Evapotranspiration: This is the combined loss of water through direct evaporation from surfaces and transpiration from plant stomata, representing a major loss of mass from the basin system.
River Discharge: This is the volume of water passing a specific point in the river channel per unit of time, typically measured in cumecs (cubic meters per second).
Discharge Formula: The volume of flow is calculated as , where is discharge, is the cross-sectional area of the channel, and is the mean velocity of the water.
| Process | Location | Description |
|---|---|---|
| Throughfall | Above Ground | Precipitation that reaches the ground directly or by dripping from leaves. |
| Throughflow | Below Ground | The lateral movement of water through the soil layer toward the river channel. |
| Infiltration | Surface Interface | The initial entry of water from the surface into the upper soil pores. |
| Percolation | Sub-surface | The vertical movement of water from the soil down into the underlying permeable rock. |
System Classification: Always identify the drainage basin as an open system and be prepared to contrast it with the global hydrological cycle, which is a closed system.
Factor Analysis: When asked why one basin responds differently to a storm than another, categorize your answer into Physical Factors (geology, relief, soil type) and Human Factors (urbanization, deforestation).
Unit Precision: Ensure discharge is always discussed in (cumecs) and precipitation in . Misidentifying a 'store' as a 'transfer' (or vice versa) is a common way to lose marks.
Sanity Check: If a question involves land use change, remember that urbanization always decreases infiltration and increases overland flow, leading to a 'flashy' response.
