Rivers

Rivers

discharge

the amount of water in a river at a particular point

tributary

a smaller river which joins a larger river

mouth

where the river flows into the sea/lake

watershed

the boundary dividing one drainage basin from another; a ridge of high land

confluence

the point at which two rivers join

source

the upland area where the river begins

catchment area/drainage basin

the area from which water from a river and its tributaries is drained

drainage density

total length of all the streams in the basin divided by the total area of the basin

flood plain

the land that floods when the river overflows

what cycle is the drainage basin system a part of

hydrological (water) system

is the hydrological cycle a closed or open system

closed system

are drainage basins closed systems or open systems

open systems

inputs of the drainage basin

precipitation

stores of the drainage basin

• interception

• groundwater storage

outputs of the drainage basin

• river runoff

• evaporation

• transpiration

flows (transfers) of the drainage basin

• infiltration

• groundwater

• throughflow

• surface runoff

• percolation

• groundwater flow

outputs of the drainage basin

• river runoff

• evaporation

• transpiration

which direction do all rivers flow

downwards towards sea level, even if they don’t reach the sea

from where does a river get wider

gets wider as it goes from source to mouth

transpiration

water vapour released through stomata in leaves

interception

water is stored on leaves and branches of vegetation

throughflow

water flows horizontally through soil into river

percolation

water flows vertically through soil rocks

infiltration

water seeps into the ground

groundwater flow

water flows horizontally through rock into river

evaporation

water turns from droplets into vapour

surface runoff

water flows horizontally over land into river

the three processes of rivers

• erosion- wearing away

• transportation- carrying

• deposition- dropping

courses of a river

• upper course

• middle course

• lower course

features of the upper course

• erosion dominates

• lots of energy

• fast flowing

• steep

• narrow

• steep sided, V shaped valley

• narrow, not deep channel

• mainly vertical erosion as its steep

• lot of traction occurs as theres enough energy to roll heavy boulders

• waterfalls

features of the middle course

• less energy

• slower flow

• erosion and deposition- neither dominant

• gentle-sloping valley

• wider and deeper than the upper course

features of the lower course

• little energy

• slow flowing

• wide

• deposition dominates

• wide and flat valley

• wide and deep channel

• mainly lateral erosion as its flat

river course

the path the river takes from its source

what does the long profile of a river show

shows how the steepness of a river changes over the course

how does the gradient of the river change as the river moves from upper to the lower course

the gradient decreases and the slope becomes gentler

erosion

the wearing down and removal of rock; shapes our landscape

where does erosion mostly occur

upper course

methods of erosion

• hydraulic action

• attrition

• abrasion/corrasion

• solution/corrosion

how does hydraulic action work

force of river against the bed and banks can cause air to be trapped in cracks and crevices; pressure weakens banks and gradually wears it away

when is hydraulic action most effective

when water moving fast and there’s a lot of it (upper course)

how does attrition work

rocks being carried by the river smash together and break into smaller, smoother, rounder particles

how does abrasion work

river load rubs against bed and banks of river; this action causes some of the material to break off, by a sandpapering action, and causes the banks to collapse

how does solution work

soluble particles are dissolved into the water

which directions does a river erode in

both downwards and sideways: vertical and lateral erosion

which part of the course does vertical erosion take place

upper, where the gradient is steep and the river flows quickly

what happens during vertical erosion

causes the channel to deepen to form a deep sided V-shaped valley

which course does lateral erosion take place in

lower course, where the gradient is gentler and the volume of water is higher

how does lateral erosion work

the speed of flow is slow and causes the river to erode horizontally, causing the river channel to widen and forms a broad and flat valley

methods of transportation

• traction

• saltation

• suspension

• solution

traction

large boulders and pebbles are rolled along the river

where does traction mainly occur and why

upper course as it has the energy needed to push heavy boulders and goes downhill so gravity helps to move them

saltation

small stones, pebbles and silt bounces along the river bed

which course does saltation mainly occur in

middle and lower course, as there’s less energy

suspension

fine material, such as clay and sediment, is carried by the river

which course does suspension mainly occur in

every course

solution

dissolved minerals are carried by the river

what course does solution mainly occur in

any course, as minerals are always present in water

when does deposition occur

when the river loses energy as it cannot carry the material anymore, such as:

