CHPTR 15 Surface Processes: Water Flashcards
Hydrosphere
water at and near the surface of the Earth
outgassing
original source of water
planetesimals
added to the Earth’s source of water
Cycle of water through the Earth
Ocean, subduction, mantle, volcano
Water in mantle compared to ocean
1-10x
Hydrosphere - Atmosphere
Precipitation and Evaporation
Hydrosphere - biosphere
Transpiration and absorbed by plants
Hydrosphere - Lithosphere
infiltration, springs/volcanoes
%Water in oceans
97.5%
%Water in Ice
1.8%
%Water in Groundwater
0.63%
%Water in Lakes and Rivers
0.016%
%Water in Atmosphere
0.001%
How long does water sit in rivers
months
how long does water sit in ice caps and oceans
millenia
stream
body of flowing water confined to a channel
headwater/head
stream start point
drainage basin/watershed
region from which water is collected
stream mouth
where a stream empties into another water body
stream bed
base of stream
banks
confine stream during normal flow
floodplane
region covered during a flood where sediment is deposited
laminar flow
away from banks;
smooth constant flow
transports more water
turbulent flow
near banks and bed (friction);
chaotic flow
transports less water
stream gradient
slope of a stream
greater at the head
lesser at the mouth
discharge + eqn
how much water is flowing through a river at a given point
Cross sectional area x Vavg
stream discharge units
m^3/2
Controls for Discharge
shape of channel;
deeper = less turbidity = more water flowing
bed texture;
smooth sand = less friction = laminar flow = more water flowing
pothole
circular indent in river cause by erosion
water flows in a circle in it
Stream sediments
dissolved load
suspended load
bed load
dissolved load
chemical sediment
suspended load
mechanical sediment
carried in stream current
bed load
sediments in river transported by saltation, rolling, sliding
saltation
“jumping of grains”
capacity
maximum load of solid particles that a stream can transport
capacity units
kg/m^3
competence
max particle size that a stream can transport
competence units
EMAILED THE PROF
Channel deposits
intrachannel bars
point bars
intrachannel bars
deposited sediments bars parallel to river centre line
point bars
crescent shaped depositions on inside of a meander
Formation process of natural levees
flood plain deposits (sand banks)
water rises above the banks of the river onto the floodplain
it deposits sediments in decreasing competence
Base level
- lowest level to which stream can erode to
- often sea level, can be lake
- no slope; the stream bed is flat
- equilibrium between erosion and deposition
How does increasing sea level affect base level
Increase sea level;
sea moves inland, stream would adjust by moving deposition inland (to make upstream have a higher elevation and greater slope)
How does decreasing sea level affect base level
sea moves away, there is now a greater slope = more erosion, so deposition moves downstream
Waterfall
resistant layer of rocks erodes more slowly, creating a larger gap. It will eventually also erode
How dams affects a streams base level
raises the streams base level (it is a new temporary base level); the reservoir will eventually fill with deposition (until it can flow over the dam)
V-shaped valley
formed by rivers
1. rivers cut straight down
2. the straight sides undergo weathering
3. the sediment is transported away by the river
What would cause a wide stream valley
less of a gradient(slope); less cut down into the Earth; more erosion of the edges = widening
erosional floodplain
formed by side to side migration of channel
depositional floodplain
formed either downstream or when sea-level rises
meander
bends in a river
point bar/cut bank formation
- water on the outside of a meandering river flows faster than the inside.
- The faster water erodes the out bank (creating a cut bank)
- The slower water on the insider deposits sediment (creating point bars)
Positive feedback loop example
birth, meandering rivers
oxbow lake
the water erodes to the point it reconnects to the other side of the meander. Water takes the shortest route and deposits sediment; which separates the oxbow from the stream
braided stream
- occurs in streams with high sediment load
- deposited sediment partially blocks channels
- river goes around
anastomosed streams
- separated by islands with vegetation
- multiple channels develop
braided stream energy
high energy
anastomosed streams
low energy
alluvial fan
abrupt change of gradient from steep to flat causes the water to spread out and deposition to occur in a large area
delta formation
- distributary stream enters lake or ocean
- the stream extends its channel; reducing the gradient
- river floods
- river is diverted to a route with a higher gradient route; forming a new distributary stream
drainage basin
area that is drained by a stream to a specific point (BIG watershed)
ie. Arctic Sea, Gulf of Mexico, Endorheic lake
divide
separates drainage basins
endorheic lake
water basin drains to lake then evaporates in summer - no outlet
What drainage basin is Edmonton in
Hudson Bay
Altiplano + economic value
South America internal drainage basin (no outlet)
forms big salt flats
lots of lithium
dendritic drainage pattern
like a tree. one river branches off into many
radial drainage pattern
circle with a radius of streams extending from it.
Ie from the top point of a volcanoe
rectangular drainage pattern
rectangular;
caused by faults and contact between different rock types
trellis drainage pattern
vine trellis
rock resistant ridges limit river from cross across boundaries
valleys from non-resistant rocks
stage
elevations of water surface
flood stage
stream stage > bank height
crest
max stage
flood
when discharge of run-off > volume of channel
upstream flood
“flashflood”
- upper part of the stream
- small area, with heavy rainfall
- does not last long
downstream flood
- downstream part of the stream
- from prolonged heavy rain/lots of snow
- rises slowly + lasts longer
Ice jam flood
surce ice blocks river
dam failure flood
quickly releases all reservoir water
Which occurs more often, small or large floods
small
“100 Year Flood”
a big flood that occurs on average every 100 years
Flood frequency curve
Discharge vs average repeat time
Find your point, read as;
“you get a flow rate of _____ every _____years”
flood control methods
artificial levees, dams, channelization, replace vegetations
artificial levees impact on flooding
- by making levees; you don’t allow water to escape which makes floods worse downstream
- if levee breaks, you are fucked
dams impact on flooding
- spread crest of flood
- eventually reservoir will fill up with deposition
channelization impact on flooding
dig channels;
- dig stream deeper: problems moved downstream
- dig new stream: moves the flood elsewhere
What could cause daily variation of stream crest
hydropower
Post glacial rebound definition and how it affects flooding
- glaciers cause indents on Earth
- glaciers melt faster than Earth rebounds
- causes river gradients to decrease
how does replacing areas of vegetation affect flooding
- increases the infiltration rate of cities
- (plants absorb more water)
What causes large rivers to flood + when
snow melting in Spring
prolonged/heavy rainfall
What causes medium rivers to flood + when
late spring as rain begins
fall as early snow melts
What causes small rivers to flood + when
all year snow melting and rainstorms
Factors affecting flood severity (3)
heavy precipitation
topography
vegetation
how does topography affect flood severity
greater slope = greater runoff = less time for absorption
how does vegetation affect flood severity
- slows runoff
- roots increase permeability
- absorb water
