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!