rivers and floods Flashcards
What is base level?
- 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
what is a stream and what determines the size
- 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
stream valley
SEE NOTES
- area between tops of slopes on both sides of the river
channel
SEE NOTES
- trough through which water flows
flood plain
- area that will flood in times of increases precipitation
SEE NOTES
thalweg
line connecting deepest parts of the channel
discharge
- volume of water flowing downstream/unit time (m^3/sec)
where are highest flow veolcities in a stream
straight areas
- centre of channel
- just below water surface
around meanders
- outsider of meander bend
- friction from channel itself and air friction causes this
how does the shape of a valley change downstream
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
how does the slope of a stream change downstream
longitudinal profile
- steep gradients near source
- low gradients downstream (angle of elevation
what kinds of forms can streams have?
- meanding streams
- obow lake
- floodplain
- braided stream
channel morphology
- 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
meandering streams
- 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
oxbow lake
- crescent shaped laked formed where a meander is cut off from a stream
- ex. slave river, northwest territories
floodplain
- 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
braided streams
- 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
urban river systems
- 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
what happens once ater falls to the ground
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
urban system
- 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
Why do different river types develop in different geographic settings?
Where does sediment erosion and sediment deposition occur in a river? How is sediment moved by a river?
What environmental hazards are associated with fluvial environments?
