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Option A: Freshwater

SDG 6: Clean water and sanitation

SDG 14: Life below water

A.1 Drainage basin hydrology and geomorphology

The hydrological cycle: 

Stores:

  • Groundwater.

  • Aquifer.

  • Lake.

Flows:

  • Overland flow.

  • Throughflow.

  • Groundwater flow.

  • Stem flow.

 

Aquifer: an underground water store (groundwater storage)

 

The cryosphere: global water in its frozen form. E.g. ice caps, snow and glaciers.

 

Temporal factors affecting river characteristics:

  • Seasonality: Seasonal changes in precipitation and temperature affect discharge. For instance, rising temperatures after winter increase discharge due to meltwater.

  • Abnormal weather conditions: Variations in precipitation or temperature impact the drainage basin. Higher temperatures elevate evaporation, reducing discharge.

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Types of river erosion and transportation:

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river-transportation-processes.png

Discharge and flow relationships:

  • Discharge formula: Velocity × cross-sectional area.

  • Discharge and flow link: Faster velocity typically increases discharge.

Hydraulic radius and discharge relationships:

  • Hydraulic radius: Cross-sectional area ÷ wetted perimeter.

  • Discharge and hydraulic radius link:

    • Higher discharge indicates greater water volumes at faster velocities.

    • A larger wetted perimeter or cross-sectional area allows for higher water volume.

    • Increased hydraulic efficiency minimises friction, boosting velocity and hydraulic radius.

 

Waterfall formation process:

  • It requires two rock types with different erosion resistances.

  • Erosion of less resistant rock: Occurs via corrosion and corrasion.

  • Undermining: Less resistant rock erodes, leaving the more resistant rock unsupported.

  • Waterfall creation: River flows over resistant rock, with falling water eroding the base through hydraulic action.

  • Collapse: Undercutting causes the resistant rock to collapse, forming debris in a plunge pool, which is further eroded.

  • Retreat: Continuous processes cause the upstream retreat of the waterfall, forming a gorge.

A.2 Flooding and flood mitigation

Hydrograph:

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Steeper rising limb factors:

  • Impermeable rock: Limits infiltration, preventing rainfall from reaching the channel through throughflow or groundwater flow. Instead, overland flow causes a rapid discharge increase.

 

Human factors affecting hydrograph shape:

  • Building on floodplains: Reduces infiltration and increases overland flow, shortening lag time and raising peak discharge.

  • Dam construction: Increases lag time by holding water behind the dam, reducing flood risk and moderating discharge.

 

Benefits of monitoring hydrographs for stakeholders:

  • Stakeholders: Environmental departments and other government bodies monitor hydrographs to manage water resources.

  • Flood prediction: Monitoring helps identify potential flooding, influencing residential and industrial development planning.

  • Drought prediction: Decreasing discharge over time signals drought onset, providing additional water sources.

 

Soft engineering strategies:

  • Tree planting: Increases interception, reducing rainfall reaching rivers via overland flow or throughflow.

  • Vegetation roots: Bind soil, reducing erosion and maintaining the river's water-holding capacity.

  • Flood risk reduction: Combined effects lower the risk of flooding.

Hard engineering strategies:

  • Flood walls: Prevent floodwater from reaching areas beyond the river.

 

Characteristics of channel modification:

  • Types: Straightening, dredging, or lining a channel.

  • Straightening: Increases water flow speed, reducing flooding risk in vulnerable areas.

  • Dredging: Deepens and widens the channel, increasing capacity and reducing flooding likelihood.

  • Lining with concrete: Creates a smoother wetted perimeter, reduces friction, and allows water to flow more efficiently, increasing the hydraulic radius.

 

Purpose of climate modelling in relation to flooding:

  • Flood risk assessment: Helps engineers and planners understand how future climate changes may impact flooding.

  • Scenario analysis: Demonstrates the effects of scenarios, such as more intense rainfall during certain times of the year, which could increase flooding risk.

A.3 Economic water scarcity

Types of water scarcity:

  • Economic water scarcity: Water is available, but access is limited due to factors like lack of capital or infrastructure to extract it.

  • Physical water scarcity: Water is available, but consumption is unsustainable, with extraction rates exceeding 60%.

  • Key difference: Economic scarcity involves an inability to extract water, while physical scarcity results from overconsumption.

 

Drought and its types:

  • Drought: Prolonged period with abnormally low rainfall.

  • Meteorological drought: Below-average precipitation over an extended period.

  • Agricultural drought: Insufficient water for crop growth.

  • Hydrological drought: Shortfall in surface/subsurface water supply due to inadequate precipitation.

Impacts of drought:

  • Economic: Reduced rain-fed crop yields, affecting subsistence farmers without water reserves.

  • Social: Reduced food production can lead to malnutrition and related diseases.

  • Environmental: River drying causes the death of organisms dependent on water.

 

Eutrophication:

  • A process where algae growth depletes oxygen and biodiversity in aquatic ecosystems.

  • Caused by excess nutrients from chemical fertilisers or sewage.

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Salinisation:

  • An increase in soil salt content.

  • Occurs when rainfall, underground water, or irrigation water evaporates, leaving salt behind.

 

Human pressure on aquifers:

  • Aquifer use: Aquifers are heavily used for residential, industrial, and food production needs.

  • Rising demand: Population growth, increasing consumerism, and the global middle class have increased water demand, particularly for food production.

  • Climate change effects: Depletion of surface water forces agricultural communities to extract more water from aquifers, while migration to urban areas puts additional pressure on urban aquifers.

A.4 Water management futures

IDBM: Integrated Drainage Basin Management

Characteristics of Wetlands:

  • Wetlands include swamps, marshes, and bogs.

  • They are saturated with water for part or all of the year.

  • Water sources include groundwater, river or lake flooding, or tidal movement from seas or oceans.

  • Wetlands are biologically diverse, with a variety of flora and fauna.

  • Wetlands can vary, such as tidal vs. non-tidal types.

The Ramsar Convention:

  • Signed in 1971 in Ramsar, Iran, to recognise wetland importance and establish protective regulations.

  • Wetland management should include sustainable use in food production and recreation.

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