Streams

Question 1

What are the processes involved in the hydrologic cycle?

Answer 1

Evaporation

Precipitation

Infiltration

Runoff

Transpiration (moisture released by plants)

Question 2

what are streams

Answer 2

considered a body of water that carries rock particles + dissolved ions + flows down slope along a clearly defined path (channel)

Question 3

Why are streams important?

Answer 3

Deliver much of the water from land to sea

Erode lots of sediment particles + transport them to lower elevations
- Being important in the formation of sediment + sedimentary rocks

They sculpt Earth’s surfaces through processes of erosion + deposition

Carry dissolved ions (weathered from rocks on land) to the sea (this is why the sea is salty)

Question 4

what can water that falls onto the ground as precipitation do?

Answer 4

Water that falls to the ground as precipitation can:

Evaporate back into the atmosphere

Soak into the ground (becoming groundwater)

Flow on the surface as runoff

Question 5

What is a sheetflow

Answer 5

Runoff initially moves over the surface in a thin, continuous sheet (sheetflow)

Question 6

what is a rill?

Answer 6

The flow of sheetflow eventually becomes confined to tiny channels called rills

Question 7

what is a channel flow

Answer 7

Rills merge into larger, more permanent, stream channels

Question 8

what are drainage basins

Answer 8

Stream systems can collect water from large areas

The water catchment area/region for a given stream system is called a drainage basin

Question 9

what is the area bounding drainage basins called?

Answer 9

divides

Question 10

Streams tend to erode ____ in effort to reach base level (sea level)

Answer 10

downward
- the greater the elevation above sea level, the greater the rate of downcutting

Question 11

where does erosion tend to dominate?

Answer 11

at headwaters (highest elevation above base level)

Question 12

what is the gradient of a stream

Answer 12

The gradient (slope) tends to be higher at the upper reaches of a stream (headwaters) than its lower reaches (close to its mouth)

This concave-upward profile is called a “graded” profile

Question 13

In what 2 ways can streams carry clastic sedimentary particles?

Answer 13

bedload
suspended load

Question 14

what is a bedload

Answer 14

large and/or dense particles that remain on the bed of a stream most of the time, but can move by tumbling + saltation (in turbulent layer)

Question 15

what is a suspended load

Answer 15

small and/or light particles that are suspended in water most of the time (in turbulent + laminar layers)

Question 16

waht happens to volume + sediment grain size of bedloads and suspended load as it goes downstream

Answer 16

decreases w/ increasing distance from primary sediment source

Question 17

what are the 2 types of flows that occur in streams

Answer 17

turbulent( non-linear)
laminar (linear)

Question 18

what are turbulent flows?

Answer 18

Turbulent (non-linear) flow dominates near the bottom + sides of a stream channel where swirling eddies are generated around elements of surface roughness

Question 19

what are laminar flows?

Answer 19

Laminar (linear) flow dominates water that is out of reach of turbulent eddies

eddies (swirling of a fluid)

Question 20

How are valleys in Highland

Answer 20

River channels are bounded on either side by valleys

Valleys reflect the erosive action of streams, which undercut + destabilize their banks

Destabilized material tumbles down into stream channel, providing sediment particles for the stream to transport as bedload or suspended load

At highest reaches (in mountains), slot canyons can form due to extreme downcutting

As river continues down mountainous terrain, tend to be deep + v-shaped due to rapid downcutting

Meandering pattern not pronounced

Question 21

what is meandering pattern?

Answer 21

meander is a bend in a river channel

Question 22

What are the characteristics of a headwater channel in highlands

Answer 22

Small, shallow, channels

Coarse bedload

Turbulent flow dominant

Overall velocity often low bc drag affects most of water column

Question 23

what are the characteristics of lower course channel in lowlands

Answer 23

Large, deep, wide channels

Fine bedload

Laminar flow dominant

Overall velocity high bc drag is confined near the stream bed (well below the surface)

Question 24

what are the characteristics of highland streams

Answer 24

At slightly slower gradients (e.g. feet of mountain slopes)
- Large volumes of bedload are deposited in cone-like bodies called alluvial fans

Continuing on their downstream course, highland streams remain small + shallow

Bc they are choked w/ coarse bedload, streams are often diverted + form shallow, braided channels

Question 25

what are the characteristics of lowland streams

Answer 25

Valleys in lower parts of stream’s course (closer to base level) tend to be broad due to little downcutting + greater lateral movement

Meandering pattern more pronounced

The “flatness” of the valley floor is accentuated by the deposition of sediment during floods

Areas adjacent to the channel that are built up by sediments during floods are called floodplains

Question 26

how does the meandering stream system work?

Answer 26

The path of highest flow velocity (called the thalweg) veers toward the outer bank of a meander
- This creates an area of highwater pressure at outer bend
- The inner bend is the zone of slowest flow, representing an area of low water pressure

To relieve the differences in pressure, water flows rapidly downward at outside bank, across the bottom of the channel + up the inside bank
- Produces helical flow (circulating in a corkscrew fashion)

Question 27

what are cut banks

Answer 27

area of erosion
(outer bend)
Strong flow erodes the outer bend, producing a steeply sloping cut bank

Question 28

what are point bars

Answer 28

area of deposition
(inner bend)
Weaker flow on the inner bend deposits sediment

Question 29

how does meander move in the direction of the cut bank?

Answer 29

laterally

Question 30

What are oxbow lakes

Answer 30

Meander loops become more pronounced through time, resulting in cutoffs

When a meander is isolated due to a cutoff, it can form an arc-shaped lake called oxbow lake

Question 31

what is a floodplain

Answer 31

flat area next to river or stream subject to flooding

Question 32

what is floodplain deposition

Answer 32

During a flood, water spills over river’s banks

Sudden reduction in the speed of water allows sediment to be deposited on the floodplain

Sediment deposits are thickets (+ coarsest-grained) in natural levees on either side of a flooded channel

Question 33

How does sediment enter the sea

Answer 33

In lowest part of stream’s course, it is deprived of coarse sediment but still carries lots of fine-grained sediment as bedload + suspended load

When river enters the sea (or other body of standing water)
- Flow velocity suddenly drops + sediment is deposited

Bodies of sediment deposited in this way are called deltas