1.1 The Drainage Basin

What is evaporation?

It is the process by which a liquid is changed into gas.

What are the factors affecting evaporation?

Meteorological factors such as temperature, humidity, wind speed, amount of water available, vegetation cover, and surface color (albedo).

What is transpiration?

It is the transfer of water vapor from vegetation to the atmosphere, primarily through pores in leaves called stomata.

What does evapotranspiration (EVT) refer to?

It refers to the combined water loss through both evaporation and transpiration.

What is potential evapotranspiration?

It is the water loss that would occur if there were an unlimited supply of water in the soil available for vegetation.

What is river discharge?

It is the water that flows out of a basin into an ocean.

What does interception refer to in the context of water storage?

It refers to precipitation caught and stored by vegetation before it reaches the ground.

What is soil water?

Soil water is the subsurface water in soil and subsurface layers above the water table.

What are temporary surface water stores?

Temporary stores include small puddles after a rainstorm and turloughs (seasonal lakes in Limestone, Ireland).

What type of water storage is groundwater?

Groundwater refers to the subsurface water that is stored under the surface in rocks.

What percentage of all freshwater on Earth is groundwater?

Groundwater accounts for 96.5% of all freshwater on Earth.

What is channel storage?

It refers to all water that is stored in rivers, streams, and other drainage channels.

What is throughfall?

It is water that flows through gaps in vegetation or drops from leaves and twigs.

What is stemflow?

It is precipitation that is intercepted and trickles along branches then down the main trunk.

What causes overland flow?

Overland flow occurs when soil is saturated or precipitation exceeds infiltration rate, resulting in surface runoff.

What is infiltration?

Infiltration is the process when precipitation soaks or is absorbed into the soil.

What is the infiltration capacity?

It is the maximum rate that precipitation can be absorbed by soil under given conditions.

How does vegetation affect infiltration rates?

Infiltration rate increases where there is vegetation due to throughfall, stemflow, and interception slowing the rate that water reaches the store.

What is percolation?

Percolation is the slow movement of water downwards through the soil into bedrock under gravity.

What is baseflow?

Baseflow is where groundwater seeps into the river’s bed and contributes to discharge.

What does the water table indicate?

The water table is the upper level of the phreatic zone at which pore spaces and fractures in the ground become saturated.

What is recharge in the context of groundwater?

Recharge is the refilling of water in pores where the water has dried up or been extracted.

What happens during natural discharge?

Natural discharge occurs through spring flow and seepage into surface water bodies.

What are aquifers?

Aquifers are permeable rocks that contain significant quantities of water.

What is soil moisture?

Soil moisture is water held in sub-surface soil pores.

What is the balance equation for water budget?

Balance = Precipitation – (run off + evapotranspiration + change in soil moisture).

How do sandy soils compare to clay in terms of infiltration?

Sandy soils have quick infiltration rates while clay has slow infiltration rates and holds water well.

What is the equation for water budgets?

S = P – Q – E, where S is soil storage, P is precipitation, Q is channel flow out of basin, and E is evapotranspiration.