WATER MOVING UNDERGROUND

Fresh Water

• More than 97% of the Earth’s water is salt water

• Less than 3% is fresh water, and of this, more than 2/3 is frozen in icecaps and glaciers

• So only about 0.5% is usable fresh water

The Water Cycle

• The hydrosphere is all the water on the earth’s surface

• Movement of water in the hydrosphere is described in the hydrologic or water cycle

• Evaporation + transpiration = evapotranspiration

Water Budget

Water budget is the gain and loss of water from a region

• Gain would be from rain or snow

• Loss would be from use, run-off and evapotranspiration

• Evapotranspiration is affected by air temperature (high when air is warm/hot, low when cool)

Water Budget

• When it rains and water is not used by plants, it is stored between grains of soil, called soil water recharge

• if soil becomes saturated, there can be a water surplus (rainfall is greater than need for moisture & soil water storage is full)

• If need for moisture is greater than rainfall, the plants draw water from soil water supply, called soil water usage.

• Water deficit occurs when need is greater than rainfall and soil water storage is gone

Porosity and Permeability

• Porosity is the amount of water a rock can hold (as a percentage of its volume)

• Permeability is the rate at which water can pass through the pore spaces of a rock

• Large grain size means larger spaces, therefore more permeable.

• A material that does not allow water to pass through it is impermeable.

The Water Table

• When rain falls it enters the pores in the soil and sticks to them

• If the rain keeps falling and upper layers cannot absorb it, the water moves downward until it reaches an impermeable surface

• It begins to fill the pore spaces above, and the water level rises higher.

The Water Table

• The zone of saturation is the part of the ground where all pore spaces are filled

• The surface of the zone of saturation is the WATER TABLE

• The zone of aeration is the area from the water table to the surface, because air can enter here and water can still fill it.

• The capillary fringe is right above the water table where water can rise due to capillary action

Springs and Wells

• Groundwater is reached by digging wells.• Ordinary wells contain water from the

bottom up to the level of the water table.• A well must reach below the lowest level

to which the table will fall during dry weather, or it will not supply water all year.

• A spring occurs where the water table reaches the surface and groundwater flows out, usually in mountainous regions.

ARTESIAN FORMATIONS

• Aquifers are permeable materials that contain and carry groundwater

• A sandwich of permeable ground inbetween impermeable rock is called an artesian formation

• Rain that enters the aquifer is trapped by impermeable cap rock and the rock bed below. It moves downward into the aquifer due to gravity.

• Artesian wells are wells in which the water comes from an artesian formation!