Earth Science, 13eTarbuck & Lutgens

Running Water and GroundwaterEarth Science, 13eChapter 5

Stanley C. Hatfield Southwestern Illinois College

Li River, China’s Guilin District Note karst topography, in which groundwater has dissolved large volumes of limestone (more later).

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

Running water •Drainage basin

▫Land area that contributes water to a river system

▫A divide separates drainage basins

Drainage basins and divides

Drainage basins and divides exist for all streams, regardless of size.

River systems are divided into 3 zones.

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)

Gradient (slope)•Parts of lower Mississippi: 10 cm/km•Mountain streams: 40 m/km•Steeper gradient has more energy,

more velocity

Discharge•Measured in m3 or ft3 per second•Changes over time due to amount of

precipitation in drainage basin

Measuring stream velocity1 kph – 30 kph

Straight – highest at center

Curved– highest at outer bank

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

Stream Properties – Headwaters to Mouth

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

Formation of natural levees by repeated flooding

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

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

V-shaped valley of the Yellowstone River

Continued erosion and deposition widens the valley

Characteristics of a wide stream valley

Running water •Stream valleys

▫Characteristics of wide valleys Floodplain Features often include

Meanders Cutoffs Oxbow lakes

A meander loop on the Colorado River

Running water •Drainage patterns

▫Networks of streams that from distinctive patterns

▫Types of drainage patterns Dendritic Radial Rectangular Trellis

Drainage patterns

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

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 storage of groundwater

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 6–9° 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

Old Faithful geyser in Yellowstone National Park

Water beneath the surface (groundwater) •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

Formation of a cone of depression in the water table

Artesian systems

Water beneath the surface (groundwater) •Environmental problems associated with

groundwater ▫Treating it as a nonrenewable resource ▫Land subsidence caused by its withdrawal ▫Contamination

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)

Cave features 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

Features of karst topography

End of Chapter 5