Chapter 6Chapter 6

6.1 Running Water6.1 Running Water6.2 The Work of Streams6.2 The Work of Streams

6.3 Water Beneath the Surface6.3 Water Beneath the Surface

The Water Cycle The Water Cycle

Illustrates the circulation of Earth’s water supply Processes involved in the cycle

• Precipitation• Evaporation• Infiltration• Runoff• Transpiration

>Water cycle drawing worksheet

Sources of Earth’s waterSources of Earth’s water

Running water Running water

Streamflow • Factors that determine velocity

• Gradient, or slope • Channel characteristics

• Shape• Size• Roughness

• Discharge – volume of water flowing in the stream

Running water Running water

Upstream-downstream changes • Profile

• Cross-sectional view of a stream • From head (source) to mouth

• Profile is a smooth curve • Gradient decreases from the head to the mouth

• Factors that increase downstream • Velocity• Discharge• Channel size

Running water Running water

Upstream-downstream changes • Profile

• Factors that decrease downstream• Gradient, or slope • Channel roughness

Longitudinal profile Longitudinal profile of a streamof a stream

Running water Running water

Base level • Lowest point to which a stream can erode • Two general types

• Ultimate – sea level• Temporary, or local

Adjustment of base level Adjustment of base level to changing conditionsto changing conditions

The Work of StreamsThe Work of Streams

Stream channels are eroded through• Abrasion• Grinding• Dissolving soluble materials

• Sediment transport• Dissolved load • Suspended load• Bed load

The Work of StreamsThe Work of Streams

Transportation of sediment• Load is related to a stream’s

• Competence – maximum particle size a stream can transport

• Capacity – maximum load

• Capacity is related to discharge… The greater the volume of water in a stream, the greater its capacity for carrying sediment

The Work of StreamsThe Work of Streams

Deposition

• Caused by a decrease in velocity

• Competence is reduced

• Sediment begins to drop out • Stream sediments • Known as alluvium, or well-sorted deposits from a

stream

The Work of StreamsThe Work of Streams

Deposition• Features produced by deposition

• Deltas – exist in ocean or lakes• Natural levees – Form parallel to the stream

channel

Formation of natural levees Formation of natural levees by repeated floodingby repeated flooding

The Work of StreamsThe Work of Streams

Stream valleys • Characteristics of narrow valleys

• V-shaped• Downcutting toward base level• Features often include

• Rapids• Waterfalls

A narrow, V-shaped valleyA narrow, V-shaped valley

The Work of StreamsThe Work of Streams

Stream valleys • Characteristics of wide valleys

• Stream is near base level • Downward erosion is less dominant • Stream energy is directed from side to side

• Floodplains• Features often include

• Meanders• Cutoffs• Oxbow lakes

Continued erosion and Continued erosion and deposition widens the valleydeposition widens the valley

A wide stream valley is A wide stream valley is characterized by meandering on characterized by meandering on

a well-developed floodplaina well-developed floodplain

Formation Formation of a cutoff of a cutoff and oxbow and oxbow

lakelake

Erosion and deposition along Erosion and deposition along a meandering streama meandering stream

A meander loop on the A meander loop on the Colorado River Colorado River

The Work of StreamsThe Work of Streams

Floods and flood control • Floods are the most common geologic hazard • Causes of floods

• Weather• Rapid spring snow melt• Storms / heavy rains

• Human interference with the stream system• Dam or levee failure• Building / developing on wetlands

The Work of StreamsThe Work of Streams

Floods and flood control • Engineering efforts

• Artificial levees• Flood-control dams

• Minimizing development on floodplains, allowing floodplains to naturally absorb floodwaters

Satellite view of the Missouri Satellite view of the Missouri River flowing into the River flowing into the

Mississippi River near St. LouisMississippi River near St. Louis

Same satellite view during Same satellite view during flooding in 1993flooding in 1993

The Work of StreamsThe Work of Streams

Drainage basin• Land area that contributes water to a stream• A divide separates drainage basins

Drainage basins and Drainage basins and drainage dividesdrainage divides

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Largest freshwater reservoir for humans Geological roles

• As an erosional agent, dissolving by groundwater produces

• Sinkholes• Caverns

• Helps to maintain a steady streamflow

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Distribution and movement of groundwater • Distribution of groundwater

• Belt of soil moisture (close to the surface)• Zone of saturation

• Zone of Aeration (unsaturated zone)• Pore spaces in the material are filled mainly

with air

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Distribution of groundwater• Zone of saturation

• All pore spaces in the material are filled with water

• Water within the pores is groundwater• Water table – the upper limit of the zone of

saturation

Features associated with Features associated with subsurface watersubsurface water

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Distribution and movement of groundwater • Movement

• Porosity • Percentage of pore spaces • Ability to store water

• Permeability• Ability to transmit water through connected

pore spaces (water can flow through)• Aquitard – an impermeable layer of material • Aquifer – a permeable layer of material

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Springs • Hot springs

• Water is 6–9°C warmer than the mean air temperature of the locality

• Heated by cooling of igneous rock

• Geysers • Intermittent hot springs • Water turns to steam and erupts

Old Faithful geyser in Old Faithful geyser in Yellowstone National ParkYellowstone National Park

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Wells• Pumping can cause a drawdown (lowering)

of the water table• Pumping can form a cone of depression in

the water table• Artesian wells

• Water in the well rises higher than the initial groundwater level

Formation of a cone of Formation of a cone of depression in the water tabledepression in the water table

Artesian systemsArtesian systems

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Environmental probs with groundwater• Treating it as a nonrenewable resource

• Removing it faster that it can be replenished

• Land subsidence caused by its withdrawal • San Joaquin Valley, California

• Contamination• Septic, Farm waste, inadequate or broken

sewers

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Geologic work of groundwater • Groundwater is often mildly acidic

• Dissolves calcite in limestone

• Caverns • Formed by dissolving rock beneath Earth’s

surface • Formed in the zone of saturation

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Geologic work of groundwater • Caverns

• Features found within caverns • Form in the zone of aeration • Composed of dripstone / Travertine• Calcite deposited as dripping water evaporates • Common features include stalactites (hanging

from the ceiling) and stalagmites (growing upward from the floor)

Cave Features in Lehman Caves, Great Cave Features in Lehman Caves, Great Basin National Park, and Carlsbad Basin National Park, and Carlsbad

Caverns National ParkCaverns National Park

Water beneath the Water beneath the surface (groundwater) surface (groundwater)

Geologic work of groundwater • Karst topography

• Formed by dissolving rock at, or near, Earth’s surface

• Common features • Sinkholes – surface depressions• Sinkholes form by dissolving bedrock and

cavern collapse• Caves and caverns

• Area lacks good surface drainage (few streams if any, water is mostly funneled underground)

Features of karst Features of karst topographytopography