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fill and spill hydrology
where there are many depressions in a watershed, a rainfall will replenish groundwater - needs enough volume to spill over in order before connecting to downstream parts of catchment
in prairies, bedrock, etc
flooding
can be fluvial (overflows over banks), pluvial (rain), coastal (storm surge, tsunami)
knowing risks is very important with land use etc of floodplains
flood frequency
understanding based on historical methods
return period - how often can we expect a flood greater than a specific discharge
exceedance probability of the large flood
return period equation
= (n+1)/Rank
(n - years of record)
probability equation
Rank/ (n+1)
flood protection
levees can be constructed to prevent flooding
can increase further downstream and also can be catastrophic when it fails
calgary flood control
2013 flood was extremely costly
additional control needed in bow and elbow rivers, springbank reservoir
dam under assessment, additional levees built, dry dam created
non-stationary flood frequency
need to account for climate change, land use/management (ag, forestry, etc), fires, dams/diversions/drainage, and alteration of river channel
need to account for these in modelling and projections
river morphology
headwaters (in the mountains), transfer zone comes next where lower elevation streams merge in lower slopes
in the depositional zones meandering streams flows maybe into delta, maybe sea, etc
stream power
rate of energy dissipation against the bed and banks of a river per unit downstream in length
work done by a stream to move sediment
so for example a river flowing at a constant speed which does not gain any kinetic energy needs to dissipate energy in some way and so it does as kinetic energy for sediment
stream power equation (Ω)
Ω = p*g*Q*S
p = density of water, g = acceleration due to gravity, Q=discharge, S = slope
stream power interpretation
steep rivers with a higher discharge will have greater stream power therefore a higher power to transport/erode sediments
with no sediment stream power is instead dissipated as heat vs kinetic energy
total suspended solids
measured by filtration and weighing of the filter before and after
filter pore size determines difference between a dissolved and suspended solids
dominated by silt, clay, sand but can also include organic material
increases with higher stream velocity
bedload
sediment particles which are too heavy to be suspended
move by rolling, sliding, and saltation
needs stream depth 10x sediment diameter
increases with higher stream velocity
entrainment and deposition
higher velocity needed to entrain (erode) than to keep sediment in suspension
smaller particles easier to keep in suspension, easier to erode (exception of clay/silt)
deposition caused by lower stream velocities
larger rivers able to transport more TSS and bedload
yield
total amount of sediment or other dissolved transported in a river over time, largely during high flow
ex tonnes/year
= discharge * concentration
dendritic
trellis
rockies
radial
centripetal
rectangular
cracking landscape
deranged
prairies, depressions
parallel
braided river
higher bedload, more grained sediment, decreasing bank stability, high discharge variability, high slope
meandering pattern
more suspended load, finer grain sediments, increasing bank stability, low variability discharge, low channel slope
sinuosity >1.5
sinuosity
length of thalweg / distance along valley
meandering river will have >1.5
alluvial fans
base of mountain
deposition when river slows down - less slope and loss of stream power
deltas
in lakes or oceans
deposition when river slows down - less slope and loss of stream power
human modifications of sediment transport
urbanization increases runoff, increases erosion and river incision ex in the mill creek ravine
reservoirs trap sediments, and when there is less in water downstream then increases erosion and stream incision
this can also reduce sediments in deltas which causes them to shrink (when wave erosion>deposition)
