CHAPTER 9 Running Water
236
Key Terms
abrasion (p. 223)
alluvial fans (p. 231)
alluvial channels (p. 225)
alluvium (p. 224)
back swamps (p. 231)
bars (p. 230)
base level (p. 227)
bed load (p. 223)
bedrock channels (p. 225)
braided (p. 226)
capacity (p. 224)
competence (p. 224)
cut bank (p. 226)
cutoff (p. 226)
deltas (p. 230)
dendritic drainage pattern (p. 232)
discharge (p. 221)
dissolved load (p. 223)
distributaries (p. 230)
divide (p. 218)
drainage basin (p. 218)
evapotranspiration
(p. 216)
floods (p. 233)
floodplain (p. 228)
graded stream (p. 227)
gradient (p. 220)
head (headwaters) (p. 221)
hydrologic cycle (p. 216)
incised meanders (p. 229)
infiltration (p. 216)
laminar flow (p. 219)
local (temporary) base level
(p. 227)
longitudinal profile (p. 221)
meanders (p. 225)
mouth (p. 221)
natural levees (p. 231)
oxbow lake (p. 226)
point bars (p. 226)
potholes (p. 223)
quarrying (p. 223)
radial drainage pattern (p. 232)
rectangular drainage pattern
(p. 232)
rills (p. 218)
river (p. 218)
runoff (p. 216)
saltation (p. 224)
settling velocity (p. 224)
sheet flow (p. 218)
sorting (p. 224)
stream (p. 218)
stream valley (p. 228)
suspended load (p. 223)
temporary (local) base level
(p. 227)
terraces (p. 230)
transpiration (p. 216)
trellis drainage pattern (p. 232)
turbulent flow (p. 219)
ultimate base level (p. 227)
wetted perimeter (p. 220)
yazoo tributaries (p. 231)
A river system consists of three zones based on the dominant
process operating in each zone. On the accompanying illustration,
match each process with one of the three zones:
a. sediment production (erosion)
b. sediment deposition
c. sediment transportation
1
G I V E I T S O M E T H O U G H T
A stream’ s ability to transport solid particles is described using
two criteria: capacity (the maximum load of solid particles a stream
can carry) and competence (the maximum particle size a stream can
transport). Competence increases as the square of stream velocity,
so if velocity doubles, water’ s force increases fourfold.
Streams deposit sediment when velocity slows and competence
is reduced. Stream deposits are called alluvium and may occur as
channel deposits called bars; as floodplain deposits, such as natural
levees; and as deltas or alluvial fans at the mouths of streams.
Stream channels are of two basic types: bedrock channels and
alluvial channels. Bedrock channels are most commonly found in
headwaters or regions where gradients are steep. Rapids and
waterfalls are common features. Two types of alluvial channels
are meandering channels and braided channels.
The two general types of base level (the lowest point to which
a stream may erode its channel) are (1) ultimate base level and
(2) temporary or local base level. Any change in base level will
cause a stream to adjust and establish a new balance. Lowering
base level will cause a stream to downcut, whereas raising base
level results in deposition of material.
Although many gradations exist, the two general types of stream
valleys are (1) narrow V-shaped valleys and (2) wide valleys with flat
floors. Because the dominant activity is downcutting toward base
level, narrow valleys often contain waterfalls and rapids.
When a stream has cut its channel closer to base level, its
energy is directed from side to side, and erosion produces a flat
valley floor, or floodplain. Streams that flow upon floodplains
often move in sweeping bends called meanders. Widespread
meandering may result in shorter channel segments, called
cutoffs, and abandoned bends, called oxbow lakes.
Common drainage patterns (the form of a network of streams)
produced by a main channel and its tributaries include (1) dendritic, (2) radial, (3) rectangular, and (4) trellis.
Floods are triggered by heavy rains and/or rapid snowmelt.
Sometimes human interference can worsen or even cause floods.
Flood-control measures include the building of artificial levees
and dams, as well as channelization, which can involve creating
artificial cutoffs. Many scientists and engineers advocate a nonstructural approach to flood control that involves more appropriate land use.
