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GG101 Lecture Notes - Alluvium, Dissolved Load, Bed Load

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James Hamilton

of 3
GG101 Week 11 Lecture 2
o fluvial
relating to, or occurring in a river
o alluvium
sediments transported and deposited by streams
o drainage basin (watershed)
spatial area occupied and drained by a river system
o drainage divide
boundary between adjacent basins
o discharge (Q)
volume of water passing a point in a channel per unit time
o for a simple channel, discharge is the product of channel depth (d), width (w), and
stream velocity (v)
Q = w*d*v
o figure 14.33
o how is discharge measured?
o in a given stream channel, as discharge (Q) increases there are also increases in
stream width, depth and velocity
o erosion
overall breaking down, picking up, and transportation of materials
involves a sequence of events:
detachment (hydraulic action and abrasion)
o pulls some material off the bank (detached from its position
at rest)
entrainment (function of velocity)
o brings it into the flow
transport (several modes of transport)
o sediments in a stream move by:
i) suspension
fine grain sediments suspended within flow
ii) saltation
sand grain moves through a series of
iii) traction (rolling)
rolling along
iv) solution
o deposits material somewhere else
o particle deposition occurs when the flow velocity is
reduced and the flow cannot keep the particle(s) in motion
Sediment Load
o load is the amount of material the stream is moving over some time interval
(could be seconds, days, years)
suspended load
amount being moved by suspension
dissolved load
amount being moved in solution
saltation and traction
o load is the product of discharge and sediment concentration
what is daily suspended sediment load (in kilograms) for a stream with a
width of 10 metres, a depth of 1m, an average velocity of 0.5 metres per
second and suspended sediment concentration of 100 mg/L
Q =
Fluvial Landforms (chapter 14)
equilibrium and graded streams
o stream channel form reflects an equilibrium
o form influenced by:
slope (valley gradient)
sediment load (supply)
discharge (flow)
o graded stream
has a slope that is adjusted so that, given its discharge, it is just capable of
transporting the sediments supplied to it
o change the system,
alter the equilibrium between channel form and
sediment load
o ex: change the land use in a water shed (forested water shed
to agricultural land)
o function of climate, changes
what is the impact?
climate change
o more/less precipitation, warmer/cooler temperatures
tectonic uplift
land use
o influences sediment
channel intervention (e.g. figure 14.2)
channel shape and pattern
o channel shape
width to depth ratio
narrow channels tend to have higher velocities, wider channels
tend to have more friction, less velocities
o channel pattern
form of a stream channel
the channel pattern reflects the local equilibrium that exists between
discharge, sediment load, and slope (valley gradient)
flow carried in a single channel:
meandering (sinuous)
meandering streams
braided streams