3.1.2 and 3.1.3 - Drainage basin system and River regimes Flashcards
Drainage basin system
Area of land that is drained by a river and its tributaries.
Drainage density
Total number of streams in area and how much it can hold.
Convectional rainfall
Trigger = Sun
Ground heated by sun
Warm air rises
Air cools and condenses with height, forming clouds
Cumulo-nimbus clouds are formed. Water droplets accumulate and fall due to gravity
Frontal rainfall
Trigger = Two air masses; warm and cold
Warm air forced to rise over cold air
Air cools and condenses as it rises, forming clouds and rain
Relief/ orographic rainfall
Trigger = Feeder seeder mechanism
Short duration but high intensity rainfall
Moist warm air from sea
Warm air forced to rise, cools, condenses rain occurs
The air drops down over the high ground, losing temperature and increasing the amount of water it can hold. Little or no rain.
Factors influencing storm hydrographs
- Vegetation cover
- Climate
- Slopes
- Rainfall intensity and duration
- Land use
- Soil type
- Lakes and reservoirs
- Rock type
Variation in river discharge
Temporal (change over time)
- Short term - snowmelt, increased rainfall
- Medium term - seasonal variation
- Long term - climate change, land use
Spatial (change place to place)
- Geographical location
- Climate
- Location - vegetation, soil type, geology
Overland flow - Infiltration excess
Rainfall intensity is so great water cannot infiltrate as soil is too wet or too dry.
Leaves ponds on soil surface.
Overland flow - Saturation excess
Rainfall continues over a long time.
Entire soil saturated and overland flow begins (localised).
Factors impacting storage
- Interception
- Vegetation and land use
- Seasonal differences e.g. tree type
- Global biomes
- Relief factors
RIVER SEVERN
Britain’s longest river at 350km
- Steep valleys
- Wide floodplains
- Wider lower down the river
Summer = convectional storms
Winter = Higher volume, higher rainfall on near saturated land
Human: Modification of floodplain and dredging
BEWDLEY 2000
Several periods of heavy rain.
Saturated soil and almost immediate runoff.
4 day lag time.
Slow moving pressure system .
BEWDLEY 2020
More funding made available from government for flood scheme.
Flood barriers.
PAKISTAN FLOODS 2022
Key stats
- Displaced 30 million people.
- 3 times usual amount of rainfall.
- Extremely high temperature.
- Widespread disease.
- Millions lost their homes due to location on Indus River.
- Sindh province largely effected as agricultural output. Employing 43% of population.
Causes
- 70% of country’s rain brought by monsoon.
- 3 times usual discharge.
- Long term change of heatwaves.
- Glacier melt from Himalayas.
- La nina caused increased rainfall and lasted for a third year in 2022.
River regime
Annual variation in the pattern of flow or discharge of a river measured at a particular point.
