Page 511 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 15 River Systems 475
Yazoo stream
Undercut bank
Point bar
Riparian marsh (backswamp)
Meander scar
Oxbow lake
Meander scars
Animation
Oxbow Lake Formation
Animation
Stream Processes, Floodplains
Bluffs
Floodplain
Cutoff
Alluvial deposits
(a) Typical floodplain landscape and related landscape features.
Natural levees
▲Figure 15.23 Floodplain landforms. [(b) USDA nRCS.]
(b) Riparian marshes, or backswamps, are floodplain wetlands that store floodwaters and provide habitat for wildlife. Many such wetlands were filled during the 20th century; restoration is now a priority since wetland water storage feeds streamflow during drought conditions.
(a) Map of the 1944 channel (white) with former channels for 1765 (blue), 1820 (red), and 1880 (green).
lower plain covered by an intricate maze of distributaries formed in an arcuate (arc-shaped) pattern (Figure 15.28). Owing to the high sediment load of these rivers, deltaic islands are numerous.
The Nile River delta is another arcuate delta (Figure 15.29 and GeoReport 15.1), as is the Danube River delta in Romania, where the river enters the Black Sea, and the Indus River delta in Pakistan. The Tiber River in Italy has an estuarine delta, one that is in the process of filling an estuary, the body of water at a river’s mouth where freshwater flow encounters seawater.
Numerous rivers throughout the world lack a true delta. In fact, Earth’s highest-discharge river, the Amazon, carries sediment far into the deep Atlantic offshore but lacks a delta. Its mouth, 160 km wide, has formed a subaqueous deposit on a sloping continental shelf. As a
(b) Image of the same portion of the river channel in 1999.
1765
▲Figure 15.24 Historical shifting of Mississippi River. The map and image show the portion of the river north of the Old River Control Structure (see Figure 15.31c). [(a) Army Corps of Engineers, Geological Investigation of the Alluvial Valley of the Lower Mississippi, 1944. (b) Landsat image, nASA.]
Mississippi River
Bar and swale topography
Oxbow lake
Prehistoric channel
2km
N
1880 1820