IB Geography Option A: Freshwater

What Option A covers

Option A follows the guide's four parts. Drainage basin hydrology and geomorphology: the drainage basin as a system of stores and flows, from interception and infiltration to throughflow, overland flow, percolation and baseflow; discharge and the storm hydrograph; and river erosion, transport and deposition, with the Hjulström curve and landforms such as levees. Flooding and flood mitigation: why impermeable urban surfaces and drains shorten lag time and raise peak discharge, and how floods are managed. Water scarcity and water quality: physical and economic water scarcity, water stress, eutrophication and salinisation, and groundwater in aquifers. Water management futures: large dams and the sediment they trap, inter-basin transfers, desalination, rainwater harvesting, drip irrigation and grey water, integrated water resource management, and the Ramsar Convention on wetlands.

Where students slip

• Discharge is the volume of water passing a point each second, measured in cumecs (m³ s⁻¹). It is not velocity, which is in m s⁻¹: discharge is the channel's cross-sectional area multiplied by its velocity.
• The smallest particles are not the easiest to erode. On the Hjulström curve, clay needs a higher velocity than sand to be picked up, because its particles are cohesive, though once it is moving it stays in suspension at very low velocities.
• Physical water scarcity means demand exceeds the water available, as in arid regions. Economic water scarcity means the water is there, but people lack the investment or infrastructure to use it.