Global Rivers Flashcards
what percentage of freshwater is liquid surface water?
0.3%
where is the majority of liquid surface water found
lakes
explain why rivers are important
connected to water resources, soils, ecosystems, land use
water crisis among top 5 global risks in past 7 yrs
chemical exchanged between atmosphere and biosphere
large source of methane and CO2
what is the most accurate and up to date database of global rivers and streams
GRWL database
what size is the Amazon basin (in comparison to other region)
same size as the US (roughly)
which two rivers have the largest amount of runoff
Amazon and Orinoco
types of river flow x3
perennial, intermittent (only flows seasonally when water table at max level), ephemeral (flow after occasional storms)
4 sources of streamflow
- channel precipitation
- overland flow
- infiltration into the soil (throughflow)
- groundwater leading to baseflow
what is infiltration capacity
the max rate that water can enter
when does infiltration capacity decline
during rainfall, surface can pool with water and runoff
what factors increase infiltration rate
more vegetation, sandier soil, gentler slope
what is saturation excess overland flow
when the soil is full with water and forces it to pool on the surface
what two occasions can cause hillslope runoff
- infiltration-excess overland flow- when the rate of infiltration is less than the precipitation
- saturation-excess overland flow- soil completely saturated and water table at the surface
through what process does most water reach rivers
throughflow- water travelling laterally away from a source
what is matrix flow
very fine pores, lateral throughflow will occur where hydraulic conductivity declines with depth
what is macropore flow
chemical and water transport in larger pores
important role in throughflow
what is pipeflow
transport of water very quickly through larger cavities
what is groundwater flow
all flow below the water table
what are aquifers
layers of rock porous enough to store water and permeable enough to allow water through them
what is salinisation in relation to groundwater supply
bringing up of salt in soil from deeper waters
what is the coefficient of runoff
the percentage of rainfall converted into overland flow
how does watershed shape influence streamflow
at round basins, streams meet at a central point, where the discharge increases
at elongated basins, streams join at different points, leading to a gradual increase in discharge
what is drainage density
the total length of all stream channels in a sq metre of land
what is a river regime
the seasonal variation in river flow
in what way can anthropological influence increase drainage density
farmyard erosion, land clearing
how can the removal of wetlands influence runoff
wetlands store runoff, removal causes runoff to move faster and in greater volumes
what human impacts can increase flooding
straightening channels and removing vegetation, removal of wetlands
why can flow velocity actually be greater at the mouth of the river than the head
basin size increases and riverbed gets less rough and friction-ed
