Freshwater

Source

the start of the river

Drainage basin

the area of land surrounding the river which precipitation is drained

watershed

the outer limit of the drainage basin

mouth

the end of the river

tributary

small stream contributing to the main river

confluence

where two or more rivers meet

open system

a system that exchanges both matter and energy with its surroundings.

closed system

does not exchange matter but can exchange energy

discharge = velocity x cross-sectional area

Velocity = distance/ time

hydraulic radius

measure of channel efficiency = csa/wetter perimeter

attrition

stones become smaller and rounded by rolling or rubbing against eachother

solution

small particles dissolved by chemical action

hydraulic action

force of the river causing cracks

abrasion

scraping of rocks against the bank

Transportation

saltation- lager particles transported by hops

solution - dissolved materials

traction - pebbles shunted along riverbed

suspension - small particles carries with no contact to bed or banks

floatation - carried on water surface eg leaves

waterfall

corrasion - river banks eroded by load hitting them

corrosion - water dissolves material from rock

hydraulic action

example = River Tees, England

formation of a waterfall

Upper course

Band of hard rock over soft rock

Corrasion deepens pool

Overhang left when soft rock erodes

Plunge pool created

Overhang collapses into plunge pool

Deepening of plunge pool

Retreats

Meanders

Pools - deeper water

Bluff line - outer limits of floodplain

Sinuosity - degree of meandering

Thalweg - line of lowest elevation

Riffles - shallow water created by deposition

Point bar - low curved ridge of sand and gravel along inner bank

sinuosity = channel length/displacement

Meanders develop when there is alternating riffles and pools formed

In a pool the channel is more efficient because it is deeper

In a riffle the channel is less efficient

This means erosion is stronger on one side of the river and deposition increased on the inside bend

On outside bend, channel is deep and concave therefore a lot of hydraulic action and corrasion

River cliffs form on the outside bend

Inside bend is shallower with a slip off slope made by sediment brought across by helicoidal flow

Deltas

formed where the river meets a body of water with a lower velocity

bottomset bed - made up of clay

foreset bed - coarser sediment that arent transported far

topset bed - horizontal

Cuspate delta - V shape, river meets sea head on

Arcuate delta - triangle shape, waves in alternating current direction

Birds foot delta - rivers current stronger than seas waves

Hydrograph

Run-off curve

Rising limb

Lag time - time between peak rainfall and peak discharge

Recessional limb - influenced by geology

Base flow

Peak discharge

Flashy - fast, steep limb, higher peak discharge, urban

Gentle. - long lag time, gentle limbs, low peak discharge, rural basin

Flood mitigation

Dams

Reservoirs

Afforestation

Channel modification

Planning

Dredging - bedload removed

Flood mitigation examples

China - sponge cities:

• improved water security

• Reduced urban flooding

• enhanced water quality

• high costs ( $230 billion USD)

• regular maintenance

Netherlands - The Delta Works

• 13 main strucures

• dams, locks,slucies, levees and storm surge barriers

• Flexible approach

• rising sea levels

• saline intrusion

• high storm surges exceed capacity

Water scarcity

Physical water scarcity - where water consumption exceeds 60% of supply

Economic water scarcity - where a country requires additional storage and transport facilities

Factors affecting water scarcity

Drought

Water quantity

Water quality

Water stress

Water use

Eutrophication - gerd

creation of anoxic conditions caused by excessive nitrates and phosphates.

Nutrients loads up - runoff from fertilisers

Plants flourish - growth of algae

Algal blooms, oxygen is depleted - prevents sunlight reaching other plants so they die

Decomposition further depletes oxygen levels as bacteria breaks down dead plants

Death of an ecosytem - no more possible life

Salinisation

colorado river

increase in salinity of land

leads to abandonment of land and deforestation

the more irrigation, the higher the crop yield however salt builds up after evaporation

water management strategies

rainwater harvesting in homes

stupas

improved irrigation systems

desalinisation

IDBM integrated drainage basin management - Mississippi river

multiple uses

holistic management

womens involvement

multiple perspectives

participatory approach

flood control

Wetland

land is saturated or flooded with freshwater

Ramsar Convention 1971

• work towards sustainable use of wetlands

• designate suitable wetlands for the Ramsar list and ensure effective management

• cooperate internationally on transboundary and shared wetlands as well as species

• 2500 sites across 172 countries

• UK has most, 176 wetlands

Legal prosecution

Implement specific management schemes for each site with collaboration of local agencies