FLUVIAL LANDFORMS

A. INTRODUCTION

Rivers: agents of change

Available Energy

flow velocity

flow depth

gradient (slope)

Work

degradation (vertical erosion) and lateral erosion

aggradation (vertical deposition) and lateral deposition

Base Level: lowest elevation a stream can attain through erosion

vertical erosion is most prominent in rivers high above base level

lateral erosion is most prominent in rivers close to base level

B. STREAM CHANNELS

Straight Channels

Braided Channels

Meandering Channels

Image credit: R. Simmon (1999) NASA Earth
Observatory. Mississippi River Meanders. http://earthobservatory.nasa.gov/Newsroom/
NewImages/images.php3?img_id=17383

C. MEANDERING RIVERS

Meander Details

photo credit: Louis J. Maher, Jr. photo 156-18. Turkey River, Clayton County, IA.

Oxbow Lakes and meander scars

photo credit: Louis J. Maher, Jr. photo 156-07. Pecatonica River near Mineral Point, WI.

D. FLOODS & FLOODPLAINS

Flood Frequency & Magnitude

photo credit: Andrea Booher/FEMA, photo 3438

Floodplains

land area inundated (covered by water) when rivers overflow their banks

relatively flat area of land adjacent to river channels

Floodplain Landforms

point bar deposits

bar and swale topography

incipient oxbow lakes

channel cutoffs

oxbow lakes

meander scars

natural levees

yazoo streams

terraces

photo copyright: Michael Collier, Image courtesy Earth Science World Image Bank, image imuzx5, http://www.earthscienceworld.org/images

E. SUMMARY

Rivers expend their energy eroding and depositing material on the landscape

Combination of erosion & deposition results in:

different channel forms (straight, braided, meandering)

various landforms within and along the channel (e.g. pools, riffles, point bars)

creation of V-shaped valleys high above base level due to vertical erosion

creation of floodplains at elevations closer to baselevel in response to lateral erosion & deposition

Floods are a natural part of all river flow regimes