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The water cycle and drainage basins
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Water is always on the move: from sea to sky to land and back again. Hydrology is the study of how water moves.
The water cycle
The water cycle is the continuous movement of water between the sea, the air and the land.
The sun heats water, which evaporates into water vapour. Plants also give off water: transpiration.
The vapour rises, cools and condenses into clouds, then falls as precipitation (rain, snow, sleet, hail).
It flows back to the sea over and under the ground.
The sun heats water, which evaporates into water vapour. Plants also give off water: transpiration.
The vapour rises, cools and condenses into clouds, then falls as precipitation (rain, snow, sleet, hail).
It flows back to the sea over and under the ground.
The drainage basin
A drainage basin is the area of land drained by a river and its tributaries.
The watershed is the high ground at its edge, dividing one basin from the next.
The source is where a river starts; the mouth is where it meets the sea. A confluence is where two rivers join.
The watershed is the high ground at its edge, dividing one basin from the next.
The source is where a river starts; the mouth is where it meets the sea. A confluence is where two rivers join.
Stores and flows
Interception: leaves catch rain before it hits the ground.
Infiltration: water soaks into the soil.
Surface runoff: water flows over the ground, fastest on steep or paved surfaces.
Throughflow: water moves sideways through the soil. Groundwater flow: water moves slowly through rocks.
Stores include lakes, soil, groundwater and ice.
Infiltration: water soaks into the soil.
Surface runoff: water flows over the ground, fastest on steep or paved surfaces.
Throughflow: water moves sideways through the soil. Groundwater flow: water moves slowly through rocks.
Stores include lakes, soil, groundwater and ice.
Why does building a new housing estate increase surface runoff?
- Concrete and tarmac are impermeable: water cannot soak in.
- So infiltration falls and more rain flows over the surface.
- Drains carry it quickly to rivers, so they rise faster.
Answer: Impermeable surfaces stop infiltration, so more water runs off quickly to rivers.
Water cycle: evaporation, transpiration, condensation, precipitation. A drainage basin is drained by a river and its tributaries; the watershed is its edge. Flows: interception, infiltration, surface runoff, throughflow, groundwater flow.
The interactive lesson includes the diagrams for this topic.
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