Chapter 17 Groundwater

Water Table

• Top of the saturated zone (the top surface of where all the pore spaces are fully filled with water)

• Moves seasonally with rain/drought

• affects stream flow

Stream Flow

• Gaining stream- fed by groundwater

• Losing stream- leaks into groundwater

Porosity

How much empty space a material has to store the water ( poorly sorted sediments have a low porosity)

Permeability

How easily water flows through rock or spaces

Soil Moisture

Surface layer: Water clings to soil particles

Saturation

all pores filled, this is the actual groundwater

Unsaturated(Vadose)

Mix of air and water above saturation

Aquifers

a sediment layer that is permeable (ex sand/gravel)

Aquitards

Barrier that is not permeable (ex clay)

Darcys Law

Measures groundwater flow

• Hydraulic Gradient (slope)

• Conductivity (material ability)

• Area

• Soil Moisture

• Saturation

• Unsaturated(Vadose)

Three Zones beneath Earth’s Surface (groundwater)

Artesian System

when groundwater is under pressure and rises on its own sometimes above ground level without pumping

Required Conditions for an Artesian System

• must be confined between two aquitards

• The aquifer mys

Two types of Artesian Wells

• Flowing- pressure surface is above ground, water flows out naturally

• Non Flowing- pressure surface is below ground, water rise but not all the way out

Cone of Depression

a dip in the water table that form when groundwater is pumped too quickly from a well

Environmental problems of groundwater

• Overuse

• Land Subsidence

• Saltwater Intrusion

• Contamination

What is groundwater used primarly for

irrigation

25% of drinking water comes from groundwater

Capillary Fringe

extends upward from the water table

groundwater is held in pore spaces by surface tension

Gaining Stream(water table)

water table is higher than the stream surface

Losing Streams

Water table is lower than the stream surface

Movement of Groundwater

Moves very slowly, 4cm per day

Preassure and Gravity move groundwater

Well

a hole bore into the zone of saturation

Drawdown

as water is withdrawn from the well, the surrounding water table is lowered

Perched Water Table

forms where an aquitard is situated above the main water table

Artesian Springs

Groundwater may reach the surface through fractures in the rock, creating a natural spring.

Spring

natural outflow of water from the intersection of the water table

Hot spring

a spring that produces water at notably higher temperatures than the surrounding environment.

Geysers

are intermittent hot springs in which columns of water erupt with force

Geyser Deposits

chemical sedimentary rock accumulates at the surface

due to mineral precipitation from water eruptions.

Groundwater Dissolves Rock

it is mildly acidic

Caverns

created by acidic groundwater dissolving soluble rock

Speleothem

general name for all dripstone features

Dripstone features

• stalactites (ceiling)

• stalagmites (floor)

Karst Topography

Landscape that has been shaped mainly be the dissolving power of groundwater