236
Key Terms
abrasion (p. 223)
alluvial fans (p. 231)
alluvial channels (p. 225)
alluvium (p. 224)
back swamps (p. 231)
bars (p. 230)
base level (p. 227)
bed load (p. 223)
bedrock channels (p. 225)
braided (p. 226)
capacity (p. 224)
competence (p. 224)
cut bank (p. 226)
cutoff (p. 226)
deltas (p. 230)
dendritic drainage pattern (p. 232)
discharge (p. 221)
dissolved load (p. 223)
distributaries (p. 230)
divide (p. 218)
drainage basin (p. 218)
evapotranspiration
(p. 216)
floods (p. 233)
floodplain (p. 228)
graded stream (p. 227)
gradient (p. 220)
head (headwaters) (p. 221)
hydrologic cycle (p. 216)
incised meanders (p. 229)
infiltration (p. 216)
laminar flow (p. 219)
local (temporary) base level
(p. 227)
longitudinal profile (p. 221)
meanders (p. 225)
mouth (p. 221)
natural levees (p. 231)
oxbow lake (p. 226)
point bars (p. 226)
potholes (p. 223)
quarrying (p. 223)
radial drainage pattern (p. 232)
rectangular drainage pattern
(p. 232)
rills (p. 218)
river (p. 218)
runoff (p. 216)
saltation (p. 224)
settling velocity (p. 224)
sheet flow (p. 218)
sorting (p. 224)
stream (p. 218)
stream valley (p. 228)
suspended load (p. 223)
temporary (local) base level
(p. 227)
terraces (p. 230)
transpiration (p. 216)
trellis drainage pattern (p. 232)
turbulent flow (p. 219)
ultimate base level (p. 227)
wetted perimeter (p. 220)
yazoo tributaries (p. 231)
A river system consists of three zones based on the dominant
process operating in each zone. On the accompanying illustration,
match each process with one of the three zones:
a. sediment production (erosion)
b. sediment deposition
c. sediment transportation
1
G I V E I T S O M E T H O U G H T
A stream’ s ability to transport solid particles is described using
two criteria: capacity (the maximum load of solid particles a stream
can carry) and competence (the maximum particle size a stream can
transport). Competence increases as the square of stream velocity,
so if velocity doubles, water’ s force increases fourfold.
Streams deposit sediment when velocity slows and competence
is reduced. Stream deposits are called alluvium and may occur as
channel deposits called bars; as floodplain deposits, such as natural
levees; and as deltas or alluvial fans at the mouths of streams.
Stream channels are of two basic types: bedrock channels and
alluvial channels. Bedrock channels are most commonly found in
headwaters or regions where gradients are steep. Rapids and
waterfalls are common features. Two types of alluvial channels
are meandering channels and braided channels.
The two general types of base level (the lowest point to which
a stream may erode its channel) are (1) ultimate base level and
(2) temporary or local base level. Any change in base level will
cause a stream to adjust and establish a new balance. Lowering
base level will cause a stream to downcut, whereas raising base
level results in deposition of material.
Although many gradations exist, the two general types of stream
valleys are (1) narrow V-shaped valleys and (2) wide valleys with flat
floors. Because the dominant activity is downcutting toward base
level, narrow valleys often contain waterfalls and rapids.
When a stream has cut its channel closer to base level, its
energy is directed from side to side, and erosion produces a flat
valley floor, or floodplain. Streams that flow upon floodplains
often move in sweeping bends called meanders. Widespread
meandering may result in shorter channel segments, called
cutoffs, and abandoned bends, called oxbow lakes.
Common drainage patterns (the form of a network of streams)
produced by a main channel and its tributaries include (1) dendritic, (2) radial, (3) rectangular, and (4) trellis.
Floods are triggered by heavy rains and/or rapid snowmelt.
Sometimes human interference can worsen or even cause floods.
Flood-control measures include the building of artificial levees
and dams, as well as channelization, which can involve creating
artificial cutoffs. Many scientists and engineers advocate a nonstructural approach to flood control that involves more appropriate land use.