• a river enters an area of shallow water

• gradient drops

• volume of water decreases

where does deposition mainly take place

the end of a rivers journey at the mouth, as it has less energy here and can no longer carry the load/sediment

where is the source of the river Tees

high up in the mountains, can be natural spring/rainwater/snow

what happens in the upper course of the river Tees

• water rushes downhill

• flows over roads, boulders and down deep slopes

• erosion

• valleys

• canyons

what happens in the middle course of the river Tees

• slows down at flatter land, causing meandering

• tributaries, rivers and streams join together

• larger and wider

what happens in the lower course of the river Tees

• widens into estuaries and deltas where sediment slows water down

• provides rich soil

• mouth- river flows out to sea

where is the Tees located

northeast England, starts in the moorlands, near the border to county Durham

how long is the river Tees

100km long

what is annual rainfall at the source of the river Tees

1200mm, means the bogs never dry out

where does the Tees flow

through v shaped valley, moorland and then a resevoir

name of waterfall on the river Tees

high force waterfall

what course do waterfalls form

upper course

how do waterfalls begin to form

when the river meets a hard/resistant rock

what allows a waterfall to erode rapidly

the river gains a great deal of energy where it falls over the lip of the waterfall

stages of the formation of a waterfall

1. river meets a band of softer, less resistant rock

2. underlying, softer rock is eroded away more quickly

3. rock causes abrasion of the river bed

4. hydraulic action also helps to create a deep plunge pool

5. processes of erosion such as abrasion causes undercutting

6. more resistant rock is left unsupported and overhangs

7. eventually the more resistant rock collapses onto the riverbed

8. process is repeated and the waterfall retreats upstream

9. a steep-sided river valley is created, called a gorge

what is a meander

a bend in the river

what course are meanders found in

the middle course

how is a meander formed

• a large bend in the river formed by lateral erosion

• water on the outside of the bend travels fastest and erodes away from a river cliff

• water on the inside of the bend travels slowest and deposits material to form a river beach or slip off slope

what methods of erosion are most common in the formation of a meander

mainly hydraulic action and abrasion

what occurs at the outer bend

• river cliffs

• deeper

• erosion

• more energy

• faster flow

what occurs at the inner bend

• slip-off slopes

• shallower

• deposition

• less energy

• slower flow

slip-off slope

• current is weakest where water shallowest

• sediment deposited here

• leaves a not-steep gradient

river cliff

• erosion is highest as current is strongest here

• creates a steep gradient

how is an oxbow lake formed

1. outside of the meander has the quickest flow and are eroded

2. outside of the meanders move closer together narrowing the neck in between

3. eventually (usually during floods) the river cuts straight across the neck following the quickest route

4. after this the river slows down by the old bend and deposits material cuttinf off an oxbow lake

what are the main methods of erosion to form an oxbow lake

hydraulic action and abrasion

features of the lower course

• floodplains

• levee

floodplain

the area of land surrounding a river thats likely to flood when a river overflows

to create a floodplain what form of erosion occurs

lateral erosion

stages of a floodplain formation

• river erodes laterally

• the river valley is widened creating a large flat area

• when the river overflows (floods) material is deposited as the water loses energy

• over time sediment builds up in layers creating a floodplain

levee

a raised riverbank

how is a levee formed

• lateral erosion occurs, creating a wide flat valley

• river floods onto a floodplain

• river drops the heavier sediment first, right by the river, and smaller sediment later, further away

• sediment builds up in layers forming natural embankments, which are levees

delta

low-lying bits of land where rivers meet the ocean/lake

why do deltas form

• rivers lose momentum in the flatter lower course as they reach the ocean, causing them to deposit their sediment load

• river channel can be blocked by this build-up of material

• this splits the river into lots of tiny rivers named distributaries

• if this material builds up enough, a piece of land called a delta is created

what does a flood hydrograph show

how a river responds to a rainfall event

discharge

the amount of water in a river at a particular point

peak rainfall

the max rainfall (mm)

peak discharge

the max discharge (cumecs, cubic metres per second)

lag time

the time taken between peak rainfall and peak discharge

rising limb

shows the increase in discharge on a hydrograph

falling limb

shows the return of discharge to normal/base flow on a hydrograph

what does a long lag time show about a river

respond slowly to rain and are therefore less likely to flood

physical factors effecting hydrographs

• impermeable soil

• impermeable rocks

• cold weather

• steep slopes

• drainage basin shape

• antecedent conditions

• vegetation

human factors effecting hydrographs

• deforestation

• impermeable building materials