Drainage Basin

1. A rivers drainage basin = area surrounding a river 

2. Boundary of a drainage basin = watershed - any precipitation past this point enters a different drainage basin.

3.Drainage basins are open systems with inputs and outputs.

4. Inputs: Precipitation, Outputs: evaporation, transpiration and river discharge 

Inputs - Water coming into the system

Precipitation = Main input, rain, hail, sleet, snow etc.

Storage - Water stored in the system.

Interception is when precipitation lands on vegetation or other before the soil, temporary store, evaporates quickly. 

Vegetation storage is water taken up by plants, all the water is contained in plants.

Surface storage  - water in puddles, lakes, ponds etc

Groundwater storage is water stored in the ground, either in soil or rocks

Water table - top surface of zone of saturation - zone of soil / rock where all pores are full of water, Porus rocks called aquifilers. 

Channel storage is water held in river or stream channel. 

Flows and processes - Water moving from one place to another.

Surface runoff (overland flow) water flowing over land, common in arid areas.

Throughfall is water dripping from one leaf to another

Stemflow is water running down a plant stem or a tree trunk.

Throughflow is water moving slowly downhill through the soil.

Infiltration is water soaking into the soil, rates influenced by soil type, structure and how much water is already in the soil. In a heavy storm it cant infiltrate fast enough so it flows over the surface (surface runoff) 

Percolation is water seeping through soil into water table.

Baseflow is groundwater flow that feeds into rivers through banks and beds.

Interflow is water flowing downhill through permeable rock above the water table.

Channel flow is water flowing into the river or stream itself. 

Outputs - Water leaving the system

Evaporation is water turning into vapour (gas)

Transpiration is evaporation from plant leaves - plants and water take up water through roots and transport to leaves where it evaporates,

Evapotranspiration is the process of evaporation and transpiration together,

River discharge or river flow is another output.

Groundwater flow - water flowing slowly below the water table through permeable rock, highly permeable rocks makes faster flow. eg.limestone.

Water balance - Balance between inputs and Outputs. 

Worked out from inputs (precipitation) and outputs (channel discharge and evapotranspiration) 

Affects how much water is stored in the basin

Water balance in the uk shows seasonal patterns: 

In wet seasons, precipitation exceeds evapotranspiration, this creates a water surplus. Ground stores fill meaning there is more surface runoff and higher discharge so river levels rise. 

In drier seasons, precipiation is lower than evapotrainspiration. Grounf stores are depleted as some water is used and some flows into river channel but isnt replaced by precipitation. So there is a deficit of water in the ground.