Surface Processes

Hydrologic Cycle

Groundwater

Groundwater

=>Precipitation leads to => runoff + evaporation + infiltration

infiltration => groundwater

Importance of Groundwater

misconceptions => groundwater = underground rivers

1) Groundwater is the most important source of fresh water

2) It is an agent of erosion

3) Groundwater is an equalizer of stream flow

Characteristics of Groundwater

• How can water be stored in and flow through rock?

• Porosity and Permeability

• porosity = essential for water storage

• Permeability = a measure of the rate that groundwater can flow through rock or regolith

Groundwater Distribution

• zone of saturation = aquifer

• impermeable rocks and regolith which confine water to an aquifer = aquiclude

• Upper limit of zone of saturation = Water Table

Features of the water table

• follows surface topography - elevation = head

• water table at the surface = swamp

• generally higher than -> streams and lakes

• controls lake and stream levels

• predicts productivity of wells

Groundwater Movement

• zone of recharge => towards

• zone of discharge

• Mechanisms = gravity and pressure

Rates of Flow

• Hydraulic Gradient

• Hydraulic conductivity

• Darcy’s Law

» Slow compared to streams - 0.01 - 1.4 m/day

zones of discharge

• 1) springs; 2) wells

Springs => water table intersects the surface; aquiclude forces lateral movement of groundwater

EX: perched water table

Exploiting Groundwater

• Wells => groundwater moves from surrounding aquifer into the well bore

• Drawdown

• Cone of depression

Artesian Wells

• zone of recharge is at a relatively high elevation; the aquifer is confined between two aquicludes = pressurized

• water in well rises higher than the surrounding water table (without pumping)

Problems with Groundwater Use - Over utilization

=> water table lowered

EX: Great Plains Aquifer

Groundwater = nonrenewable resource => slow rates of

movement and recharge

Subsidence

• If aquifer is unconsolidated regolith

-when water is pumped out, pores close up

- ground sinks

Saltwater contamination - coastal areas

=> freshwater lens floating on saltwater in aquifer

=> overuse brings up salt water

groundwater pollution

=> sources

=> density

=> biodegradable vs. nonbiodegradable

=> plumes

remediation

• Solutions

– Extraction

– Bio remediation

Geologic Work of Groundwater

• => 1) caverns, 2) karst topography

• Requirements

– Limestone bedrock - humid environment

Caverns

Þ erosion = disolution

Þ groundwater flowing through fractures and joints = above water table

=> enlarges them = caverns

=> water table drops = deposition

=> speleothems /dripstones

speleothems /dripstones

=> stalactites & stalagmites

=> cave pearls, flows, etc.

Karst Topography

Cavern Collapse Features

=> extensive flat-lying -Limestone Bedrock

features => sinkholes, solution valleys, “lost streams”: