Running Water and Groundwater

Earth as a system: the hydrologic cycle

Illustrates the circulation of Earth's water supply

Processes involved in the cycle• Precipitation• Evaporation• Infiltration• Runoff• Transpiration

The hydrologic cycle

Sources of Earth’s water

Running water

Streamflow • Factors that determine velocity

• Gradient, or slope • Channel characteristics

• Shape• Size• Roughness

• Discharge – volume of water flowing in the stream (generally expresses as cubic feet per second)

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

Running water

Upstream-downstream changes • Profile

• Factors that increase downstream • Channel size

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

Longitudinal profile of a stream

Running water

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

• Ultimate – sea level• Temporary, or local

• Changing causes readjustment of the stream – deposition or erosion

Adjustment of base level to changing conditions

A waterfall is an example of a local base level

Running water

The work of streams • Erosion• Transportation

• Transported material is called the stream's load• Dissolved load • Suspended load• Bed load

Running water

The work of streams • Transportation

• Load is related to a stream's • Competence - maximum particle size• Capacity - maximum load

• Capacity is related to discharge

Running water

The work of streams • Transportation

• Deposition• Caused by a decrease in velocity• Competence is reduced • Sediment begins to drop out

• Stream sediments • Known as alluvium• Well-sorted deposits

Running water

The work of streams • Transportation

• Features produced by deposition • Deltas – exist in ocean or lakes• Natural levees - Form parallel to the stream

channel • Area behind the levees may contain back

swamps or yazoo tributaries

Structure of a simple delta

Running water

Stream valleys • Valley sides are shaped by

• Weathering • Overland flow• Mass Wasting

• Characteristics of narrow valleys • V-shaped• Downcutting toward base level

Running water

Stream valleys • Characteristics of narrow valleys

• Features often include • Rapids• Waterfalls

• Characteristics of wide valleys • Stream is near base level

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

A narrow V-shaped valley

Continued erosion and deposition widens the valley

The resulting wide stream valley is characterized by meandering on a

well-developed floodplain

Erosion and deposition along a meandering stream

A meander loop on the Colorado River

Formation of a cutoff and oxbow lake

Running water

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

• Weather• Human interference with the stream system

Running water

Floods and flood control • Engineering efforts

• Artificial levees• Flood-control dams• Channelization

• Nonstructural approach through sound floodplain management

Satellite view of the Missouri River flowing into the Mississippi River

near St. Louis

Same satellite view during flooding in 1993

Running water

Drainage basins and patterns • A divide separates drainage basin• Types of drainage patterns

• Dendritic• Radial• Rectangular• Trellis

The drainage basin of the Mississippi River

Drainage patterns

Water beneath the surface (groundwater)

Largest freshwater reservoir for humans Geological roles

• As an erosional agent, dissolving by groundwater produces

• Sinkholes• Caverns

• An equalizer of stream flow

Water beneath the surface (groundwater)

Distribution and movement of groundwater • Distribution of groundwater

• Belt of soil moisture • Zone of aeration

• Unsaturated zone • Pore spaces in the material are filled mainly

with air

Water beneath the surface (groundwater)

Distribution and movement of 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 subsurface water

Water beneath the surface (groundwater)

Distribution and movement of groundwater • Distribution of groundwater

• Porosity • Percentage of pore spaces • Determines how much groundwater can be

stored • Permeability

• Ability to transmit water through connected pore spaces

• Aquitard – an impermeable layer of material • Aquifer – a permeable layer of material

Water beneath the surface (groundwater)

Features associated with groundwater• Springs

• Hot springs • Water is 6-9ºC 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

Water beneath the surface (groundwater)

Geologic work of groundwater • Groundwater is often mildly acidic

• Contains weak carbonic acid • Dissolves calcite in limestone

• Caverns • Formed by dissolving rock beneath Earth's

surface • Formed in the zone of saturation

Water beneath the surface (groundwater)

Geologic work of groundwater • Caverns

• Features found within caverns • Form in the zone of aeration • Composed of dripstone

• Calcite deposited as dripping water evaporates

• Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)

Dripstone formations in Carlsbad Caverns National

Park

Water beneath the 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

Development of karst topography

Infrared image of karst topography in central Florida