the more erosion

How does geology affect the rate of erosion?

The softer the rock, such as sand, the easier to erode

How does pH affect the rate of erosion?

Solution erosion is increased when water is acidic

How does humans affect the rate of erosion?

Deforestation, dams, bridges all interfere with natural flow and erosion

Traction

Large boulders are rolled along the bed

Suspension

Fine particles are carried by the current

Saltation

Small rocks bounce along the river bed

Solution

Tiny sediment particles dissolve in the water and are carried by the current

What factors affect the rate of transport?

Discharge and velocity

Competence

The largest particle a river can carry

Capacity

The total quantity of sediment a river can carry

What kind of sediment is found in the upper course?

Large angular boulders

What kind of sediment is found in the lower course?

Small rounded sediment

When are where does deposition occur?

The mouth of a river as it enters the sea, and the inside of a meander

What other factors affect the rate of deposition?

Seasons

Flood plain

The flat either side of the river

Levee

Build up of sediment after a flood either side of a river

What is an abandoned meander?

When a meander has been cut off. Also called an Oxbow Lake.

How is a meander formed?

When a river's thalweg runs through pools and riffles that aren't directly in line with each other. The water erodes these pools and makes them bigger and forms bends in the river

Formation of a waterfall (5)

* Forms when river runs over a band of hard rock followed by soft rock
* Plunge pool is formed as erosion such as hydraulic power and attrition wears away softer rock
* Hard rock is more resistant so less susceptible to erosion, this causes soft rock to recede creating an overhang
* The weight of water causes the unsupported overhang to collapse, providing more material to erode the softer rock in the plunge pool
* The waterfall retreats upstream

Formation of a levee

* When a river floods, its speed is reduced, slowed down by friction caused by contact with the floodplain.
* As its velocity is reduced the river has to deposit some of its load.
* It drops the coarser, heavier material first to form raised banks, at the edge of the river.
* This means that over centuries the levees are built up of coarse material, such as sand and gravel, while the floodplain consists of fine silt and clay.

What is the thalweg

Line of main current

What are pools in a river

areas of deep water and greater erosion, there is less friction so energy builds up here

What are riffles

Areas of shallow water created by deposition of coarse sediment

Formation of a meander (8 marks, 7 points)

* In a straight river channel pools and riffles will develop as water turns around obstructions.
* Once pools and riffles have developed, the thalweg flows from side-to-side in a winding course.
* A corkscrew-like flow of water called Helicoidal Flow moves material from the outside of one meander bend and deposits it on the inside of the next bend.
* Water moving faster has more energy to erode. This occurs on the outside of the bend and forms a **river cliff**.
* The river erodes the outside bends through hydraulic action, corrasion and corrosion.
* Water moves slowly on the inside of the bend and the river deposits some load, forming a slip-off slope).
* Continuous erosion on the outer bank and deposition on the inner bank forms a meander in the river, which will migrate downstream and change shape over time.

How are deltas formed

Deltas are formed as river sediments are deposited when a river enters a standing body of water such as a lake, lagoon, or ocean. Deposition occurs because velocity is reduced.

Which factors affect the formation of deltas

amount and size of load, salinity, gradient of coastline, vegetation, low energy river discharge/tidal energy

What are the 3 main forms of deltas

Arcuate, cuspate and bird’s foot

Describe features of a arcuate delta

many distributaries which branch out radially, eg. the Nile Delta

Describe features of a cuspate delta

a pointed delta formed by a dominant channel

Describe features of a bird’s foot delta

long, projecting fingers which grow at the end of distributaries, for example, the Mississippi Delta.

Types of transfers (6)

Stemflow, infiltration, percolation, through flow, surface run off, groundwater flow

Types of stores (4)

Interception by vegetation, surface storage, soil moisture storage, groundwater storage

Types of outputs (3)

Transpiration, evapotranspiration, river carrying water to the sea

Factors affecting discharge (7)

Temperature, rainfall and previous weather conditions, soil/rock type, land use, relief, seasonality, size and shape of drainage basin

How does high temperature affect discharge?

Increases the rate of transpiration so less output to channel, also increases snow melt

How does slow light rainfall affect discharge?

Most water infiltrates, and is stored, reducing surface run off to river, so discharge is not affected much

How does heavy prolonged rainfall affect discharge?

Pores in the land fill quickly causing overland flow (when water doesn't infiltrate into the soil as it is too saturated)

What is infiltration capacity?

The maximum rate at which rain can be absorbed by soil

What does antecedent moisture mean?

Previous weather conditions

How does antecedent soil moisture affect discharge?

If the soil is already saturated, then infiltration levels will be low and surface runoff will be high

Water table

The border between the unsaturated zone and the saturated zone

How does permeable/porous rock type affect discharge?

With permeable rock, water can be absorbed and therefore surface runoff is decreased

How does impermeable rock affect discharge?

There will be large amounts of surface runoff

Example of porous rock

Sandstone

Example of impermeable rock

Solid granite

Example of permeable rock

Granite with cracks or faults

How does relief affect discharge?

High land means more rainfall and lower temperatures, so less evaporation. Also steep slopes cause faster surface runoff

How does urbanisation affect discharge?

Smooth impermeable surfaces, less vegetation to store water, less evapotranspiration, sewers and drains mean a direct flow of water to river channel

How do bridges affect discharge?

Bridges restrict the width of a channel and therefore reduce the bankfull capacity

How does deforestation affect discharge?

Lots of plants and trees mean more interception as water is prevented from reaching the ground quickly, so deforestation will increase the discharge

Which factor has the greatest impact on discharge?

Seasonality

How does seasonality affect discharge?

Spring: snow melt, summer: monsoon flood, wet seasons: soil becomes saturated

How does a small size of drainage base affect discharge?

Smaller drainage basins respond quicker to rainfall conditions

How does a larger drainage basin affect discharge?

It takes longer for the lower part of the river to respond to an event in the upper course

How does the shape of a drainage basin affect discharge?

Circular basins respond more quickly thats linear basins

Flashy response hydrograph

Steep rising and falling limb, overland flow is maximised