The Water Cycle (AQA A Level Geography)

Feedback loops are active mechanisms in systems that maintain or restore equilibrium. These can either amplify (positive) or check (negative) changes in the system.

Dynamic equilibrium in relation to systems is where constant short-term adjustments are made within a system to maintain balance because a steady state of balance is difficult to achieve in nature.

Water is a colourless, tasteless, transparent and odourless liquid that forms the seas, rivers and precipitation.

False.

Earth's total freshwater is 2.5%, but only 0.9% is accessible to human

Most water is stored as saline (salt) water in oceans and freshwater as ice or within aquifers (groundwater stores); the remainder is water vapour in the atmosphere.

False?

The water cycle, also known as the hydrological cycle, is a closed system.

True.

The hydrological cycle involves energy exchange, which influences local temperatures.

The two types of aquifers are unconfined and confined.

False?

Unconfined aquifers are where porous rock is open to the surface, allowing direct recharge by precipitation.

Thick layers of rock surround confined aquifers, preventing direct recharge.

False.

Not every rock can store and transport water. Rock such as clay can store water but are not able to transfer it. Sandstone, however, is able to store and transport water.

Porosity is the measure of how much water a rock could potentially store.

Permeability is the measure of how easily water can flow within a rock.

Interception is how precipitation is prevented from reaching the ground, usually by being caught on leaves or branches.

Sublimation is when water changes from a solid (ice) to a gas (vapour) without passing through a liquid state or vice versa.

The residence time of stored water is the average amount of time water spends in a particular reservoir within the hydrological cycle.

Global processes that drive change in the hydrological system are:

• Climate change.

• Clouds and precipitation.

• Cryospheric change.

Farming practices impact stores in various ways, such as:

• Ditches drain the land and increase water flow away from the land.

• The interception by vegetation can prevent as much as 40% of precipitation from reaching the surface.

• Over-abstraction of groundwater for irrigation removes stores of water.

Percolation is the downward movement of water through soil layers and underlying rock.

True.

Industrialisation affects precipitation and water stores through the production of acid rain, which destroys vegetation and interception rates, affecting water stores

Throughflow is the lateral movement of water through the upper soil layers, perpendicular to the slope.

Urbanisation affects water stores through:

• Impermeable surfaces reduce infiltration and, therefore, groundwater storage.

• The time that surface runoff reaches river channel stores etc. is increased.

• Development impacts natural depression stores on the surface.

Infiltration is the process by which water enters the soil through small openings and pores on the ground surface.

The zone of saturation is where the height of the water table varies according to the season. Where there is permanent saturation, this is called the phreatic zone.

True.

An area of land that a river and its tributaries drain is known as a drainage basin.

Hortonian overland flow is the tendency of water to flow horizontally across land surfaces when rainfall has exceeded infiltration capacity and depression storage capacity.

Channel flow is where water flows on the surface in small channels or rills (<30 cm in width or depth) in a defined stream pattern.

False.

Drainage basins can cover many square kilometres in a number of countries. For example, the Nile River basin drainage area is more than 3 million km² over 12 countries.

False.

Drainage basins are open systems with inputs, outputs, stores and flows.

False.

Vegetation cover increases infiltration rates because it slows the rate of flow, which allows infiltration to happen. Also, the roots of vegetation break up the soil and increase the potential pore space and channels.

Percalines are lateral (sideways) lines of water seepage through the upper soil.

Drainage density is the number of tributaries within a drainage basin. The more tributaries there are, the higher the rate of drainage.

A water balance shows how much water is stored in a drainage basin system.

A soil water budget shows how much water the soil can store over a year. The budget shows the time of year when the soil is saturated, which increases the risk of flooding or a potential deficit, which increases the risk of crop failure due to drought.

Discharge is the volume of water moving past a point in a river per given time, measured in m³/sec or cumecs.

A hydrograph is a graph showing the discharge of a river over time.

False.

There are two types of hydrographs: annual and storm.

A river regime is the pattern of seasonal variation in a river's discharge over a year, also known as an annual hydrograph.

Lag time is the period of time between peak rainfall and peak discharge in a storm hydrograph.

A flashy hydrograph indicates a short lag time with high peak discharge.

False.

A flat hydrograph shows a low peak discharge.

Antecedent moisture is the amount of water already present in the soil before a rainfall event.

The three ways that water from a drainage basin is transferred to a river channel are:

• Directly into the channel—not much

• Most often, through surface flow

• Infiltration from throughflow and baseflow

Basin shape and size affect storm hydrographs in the following ways:

• Steep gradients and small basins shorten the lag time and produce flashy hydrographs.

• Shallow gradients and large basins lengthen the lag time and produce flat hydrographs.

False.

Natural climate change, such as ice ages or interglacial periods, changes the availability of water within the system.

Seawater ingress is the intrusion of seawater into freshwater aquifers, often caused by excessive groundwater extraction.

Water abstraction is the process of taking water from any source, either temporarily or permanently, for human use.

Salinisation means the increase in salt concentration in soil or water, often due to excessive water abstraction and evaporation.

False.

 Deforestation typically leads to less precipitation at the local level.

False.

Urbanisation generally decreases infiltration rates due to increased impermeable surfaces.

The water table is the upper level of an underground surface on which the soil or rocks are permanently saturated with water.

An aquifer is an underground layer of water-bearing, permeable rock, rock fractures or unconsolidated materials.