Option A- Freshwater

Hydrological Cycle

Hydrological Cycle

• evapotranspiration

  • evaporation of water into vapour

  • water vapour escaping plants

• water condenses in clouds

• precipitation = rainfall

• infiltration- water runs underground

• runoff- water travels along surface to reservoirs

Flood hydrographs

• rising limb- rising discharge after a storm

• falling limb- falling discharge after peak

• peak discharge- max river flow after event

• lag time- time between peak rainfall and peak discharge

• peak rainfall- max rainfall during storm

• drainage density- total length of all streams and rivers divided by total area of drainage basin

• bankful capacity- how much water the river can hold

  • if discharge exceeds bankful, the river floods

flatter curves with a longer lag time are well managed areas, such as gentle slopes, permeable soil, forest, rural area.

Sharp curves with a shorter lag time indicate poorly managed areas with nowhere for the water to go, eg concrete, saturated ground, heavy + quick storm, rock.

Flood prediction

• riverine flooding- river systems flood due to heavy water flow

• flash flooding- quick and dangerous, caused by lack of drainage

• storm surge- low pressure systems raise sea levels, swamp coast

• snow melt- rapid snow melt enters river systems in mountains

Flood mitigation- dams

• larger than 15m, 2 completed each day

• hold water until less risky times

• reservoirs- store excess rainwater in upstream drainage basins

Example: Aswan High Dam on Nile, Egypt- agriculture, tourism, recreation, navigation, hydroelectricity. yet, causes water loss downstream.

Flood mitigation- afforestation

• flood abatement- decreases runoff to mitigate flood’s peak

• includes: revegetation, contour ploughing slopes, sediment clearance, preservation of water reserves

  • increases interception

Flood mitigation- channel modification

• includes: raising banks, straightening river, creating new channels, steel and concrete fortifications

• artificial levees- raising banks such as on Mississippi River, USA

Flood mitigation- Planning

• personal insurance/preparation

  • sandbags, flood safe home

• loss sharing

  • disaster aid, insurance

Riperian Zone

vegetated area around a river system

Water scarcity

• physical- water consumption > 60% of useable supply

• economic- physically enough water, requires more storage and transport options

Drought

• dry weather, environment

• absolute- 15 consecutive days of less than 0.2mm of rainfall

• partial- 29 consecutive days of average daily rainfall less than 0.2mm

  • impacts- reduced yield, mortality and morbidity, fire and water bans

Water quantity

amount = rate of rainfall, evapotranspiration, river/groundwater

• <1% of freshwater is available for human use

• ~6600 m3 per person per year used → increasing to 4800 by 2025

• ¾ of rainfall falls on 1/3 of the population

Water use and stress

• water stress = <1700 m3 per capita per year in an area

• in 2016, 2.3 billion people experienced water stress

• since 1922 world population has tripled and water use increased six fold

  • rivers no longer reach sea, 1/3 of wetlands gone, 20% freshwater species endangered, aquifers and water tables falling

Water Quality

• WHO- 4 million deaths per year from water related disease

• poorer people who must buy water from vendors end up paying more than richer households who are connected to town water

• areas in Asia, Latin America, Carribbean, Africa

Eutrophication → Pollution

• too many nutrients run off into water, providing food for algae to grow

• algae block out sunlight, killing plants

• algae run out of food and die

• bacteria eat dead algae, use up oxygen in water

• anoxic water cannot support life

Salinisation → Irrigation

• salty groundwater seeps into river

• clearing native vegetation decreases water absorption → increases water going into groundwater → more salty water exists

  • worse crops, low water quality, eroded equipment

human pressures on water systems

• bigger population needs more water

• water use exceeds 3,700 km3 annually

• agriculture consumes 2/3 of water drawn from resources, industry uses 20% of water, municipal 10%

Case Study: Drainage Basin Management

Mekong River System Facts

• runs through China, Cambodia, Laos PDR, Thailand, Vietnam, Tibet

• 7th longest river in Asia, 12th in world

• Drains more than 810,000 km2 of land from Plateau of Tibet to South China Sea

Case Study: Water Security in Remote Areas

Ladakh’s Ice Stupa Project

• to cope with water pressure in the Himalayas (eg glaciers melting due to climate change)

• freezing abundant water in the off season in pyramid shapes made of buckthorn branches to melt in the spring

• provides off season access to fresh water

Integrated Water Resources Management Project

• GOAL: to reduce social conflicts from competing countries’ water needs

• Mekong River Commission adapted IWRM through 1995 Mekong Agreement Principles