Drainage patterns Video Lecture - Class 9

let's take a look at the idea of
drainage patterns now drainage patterns
reflect local topography the geology
especially things like faults and
climate
channels occur in areas where surface
runoff occurs and materials can be
loosened and transported reported by the
kinetic energy of water the
classification systems tell us something
about topographic and geologic controls
that that make water flow in different
ways and also that lead to erosion on a
landscape and much of what I'm going to
talk about here is from a book called
the physical environment this is an
introduction to physical geography by
Michael litter and there's the link
below here are a few questions to think
about as you watch this how would you
classify Hunter Creek and can you think
of an example for any of the other
classes of the systems listed below the
drainage systems let's start with
dendritic drainage it's one that we
think of most commonly and it's most
commonly used to illustrate what a
watershed is a dendritic drainage
pattern is the most common form it looks
like the branching pattern of tree roots
or tree branches it develops in areas
that are underlined by a relatively
homogeneous or material or material
that's roughly the same throughout are
not a lot of resistant and non resistant
rocks and things like that
so the subsurface geology has a similar
resistance to weathering so there's no
apparent control over the direction the
tributaries take
tributaries joining larger trivet
streams they join larger streams that
acute angles which means that that's at
less than 90 degrees and that's how you
get the branching effect that we see
that's so common a lot of surface
drainage systems is questioning the
sierras parallel drainage of drainage
patterns here illustrated by by the
little dots on the dotted lines on the
map our patterns that form where there's
pronounced slope to the land surface so
one that where we would have a mountain
face training say for example into a
valley the parallel pattern develops and
regions of parallel elongated landforms
like outcropping resistant band rock
bands tributary streams tend to stretch
out in a parallel fashion following the
slope of the surface a parallel pattern
sometimes indicates the presence of a
major fault the cross it cuts across an
area of steeply folded bedrock all forms
of transitions can occur between
parallel dendritic and trellis patterns
and let students see the shelter
the trellis drainage idea is interesting
limits it's named after the kind of the
the common garden trellis this kind of
drainage develops in folded topography
like that part of the Appalachian
Mountains of North America there are
these down folded down turn folds called
sink lines that form valleys in which we
find the main channel of a stream short
tributary streams into the main channel
at sharp angles as they run down the
sides of the parallel ridges called
antic lands tributary join trim trees
joined the main stream at nearly right
angles the rectangular drainage pattern
is found in regions that have under
undergone faulting streams follow the
path of least resistance and are
concentrated in places that are exposed
to rock that's the weakest the movement
of the surface to defaulting offsets the
direction of the stream and as a result
tributary streams make sharp bends and
enter the main stream at high angles
this is an example of a drain on the San
Andreas Fault in California radial
drainage develops around a central
elevated point for example here a
mountaintop this Pat this pattern is
commonly is common commonly found when
you have conical shaped features such as
volcanoes the streams extend from the
head word reaches upslope toward the top
of the volcano so we have the headwaters
of several streams that originate near
the top of the volcano and then join
together as they reach the base of the
volcano and here's Mount Rainier as an
example of that
centripetal drainage this is an example
of a small Playa that's near the bits
between Empire and Nixon and if you look
carefully you can see the evidence of
drainage on both sides of the playa
draining directly into the end of the
Playa itself and here this is the
opposite of a radial drainage system
because the streams are flowing into a
central depression this would be a very
common drainage system in the state of
Nevada because all of our drainage
actually flows into the state and none
actually goes out of the state to the
ocean this is a pattern that's typical
to western and southwestern portions of
the United States or basins exhibit
interior drainage that is the drainage
flows into these playas and never leaves
except from except by evaporation in
wetter times of the year the streams
feed small lakes that evaporate during
dry periods and these create these large
flat salt salt beds sometimes these dry
lakebeds that as the salt dissolved in
the lake water precipitates out of
solution and it stays behind as a white
evaporate
we have the deranged and contorted
patterns here we have these are these
are developed in the disruption of
pre-existing drainage patterns and here
in this case we see a dendritic pattern
that was altered by alter altered but
then overrun by a glacier the glacier
left behind all fine grain material that
forms wetlands and deposits that dam the
stream to impound a small lake
finally the tributary streams appear
significantly more contorted than they
were prior to glaciations as partly
because again material has been
deposited in a way that's very different
and it's also it's topography of the
landscape which also alters water flow
patterns
so here are questions how would you
classify a tart week well let's take a
look at hundred Greek and through the
ArcGIS website here's an image of it
this looks very much we see the outlet
for drainage up here in the north
northeastern corner you can make out
though when you look specifically at the
map with using the ArcGIS tool you can
make out that the mapper - that the
drainage pattern itself is very much the
dendritic dendritic pattern
finally if we want to look at if you
want to look for other classes of
systems listed be old I suggest it or
the systems that we looked at i suggest
first of all that you look at some of
the playa brainy systems to look for
some of the systems that are actually
internal rating internal that would be
for example a central drainage system if
you're interested in a drainage system
that is more of a radial drainage system
look on the flanks of Mount lassen to
see what the drainage patterns look like
they're about lassen is a fairly recent
volcanic oh as a result of a fairly
recent volcanic eruption you'll probably
find a radial pattern in that kind of
terrain