Geography IB Diploma, notes

Option A Freshwater – Drainage Basins

1 Drainage Basin Hydrology and Geomorphology

  • Drainage Basin: Area drained by a river and its tributaries.
  • Open system with inputs, stores, processes, and outputs crossing the boundary.
  • Inputs: Precipitation (dew, hail, rain, sleet, snow), total and intensity important for overland flow.
  • Interception: Capture of raindrops by plant cover, reducing direct soil contact. Prolonged rain leads to throughfall (water dropping to the ground) and stemflow (water trickling along stems/trunks).
  • Evaporation: Liquid becomes gas, influenced by vapor pressure, air temperature, wind, and surface type. Bare soils have high evaporation rates.
  • Transpiration: Water loss from vegetation.
  • Evapotranspiration: Combined water loss from vegetation and water surfaces.
  • Potential Evapotranspiration: Rate of water loss with unlimited water.
  • Infiltration: Water sinking into the ground.
    • Infiltration capacity: Amount of moisture soil can hold.
    • Infiltration rate: Speed at which water enters the soil.
  • Throughflow: Lateral water movement in soil, following natural pipes (percolines).
  • Overland Run-off: Occurs when precipitation exceeds infiltration rate or capacity; soil is saturated.
  • Percolation: Water moving deep into the groundwater zone.
  • Baseflow: Groundwater movement providing hydraulic gradient for water movement; water table must rise above river level.
  • Stores: Vegetation, soils, aquifers (rocks holding water), and the cryosphere (snow and ice).
    • Soil moisture: Varies with porosity (pore spaces) and permeability (ability to transmit water).
    • Cryosphere: Largest freshwater store, water may be stored for millennia.
    • Vegetation: Trees store the most water.

2 Option A – Freshwater

  • Discharge: Volume of water passing a point per unit time (cumecs).
  • Discharge normally increases downstream (Bradshaw model).
  • Bradshaw Model: Water velocity and discharge increase downstream, while channel bed roughness and load particle size decrease.
  • Erosion Types:
    • Abrasion (Corrasion): Wearing away bed/bank by river's load.
    • Attrition: Wearing away of the load, making particles smaller and rounder.
    • Hydraulic Action: Force of air and water on river sides and in cracks.
    • Solution (Corrosion): Removal of chemical ions (calcium), dissolving rocks.
  • Factors Affecting Erosion:
    • Load: Greater weight and sharpness increase erosion.
    • Velocity/Discharge: Greater velocity and discharge increase erosion.
    • Gradient: Increased gradient increases erosion rate.
    • Geology: Soft rocks erode easily.
    • pH: Solution rates increase with acidity.
    • Human Impact: Deforestation, dams, bridges interfere with flow, increasing erosion.
  • Transportation Types:
    • Suspension: Small particles held by turbulent flow.
    • Saltation: Heavier particles bounce along the bed.
    • Solution: Chemical load dissolved in water.
    • Traction: Heaviest material dragged/rolled along the bed.
    • Floatation: Leaves carried on the surface
  • Stream Capacity: Largest amount of debris a stream can carry
  • Stream Competence: Diameter of largest particle a stream can carry
  • Critical Erosion Velocity: Lowest velocity to move grains.
  • Hjulström Curve: Shows relationship between velocity and grain size for erosion, transportation, and deposition.
    • Smallest and largest particles need high velocities to lift.
    • Entrainment needs higher velocities than transport.
    • Velocity decreases leading to particle deposition below settling or fall velocity.

3 Temporal Variations in Processes: River Landforms (1)

  • River Regime: Annual variation in river flow.
  • Influenced by precipitation amount/nature, local rocks (porosity/permeability), vegetation cover.
  • More precipitation increases solution.
  • Waterfalls occur on horizontally bedded rocks. Soft rock is undercut by hydraulic action and abrasion causing collapse and retreat.
  • Deposition: Occurs as river slows, losing energy (flooding, entering sea, behind dam, low flow).
  • Larger, heavier particles deposit first; smaller, lighter ones later.
  • Floodplains: Flat areas in lower river parts, made of clay, silt deposited during floods across floodplain..
  • Levees: Raised banks of coarse material (sand/gravel) deposited during floods, forming friction and slowing the river; floodplains consist of fine silt and clay.

4 River Landforms (2)

  • Meanders: Normal behavior of fluids/gases in motion on various materials.
  • Meander development: Channel slope, discharge, and load means the stream uses energy equally throughout.
  • Sinuosity Ratio: actual  channel  lengthstraight  line  distance\frac{actual \; channel \; length}{straight \; line \; distance}
  • A river is meandering when its sinuosity ratio exceeds 1.5.
  • Oxbow Lake:
  • The wavelength of meanders depends on channel width, discharge, and bed/bank nature.
  • Deltas form as river sediments deposit when entering standing water (lake, lagoon, ocean).
    • Deposition occurs due to reduced velocity.
    • Factors: Load amount/size, salinity, coastline gradient, vegetation, low energy discharge.
    • Delta Forms:
      • Arcuate: Many distributaries branch radially (Nile Delta).
      • Cuspate: Pointed delta from a dominant channel.
      • Bird’s Foot: Long, projecting fingers from distributaries (Mississippi Delta).

