Water and Carbon Cycles: Drainage Basins Flashcards
What are the inputs in a drainage basin?
Precipitation
What are the outputs in a drainage basin?
River Discharge and Evapotranspiration
What are the flows in a drainage basin?
Interception, stemflow, throughfall. overland flow, infiltration, throughflow, percolation, groundwater flow and channel flow
What are the stores in a drainage basin?
Interception storage, surface storage, soil storage, groundwater storage, channel storage
What type of system are drainage basins?
Open, local hydrological cycles with the boundary being the watershed
What is evapotranspiration?
The total output of water from the drainage basin directly back into the atmosphere
What is run-off?
All the water that enters a river channel and eventually flows out of the drainage basin
What factors influence evapotranspiration?
- Most important factor is high temperatures, causes water to evaporate at a faster rate as there’s more KE, increased rate of transpiration, invigorates plant growth (increases flow)
- Plant growth increases flow, as it increases the total respiration of plants which releases water as a product
- High humidity decreases rate of flow as the air is saturated, less capacity to hold water
What factors influence interception?
- High density of vegetation increases store as there is more vegetation thats intercepting and more water held in store
- Plants with broader leaves increase store as there is a larger SA to intercept rainfall
- Intense wind and rains decrease stores as they shake leaves and trees, instead increasing throughfall and stemflow
What factors influence overland flow?
- Perception, if there is little precipitation the overland flow won’t be large
- Topography, if its flat water will sit directly on the surface, if it’s stepp water can’t infiltrate soil so flows downhill
- Impermeable surfaces reduce infiltration and therefore enhance overland flow, permeable surfaces have the opposite impact
What factors influence infiltration?
- Small pores (soil porosity) lead to soil becoming easily saturated, reducing capacity t hold water and reduce rate of infiltration
- Land use, urban areas decrease rate of infiltration as there is a large areas of impermeable surfaces (increasing overland flow)
- Intense and long periods of rainfall (intensity + duration) declines rate as soil becomes saturated
What factors influence groundwater storage?
- Rock porosity, large air spaces in rock allows store to increase, larger capacity to hold water
- Abstraction rate, if rate is high enough the store will decrease (over-abstraction)
- Intense precipitation causes water to run-off straight into rivers, not being absorbed into groundwater storage
What factors influence river discharge?
- Characteristics of the drainage basin (large + steep relief + impermeable rocks and soils = high discharge)
- High precipitation leads to a high increase in river discharge
- More impermeable surfaces, water runs into drains and makes its way quickly into rivers
- Deforestation, more water reaches the ground faster, ground becomes saturated, makes it way quicker to river
What is the concept of the water balance?
Within the drainage basin the balance between the inputs (precipitation) and outputs (evapotranspiration and channel discharge) is known as the water balance
What is the equation of the water balance?
Precipitation (P) = Discharge (Q) + Evapotranspiration (E) +/- Changes in stores (S)
Describe water balance in the wet seasons?
- precipitation will be higher than evapotranspiration
- this creates water surplus
- ground stores fill very quickly so there’s more surface run-off
- higher river discharge and water levels rise
- input is greater than output
Describe the water balance in the drier seasons?
- precipitation is lower than evapotranspiration
- ground stores are being depleted as water is being used, not being replaced by precipitation
- deficit of water
- output greater than input