Ch 15; river systems

Question 1

Drainage basin and divide

internal drainage

drainage patterns

Answer 1

basin: An area that drains all precipitation received as a runoff or base flow into a river or body of water

divide: separates drainage basins and is located on high ground

They are open systems

Internal drainage does not reach the ocean, so the run off of precipitation just gets evaporated

Drainage patterns: The arrangement of channels in an area. Patterns are quite distinctive and are determined by a combination of regional steepness and relief; variations in rock resistance, climate, and hydrology; and structural controls imposed by the underlying rocks

Question 2

Gradient and its affects on deposition and erosion

Answer 2

The stream’s degree of inclination, or gradient. The drop in elevation from a stream’s headwaters to its mouth, ideally forming a concave slope

gradient affects a river’s its energy and ability to move material; in particular, it affects the velocity of the flow

Question 3

River discharge

Answer 3

the volume of water flowing through a river channel

discharge = channel width x channel depth x stream velocity

Question 4

Flash flood

Answer 4

Sudden rare or large precipitation event in a desert filling a stream channel

Question 5

Are drainage systems open or closed systems?

Answer 5

Drainage basins are open systems. Inputs include precipitation and the minerals and rocks of the regional geology. Energy and materials are redistributed as the stream constantly adjusts to its landscape

Question 6

Base level

Answer 6

The level below which a stream cannot erode its valley

Question 7

erosion:

Answer 7

The process by which water dislodges, dissolves, or removes weathered surface material

Question 8

deposition:

Answer 8

after weathered surface material gets transported to new locations, where it is laid down

Question 9

Hydraulic action:

Answer 9

erosive work done by water turbulence

Question 10

Abrasion

Answer 10

mechanical wearing and erosion of bedrock accomplished by the rolling and grinding of particles and rocks carried in a stream, removed by wind in a “sand blasting” action, or imbedded in glacial ice

Question 11

multiple thread channels:

Answer 11

• Braided or anabranching
• Areas with reduced discharge and abundant sediment

Question 12

Single thread channels:

Answer 12

Straight or meandering (snakelike)

Question 13

Meandering stream:

Answer 13

energetic outer portion subjected to the greatest erosive action, and the inner portion with low energy receiving sediment deposits.

Question 14

Undercut banks and Point bars

Answer 14

Undercut bank: the outer portion of each meandering curve is subject to the fastest water velocity, it undergoes the greatest erosive action possibly forming an undercut bank

point bar: the inner portion of a meander experiences the slowest water velocity therefore causing an accumulation of sediment on the inside of a meander bend

Question 15

Oxbow lake:

Answer 15

the former meander becomes isolated from the rest of the river. Circle separate river, away from the meander

Question 16

graded stream:

Answer 16

A stream where its channel slope has adjusted, given the discharge and channel conditions, so that stream velocity is just enough to transport the sediment load

Question 17

Nickpoint:

Answer 17

When the longitudinal profile of a stream contains an abrupt change in gradient, such as at a waterfall or an area of rapids

Question 18

Alluvium:

Answer 18

clay, silt, sand, gravel, and mineral fragments deposited by running water

Question 19

Floodplain:

Answer 19

The flat, low-lying area adjacent to a channel and subjected to recurrent flooding

Question 20

What are natural levees, and how are they formed?

Answer 20

The low ridges of coarse sediment o either bank of a river or stream

They are formed as discharge increases during a flood, the river overflows its banks, loses stream competence and capacity as it spreads out, and drops a portion of its sediment load. Coarser, sand-sized (or larger) particles are deposited first, forming

Question 21

Alluvial terraces:

Answer 21

A floodplain that is subsequently
eroded by a stream that has experienced a change in gradient and is downcutting.

formed by an uplifting of the landscape or a lowering of base level may rejuvenate stream energy so that a stream again scours downward with increased erosion

Question 22

Alluvial fans

Answer 22

prominent cone-shaped, or
fan-shaped, deposits of
fluvial sediments. They
commonly occur at the
mouth of a canyon where an ephemeral stream channel exits the mountains into a flatter valley.

Question 23

Playa:

Answer 23

salt crust on the floor after water evaporates

Question 24

River delta:

Answer 24

Located at the mouth of a river where it reaches its base level.

Stream velocity decreases as it enters a larger body of water and sediment is
deposited