River environments

Hydrological cycle

the circulation of water around the Earth’s system. This is a closed system.

A Closed system

When no water enters or leaves the system

Examples of atmospheric stores

water vapour and droplets in clouds

Examples of land stores:

rivers, lakes, rsevoirs + water in plants, groundwater/aquifer (sored as liquid or snow/ice)

Examples of water stores in sea:

icebergs and liquid

Evaporation:

the conversion of water to gas

Transpiration:

plants taking up water

Evapotranspiration:

conversion of water to gas + plants taking up water and releasing water vapour

Condensation:

the conversion of water vapour into liquid

Precipitation:

the transfer of water in any form( rain, hail or snow) from the atmosphere

Overland flow/ Surface runoff:

movement of wtaer over the Erath’s surface leading to a river, sea, etc.

Infiltration:

the soaking of wtaer through soil to a aground water store/ aquifer

Percolocation:

the soaking of water through rock to a groundwater store/ aquifer

Through flow:

movment of wtaer through soil to a river or stream

Groundwater flow:

movment of water through the rocks underground to a river, sea, etc.

What is the the fastest tranfer/flow?

Overland flow

Drainage basin:

the area of land drained by it’s rivers and tributaries. It is an open system withexternal inputs+ outputs.

Watershed:

an imaginary line around the edges of a drainage basin to seperate if from others

Confluence:

the joining of two rivers

Mouth/ estuary:

where the river flows out to the sea

Discharge:

the amount of water moving past a particular point along the river’s course

River regime:

the discharge levels in the longterm responding to the climate

Storm Hydrograph:

the discharge levels in the short term responding to the weather

lag time:

the delay between peak rainfall and peak discharge

Base flow:

the ‘normal’ discharge of the river

Storm flow:

the additional discharge of the river as a result of the rainstorm

Rising limb:

the rising flood water in the river

Recession:

falling flood water in the river

The shorter the lag time…

the steeper the rise in discharge

Physical Factors that affect lagtime:

• Vegetation

• Geology

• Intesnity of precipitation

Human factors that affect lagtime:

• Urbanisation

• Deforestation

• Agriculture

How does vegetation affect lagtime?

• Lagtime is slower in a forested basin

Vegetation intercepts percipitation by absorbing water, reducing the amount of runoff. This allows more time for water to infiltrate into the ground, increasing lagtime.

How does Geology affect lagtime?

Impermeable rocks slow down water infiltration, increasing overland flow, decreasing lag times. (saturation excess overland flow) Additionally, the presence of geological features such as slopes or valleys can increase overland flow, decreasing lag time.

How does Intensity of precipitation affect lagtime?

If rain is falling faster than the infiltration rate, there is infiltration-excess overland flow. This decreases lag time.

How does Urbanisation affect lagtime?

Overland flow is higher in urban areas because of urban surfaces (tarmac, concrete, etc) prevent infiltration, as well as sewers, transfer water rapidly to rivers. This decreases lag time.

How does deforestation affect lagtime?

Less interception → less evapotranspiration → more overland flow because saturation of the ground is much faster → decreased lagtime

How does Agriculture affect lagtime?

Drainage channels and ditches increase overland flow. When fields are harvested, interception is reduced, and overland flow is increased. Decreased lagtime.

What is a Fluvial process?

a process that takes place in the river

Weathering:

the breakdown and decay of rock by natural processes, without the involvement of any moving force

Mechanical weathering (freeze thaw):

when water fills up the cracks of a rock and breaks itinto smaller pieces as it freezes and expands

Chemical weathering:

this causes rocks to decay and disintegrate in acidic rain

Biological weathering:

the roots of plants, especially trees, growing into cracks in the rocksand gradually spliting the rock apart.

