Rivers & Coasts

Inputs in a hydrological cycle

Precipitation from clouds

Interception

Rainwater collected by leaves and plants

Infiltration

Water that enters the soil from the surface. (Surface → soil)

Surface runoff

Water that does not infiltrate the ground and flows over the surface into the river

Throughflow

Lateral movement of water through in layers of soil into the river. Slower than surface runoff.

Percolation

Downward flow of water through soil and porous rocks.(Soil → Rocks)

Groundwater flow

Movement of water entirely within rock layers. Very slow.

Storage in hydrological cycle

• Water on the surface is stored as lakes or rivers

• Water in the ground is stored as groundwater

• Water can also temporarily be stored during interception by leaves

Tributary

Stream or river that joins a main river channel

Confluence

Point where a tributary joins the main river

Distributary

Channel diverging from the main river

River mouth

Where a river ends it’s flow

Drainage basin

Land area drain by river and tributaries (catchment area?)

Watershed

Boundary of a drainage basin, along the top of hills or ridges (contour lines)

Factors influencing speed

• Gradient of a channel → Steeper is faster

• Roughness of a channel → A smoother channel has less friction

• Shape of a channel → Smaller wetted perimeter reduces friction generated

• Volume of flow → More volume has more water not in contact with channel (in the middle) and lower friction

• Shape of the river course → Less bends and meanders would lead to less slowing down

Factors influencing volume

• Size of a drainage basin → Larger has more tributaries

• Presence of vegetation → Less vegetation brings more surface runoff

• Permeability of rock → Less permeable rocks bring more surface runoff

• Climate → Precipitation

Corrasion

• Rock fragments grid against side and bed of channel

• Dislodges rocks which are then carries by the river

• Widens channel through lateral and vertical erosion.

Attrition

• Rock fragments in the river collide against one another

• Larger fragments become smaller, smoother and rounder

  • Can be seen through pebbles

Solution

• Solvent action of water dissolves soluble materials and carries them in the river

• For example limestone is dissolved

Hydraulic action

• Fast flowing water surges into lines of weakness

• Continuous surging enlarge cracks until they break away into the river

• Can be seen in plunge pool at foot of a waterfall

Traction

• Move the largest rock fragments that can’t float

• Moved by rolling or gliding on river bed

• Needs high velocity/river energy

Saltation

• For course sand and rock fragments (gravel)

• Moved by hopping and bouncing on the river bed

Suspension

• Fine particles like silt and clay are suspended in the upper level of the river

• Makes river appear muddy

Solution

• Soluble materials that dissolve and is carried by water

• Changes chemical composition

• Water appears clean

• Can occur at low velocity and volume

Upper course

• Steeper gradient

• Lower velocity

• Small volume

• Small load

• Contains mainly erosional process

• Transported by traction and saltation

• Little deposition

Middle course

• Gentle gradient

• Moderate velocity

• Moderate volume

• Moderate river load

• Mainly erosional and depositional processes

• Transported by saltation & suspension

• Some deposition

Lower course

• Gentle to flat gradient

• High velocity

• High volume

• High river load

• Mainly depositional

• Transported by suspension and solution

• High deposition