Freshwater

Drainage basin

an area that is drained by a river and its tributaries

precipitation

the transfer of moisture to the earth’s surface from the atmosphere

interception

the capture of raindrops by plant cover that prevents direct contact with the soil

evaporation

the physical process by which a liquid becomes gas

transporation

the loss of water from vegetation

evapotranspiration

the combined loss of water from vegetation and water surfaces to the atmosphere

potential evapotranspiration

the rate of water loss from an area if there were no shortage of water

infiltration

the process by which water sinks into the ground

infiltration capacity

the amount of moisture that a soil can hold

infiltration rate

the speed with which water can enter the soil

throughflow

water moving in soil, laterally flowing pipelines (percolines) or between horizons

when does overland run-off occur

when precipitation intensity exceeds the infiltration rate, or when the infiltration capacity is reached and the soil is saturated

percolation

water moving deep into the groundwater zone

baseflow

the movement of groundwater - for water to flow the water table must rise above the river level to provide the hydraulic gradient needed for water movement

name stores in a drainage basin

vegetation, soils, aquifers and the cryosphere

aquifers

rocks that hold water providing the most important store of water, regulate the hydrological cycle and maintain river flow

the cryosphere

frozen water store e.g. ice - the largest store of freshwater, and water may be stored for a millenia

discharge

the volume of water passing a certain point per unit of time (cumecs)

bradshaw model’s prediction for discharge downstream

increase

bradshaw model’s prediction for width downstream

increase

bradshaw model’s prediction for depth downstream

increase

bradshaw model’s prediction for load particle size downstream

decrease

bradshaw model’s prediction for velocity downstream

increase

bradshaw model’s prediction for channel bed roughness downstream

decrease

bradshaw model’s prediction for load quantity downstream

increase

bradshaw model’s prediction for gradient downstream

decrease

abrasion

wearing away of the bed and bank by the load carried by a river

attrition

the wearing away of the load carried by a river creating smaller, rounder particles

hydraulic action

the force of air and water on the sides of rivers and in cracks

solution

the removal of chemical ions causing rocks to dissolve

factors affecting erosion

• load

• velocity and discharge

• gradient

• geology

• pH

• human impact

how does load affect erosion

the heavier and sharper the load the greater the potential for erosion

how does velocity and dishcharge affect erosion

the greater the velocity and discharge the greater the potential for erosion

how does gradient affect erosion

increased gradient increases the rate of erosion

how does geology affect erosion

soft, unconsolidated rocks, such as sand and gravel, are easily eroded

how does pH affect erosion

rate of solution are increased when the water is more acidic

how does human impact affect erosion

deforestation, dams, and bridges interfere with the natural flow of a river and frequently end up increasing the rate of erosion

the five types of river transportation

• suspension

• saltation

• solution

• traction

• floatation

suspension

small particles are held up by turbulent flow in the river

saltation

heavier particles are bounced or bumped along the bed of the river

solution

the chemical load is dissolved in the water

traction

the heaviest material is dragged or rolled along the bed of the river

floatation

leaves and twigs are carried on the surface of the river

capacity of a stream

the largest amount of debris that a stream can carry

competence of a stream

the diameter of the largest particle thay can be carried

critical erosion velocity

the lowest velocity at which grains of a given size can be moved

what does a Hjulstrom curve show

the relationship between capacity, competence and critical erosion velocity

three features of the Hjulstrom curve

• the smallest and largest particles require high velocities to lift them

• higher velocities are required for entertainment than for transport

• when velocity falls below a certain level particles are deposited

river regime

the annual variation in the flow of a river

factors that the river regime may be affected by

• the amount and nature of precipitation

• the local rocks, especially porosity and permeability

• the amount and type of vegetation cover

when does deposition occur

as a river slows down and looses its energy

what type of sediment is deposited first

larger, heavier particles

name three depositional landforms

floodplains, levees and deltas

storm/flood hydrograph

a graph that shows how a river changes over a short period and how a river channel responds to the key processes of the hydrological cycle

what does a hydrograph measure

the speed at which rainfall falling on a drainage basin reaches the river channel

rising limb (on a hydrograph)

indicated the amount of discharge and the speed at which it is increasing - steep in a flash flood or small drainage basins where response is rapid (urban areas)

lag time (on a hydrograph)

the time interval between peak rainfall and peak discharge, influenced by basin shape, steepness and stream order

run-off curve (on a hydrograph)

the relationship between overland flow and throughflow

baseflow

the seepage of groundwater into the channel - slow movement and is the main, long-term supplier of the river’s dishcharge

recessional limb (on a hydrograph)

influenced by the basin size, geological composition and behaviour of local aquifers.
flatter gradients larger catchments and permeable rocks have gentler recessional limbs