Mass movement:

the movemnet of weathered material down a slope due to force of gravity

Soil creep:

individual particles of soil move slowly down a slope

Slumping:

material moves rapidly down a slope in the go

• mudslide(soil)

• landslide(rock)

Flows:

material mixed with water flows like liquid downhill

Transportation:

the movement of eroded material

Traction:

rolling boulders + stones along the river bed ( requires most energy)

Saltation:

sand sized particles bounce along the river bed

Suspension:

silt + claysized particles are carried within the wtaer flow

Solution:

some minerals dissolve in the water and travel with the flow

Ersoion:

the wearing away and removal pf material by a moving force, in situ

Hydraulic action:

the force of the water hitting the bed + wearing them away

Abraision:

metrial carried in the river rubs against each other bed + banks + wears away

Attrition:

sediment particles carried in the river knock against each other knock off the edges

Solution:

minerals in the rocks forming the sides of the river channel are dissolved by the acid past them

Deposition:

the dropping of material being carried by a moving force

When and where does deposition take place?

Deposition takes place when the river’s velocity falls, such as at the base of a wtaerfall, towards the mouth, inside the bend of a meander, or a shallow river.

Name 5 factors that affect erosion:

Climate, Slope, Geology, Altitude and Aspect

How does climate impact erosion?

the warmer the weather, the more melt water from gkaciers → more river discharge → more hydraulic action (erosion)

How does slope impact erosion?

Rivers on steep slopes are fast which means increased erosion.

How does Geology impact erosion?

Erosion is less likely in areas of hard more resistant rock becauseit takes more energy to wear away

How does altitude affect erosion?

It is more likely in high altitudes during spring because of meltwater increasing river discharge which then increases hydraulic action

How does aspect affect erosion?

Erosion is less-likely on the leewrad side of the mountain leading to low discharge and therefore less erosion.

Name 3 factors that affect weathering:

Climate, Altitude, and Aspect

How does Climate affect weathering?

It is liess likely to occur in places with low rainfall as there is less acid to dissolve minerals in

How does altitude affact weathering?

High altitude → low temperature → increased freeze-thaw

How does aspect affect weathering?

North facing slopes are more likely to be experience freezethaw cuz of colder tempertatures

Name 4 factors that affect mass movement?

Climate, Slope, vegetation and Geology

How does climate affect mass movement?

It is more likely in areas of high rainfall because of lubrication

How does slope affect mass movement?

Mass movement is more likely to hapen becaus of gravity. If the angle is 5>, more likely.

How does Geology affect mass movement?

Landslides are more likely in places with rocky mountains

How does vegetation impact mass movement?

mud slides less likely on forested slopes because roots bind soil together

Increased erosion and mass movemnet lead to …

increased transportation

Bradshaw model:

predicts how certain parameters are expected to change as you follow a river source to mouth

As the river moves downstream, channel depth…

increases

As the river moves downstream, channel width…

increases

As the river moves downstream, mean velocity

increases

As the river moves downstream, discharge…

incraeses

As the river moves downstream, Hydraulic radius…

increases

As the river moves downstream, load particile size…

decreases

As the river moves downstream, channel bed roughness…

decreases

As the river moves downstream, gradient…

decreases

Why does channel depth increase downstream?

Closer to the source, the river is high above base level so there is losts of gravity, therfore vertical erosion by H.A + abrasion of the river bed.

Why does channel depth increase downstream?

closer to base level so erosion is lateral due to less gravity. H.A + abrasion wears away river banks

River long profile:

shows a river’s gradient as it changes from source to mouth

Cross profile:

shows how a river and its valley changes in shape + sizefrom source to mouth

What are some characteristics and landforms of the upper course?

• steep sides, narrow base, v-shaped and deep valley

• high relief and altitude, steep gradient

• high GPE

• deposits large boulders

• landforms: v-shaped valleys, interlocking spurs, waterfalls +gorges

What are some characteristics and landforms of the middle + lower course?

