ENVS 1017/6202 - Introduction Notes

ENVS 1017/6202 - Introduction

Hydrological Cycle

• The continuous movement of water on, above, and below the surface of the Earth, which includes processes such as evaporation, condensation, precipitation, infiltration, and runoff.

• This cycle is crucial for sustaining ecosystems and regulating climate, as it influences weather patterns and the distribution of freshwater resources.

  
  

• The lecture will cover:

  • The hydrological cycle.

  • Catchments and their importance.

  • Catchment aspects that can be measured and compared.

  • Water transfer processes within catchments.

  • Rainfall and its pathways.

  • Water stress and climate change dynamics.

Hydrological Cycle Details

• Describes water movement and storage as solid, liquid, or gas.

• Processes: evaporation, precipitation, infiltration, runoff, plant uptake.

• Water can be stored in the ground, plants, lakes, rivers, or the ocean.

• The ocean is the largest store of liquid water.

• The global water cycle is a closed system (no water from space).

• Finite water requiring careful management because no new water enters the system.

• The hydrosphere, lithosphere, biosphere, and atmosphere are key components.

Water Distribution and Availability

• $\approx 97 \%$ of water on Earth is saltwater in the ocean.

• $\approx 3 \%$ is freshwater

• Of the freshwater:

  • Most is locked in ice sheets and glaciers.

  • The next largest proportion is groundwater.

  • Only $0.02 \%$ is readily available terrestrial water.

• Rivers contain a tiny percentage of accessible water.

• The most critical water is the least available.

Water Residence Times

• Biological water: ~ 1 week.

• Atmosphere: 8-10 days.

• Lakes/reservoirs: $\approx$ 2 weeks.

• Rivers: $\approx$ 2 weeks.

• Soil water: Up to a year.

• Groundwater: Days to thousands of years.

• Oceans/seas: Thousands of years.

• Ice: Tens of thousands of years.

Importance of Freshwater

• Vital for life

• Mediates global ecosystems.

• Promotes biogeochemical reactions.

• Determines water/material fluxes (nutrients, sediments).

Water-Related Problems

• Hazards: floods, dam breaks, droughts.

• Water stress: imbalance between water needs and availability.

Water Stress Prediction

• Future predictions show significant water stress in regions like Australia, Asia, the Middle East, Africa, and the US.

• Climate change exacerbates water stress through changing rainfall patterns and increased evaporation.

Useless Facts About Water

• Water molecules have been cycling on Earth for billions of years (dinosaur water).

• 1/3 of the world’s freshwater is trapped in dams.

• Water storage impacts Earth's rotation.

• The largest engineering project is an aqueduct in China, used for water transportation.

Catchments

Catchment Introduction

• Rainfall that hits a catchment and the way the runoff moves.

Catchment Concepts

• A catchment is an area where water flows to a common outlet.

• Defined by topography, with hills separating catchments (interfluve).

• Also called a drainage basin or watershed.

• Consists of streams/creeks/rivers that drain water.

• The outlet can be a river mouth, lake, estuary, or ocean.

• Some inland catchments end on land with water evaporating.

Sub-Catchments

• Catchment broken into smaller tributary sub units.

• Each sub catchment contributes to a larger network.

• Typically a trunk stream drains centrally into further tributaries.

Local Catchment Example

• Lane Cove River catchment around Macquarie University area.

• Outlet: Sydney Harbour.

• Headwaters: Thornleigh, Pennant Hills, Carlingford.

• Sub catchments feed Lane Cove River i.e. Mars Creek.

Reading the Landscape

• Looking at the landscape and observing.

Stream Types

• Perennial: Continuous water flow.

• Seasonal/Intermittent: Water flow during specific seasons.

• Ephemeral: Mostly dry with occasional flash floods.

River Definition

• Rivers identified by the bed and banks, not just the presence of water.

Catchment Measurement

• Catchments can be measured and assessed globally.

• Key characteristics reduce complexity (size, relief, shape, drainage density).

Catchment Characteristics

Size

• Area measured in square kilometers.

• Largest: Amazon River.

• Longest: Nile River (6,500 km).

• Murray Darling Basin: Australia's food bowl and eighteenth largest.

Relief

• Topographic change from high to low points.

• Important measure because steepness of terrain will dictate the relative speed of water running off the slope.

Slopes

• High slope = faster water flow.

• Low slope = slower water flow.

• High relief (mountains) vs. low relief (flatlands).

Shape

• Varies (long/skinny vs. broad/bowl-shaped).

• Influences water flow speed based on rainfall location and distribution.

Drainage Density

• Channel density per square kilometer.

• Linked to landscape aspects.

• High density (many channels) vs. low density (few channels).

• Australian catchments tend to have low count.

Drainage Pattern

• Arrangement of streams/water flow.

• Can be affected by rock type or structure or geological events.

• Concentric (volcanoes).

Stream Order

• Method of determining Catchment Operation, how it's built up

• Hierarchical ordering of streams.

• First order: smallest streams.

• When two first-order streams meet, they form second-order.

• So on and so forth until you have a trunk(main) stream.

• Only same-order streams can create the next level.

Rainfall on Land

• Also Precipitation.

• Rainfall is only one precipitation form.

• The rest is ice and snow.

• Liquid precipitation is the focus.

• Only <20% Rainfall On Land.

Rainfall amount

• 80% straight into the ocean anyway.

• Sydney gets $\approx$ 1,200mm of rain annually.

• Rain comes from southern storms or meeting area of warm and cool air.

• Most rain happens on coast and mountain side.

• Leads to coastal catchments being wetter vs the Murray Darling Basin which is drier.

• Decline is rainfall is expected in the future.

  • Leads back to idea of water availability issues.