Fluvial Systems

Question 1

how much of earth’s weather is in stream channels?

Answer 1

0.001%

Question 2

what is the annual volume of stream flow?

Answer 2

up to 36,000 km3

Question 3

what is the most important agent of erosion?

Answer 3

rivers

Question 4

why are rivers important?

Answer 4

Major link in hydrologic cycle
Dominant agent of landscape alteration
Human history ?
Interpretation of ancient rocks
Potential hazard e.g. floods

Question 5

why are fluvial systems open?

Answer 5

inputs and outputs of water and sediment

Question 6

what are the components of a fluvial (river) system?

Answer 6

1) Collecting basin: precipitation into tributaries in headwater region (catchment, watershed)
2) Transporting system: via slope runoff & groundwater into channel network
3) Dispersing system: output to deltas, lakes, ocean … deposition is dominant

Question 7

what are some examples of North American drainage basins?

Answer 7

Mississippi

rio grande

Question 8

which rivers have the largest fluvial sediment output?

Answer 8

colorado, Mississippi, ganges

Question 9

what is the fluvial sediment output of the Fraser river?

Answer 9

17x10^6 tons/year

Question 10

What controls river form and function at a regional scale?

Answer 10

climate
geology
topography
vegetation

Question 11

What controls river form and function at the drainage basin scale?

Answer 11

flow discharge (Q, measured as m3/s) [volume of water flowing past a certain point in a given time period]
sediment load
slope (stream gradient)
base level (elevation at the outlet)
land use activities

Question 12

All rivers ‘grade’ to achieve …?

Answer 12

dynamic equilibrium

Question 13

how does the form of a river change from head to mouth

Answer 13

steep -> shallow gradient

Question 14

what is base level?

Answer 14

lowest elevation that a river ‘grades’ to

Question 15

how does a river get a new equilibrium profile?

Answer 15

(1) Profile disrupted
(2) Headward erosion; downstream deposition
(3) New profile - equilibrium

Question 16

dams affect the….

Answer 16

equilibrium profile

result -> silting

Question 17

what is the Niagara Falls escarpment an example of?

Answer 17

a river working to achieve equilibrium

Question 18

how much has headward erosion at Niagara Falls increased the valley length by?

Answer 18

11.5 km in 12,300 years

Question 19

what can headward erosion lead to?

Answer 19

stream piracy and beheading

Question 20

how do rivers change overtime?

Answer 20

Continual base level change, deposition and downcutting

Question 21

what does the amount of sediment moved depend on?

Answer 21

discharge, velocity
gradient
sediment available

Question 22

what is stream competence?

Answer 22

ability to transport a certain size of sediment particle

Question 23

what is stream capacity?

Answer 23

ability to transport a certain volume of sediment

Question 24

what are the types of fluvial sediment transport?

Answer 24

(1) bedload: rolling, sliding, saltation (bounce) of coarse particles
(2) suspended load: fine particles in suspension
(3) dissolved load: dissolved material in solution

Question 25

what is erosion?

Answer 25

net removal of material

Question 26

How do rivers erode the landscape?

Answer 26

Removal and transport of regolith (weathered rock & soil)
Down cutting of valleys due to abrasion by load
Headward erosion of channel network

Question 27

what are the main channel pattern types?

Answer 27

Straight
Meandering
Braided

Question 28

in a straight channel where is flow fastest?

Answer 28

in the centre of the river

Question 29

in a meandering channel where is flow fastest?

Answer 29

on the outside of the bend

Question 30

what is velocity pattern controlled by?

Answer 30

curvature

Question 31

what will a meandering river create?

Answer 31

cut banks, point bars, oxbow lakes

Question 32

what are examples of meandering rivers?

Answer 32

Colorado River

Nowitna River, Alaska

Question 33

what are the characteristics of a braided channel river?

Answer 33

Multiple channels
High sediment load
Unstable bars/islands
Strong seasonal changes in flow

Question 34

what are some Canadian examples of braided channel rivers?

Answer 34

Mackenzie, Yukon, St. Lawrence, Ottawa and Bow Rivers

Question 35

where are braided streams common?

Answer 35

in systems of high sediment supply from glaciers

Question 36

what are alluvial fans?

Answer 36

Fan-shaped deposits where rivers emerge from uplands into a broad valley or plain

Question 37

what is a delta?

Answer 37

Deposition at mouth where rivers flow into sea, lake, reservoir or estuary (i.e. into a larger water body)

e.g. Mississippi delta, fraser delta

Question 38

what is the most frequent natural disaster?

Answer 38

flooding

Question 39

why does natural flooding occur?

Answer 39

Prolonged rainfall or high spring snowmelt

• > flow discharge (Q) exceeds channel banks
• > Levees and deposits in floodplain

Question 40

what is ‘Recurrence interval’ (R, yrs)?

Answer 40

average time between floods of a given size
100-yr flood = 1% chance in any given year…(not every 100 yrs!)
50-yr flood = 2% chance…
10-yr flood = 10% chance…
2- yr flood = 50% chance…

Question 41

what was the Red River flood (Manitoba, 1997) caused by?

Answer 41

spring melt of high snowpacks, saturated soil from heavy rainfall & a major storm

Question 42

How do human activities influence river systems?

Answer 42

Alter most factors that control river form and function:
Amount & timing of discharge
Amount of sediment load
Slope & base level

Question 43

what is flooding encouraged by?

Answer 43

Paved surfaces - increase amount and rate of surface runoff

Bridges, concrete banks - constrict natural flow of floodwaters

Question 44

What percentage of rainfall is surface run-off in a forested area?

Answer 44

0-20%

Question 45

What percentage of rainfall is surface run-off in a urban area?

Answer 45

90-100%