3 - temporal variations in river discharge ✅ Flashcards
what is a river regime
annual variations in river discharge throughout the year
this annual flow is supplied by storm, overland and throughflow and snow melt
what is a simple vs complex regime
SIMPLE = one maximum and one minimum/year exist because of glacier melt, snowmelt, season rainfall
COMPLEX = river has more than one period of high/low water levels. more common on large rivers through variety of reliefs eg River Rhone
what is unique about the colorado rivers regime
- discharge is naturally very uneven marked with summer maximum and lower flow between sept. and april
- this is because of its massive drainage basin
- water management schemes have altered the natural regime and peaks have been smoothed out by dam building - the Hoover Dam (1935)
why is there need to manage the colorado river regime
- clearer water
- disappearing sandbanks
- colder water
- vanishing species
- fishing and rafting
what are the factors influencing river regimes (12)
- climate
- seasonality
- natural lay of the land
- drainage basin size and shape affecting regime
- human influences and land use
- precipitation
- snowmelt
- vegetation
- temperature and rainfall variations
- geology
- irrigation
- agriculture
how does climate affect river regimes
- different levels of rainfall and evaporation rates
- eg seasonal rivers dry up during summer months
how does seasonality affect river regimes
- linked to climate
- dry vs wet seasons
- variations in sunshine therefore variations in evaporation rates
how does natural lay of the land affect river regimes
- rock permeability (permeable rocks can hold high amounts of water)
- eg hydrograph of Derwent river vs Wye river
- amount, density, type of vegetation
how does the drainage basin size and shape affect river regimes
- larger drainage basins capture more precipitation, peak discharge higher than small drainage basin
- shape:
ELONGATED basin = low stream order = shorter lag time = attentuated hydrograph
ROUND BASIN = higher order streams = longer lag time due to accumulation of discharge at main stream = higher peak discharge = flashier hydrograph
how do human influences and land use affect river regimes
- physical characteristics of river alter velocity and flow patterns
- these can be altered by agricultural change, deforestation, urbanisation
- humans taking water from rivers/groundwater = reduction in natural flow rates, increase in water stress
- low flows artificially enhanced
- trends in river flows over time may be more a reflection of artificial changes than climatic changes
what is the difference between a river and storm hydrograph
HYDROGRAPH - line graphs that plot changes in a river’s discharge over time
STORM HYDROGRAPHS - plot individual storm event, show how river responds to one particular storm event, shows how river responds to period of heavy rain
what is a ‘flashy’ hydrograph
how quickly the rivers discharge increases in response to the precipitation event
it has a short lag time
what is peak discharge
the highest level that discharge reaches in cumecs
what is the rising limb
the rising flood water in the river
what is peak flow
maximum discharge in the river
what is the recession limb
falling flood water in the river
what is the basin lag time
time difference between the peak of the rain storm and the peak flow of the river
what is the base flow
normal discharge of the river
what affects the shape of a hydrograph (8)
- previous conditions
- geology and soil
- vegetation
- land use
- type, amount and duration of precipitation
- drainage density
- temperature
- gradient of the valley sides
what are the two factors affecting storm hydrographs
- climatic factors
- river catchment characteristics
what causes a long lag time and a small peak discharge (3)
- deep soil layer
- porous rock
- afforestation
what causes a short lag time and a high peak discharge (7)
- impermeable surface
- intense prolonged rain
- small river basin
- steep topography
- long drought before rainfall
- urban growth on farmland
- rapid snow melt
what is drainage basin density and what is its importance
- drainage density is the total length of all the streams and rivers in a drainage basin divided by the total area of the drainage basin
- measures how well/poorly a watershed is drained by stream channels
- a high drainage density = flashier the hydrograph
what is topography
the arrangement of the natural and artificial physical features of an area.
