Importance of fluvial geomorphology
- Major city proximity to rivers (transport corridors)
- Anthropological change to fluvial systems (hydro dams, bridges, drinking water, irrigation...)
- Flood mitigation
- Ecosystem functions (fish spawning, floodplain/riparian ecology...)
Flowing water above vs below ground
Fast on surface, slow underground
Groundwater table
Upper surface of zone of saturation for underground water
- Separates aeration zone from the phreatic zone and moves up and down with topography
Porosity
Ratio or % of the volume of void space to the total volume of a material
Permeability
Capacity of a porous material to transmit fluids
Aquifer
Rock or sediment layer with sufficient porosity & permeability to store and transmit groundwater, typically sandstone
Aquiclude
Impermeable layer which prevents groundwater flow, generally clay or shale
Piezometric surface
Hypothetical surface defined by the level to which water in a confined aquifer rises in observation boreholes
Artesian well
A well dug into a confined aquifer through which water flows upwards under pressure.
Other name for drainage basins
Watersheds
How drainage basins are defined
Outflow location
Outflow locations of these rivers
Hay and Peace river -> Arctic ocean
Athabasca, Churchill, N. and S Saskatchewan -> Hudson's Bay
Missouri River -> Gulf of Mexico
Longest Canadian river
The Mackenzie river
Deltas
gorged - where fluvial sediments are
deposited
in standing water, sometimes
forming a great plain of alluvial flats
Estuaries
starved - where river sediment load is low
or
where currents sweep sediments away from
the river mouth
Sediment deposition, deltas vs estuaries
gorged vs starved
Nickpoints
‘steps’ in the longprofile of a river
where downcutting is
delayed by resistant rock,
forming waterfalls
Cause of nickpoint formation
FALLING SEA LEVEL OR UPLIFT OF LAND
Channel belt and what it's not
The distance between the start and end of a river, not the course which the river takes
As the crow flies vs actual path
Percentage of world rivers with anabranching sections
~50
Braided and anastomosing channels
For anastomosing rivers (aka anabranching rivers) the branch
locations are stable in their
channel belts while braided rivers
change year to year
BRAIDED RIVERS
- have numerous streams that split off and rejoin
- develop in the upper torrent section
- Mainly gravel and coarse sand
- Carry lots of sediment
MEANDERING RIVERS
• are sinuous and slowly migrate down-stream
• lengthen the
courseof the river and
reduce the gradient
• start in the
lower torrent section, but best
expression in lower floodplain
Thawleg
-a line following the lowest part of a valley whether under water or not
-the middle of the chief navigable channel of a waterway which constitutes a boundary line between countries/states
RIVER TERRACES
Benches with horizontal surface above the current
floodplain
Develop through stream incision (rejuvenation – can be
tectonic or climatic)
RIVER ENTRENCHMENT
RAPIDLY FALLING SEA LEVEL
OR UPLIFT OF LAND CAUSING DOWNCUTTING
and
ENTRENCHMENT OF RIVERS
(Grand Canyon)
RIVER PIRACY
• the diversion of the headwaters of one stream into another
one
• can dramatically change the routing of water &
sediment, affecting landscape evolution + downstream hydrology and ecology.
STREAM AVULSION and two causes
River channel abandonment
- Narrowing of the neck of a meander followed by the neck cut-off
- Backfill of a parent stream slows down the lower
reach of the river, causing a levee
breaches and formation of a “daughter channel”-> stagnation -> abandonment of the parent channel