5 Hydrographs

  • Storm Hydrograph: Graph showing river changes over a day or two in response to hydrological cycle processes.
  • Measures speed of rainfall reaching river channel, discharge vs time.
  • Characteristics:
    • Discharge (Q): Volume of flow through a cross-section (cumecs i.e., m3s\frac{m^3}{s}).
    • Rising limb: Indicates increasing discharge speed. Steep in flash floods, small/urban basins.
    • Peak Flow/Discharge: Higher in larger basins. Catchment steepness and infiltration rates affect peak.
    • Lag Time: Time between peak rainfall/discharge. Influenced by basin shape/steepness/stream order.
    • Run-off curve: Overland flow and throughflow relationship. High overland flow if infiltration low.
    • Baseflow: Groundwater seepage into channel; important in rocks with high pore spaces and a hydraulic gradient.
    • Recessional Limb: Influenced by basin size, geology, aquifer activity. Gentle in large catchments with permeable rocks.
  • Hydrograph Size: The greater rainfall, the higher discharge
  • Variation in Hydrographs: The hydrograph is inffluenced by:
    * Climate (rainfall, intensity, seasonality)
    * Soils (impermeable soils increase flooding)
    * Vegetation (intercepts rainfall, reducing flooding)
    * Infiltration Capacity (low infiltration leads to overland flow)
    * Rock Type (permeable rocks reduce flood peak)
    * Slope Angle (steeper slopes increase run-off)
    * Basin Size/Shape/Relief (small, steep basins reduce lag time)
  • Urban Hydrographs: Shorter lag time, steeper rising/recessional limbs, higher peak flow due to impermeable surfaces/drainage channels.

6 Land-Use change and flood risk

  • Urbanization effects: Removal of trees/vegetation, construction, and storm drains impact hydrology more in the lower basin.
  • Deforestation: Reduces interception/evapotranspiration, increases overland flow leads to shorter lag times, higher peak flow on flood hydrographs.
  • Increased floor magnitudes and reduced reoccurence intervals.
  • Channel modifications: include channelization (straightening creates faster movement), enlargement (levees enabling more water), but purpose to reduce flood threats.

7 Flood Prediction and Mitigation

  • Forecasting/Warning: Improve rainfall estimates/forecasts, river gauging, sharing information, technology use, meteorological/hydrological data sharing between nations.
  • Emergency Measures: Remove people/property, flood-fighting (sandbags), flood-proofing (sealing walls).
  • Prevention/Amelioration:
    • Loss-Sharing Adjustments: Disaster aid and insurance (limited use in poor countries).
    • Event Modification Adjustments: Environmental control and hazard-resistant design, decrease the amount of surface run-off.
    • Flood Abatement: Reforestation, contour ploughing, vegetation management, sediment clearance, water storage areas/lakes.
    • Flood Diversion Measures: Levees, reservoirs, channel modifications.
  • Case Study: The Mississippi River has been protected for over a century, but it affects agricultural regions the most. Methods have included: levees, building dams, and channel straightening to remove water speedily.

8 Embankments

  • Flood embankments with sluice gates may raise flood levels upstream and downstream.
  • Channel enlargement to accommodate larger discharges means the enlarged channel is only rarely used it becomes clogged with weed.
  • Flood-relief channels bypass costly modifications to the original channel; for example, the food-relief channels around Oxford UK.
  • Intercepting channels: Divert only part of the flow away, allowing flow for town and agricultural use, e.g. the Great Ouse Protection Scheme in the UK.
  • Flood storage reservoirs such as those used along the Loughton Brook, UK may have a secondary flood control role.
  • The removal of settlements: This is rarely used because of cost, although many communities were forced to leave as a result of the 1993 Mississippi oods, e.g. Valmeyer, Illinois.

9 Water Scarcity and Water Quality

  • Physical Water Scarcity: Water consumption exceeds 60% of the usable supply.
  • Some examples include: Saudi Arabia and Kuwait import much of their food and invest in desalinization plants
  • Economic Water Scarcity: Sufficient water resources exist, but storage/transport facilities are lacking.
  • Drought: Extended dry period causing extreme dryness.
    • Absolute Drought: At least 15 consecutive days with less than 0.2 mm rainfall.
    • Partial Drought: At least 29 consecutive days with average daily rainfall under 0.2 mm.
  • Drought Impacts: Reduced crop yields, animal mortality, illness, forest fires, bans on water usage.
  • Water Quantity/Quality Distribution: Uneven geographically.
  • Three-quarters of rainfall is in areas with less than a third of world population.
  • Two-thirds of the world’s population live in areas limited an area receiving only a quarter of annual rainfall.
  • World deaths from water related disease stands at around 4 million.
    *Quality in developing countries is affected by lack of access to safe and affordable water supplies and sanitation.
    *Quality may be affected by organic waste from sewage, fertilizers and pesticides from farming, and by heavy metals and acids from industrial processes and transport.
  • Water Availability: Includes: Water availability, Water infrastructure, Cost of water.

