Earth Science, 13e

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

▫Earth’s most important erosional agent Downcut, widen

streams Transport sediment

which can erode banks, channel, bedrock

• MG: Sediment transport by streams

Running water•Transportation – transported material is

called the stream’s load▫Dissolved load

From groundwater, dispersed through flow Expressed in ppm Velocity of streamflow has no effect on

stream’s ability to carry dissolved load Precipitation only if water chemistry changes

Running water• Transportation – transported material is called

the stream’s load▫Suspended load

Biggest portion of river’s load Usually fine particles s/a silt, clay but could be sand or

gravel, especially during flood (which can also increase quantity)

Controlled by flow velocity and settling velocity (speed @ which particle falls through still fluid) Slow settling + high flow = longer suspension

▫Bed load

Running water•Suspended load,

Colorado River

Running water•Transportation – transported material is

called the stream’s load▫Bed load – solids are to large to be carried

in suspension, settle along stream bed Erosional action – move by rolling, sliding,

saltation (jumping or skipping) < 10% of total load

Running water •The work of streams

▫Transportation Load is related to a stream’s

Competence ▫maximum particle size ▫increases proportionately to square of velocity

(swift streams have greater competence Capacity

▫maximum load ▫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•Bedrock channels vs. alluvial channels

▫Bedrock – headwater, steep▫May contain rapids/waterfalls

Rapid section of river where river bed has a relatively

steep gradient  increase in water velocity and turbulence river becomes shallower and has

some rocks exposed above the flow surface

Running Water

Running Water•Bedrock channels

vs. alluvial channels▫Bedrock –

headwater, steep▫May contain

rapids/waterfalls Waterfall – place

where water flows over a vertical drop in the course of a stream or river

Running Water•Bedrock channels vs. alluvial channels

▫Alluvial – loosely consolidated sediment (alluvium) Meandering

mostly suspended load evolve over time as bends migrate floodplain most erosion @ outside of bend

Running WaterCut bank – zone of active erosion

Point bar – coarser material deposited

Running Water

Running Water•Braided Streams

▫Complex network of diverging channels

▫Coarse grains are transported as bed load

South-looking photograph showing diamond-shaped bars and meandering braided stream channels, East Fork Toklat River, Alaska Range, Denali National Park, Alaska.

South-looking photograph showing diamond-shaped bars and meandering braided stream channels, East Fork Toklat River, Alaska Range, Denali National Park, Alaska.

Rakaia River, South Island New Zealand

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

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 – see next slide

Land is uplifted – meandering river downcuts

Running water • Features produced by deposition

▫Deltas exist in ocean or lakes formed from the deposition of the sediment carried

by the river as the flow leaves the mouth of the river Human activities s/a diversion of water, dams can

radically alter delta ecosystems dams block sedimentation which can cause the delta to

erode away use of water upstream can greatly increase salinity

levels as less fresh water flows to meet the salty ocean water

Nile Delta and Colorado River Delta are some of the most extreme examples of the ecological devastation caused to deltas by damming and diversion of water.

Nile River delta

Running water •Features produced by deposition

▫Natural levees form parallel to the stream channel commonly form around lowland rivers and

creeks without human intervention▫Area behind levee is characteristically poorly

drained (water can not flow up the levee and into the river) Marshes called backswamps result. Yazoo tributaries

Since tributary stream can not enter river, it has to flow parallel to the river until it can breach the levee

Name comes from the Yazoo River, which runs parallel to the Mississippi River for 280 km (170 mi) before converging

Formation of natural levees by repeated flooding

Running water •Features produced by deposition

▫Alluvial Fan - fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads, typically at the exit of a canyon onto a flatter plain

▫As stream's gradient decreases, it drops coarse-grained material Reduces capacity of channel Forces it to change direction and gradually build

up a slightly mounded or shallow conical fan shape. 

Alluvial Fan – Lake Louise, Alberta

Running water •Floods and flood control

▫Floods are the most common geologic hazard

▫Causes of floods Floods are caused by many factors and can

be exacerbated by increased amounts of impervious surface or by other natural hazards such as wildfires, which reduce the supply of vegetation that can absorb rainfall.

Causes of floods•Heavy rainfall•Highly accelerated snowmelt•Severe winds over water•Unusual high tides•Tsunamis•Failure of dams, levees, retention ponds,

or other structures that retain water

Running water •Floods and flood control

▫Engineering efforts Artificial levees

Steeper slope than natural levee Sometimes made of concrete

Flood-control dams Store water, then let it out slowly Destroy farmland, etc. Trap sediment leading to erosion downstream

Running water •Floods and flood control

▫Engineering efforts Channelization – altering channel

Clearing obstructions, dredging Artificial cutoffs – increase gradient and velocity,

lower chance of flooding▫Nonstructural approach through sound

floodplain management Zoning regulations that minimize development

and promote more appropriate land use

Satellite view of the Missouri River flowing into the Mississippi River near St. Louis

Same satellite view during flooding in 1993

Inside Hurricane Katrina•Part 1•Part 2•Part 3•Part 4•Part 5

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