• gentle side, wider base

• hilly / low relief and low altitude + gentle / flat gradient

• low GPE

• Landforms: (deltas), meanders, oxbow lakes, flood plains, levees

Describe the formation of v-shaped valleys and interlocking spurs:

1. Upper course is high above base level → more GPE → verticle erosion by Hydraulic action + abrasion in high discharge conditions

2. Weathering breaks down the rocks on valley sides → mechanical (freeze thaw) weathering due to high altitude having cold temperatures

3. Mass movement of weathered rocks by sliding + slumping → more river load to wear away by Hydraulic action + abrasion

4. Interlocking spurs: Hard more resistant rocks wear away more slowly than soft rocks → water flows around rock without eroding → protruding pieces of hard rock

Describe the formation of the waterfalls and gorges:

1. Bands of hard, more resistant rock overlie bands of soft, less resistant rock. Soft rocks wear away more quickly than hard rock by hydraulic action + abrasion → step is created.

2. ‘Step’ enlarges to a plunge pool → it is deepened by vertical erosion by H.A + abrasion, and is widened by solution. → undercutting of soft rock creates overhang

3. Continued undercutting reduces overhang support until it collapses under gravity

   → more river load to erode by H. A and abrasion

4. Gorges: the process continually repeats → waterfall retreats upstream to leave behind a steep-sided gorge

Describe the formation of Floodplains and levees:

1. the migration of a meander downstream by lateral erosion through H.A + abrasion creates wide, flat vallet floor either side of a river

2. in high river discharge, the river overflows, flooding the floodplains. Vegetation increases friction and decreases velocity → deposition of largest sediment happens first as more energy is needed. Finer sediment, worn by attrition deposits further.

3. After several floods, leveesbare builts up + channel capacity increases

Describe the formation of meanders and oxbow lakes:

1. As a river increases in sinuosity, the thalweg favours one side of a river channel. Lateral erosion takes place by H.A + abrasion forms outside bend with river cliff → deep channel with reduced fricition + velocity → more lateral erosion

2. A shallower channel on inside bend means increased friciton + low velocity → deposition of fine loa eroded by attrition transported by saltation + suspension → creates a slip-off slope

3. As more lateral erosion occurs river cliffs migrate towards each other, the meander neck narrows

4. Oxbow lake: the river breaks through the meander neck in high river discharge → water favours the straighter channel as quicker to base level → deposition cuts off bend to form oxbow lake

Flooding:

when the amount of water moving down a river exceeds the capacity of the river’s channel, the excess water overflows the banks and spills out across the floodplain.

Physical factors and how they cause river flooding:

• Relief: steep slopes cause rapid runoff

• Vegetation: less vegetation → less interception → more overland flow

• Heavy rainfall: water exceeds infiltration capacity + increases over land flow

• Prolonged rainfall: soil becomes saturated → more water enters the river channel

• Rock: impermeable rocks limit percolation and encourage surface runoff

Human factors and how they cause river flooding:

• Urbanisation: concrete + tarmac surfaces and drains lead to quicker delivery of rainwater to a river

• Deforestation: no intereception so high overland flow

• Agriculture: baresoil, overgrazing, monoculture increases risk of flooding

• Burning fossil fuel: raised gloabl temperature → more snow melt → water reaches streams, etc + can immediately flood them

Hard engineering:

man-made structures that change the shape of the river or control the flow of the river of the water

What are dams and their +ves/-ves?

a concrete blockade that stores and controls the flow of water in the upper course

+ve: reduces floods and generates electricity

-ve: visually unappealing + villages may flooded for resevoir

What are embankements and their +ve/-ves?

banks of a river are built to increase channel capacity

+ve: reduces lateral erosion so river doesnt grow wider + protects property

-ve: looks unnatural + destroys habitats along banks

What is dredging and their +ve/-ves?

rubbish + sediment are dug up from the bottom of the river

+ve: widens the river channel, removes pollution + cheap

-ve: takes time + must be done regularly