rivers and floods

Question 1

What is base level?

Answer 1

• deepest level to which streams can erode
• usually sea level (but not always)
• determined often by global sea level
• water must follow gravity
• ex. a dam can change local base level

Question 2

what is a stream and what determines the size

Answer 2

• a body of water confined within a channel, supplied with water by its drainage basin
• interchangable with river/creek
• it doesnt matter how large or small it is

size determinants:
- climate
- size of drainage basin
- substrate
- vegetation

Question 3

stream valley

Answer 3

SEE NOTES
- area between tops of slopes on both sides of the river

Question 4

channel

Answer 4

SEE NOTES
- trough through which water flows

Question 5

flood plain

Answer 5

• area that will flood in times of increases precipitation
  SEE NOTES

Question 6

thalweg

Answer 6

line connecting deepest parts of the channel

Question 7

discharge

Answer 7

• volume of water flowing downstream/unit time (m^3/sec)

Question 8

where are highest flow veolcities in a stream

Answer 8

straight areas
- centre of channel
- just below water surface

around meanders
- outsider of meander bend
- friction from channel itself and air friction causes this

Question 9

how does the shape of a valley change downstream

Answer 9

cross sectional profiles
- steep-sided, v-shaped near source, canyons
- broader valleys donstream
- the valley changes shape
- the volume of water increases the farther down it goes so there is increased erosion

Question 10

how does the slope of a stream change downstream

Answer 10

longitudinal profile
- steep gradients near source
- low gradients downstream (angle of elevation

Question 11

what kinds of forms can streams have?

Answer 11

• meanding streams
• obow lake
• floodplain
• braided stream

Question 12

channel morphology

Answer 12

• sinuosity is used to classify channels
• ratio of stream length: valley length
• low sinuosity is not very bendy and high sinuosity is bendy
• there is straight and meandering streams
• sinuosty is calculated by the stream and valley length

Question 13

meandering streams

Answer 13

• common in areas with low slopes
• thalweg close to outer bend of meander
• most erosion occurs at the outside bend of meander- deepest water, highest flow velocityes- cutbank
• most deposition- inside bend of meander- point bar
• ex. innoko national wildlife refuge, alaska
  erosion of cutbank, deposition of point bar= migration of meanders
• meaders can join and form neck cut off since the water will go through point of least resisitance
• on th point bar:deposits sands and silts (ripples and dunes)
• on floodplain: deposites silts and clays (because its not moving)
• with migration forms: fining upwards sequence

Question 14

oxbow lake

Answer 14

• crescent shaped laked formed where a meander is cut off from a stream
• ex. slave river, northwest territories

Question 15

floodplain

Answer 15

• broad strip of land built by sedimentation on each side of the channel
• covered when river floods (floods during increased precipiption)
• coasrest material depositied closest to the channel- formed LEVEES (these are not strong and wont protect againt future floods)
• finer grained material carried futher away- clays and silts
• is is bas idea to build on a flood plain

Question 16

braided streams

Answer 16

• multiple channels
• common on steep slopes
• common in glaciated or arid regioans
• channels are offen changin; qite volitile/dynamic (increase dischange)
• what sediments: coarse grained like gravels and sands
• channels split and erjoin
• areas of deposition between channel: BRAID BARS

Question 17

urban river systems

Answer 17

• ground less permeable
• less info;tration of rainwater
• more strom run off which is increase flooding
• ex. calgary which is on a flood plain
• a flood hydrograph shows the effect of strom even on river dischange
• urban rivers have flashy dichange: water entres river wuickly, causes high flood peaks
• compared to normal which is slower
• ex. hamilton is likely to experience floodinf this year are Lake ontario is histroically high. city has very few optons for prevention due to length of shoreline. sandbags no effective due to force of wave action. popular trails being flooded alonf with parking los near ahrbout
• ex. ottawa. sever flooding since april 2019

Question 18

what happens once ater falls to the ground

Answer 18

infiltration
- process through which water on the ground enters into the soil
- collects on top and if there is pore space it fills up
- infiltration is good in nature becase increased vegetation
- bad in urban environment because concrete etc

amount of infiltration dependant on:
- soilmositure
- substrate
- slope
- type of vegetation
- intensity of precipipation

Question 19

urban system

Answer 19

• erosion of stream banks, clogs channels
• sediment poses problems for fis
• there is creek modifiction for flood and ersion control
• reduced water quality due to urban runoff contained road salt, grease oil
• ex. bluffers park, scarborough, 1991

Question 20

Why do different river types develop in different geographic settings?

Question 21

Where does sediment erosion and sediment deposition occur in a river? How is sediment moved by a river?

Question 22

What environmental hazards are associated with fluvial environments?