Water Catchment Issues (fact Sheets 1-2) Flashcards
Hydrology
Definition
The science of the distribution and movement of water.
Greatest natural hazard to people is…
flooding
Water controls the movement of…
nitrates, lake eutrophication
acid rain, river acidification
landfill leachates, pollution of ground water
movement of sediment to rivers, soil erosion
Water resource
Total amount of water available in the environment
Water supply
Quantity of water abstracted from the environment
Eutrophication
Nitrogen or phosphorus enrichment of rivers and lakes that results in algal blooms that deplete oxygen levels and hence affect fish and macro-invertebrate populations
Leachates
Mostly dissolved substances moving within subsurface (ie, below ground surface) water flow
Catchment
The area of land that delivers all of its directly received precipitation (minus evaporation) to a point on a river
Point on a river that measure catchment
gaging station
Watershed
Edge/boundary of catchment
Catchment water budget/ water balance
States that the water lost by the catchment (as riverflow or evapotranspiration), plus any change in subsurface water storage is equal to the incoming precipitation.
Catchment water budget equation
P = E + Q (±∆S)
What does P stand for in the catchment water-budget equation
and units
P= precipitation units = mm hr-1
What does E stand for in the catchment water-budget equation
and units
E= Evapotranspiration units = mm hr-1
What does Q stand for in the catchment water-budget equation
and units
Q= river discharge units= M3 S-1 (cumecs)
What does ∆S stand for in the catchment water-budget equation
∆S= change in subsurface water storage
Discharge per unit catchment area
Q/A (catchment area)
m3 S-1/m2,
=q ms-1
When can ∆S be omitted from the equation?
over the period of a year (or more) the ∆S averages to 0 so can be omitted from the equation
What normally defines river catchments?
surface topography,
the assumption that water entering the subsurface hydrological systems eventually emerges within the same river catchment
When the catchment can be wrong
3
- different rock-head topography of surface of impermeable to ground surface
- dipping impermeable strata
- karstic systems (caves)
Where catchments ‘leak’ water …
this exchange of subsurface waters is called ‘deep seepage’
When leakage of water is below the river outlet gauge…
gauge underflow
Typical size of experimental catchments
1-10km2 in area
Precipitation
Water reaching a catchment as rainfall, snow, hail, dew or occult (i.e. mist/fog) forms
Headwaters
Tributary streams close to the source (i.e. head) of a large river
Hydrological cycle
The concept that evaporation gives water for precipitation, which becomes subsurface water, then river-water, then sea-water and evaporation once more.
Evapotranspiration
The water lost to the atmosphere by open-water evaporation, water intercepted by the vegetation and directly re-evaporated, plus biological transpiration from plants.
Subsurface water
All water below the ground surface, including ‘soil water’ (i.e. the subsurface systems close to the ground surface or water in the unsaturated zone) and groundwater (water below a regional water-table)
