Section 6- Fluvial Systems

Question 1

Fluvial

Answer 1

processes associated with streams and rivers

Question 2

Drainage Basin (or watershed)

Answer 2

the movement of fluid from higher elevation to lower elevation through a converging network of rivers

Question 3

Gradient

Answer 3

elevation over distance

Question 4

Discharge

Answer 4

amount of water flowing in a stream at a particular location at an instant in time
Area X Velocity

Question 5

flooding

Answer 5

floods occur when discharge of the stream becomes too high to be accomodated by normal stream channels
when discharge becomes too high, stream widens its channel by overtopping its banks and flooding the low-lying surrouding areas

Question 6

Sediment Erosion

Answer 6

sediminets are eroded due to dissolution (soluble minerals are dissolved by water), entrainment (sediment particles are lifted and carried away), and abrasion (sediment scrapes against riverbed and wear it down)

Question 7

Sediment Transport

Answer 7

load = mount of sediment a river transports
transported in 3 ways:
1.rolling, sliding or saltation(jumping) of bed-load particles (larger paricles)
2.suspended load (small particle)
3.dissolved load transport (solutes)

Question 8

sediment deposition

Answer 8

sediment is deposited when energy level decreases
-high velocity =erode
-smaller particles+low velocity=transport
-larger particle+low velocity=deposited
-for medium particles, very short amount of transport before erosion
-

Question 9

what is channel form determined by

Answer 9

1.channel gradient
2.type of material channel is cutting through(incising)
3.type and amount of sediment being transported

Question 10

Braided streams

Answer 10

-streams that flow in broad, shallow channels and consist of multiple subchannels separated by islands or bars
-shallow, high velocities close to stream bed, so coarse sediments are deposited as bars, locally dividing channels into more channels
-develop if stream is unable to transport all bed load continuously
-very dynamic, discharge varies
-commonly form where elevation loss is high->high sediment supply
-

Question 11

Meandering Streams

Answer 11

sinusous (many curves and twists)
tend to be narrow and deep
-degree of meandering given by sinuosity=ration of channel length to valley length
-common where elevation change and sediment suppply is low
-primary transport is suspended load
-erosion in lateral direction

erosion happens on outside of curves, can form oxbow lakes

Question 12

Deltas

Answer 12

formed when streams enter a body of water
sediment deposition occurs because the stream current slows, dissipates and loses energy

Question 13

alluvial fan

Answer 13

formed when streams enter a flat valley floor, causing loss of energy and sediment deposit

Question 14

Graded Streams

Answer 14

fluvial systems that have established an equilibrium with a profile that is smooth and concave up
sediment size being deposited decreases uniformly downstream(large sediment at top, fine sediment at bottom)
system maintain equilibrium unless something upsets it, like tectonic activity or man-made disruption

Question 15

Base level

Answer 15

lowest point to which it can flow
“mouth of the river”
for large rivers, usually sea level, but can also be larger river or lake
all rivers and streams erode toward sea level, known as “ultimate base level”

Question 16

four occasions for river engineering

Answer 16

1.flood protection
-dikes/levees
2.ease of transportation
-bridges; need strong foundation
3.hydroelectric power production
4.water storage
-dams (disrupt equilibrium, sediment deposited at base of dam)