Hydrology CIE Geography

Hydrology + Fluvial geomorphology

Evaporation

Evaporation

The transformation of water from a liquid state to a vapour state

Evapotranspiration

the water vapour released from the earth’s surface and plants

Calculating Discharge

Q = A x V

Measured in cumecs

(Q is discharge, A is cross-sectional area and V is the average velocity)

Interception

the process where precipitation is captured by vegetation before reaching the ground. it plays a key role in managing runoff, as a temporary store of water

surface water

all water bodies like lakes, wetlands and rivers on the earth’s surface

ground water

the water found in the saturated zone of the soil, filling the pore spaces betweeen sediment and rock

aquifers

underground layers of water-permeable rock or unconsolidated material from which groundwater can be extracted

porosity

the amount of space between soil or rock particles, determining the water holding capacity

permeability

the ability of rock or sediment to allow water to pass through it

channel storage

the water stored in the river or stream channels

throughfall

where precipitation passes through gaps in the vegetation canopy or drips off leaves and branches, reaching the ground

stemflow

the movement of water down the stems and trunks of plants and trees

overland flow

(or surface runoff) is the flow of water that occurs when excess stormwater, meltwater or other sources flows over the grounds surface

channel flow

the movement of water within a river or stream channel, a critical aspect of fluvial geomorphology

laminar flow

layers of water sliding smoothly over each other, very rare in natural channels. seen in slow moving shallow streams

turbulent flow

chaotic, swirling currents, is more common and influences erosion and sediment transport

infiltration

the initial movement of water from the surface into the subsurface layers

percolation

the downward movement of water from the soil layers into the groundwater. Helps to recharge aquifers and maintaining groundwater levels

factors affecting percolation

• permeability of soil and rock layers

• gravitational force

  • aquifer recharge

throughflow

the horizontal movement of water through the soil layer

groundwater flow

the movement of water within aquifers, and underground layers of permeable rock

water tables

the upper limit of the zone where groundwater fills the pores in soil or rock. it is a dividing line between the saturated and unsaturated zones. it fluctuates seasonally

artesian springs

result from pressure in confined aquifers where groundwater is trapped between two impermeable layer. when the pressure is sufficient water is forced upwards, forming a spring

storm hydrographs

representations of flow rate in a stream or river in responce to a specific rainfall event.

peak discharge

the highest flow rate recorded on the hydrograph following a storm

lag time

the duration betweent he peak rainfall and peak dicharge

rising limbs

when the hydrograph shows a rapid increase in dicharge following a rainstorm. it indicates how quickly a river responds to rainfall

falling limb

shows the rate at which the river returns to its normal level

annual hydrographs

show the flow variation within a river over a year, highlighting the impact of seasonal changes on river systems

precipitation

varies from rain, snow, sleet, and hail. primary input in the hydrological cycle

antecendent moisture

the existing moisture level in the soil before a precipitation event, affecting infiltration and runoff

effect of drainage basin size

it plays a role in determining the volume of water it can collect and the time it takes for water to travel across the basin to the river. larger basins have longer lag times due to greater distance

effect of drainage basin shape

circular basins are more efficient in transferring water, lead to quicker responses. elongated basins show a more delayed response due to the varied travel times across different parts of the basin

drainage density

measure of total length of all the streams and rivers in a basin divided by the total area of the basin

high drainage density

a dense network of streams and rivers which accelerates movement of water across the surface

low drainage density

means fewer streams and rivers, causing more infiltration and less surface runoff

steep slopes

lead to faster runoff, as gravity pulls the water down more rapidly so more peak discharge and erosion

gentle slopes

means more infiltration and slower runoff meaning less flooding and erosion but also lower river levels during dry periods

abrasion/corrasion

the process where the load carried by the river acts as an abrasive force, eroding river banks and beds

solution

chemical erosion using acidic river water, from dissolved carbon dioxide, chemically interacting with soluble minerals in the rocls

cavitation

the formation and collapse of air bubbles in water, which occurs when the pressure of the water drops suddenly. forms potholes

hydraulic action

the process involves the sheer force of moving water entering cracks and joints in the river bed and banks

traction

the movement of large particles along the river bed, driven by the force of the river’s flow. the particles, often larger than 2.., include pebbles, gravel and sometimes boulders

saltation

the bouncing movement of medium sized particles, primarily sand grains due to gravity and the lifting force of water

suspension

fine material is carried within the water column. moves a large amount of sediment over long distances

sedimentation

the process where materials carried by the river are deposited due to a decrease in the energy of the river flow

point bars

develop on the inner sides of meanders where the water flow is slow, leading to the deposition of sediment

levees

formed by the deposition of the heaviest sediments during floods and grow with each flooding event. they act as natural barriers against flooding

alluvial fans

cone shaped deposits that are found at the base of mountains or steep terrains where rivers lose energy rapidly

velocity

the speed at which the water flows in a river

helicoidal flow

a complex flow pattern that resembles a corkscrew or a spiral motion. it plays a crucial role in the formation of meanders with erosion on the outer banks and deposition on the inner banks

thalweg

the deepest and fastest-flowing part of a river channel, it marks the most efficient path for water flow and shows where the maximum energy of the river is concentration and so the most significant erosion.

straight channels

less common in natural settings, with a linear course and a more uniform and less turbulent flow. they often show symmetrical cross-sectional shapes.

braided channels

a complex network of dividing and converging with variable water flow that are changing constantly

meandering channels

serpentine paths due to lateral erosion on the outer bend, where the speed of the river is greater and deposition on the inner bends. they read to floodplains, oxbow lakes and levees

pool and riffle sequences

alternating shallow and deep areas within a river channel, key for aquatic ecosystems. key for regulating flow and oxygenation of water, supporting diverse aquatic life

riffles

shallow, rapid water over coarse substrate, form due to the accumulation of larger sediment particlesp

pools

deeper and with slower moving water, where finner materials settle

waterfalls and gorges

when a river encounters a resistant rock strata overlaying softer rocks. erosion undercuts the harder rock, leaving a vertical drop. can lead to gorge development, eith deep valleys and steel rocky walls

floodplains

extensive flat lands adjacent to rivers, shaped by flood waters. over time floodwaters deposit alluvium, creating fertile plains.

deltas

the slowing of river velocity upon meeting a larger body of water causes sediment to settle out.

deforestation on hydrological cycle

leads to significant decrease in interception capacity, and so more runoff as well as leading to more soil compaction, decreasing the soil’s infiltration capacity, accelerating soil erosion and recuding groundwater recharge

afforestation on hydrological cycle

newly planted trees improve soil structure, reducing severity of floods and moderating river flows by allowing continuous water supply

urbanisation on hydrological cycle

impervious surfaces prevent infiltration leading to greater surface runoff anf urban flooding. also the alteration of natural watercourses to allow for urban development.

water abstraction

lowers the water table causing reduced flow in springs and wetlands. also can reduce river flow which can reduce water quality by concentration pollutants

water storage

reservoirs and dams, store water and affect the natural flow of rivers such as timing and magnitude

social concequences of flooding

• displacement and relocation

  • heath risks from contaminated water

economic consequences of flooding

• infrastructure damage

• agricultural losses

environmental consequences of flooding

• ecosystem distribution

  • soil erosion

dams

to control river flow and prevent floods and can have hydroelectric power but can lead to displacement of communities, and affect river ecology by allowing sediment to build up

channel straightening

altering river flow by straightening channels, allowing water to flow more quickly through cities but can increase downstream flooding

manmade levees

embankments formed on riverbanks to protect adjacent land from flooding