Earth as a System: The Hydrologic Cycle

© 2015 Pearson Education, Inc.

Running Water and Groundwater

Chapter 5 Lecture

Jennifer ManganJames Madison University

Earth ScienceFourteenth Edition


Earth as a System: The Hydrologic Cycle

• Illustrates the circulation of Earth’s water supply• Most water is in the oceans


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

Earth as a System: The Hydrologic Cycle


The Hydrologic Cycle


Running Water

• Drainage basin– Land area that

contributes water to a river system

• Divide– Separates drainage

basins


Mississippi River Drainage Basin


River Systems

• Three zones– Sediment production– Sediment transport– Sediment deposition


• Networks of streams form distinctive patterns• Drainage pattern varies by terrain• Four common drainage patterns

– Dendritic– Rectangular– Radial– Trellis

Drainage Patterns


Drainage Patterns


• 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


Channel Changes from Head to Mouth


• Upstream-downstream changes – Profile

• Factors that increase downstream – Channel size

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

Running Water


Longitudinal Profile of a Stream


Work of Running Water

• Erosion• Transportation

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


Potholes Due to Erosion


• Transportation– Load is related to a stream’s

• Competence – maximum particle size• Capacity – maximum load

– Capacity is related to discharge



• Transportation– Deposition

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

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



• 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



• Bedrock channels – cut into strata• Alluvial channels – loosely consolidated sediment

Stream Channels


• Meandering streams – move in sweeping bends• Braided streams – complex network of channels

Stream Channels


Braided Stream


• 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

Shaping Stream Valleys


Base Levels


• Valley sides are shaped by – Weathering – Overland flow– Mass wasting

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



• 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



V-shaped Valley of the Yellowstone River


Erosional Floodplain Development


• Characteristics of wide valleys – Floodplain – Features often include

• Meanders• Cutoffs• Oxbow lakes



Meander Loop on the Colorado River


• Floods are the most common geologic hazard • Causes of floods

– Weather– Human interference with the stream system

Floods and Flood Control


• Engineering efforts – Artificial levees– Flood-control dams– Channelization

• Nonstructural approach through sound floodplain management

Floods and Flood Control


Mississippi River Flood of 1993


• Largest freshwater reservoir for humans • Geological roles

– As an erosional agent, dissolving by groundwater produces

• Sinkholes• Caverns

– An equalizer of stream flow

Groundwater: Water Beneath the Surface


• 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

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

Groundwater


Groundwater Features



• Porosity – Percentage of pore spaces – Determines storage of groundwater

• Permeability– Ability to transmit water through connected pore spaces – Aquitard – an impermeable layer of material – Aquifer – a permeable layer of material

Groundwater


• Features associated with groundwater– Springs

• Hot springs – Water is 6–9° C (10–15° F) 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

Groundwater


Old Faithful Geyser in Yellowstone National Park


• Features associated with 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

Groundwater


Cone of Depression Formation


Artesian Systems


• Environmental problems associated with groundwater – Treating it as a nonrenewable resource – Land subsidence caused by its withdrawal – Contamination

Groundwater


Subsidence


• 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

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)

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

Groundwater


Development of Karst Landscape

Documents

Earth as a System: The Hydrologic Cycle