Make your own free website on Tripod.com

Chapter Four:  Running Water and Groundwater

Chapter Objective:

Chapter Outline

Hydrologic cycle

Illustrates the circulation of Earth's water supply

Processes involved in the cycle

Precipitation

Evaporation

Infiltration

Runoff

Transpiration

Cycle is balanced

 


Running water

Streamflow

Factors that determine velocity

Gradient, or slope

Channel characteristics

Shape

Size

Roughness

Discharge

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

 

Factors that decrease downstream

Gradient, or slope

Channel roughness

 

Base level

Lowest point a stream can erode to

Two general types

Ultimate

Temporary, or local

Changing causes readjustment of the stream

 

Work
of
streams

Erosion

Transportation

Transported material is called the stream's load

Types of load

Dissolved load

Suspended load

Bed load

Load is related to a stream's

Competence

Maximum particle size

Determined by velocity

Capacity

Maximum load

Related to discharge

 

Deposition

Caused by a decrease in velocity

Competence is reduced

Sediment begins to drop out

 

Stream sediments

Called alluvium

Well-sorted deposits

 

Features produced by deposition

Deltas

Exists in oceans or lakes

Disturbances often form in channel

Natural levees

Form parallel to the stream channel

Area behind the levees may contain

Back swamps

Yazoo tributaries

 

Stream valleys

Valley sides are shaped by

Weathering

Overland flow

Mass wasting

 

Characteristics of narrow valleys

V-shaped

Downcutting toward base level

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

Floodplain

Features often include

Meanders

Cutoffs

Oxbow lakes

 

Drainage basins and patterns

A divide separates drainage basins

Types of drainage patterns

Dendritic

Radial

Rectangular

Trellis

 

 

Stages of valley development

Youth

Rapids and waterfalls

V-shaped valleys

Vigorous downcutting

Steep gradient

 

Maturity

Downward erosion diminishes

Lateral erosion dominates

Floodplain beginning

Gradient lower than at youth

 


Old age

Large floodplain

Widespread shifting of the stream

Characteristic features

Natural levees

Backswamps

Yazoo tributaries

 

Rejuvenation

" Made young again "

Characteristic features

Entrenched meanders

Terraces

 

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 streamflow

 

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

Zone aeration

Area above the water table

Pore spaces in the material are filled mainly with air

Movement of groundwater

Porosity

Percentage of pore spaces

Determines how much groundwater can be stored

Permeability

Ability to transmit water through connected pore spaces

Aquiclude - an impermeable layer of material

Aquifer - a permeable layer of material

 

Water features

Springs

Hot springs

Water is 6-9 degrees 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

 

WELLS

Pumping can cause a drawdown (lowering)of the watertable

Pumping can form a cone of depression in the water table

Artesian wells

Water in the well rises higher than the initial groundwater level

Types of artesian wells

Non flowing

Flowing

 

 

Environmental problems associated with groundwater

Treating it as a nonrenewable resource

Land subsidence caused by its withdrawal

Contamination

 

Features produced by 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

Features found within caverns

Form in the zone of aeration

Composed of dripstone

Calcite deposited as dripping water evaporates

Common features

Stalactites hanging from the ceiling

Stalagmites developing on the cave floor

 

Karst topography

Formed by dissolving rock at, or near, Earth's surface

Common Features

Sinkholes

Surface depressions

Formed by

Dissolving bedrock

Cavern collapse

Cave and Caverns

Area lacks good surface drainage

Go Back To:  The Wizard's Homepage