chapter 6- water resources

hydrologic cycle

an open system

residence time

how long water resides in a location

atmosphere (hydrologic cycle)

short residence time

• Evaporation: net movement of free water

• Transpiration:water moving from surface or transpired through stomata

• Evapotranspiration: accounts for 14% of atmosphere

surface (hydrologic cycle)

water interacts with surface many ways

• Intercepted: plants, ground cover, not touching ground

• Infiltrate: reaches ground, moves through soil

• Runoff: land cannot absorb water and flows away into a basin or channel

subsurface (hydrologic cycle)

after infiltration

• After a very long time, groundwater

• High residence time

• Base flow: GW discharging into stream

  • Flow to ocean

water budget

used to determine portions of water in different parts of the cycle

surplus

too much water initiates flooding from runoff

deficit

not enough water causing drought

largest freshwater lake by volume in the world

lake Baikal

Aral Sea disaster

the lake has been greatly reduced in size because of irrigation withdrawals from the rivers that feed it

groundwater mining/ mining an aquifer

to pull out more water than is recharged

• No recharging is effective

confined aquifer

an aquifer that is bounded on the top and bottom by confining beds

artesian well

water under pressure reachers potentiometric surface

unconfined aquifer

permeable layer above with impermeable underneath

aquitard

rock or sediments with low permeability

permeable

allows water to flow through it

high porosity

transmissible

• large pore spaces- sit, sand, gravel

cone of depression

pumping of well faster than the water can replenish

drawdown

lowering the water table due to stress on the ground water system due to pumping

springs

ground water overflows onto the surface

• Hillside, valley, quarry hits ground water

evapotranspiration- in relation to water budget

moisture demand (withdrawal)

precipitation- in relation to water budget

addition to budget (deposit)

impact of groundwater mining

land subsidence

land subsidence

pore spaces collapse when water is removed

• Cannot reinflate with water

• Land compacts and sinks

Ogallala and High Plains

Aquifer aquifer that supplies the great plain states of the U.S.