Human activities significantly alter drainage basin systems, making this topic central to IB Geography, particularly within Option A: Freshwater – Drainage Basins. While drainage basins naturally function as balanced systems, human intervention often disrupts inputs, flows, stores, and outputs, increasing flood risk and altering river behaviour.
One of the most influential human activities is urbanisation. As cities expand, natural land surfaces are replaced with impermeable materials such as concrete and asphalt. These surfaces reduce infiltration and increase surface runoff, meaning water reaches river channels more quickly. Storm drains and artificial channels further speed up water transfer, shortening lag time and increasing peak discharge. As a result, urban drainage basins often experience more frequent and severe flooding.
Deforestation also alters drainage basin systems. Trees intercept rainfall, increase infiltration through root systems, and stabilise soil. When forests are cleared, interception is reduced and soil becomes more compacted and vulnerable to erosion. This increases surface runoff and sediment transfer into rivers. Sediment accumulation can reduce channel capacity, further increasing flood risk downstream.
Agricultural activities influence drainage basins in several ways. Soil compaction caused by heavy machinery reduces infiltration capacity, increasing runoff during rainfall events. Field drainage systems, designed to remove excess water quickly, speed up water transfer to rivers. Overgrazing removes vegetation cover, exposing soil and increasing erosion and runoff. These changes alter natural flow pathways and destabilise the system.
River management schemes are another major form of human impact. Dams and reservoirs increase storage within the drainage basin, regulating river discharge and reducing flood risk downstream. However, they also alter natural flow regimes, affect sediment transport, and disrupt ecosystems. Reduced sediment supply downstream can increase erosion and degrade river habitats.
Channelisation and embankments are often used to protect settlements from flooding by speeding up water flow and increasing channel capacity. While effective locally, these measures can increase flood risk further downstream by transferring water more quickly through the system. In IB Geography, this highlights the concept of risk transfer rather than risk reduction.
Water abstraction for domestic, agricultural, and industrial use also alters drainage basin systems. Removing water from rivers and groundwater stores reduces discharge and can lower water tables. During dry periods, this may reduce baseflow and increase the risk of water shortages and ecosystem damage.
In IB Geography exams, students are expected to link human activities to changes in flows, stores, and system balance. Clear explanation of cause and effect is essential for high-level answers.
Overall, human activities significantly modify drainage basin systems, often increasing flood risk and reducing system stability. Sustainable management requires balancing human needs with natural system processes.
RevisionDojo helps IB Geography students understand human impacts on drainage basins clearly, linking physical processes and management strategies into confident, exam-ready explanations.
