Chapter 16- Groundwater

• What is groundwater?• -water that is beneath

Earth’s surface.• It is our fresh water

source.

• What is an aquifer?• A body of rock or

sediment that stores groundwater.

• For water to flow the pores or fractures of the aquifer must be connected.

What would that look like?

What is porosity?

• The % of the total volume of a rock or the sediment that consists of open spaces.

Sorting means that the size of the rock particles are about the same.

• So what? Well sorted will allow better porosity.

• Loosely packed particles allow for better porosity than tightly packed particles.

What else might affect porosity?

• The shape of the grain particles.

• The more irregular will be more porous.

Permeability is the ease with which water passes through the porous material.

• The open spaces must be connected.

Two zones of aquifers:

• Zone of saturation means that the pore space is completely filled with water.

The water table is the upper area above the zone of saturation

• The zone of aeration lies between the water table and the Earth’s surface.

The zone of aeration contains “3” regions:

• Uppermost holds soil moisture-forms a film around grains of topsoil

• Next is a dry area unless it has been raining

• Lowest area is the capillary fringe. Water from the zone of saturation is drawn up by capillary action—remember how water molecules will adhere to each other and then pull up the next water molecule?

Zones of aeration

Groundwater flows downward due to gravity and the gradient.

• The water table depends on:• Surface topography• Permeability of the aquifer• Amount of rainfall• Rate at which humans are using the water.

• Drought causes the water table to fall and rainfall causes it to rise.

What is a perched water table?

• A rock layer that is impermeable and lies above the main water table-most areas only have one water table. This

prevents the water from reaching the main water table.

What about the topography?

• The water table will mirror what lies below:

Conserving groundwater

• Collects and moves slowly.

• Recharge zones are where the water enters the aquifer and is generally precipitation.

• Pollution can enter the aquifer in the same way that precipitation does.

• Discharge zones are where the water reaches the surface.

Wells and springs

• A well is a hole that is dug to below the level of the water table and then the water is brought to the surface.

Springs are naturally flowing groundwater to the surface

When water is pumped from a well it forms:

• A cone of depression. If too much water is pumped it may drop to the bottom of the well and the well will go dry.

Ordinary springs are found in rugged terrain where ---

• The ground surface drops below the water table. Hence, they may not flow continuously.

• During a drought these types of springs may go completely dry.

Artesian wells and springs

• Generally a sloping layer of permeable rock that is sandwiched between two layers of impermeable rock.

Artesian wells generally will flow without being pumped.

• Why? Because the water enters at a recharge zone and flows downhill which causes pressure to enable the water to freely flow.

• These are often the source of many springs.

Hot springs

• Just what it says—heated by a rock that has been heated by magma. Must be at least 37 degrees C. This water deposits minerals called travertine.

Geysers

• Hot springs that erupt periodically due to the buildup of steam inside that blows out and when the water is gone—it begins the process over again.

Now for the underground and chemical weathering

• Introduced with a cave video------