option A hydrology Flashcards
drainage basin
the area drained by a river and its tributaries
freshwater
rivers, lakes, wet lands, glaciers, groundwater, ice caps.
hydrological cycle
conceptual model describing the storage and movement of water between the biosphere, atmosphere, lithosphere and the hydrosphere.
water shed
drainage divide: imaginary line defining the boundary of a river or steam drainage basin separating it from adjacent basin.
discharge
volume of water passing a given point over a set time
physical water scarcity
lack of available water- resource development is approaching or has exceeded unsustainable levels- relates availability to demand and implies that arid areas are not necessarily water scarce
economic water scarcity
lack of water where it is available locally but not accessible for human, institutional or financial capital reasons
storm hydrographic
graph showing how a river changes over a short period (couple of days/ day)
flood
a discharge great enough to cause a body of water ti overflow its channel and submerge surrounding ground.
open systems
contains varying inputs (precipitation of varying intensity), outputs (evaporation and transpiration), flows and stores.
flows examples
- infiltration
2 .throughflow - overland flow
- baseflow
stores examples
- vegetation
2 soil
3 aquifers
4 cryoshpere (world ice)
closed drainage basin
does not reach the sea but drains into an inland depression
outputs- losses in hydrological cycle
1 evapotranspiration
2 runoff
evaporation
process by which liquid or solid is changed into gas- conversion of precipitation to water vapour in the atmosphere
factors affecting evaporation
temperature (most important)
humidity
winded
water availability
vegetation cover
colour of surface (albedo)
transpiration
water vapour escaping from living plants (leaves) into atpmosphere
evapotranspiration (EVT)
combined effects of transpiration and evaporation
precipitation
flow of water into a drainage basin by rainfall, snow frost, hail and dew
characteristics of precipitation affecting hydrology
total amount of precipitation
intensity
type
geographic distribution
variability
additional inputs to drainage basin (not precipitation)
irrigation water
water transfer schemes
use of desalinated water
potential evapotranspiration
-moisture availability
water loss that would have occurred if there was an unlimited supply of watering soil for vegetation use
infiltration
infiltration capacity
-process where water is soaked into the ground and absorbed by the soil
-maximum rate at which rain can be absorbed by soil conditions
why does infiltration capacity decrease over time?
during rainfall periods- decrease in capacity as the soil soaks up water until a more or less constant value is reached
clay soils infiltration rate
sand soils infiltration rate
clay- 0-4 mm^-1/hour
sand- 3-12 mm^-1/hour
why does vegetation increase infiltration
intercepts some of the rainfall slowing down arrival at ground
overland flow (surface run off)
water that flows over the land’s surface
2 ways of over land flow
-precipitation exceeds infiltration rate
-soil is saturates (all pores are filled with water)
throughflow
water flowing in natural pipes and percolines
percolines
lines of concentrated water flow between soil horizons
base flow
part of a river’s discharge provided by groundwater seeping into the bed of the river
(relatively constant but increase slightly follow¡wing a wet period)
vegetation
water that is caught and stored by vegetation
vegetation elements (3)
- interception
-throughfall
-stemflow
interception
- interception- water retained by plant surfaces and which later evaporates away or is absorbed by the plant and used (photosynthesis)
throughfall
water that wither falls through gaps in vegetation or drops from leaves, twigs or stems
stemflow
water that trickles along twigs and branches and finally down the main trunk
soil moisture
subsurface water in the soil
field capacity
amount of water held in soil after excess water drains away (saturation or near saturation)
wilting point
range of moisture - permanent wilting of the plant
aquifers
rocks that contain significant quantities of water
groundwater
subsurface water
percolation
water moving slowly from soil to bedrock (dependent on permeability of rock)
phreatic zone
permanently saturated zone in solid rocks and sediments
water table
upper layer of phreatic zone
freshwater distribution on earth
69% resides in glaciers, 30% underground, and less than 1% is located in lakes, rivers, and swamps.
recharge
refiling of water in pores where the water had dried up or been extracted by human activity.
when is water not a renewable source?
when the location does not go through recharge process
why does water in aquifers move slow
it acts as a natural regulator in the cycle- absorbs rainfall that would otherwise reach streams rapidly
maintains stream flow during dry periods
groundwater recharge reasons:
-infiltration- part of the total precipitation at the ground surface
-seepage through the banks and bed of surface water (ditches rivers, lakes and oceans)
-groundwater leakage, inflow from rocks and aquifers
-artificial recharge- irrigation, reservoirs etc
discharge formula:
(cross section area of river)x(mean velocity of the water) -m^3/sec
impact of weight/depth ratio
large rivers- high width to depth ratio more effective than small
velocity
speed at which water is moving down a channel
channel shape
measured by hydraulic radius:
(cross sectional area)/ (wetted perimeter)
erosion
corrasion/abrasion (interchangeable) - wearing away of the bed and bank by the load carried by the river.
erosion elements:
attrition
hydraulic action
solution
attrition
wearing away of load carried by river - created smaller rounder particles
hydraulic action
force of air and water on sides of river and cracks- formation of air bubbles that damage the rock on the banks breaking it apart
solution
removal of chemical ions (calcium)- mostly occurs when fast flowing water passes over soluble rocks (limestone)
factors impaction erosion
-load
-velocity
-gradient
-pH
-human impact (deforestation, dams, bridges)
transport
load in river transported down stream
transport elements
-suspension (smallest particles- silts and clays)
-saltation (larger particles hopping across bed)
-solution (material carried dissolved in the water)
deposition
deposition of sediment on river banks
causes for deposition
-shallowing gradient decreasing velocity and energy
-decrease in volume of water
-increase in friction between water and channel
river landforms
waterfalls
floodplains
meanders
levees
deltas
waterfall formation
-horizontally bedded rock
-soft rock undercut by hydraulic action+abrasion
-weight of water and lack of support cause waterfall to collapse and retreat
flood plains
-main features of deposition
-areas of low relief formed by flooding of plains by the banks
-soil generally a mixture of sand gravel, transported by the river.
uses of flood plains
due to the fertility of sediment making up the ground of flood plains, and proximity to river (water) - often used for agriculture
meanders
meanders occur to allow store to spread energy over entire length of the channel.
- created by riffles and pools that change water velocity and direction costing a change in deposition patters which result in bends in the river (meanders)
levees
-raised banks of rivers
-involve deposition of sediment on the banks of a channel due to flooding
deltas
- arcuate delta (curved shoreline)
-bird’s foot delta (looks like a birds foot)
