(TEST 2) Earth Science, Lecture pt 4 (ch 8)

Question 1

Why are stream runoffs considered an important geologic agent?

Answer 1

• Erodes, transports, and deposits ions and sediments
• Sculpts landscapes
• Transfers mass from continents to ocean basins

Question 2

What is overland flow?

Answer 2

Precipitation moving downslope over the land surface

Question 3

What is stream discharge?

Answer 3

Volume of water moving through the channel in a given time

Question 4

What is groundwater baseflow?

Answer 4

Groundwater that discharges to the surface

Question 5

What are some qualities of a gaining stream?

Answer 5

• Water flows all year
• At or below the water table
• Humid or temperate climates
• Sufficient rainfall
• Lower evaporation

Question 6

Gaining streams are also known as _____?

Answer 6

Permanent streams

Question 7

What are some qualities of a losing stream?

Answer 7

• Dry up part of the year
• Above the water table
• Dry climates
• Low rainfall
• High evaporation

Question 8

Losing streams are also known as ______?

Answer 8

Ephemeral streams

Question 9

Is velocity uniform in a channel?

Answer 9

No

Question 10

What is a hydrograph?

Answer 10

Plot of discharge versus time

Question 11

What is a watershed?

Answer 11

An area of land that drains into a stream

Question 12

What do drainage divides separate?

Answer 12

Drainage basins

Question 13

What is a stream gradient?

Answer 13

Change in elevation per distance flowed

Question 14

What are some physical characteristics near the headwater of a stream?

Answer 14

They tend to be steep and straight

Question 15

What are some physical characteristics near the mouth of a stream?

Answer 15

They tend to be flat and curved

Question 16

Why is erosion is greatest during a flood?

Answer 16

Because energy is higher which causes more erosions and more transportations

Question 17

How do streams erode?

Answer 17

Streams break, abrade, and dissolve material
Scouring – water picks up and moves sediment
Breaking and lifting rocks and sediments
Abrasion – the “sandblasting” of rock by particles in fast-moving water
Dissolution – running water can dissolve soluble minerals

Question 18

What is river erosion?

Answer 18

The energy of flowing water is from mass and gravity

Question 19

How do streams transport sediments?

Answer 19

Through sediment load

Question 20

What is sediment load?

Answer 20

Material moved by running water

Question 21

What are three types of sediment load?

Answer 21

• Dissolved load: ions from chemical weathering
• Suspended load: fine particles (silt and clay) in the water
• Bed load: larger particles roll, slide, and bounce along the bottom

Question 22

Bed load moves by a process called……?

Answer 22

Saltation

Question 23

How does decrease in water velocity affect sediment transport?

Answer 23

• Competence reduced, sediment drops out
• Boulders, then gravels, then sands fill channel bottoms
• Sands form inside banks (point bars)
  Silts and clays drape floodplains

Question 24

What do meander streams look like from a top-down view?

Answer 24

They have winding, looping curves

Question 25

When do meandering streams form?

Answer 25

- The stream gradient is low - The substrate is soft and easily eroded - The stream exists within a broad floodplain

Question 26

T/F: Meander streams evolve during times of flood

Answer 26

True, because the channel is modified during periods of flood

Question 27

How does fast water impact stream bank?

Answer 27

It erodes the outside stream bank (or cut bank)

Question 28

How does slower water impact stream bank?

Answer 28

It deposits point bars within the curve

Question 29

How are oxbow lakes formed?

Answer 29

They are formed from cutoff meanders

Question 30

What are some properties of the base level in meandering streams?

Answer 30

- Lowest level to which a stream can cut downward - Sea level is the ultimate base level - Lakes, reservoirs, and resistant rock bodies can create temporary base levels

Question 31

What happens as streams approach their base levels?

Answer 31

- Stream gradient decreases - Meanders get wider - Stream carves out a wider floodplain - Oxbows develop during times of flooding

Question 32

How is a delta formed?

Answer 32

A delta is formed when a stream enters standing water

Question 33

What happens when a stream enters standing water?

Answer 33

- Stream divides into a fan of distributaries - Velocity slows; sediment drops out

Question 34

In flood, the river may break through a levee, which is a process called .....?

Answer 34

Avulsion

Question 35

What type of plain forms when distributaries continue to provide sediment?

Answer 35

Delta forms

Question 36

When do abandoned delta lobes degrade over time?

Answer 36

When sediment supply is reduced/ eliminated

Question 37

How does a reduction of sediment supply causes degradation in abandoned delta lobes?

Answer 37

- Compaction causes subsidence, which causes the delta surface to sink - Submarine slumps and storm waves attack the delta front

Question 38

Floods occur when

Answer 38

Flow exceeds channel capacity

Question 39

What different conditions are floods triggered by?

Answer 39

- Torrential rains rapidly dumping large volumes of water - Long period of continuous rain; ground is saturated - Rapid snowmelt across a large drainage basin - Failure of dam or levee

Question 40

What are some different types of floods?

Answer 40

- Flash floods - Dam failure - Downstream floods

Question 41

What are flash floods?

Answer 41

Water that rises with little warning

Question 42

How are flash floods caused?

Answer 42

- By intense rainfall or dam failures - By rapidly moving wall of debris-laden water

Question 43

What is a dam failure?

Answer 43

Catastrophic amounts of water released from impoundment in a very short period of time

Question 44

What are downstream floods?

Answer 44

Where a river in the lower part of a drainage basin leaves its channel, flowing out onto its floodplain

Question 45

What are most downstream floods caused by?

Answer 45

Most are caused by regional accumulations of water and not just a single storm

Question 46

What structures aim to prevent overflow to floodplains?

Answer 46

Levees and flood walls

Question 47

What do artificial levees do?

Answer 47

They transmit flood problems downstream and they're used to protect cities from flooding

Question 48

Why are many parts of the city located below sea level?

Answer 48

- Draining of the back swamps - Subsidence

Question 49

What do artificial levees prevent?

Answer 49

Sediments from reaching the floodplains

Question 50

What land-use activities increase the hazards associated with flooding?

Answer 50

- Removal of natural vegetation - Destruction of wetlands - Construction activity - Urbanization

Question 51

Why does the removal of natural vegetation contribute to the hazards of flooding?

Answer 51

Because it leaves soils exposed and greater overland flow

Question 52

Why does the destruction of wetlands contribute to the hazards of flooding?

Answer 52

Because wetlands are used to capture and store large amounts of water

Question 53

What are some ways to reduce flooding?

Answer 53

- Dams - Artificial levees - Channelization - Retention Basins - Erosion Controls - Wetlands Restoration - Floodplain Management - Education