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Environmental Science
Course Code
Jovan Stefanovic

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Lecture Six
x Precipitation
o Precipitation measured in mm
For example 20mm of rain would mean in 1 m2 there would be
20 L of rain, or that the thickness of the amount of rain that fell
is 20mm
o High Intensity & Short Duration Large amount of precipitation
falling in a very short time can create flash floods
o Lower Intensity & Long Duration Large amount of precipitation falls
steadily over a longer time
o Hurricanes
Ex: Hazel in 1954 or Katrina in 2005
o Monsoon
Ex: Pakistani floods began in July 2010 following heavy
monsoon rains
x Watershed (Drainage Basin)
o The upstream area from which surface water flows towards the
o Drainage Divide Topographic line or boundary separating
x 99.9% of all rivers flow only to one ocean/sea/etc.
o One exception is Two Ocean
Creek in Kicking Horse Pass
x River Flow and Sediment Transport
o Discharge Q (m3/s)
Measured volume of water
flowing past a cross section
of a river in a given amount
of time.
o Water flows fastest at top of
river due to decreased
o Hydrograph A graph of how
discharge changes over time.
Can show how long
flooding is and when
the peak of it is
o Stream Gradient & Floodplains
Gradient Slope of the river channel; typically decreases
Floodplain relatively flat lowland that borders a river, usually
dry but subject to flooding
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Base Level an elevation that a stream cannot erode,
controlled by level of the body of water that the stream
discharges into.
x Ex: Level of lake Ontario is local base level for Highland
River, and the level of the ocean that lake Ontario
deposits to is the ultimate base level.
x Two General Types
o Ultimate sea (ocean) level
o Temporary/Local Lakes, main streams
x Changing causes readjustment of the stream
o Rising Base (ocean & sea) level deposition
o Lowering base level erosion
o Work of streams
x Erosion
x Transportation transported materials is called the
x Materials Transported
o Suspended Load finer particles, such as clay,
silt, and fine sand, carried in suspension
o Bedload heavier sediment in a stream that is
moved along the streambed rather than in
o Dissolved Load derived from chemical weather
of rocks.
o Alluvial Fan A fan-shaped deposit of sand and gravel at the mouth of
a mountain canyon, where the
stream gradient flattens at the
main valley floor.
o Delta Accumulation of
sediment deposited by a river at
its entrance into a large water
bode (ocean, sea, or lake)
o Natural Levees Form as the
flood waters deposit sediment
on the edge of the channel
where the velocity is lower than
in the channel
o Alluvial Channels Rivers that
flow in their own deposits
Unconsolidated sediment
of relatively recent
geologic age that was
deposited by flowing water
x River Classification and Flooding
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