10 Irrigation

  • Irrigation: Water addition where deficient for crop growth.
  • Taken from surface or groundwater, methods range from flooding to drip irrigation.
  • Consequences of Irrigation:
    • Texas water table reduced by up to 50 m; Indus Plain raised by up to 6 m, causing salinization.
    • Albedo may be reduced by 10% as reflective soils are replaced by green surfaces.
    • Precipitation may change i.e increased rainfall, hailstorms, and rainfall.
  • Salinization: Increased soil salt content as ground water levels rise and capillary forces bring water to surface where it may be evaporated.
  • Eutrophication: Nutrient enrichment causing algal blooms, oxygen starvation, reduced species variety.
  • Stakeholders Involved: chemical fertilizer companies, governments, farmers, health organizations, environmental organizations, and consumers.

11 Human Pressures on Lakes and Aquifers

  • Population Growth: Increases pressure on water resources, impacting certain locations, Middle East and North Africa (MENA) region experiences the greatest water stress.
  • Pollution: Run-off from chemical fertilizers, phosphates, sewage, oil, acidication, industrial euent.
    * Global variations in eutrophication are prevalent in: Asia-Pacic 54%, Europe 53%, Africa 28%, North America 48%, and South America 41%.
  • Non-renewable; annual use exceeding regeneration will shrink the aquifer.
    *Case Study: The World Health Organisation suggest arsenic in ground water to be the cause of as many as 85 million cancer deaths from naturally occurring arsenic in groundwater of Bangladesh.

12 Internationally Shared Water Resources

  • A limited Water resources leads to equity of usage and political consequences. When water supplies fail, populations will be forced to take drastic steps, such as mass migration. Water shortages may also lead to civil unrest and wars.

  • Stakeholders: Stakeholders in rivers such those in Nile basin include governments of Egypt, Ethiopia, Sudan, as well as the people of each nation.

*Beneficial Nile stabilizing dam flow to Sudan; whereas the Nile provides nearly all of Egypt’s water, threatening their agricultural sector.

13 The Building of Large Dams

  • Famous dams include the Akosombo (Ghana), Tucurui (Brazil), Hoover (USA), and Kariba (Zimbabwe).

*Case Study: The 3 Gorges dam is the world’s largest at 2 km long and 100 meters high. It will generate 18,000 MW, supply Shanghai and Chongqimg, and protect 10 million from flooding. It has also moved up to 1.2 million people, risks silting upstream, increased coasts erosion, seismic activity, is expensive ($70B), and interferes with aquatic life.

14 IDBM Plans

  • Integrated drainage basin management (IDBM) plans aims to deliver sustainable use of the world’s limited freshwater resources:
    Uses a basin-wide framework for water management that is economically, socially and environmentally sustainable. It is limited when divided by the Cold war
    *The Danube has high biodiversity, provides drinking water for 20 million people, is economically critical for industry, and transport.
  • Lower Danube Green Corridor consists of a 400,000 ha network of protected wetland areas to protect biodiversity
  • Costa Rica payments for forest owners regulating water quality and quantity, leading to reduced sedimentation behind dams.

15 Wetlands

Ramsar Convention defines wetlands are "areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt".

Wwtlands now represent 6% of the earth's surface, of which 30% are bogs, 26% are fens, 20% are swamps, 15% are oodplains and 2% are lakes.

functions: Flood control,
fisheries Groundwater recharge
food-chain support/cycling timber water transport
water transportation tourism/recreation

Products Attributes Biological diversity
Culture and heritage Water purication
Water Storage of organic matter

The factors of degradation include: increased demand for agricultural land population growth development river ow regulation invasion of non-native species and pollution natural causes such as drought and hurricanes.

CASE STUDY restoration of the Kissimmee River cost over $410 million, but increased local vegetation, bird populations tripled, oxygen levels doubled, and recreational revenue increased.

16 Water Supply

Water resources can be managed sustainably with both individual and community participation with national government support. Resources can be reduced by:
self restraint minimizing waste reuse retention retention, and redistribution

  • Water harvest includes extraction from rivers and lakes where gravity may be used. Pumping may be used with low and high technology as long as water is replenished.
  • Water law: Water shall not be owned but only used for public sustainability, equity, and efciency in a manner which reects the value of water to society while ensuring basic domestic needs, and the environment requirements are met.
  • Responsibility should be delegated for interested parties to have access and to contribute to their healthy enjoyment.