Block 2 (Catchment Hydrology - The Drainage Basin As A System) Flashcards
Define a drainage basin?
Catchment area of land which is drained by a particular river/body of water
Define watershed?
Dividing line between adjacent drainage basins (often marked by high relief features, e.g. mountains)
What type of system is a drainage basin?
Open system
- Inputs + outputs of energy + matter
What is the one input into a drainage basin?
Precipitation
How can precipitation vary?
- Different types
- Different amount
- Different intensity
- Different duration
How can precipitation type vary (what are the three types?)
- Orographic/relief
- Convectional
- Frontal
How can precipitation amount vary?
Different volumes of precipitation can fall
How can precipitation intensity vary?
Amount of rain that falls in a certain period can vary
How can precipitation duration vary?
Length of time precipitation falls for can vary
What are the eight drainage basin flows?
- Throughfall
- Stemflow
- Infiltration
- Throughflow
- Percolation
- Groundwater flow
- Surface runoff/overland flow
- Channel flow
Define throughfall?
Water dripping from leaves of veg -> ground
A drainage basin flow
Define stemflow
Water dripping off veg down stem/trunk -> ground
A drainage basin flow
Define infiltration
Water movement from ground surface -> soil
A drainage basin flow
Define throughflow
Water movement laterally through the soil
A drainage basin flow
Define percolation
Water movement from soil -> underlying bedrock
A drainage basin flow
Define groundwater flow
Water movement vertically + laterally through underlying bedrock
(A drainage basin flow)
Define surface runoff/overland flow
Water movement over the land surface
A drainage basin flow
Define channel flow
Water movement through the river channel
A drainage basin flow
What is the water level?
Level at which the ground is saturated up to
What two factors affect the amount of groundwater flow (through underlying bedrock)?
- Porosity (amount of water that can be held in rock)
- Permeability (ease of flow through rock)
What are the two reasons why surface runoff/overland flow can occur?
SATURATION-EXCESS OVERLAND FLOW
- High duration of rainfall
- Soil becomes saturated, so no more water can infiltrate
INFILTRATION-EXCESS OVERLAND FLOW
- High intensity of rainfall
- Ground may not be saturated, but intensity is so great that not all rain can infiltrate
Which area of the drainage basin becomes saturated first during rainfall?
Areas close to bottom of slopes - form SATURATED WEDGE
What does it mean to be a drainage basin flow?
A way in which inputs are transferred through the drainage basin
What are the six drainage basin stores?
- Interception store
- Vegetation store
- Surface store
- Soil moisture store
- Channel store
- Groundwater store
Define interception store
Temporary store of water on plant surfaces
Define vegetation store
‘Green water’ held within vegetation biomass
Define surface store
Water collected on ground surface (as snow or rain in hollows)
Define soil moisture store
Water held in soil
Define channel store
Water held in river channel
Define groundwater store
Water held in bedrock underneath soil
What are the three ways water can be held in the soil moisture store
1) Hydroscopic water - thin films of water molecularly attracted to surface of soil particles
2) Capillary water - thicker films of water held into small soil pores by surface tension
3) Gravitational water - water occupying large spaces in soil after rainfall
Define field capacity?
Total water in soil moisture store when all gravitational water is drained away (the amount of water constantly available in soil - without any precipitation event)
Define wilting point
When water stores become too low to compensate for plant loss via transpiration
What are the four drainage basin outputs?
- Channel discharge
- Evaporation
- Transpiration
- Evapotranspiration
Define channel discharge
Volume of water leaving a drainage basin via main stream/river
(A drainage basin output)
Define evaporation
Water changes from liquid to gas when heated, transferring it from surface stores in basin -> atmosphere
(A drainage basin output)
Define transpiration
Water changes from liquid to gas, diffusing out of plant stomata in basin -> atmosphere
(A drainage basin output)
Define evapotranspiration
Combination of evaporation + transpiration removing water from the soil and the plants growing within it
(A drainage basin output)
What are three factors that may increase the rate of evaporation or transpiration
- High heat
- High wind speed (increase water conc gradient)
- Low humidity (increase water conc gradient)
What does it mean to be an input to a drainage basin?
A way that water enters the drainage basin system
What does it mean to be an output to a drainage basin?
A way that water leaves the drainage basin
