Rivers

Rivers (definition)

Natural stream of fresh water that have a current

Parts of a river

Hydrological Cycle

Transpiration

Stream FLow

Infiltration

Precipitation

Interception

Stem Flow

Water Table

Groundwater flow

Evapotranspiration

Overland Flow

Through Flow

Evaporation

Transpiration

movement of water from plant cells to atmosphere

What causes a change in amount of transpiration?

High temperatures increase it

Low temperatures or humidity decrease it

Stream Flow

movement of water within rivers/streams

Infiltration

movement of water into soil layers

What causes changes in the amount of infiltration?

Increases due to removal of vegetation

Decreases due to hard baked soil, and impermeable land

Precipitation

process in which water reaches surface (rainfall)

What Changes amount of precipitation?

Increases with seasons and global warming

Decreases with changing weather patterns

Interception

Vegetation that prevents moisture from reaching ground directly

Stem Flow

movement of water from vegetation to ground

Water Table

Upper level of saturated rocks

Groundwater flow

Movement of water through the soil (under gravity or parallel to ground surface)

Evapotranspiration

combined processes in which water is lost by evaporation and transpiration

Overland flow

movement of water over ground surface (surface runoff)

Throughflow

process by which water moves through a landscape

Evaporation

change of water as a liquid into water vapour

Hydrological stores examples

• underground (water table) - groundwater store

• In rivers, lakes and oceans - channel store

• In ice and snow (on mountains)

• In the atmosphere

• In vegetation - interception store

Erosion

Processhat wears away river bed and bands - breaking up rocks carried by water

Processes in Erosion

• hydraulic action

• Abrasion

• Attrition

• Solution

Hydraulic action

power of water as it smashes against river banks causing rocks to break apart and air to become trapped

Abrasion

When pebbles grind along river bed in a sand paper way to erode the bed

Attrition

when rocks that the river carries knock against each other, becoming smaller andmore rounder

Solution

when water dissolves certain rocks (limestone)

Physical Factors of Erosion

• floods

• Heavy rainfall

• Sedimentation

• Strong current of rivers

Human Factors of Erosion

• deforestation

• Housing near banks fo water

• Soil extraction by humans

Traction

large heavy pebbles are rolled along the

Saltation

Pebbles bounce along river bed, mostly commonly near source

Suspension

lighter sediment is carried within the water, most commonly near the mouth

Solution

transport of dissolved chemicals that depend on the presence of soluble rocks

Bradshow Model of long profile river

line that represents journey or route of a river from source to mouth

Upper course of river

from source, the gradient is steep and has deep valley sides due to vertical erosion

Middle course of river

is wider and holds more water as tributaries join together and there is vertical and lateral erosion

Lower Course of River

has widest shape and is the deepest as a lot of water has joined the main river

Parts of Upper Course of River

• v-shaped valleys and interlocking spurs

• Waterfalls

V-shaped valleys formation

abrasion and landslides or avalanches caused a v-shaped appearance

Waterfalls formation

1. Undercutting - when water runs over hard and soft rock, eroding the soft rock quickly and leading to the formation of a ledge

2. Overhang - ledge becomes too heavy and collapses leading to debris speeding up erosion 

3. Plunge pool develops due to this erosion that continuously happens

4. Eventually the water retreats upstream

5. A steep gorge-like valley is developed

Rapids Formation

An unevenness in the riverbed causes water to become fast flowing (this water is called rapids)

Parts of middle course

• meander

• Oxbow lake

• Confluences

Confluences

where two bodies of water flowing different courses join together

Meander

River following a winding course that twists and turns, leading to water movement in some areas being faster than others

Meander formation

formed through continuous erosion on outer bank and deposition on inner bank

Note: sometimes deposition can completely cut of meanders

Oxbow lake

curved Lakes from a bend in a river where main stream has cut across narrow end - water does not flow of from river to oxbow lake

Oxbow Lake formation

Formed when:

• river erodes laterally and flows slowly on inside bend, while on outside bend, river flows fast

• Continuous erosion and deposition narrows neck of meander and eventually breaks of to become an oxbow lake

Parts of Lower Course of River

• mouth

• Levees

• Delta

• Floodplains

delta types

• arcuate delta which is most common and is fanshaped in a curved arc like form

• Birds foot delta which has three distinct widely spaced channels that extend outwards

Floodplains

wide, flat areas of land formed from sediment during floods

Located towards the mouth

effect of climate change on deltas

all along deltas, river banks and eroding and with rising sea levels, sea water begins to seep into rivers

mouth

end of river connecting to an ocean

levees

Embankment built to prevent overflow of river (flooding)

Formation of levees

1) when a river floods, silt is deposited

2) in between floods, slow moving river deposits more silt in river bed

3) with each flood, levees build up and begin to flow ABOVE the flood plain

• this protects the plain from flooding

Features of Bradshaw Model

• discharge

• Erosion

• Transportation

• Deposition

• Load size

• Average velocity

• Occupied channel width

• Channel depth

• Load quantity

• Channel bed roughness

• Slope angle

Discharge

water which flows through river in a given time (m3/sec)

Increases downstream

Load size

Size of objects

Decreases downstream

Erosion

Wearing away of landscape

Decreases downstream

Transportation

Movement of sediment

Increases downstream

Deposition

material left behind that river carries

Increases downstream

Average velocity

speed of water (m/s)

Steady increase downstream 

Occupied Channel Width

distance across channel

Increases downstream

Channel Depth

height from water surface to channel bed

Increases downstream

Load Quantity

amount of material a river is carrying

Increases downstream

Channel Bed Roughness

irregularities on the surface that slows water flow

Decreases down stream

Slope Angle

angle between different points of the river

Decreases downstream