2.1.2 Catchment hydrology –the drainage basin as a system

What is a drainage basin?

An area of land drained by a river and its tributaries bounded by a watershed.

Why is a drainage basin described as an open system?

Because it receives inputs and transfers outputs beyond its boundaries.

What is the main input to a drainage basin?

Precipitation including rain

What are the main outputs of a drainage basin?

Evapotranspiration and river discharge.

What are the main stores in a drainage basin?

Interception

What is interception storage?

Water temporarily held on vegetation before evaporating or reaching the ground.

What is soil moisture storage?

Water held within soil pores that influences infiltration

What is groundwater storage?

Water stored in permeable rocks (aquifers) beneath the surface.

What is infiltration?

The downward movement of water from the surface into the soil.

What is throughflow?

The lateral movement of water through the soil layer above the water table.

What is percolation?

The downward movement of water from soil into underlying bedrock and aquifers.

What is surface runoff?

Water flowing over land when rainfall exceeds infiltration capacity or soil is saturated.

What is baseflow?

The slow release of groundwater into rivers

What is evapotranspiration?

The combined loss of water through evaporation and plant transpiration.

What is the water balance equation?

P = Q + ET ± ΔS.

What does ΔS represent in the water balance?

The change in water stored within the drainage basin.

What happens to the water balance in winter in the UK?

Precipitation exceeds evapotranspiration leading to soil saturation and water surplus.

What happens to the water balance in summer in the UK?

Evapotranspiration exceeds precipitation causing soil moisture deficit.

How does geology affect drainage basin processes?

Permeable rocks increase infiltration and groundwater flow while impermeable rocks increase surface runoff.

How does vegetation affect drainage basins?

It intercepts rainfall

How does urbanisation affect drainage basins?

It reduces infiltration and increases runoff

Why is soil moisture important in the hydrological cycle?

It regulates infiltration

How does climate influence drainage basin inputs?

Climate controls the amount