Flooding - Streams Flashcards
streams can be subdivided according to
- whether they are water-holding or not
- linear form of the river
- cross-profile or “transverse section” of the river
- length-profile or “longitudinal profile”
- genesis or evolution of the river
three types of streams
perennial, ephemeral, intermittent
A stream that has flowing water year-round during a typical year. The water table is located above the streambed for most of the year. Groundwater is the primary source of water for stream flow. Runoff from precipitation is a supplemental source of water for stream flow.
perennial
A stream that has flowing water during certain times of the year, when groundwater provides water for stream flow. During dry periods, this stream may not have flowing water. Runoff from precipitation is a supplemental source of water for stream flow.
intermittent
A stream that has flowing water only during or for a short duration after precipitation events in a typical year. In many states, this term refers to streambeds that are located above the water table yearround and streams where groundwater is not a source of water for the stream.
ephemeral
a smooth concave profile which is steep a the source and gentle at the mouth. It has no obstructions.
graded profile
The pattern of drainage which arises from and closely follows the trends of the underlying strata is called
concordant drainage
Those streams whose courses are the direct consequence of the initial topography
consequent streams
this stream flows in the same direction as that of the initial consequent stream, but which develops in response to a new base level formed due to inversion of relief.
resequent stream
are loose rock particles/sediments deposited on a stream
alluvium
what are the types of load?
bed load
suspended load
dissolved load
one of the key factors in a stream’s ability to erode the landscape is __________
velocity of water
what happens when water enters a meander bend?
it is forced to slow down on the inner part of the bend, but speeds up on the outer part
are unstable overhang located at the outer bank which is produced by the velocity increase on the outer bank and subsequently enhances the ability of the water to erode into the bank
cutbanks
accumulation of sediments on the inner bank due to slowing down of water
point bar
manifestations of active stream erosion
cutbanks
point bar
explain how stream channel migrates and become wider
when a stream erodes away one bank and deposits sediment along the opposite side.
as flowing water erodes cutbanks, it creates an unstable overhang which then will collapse (mass wasting.
the lateral migration of stream combined with mass wasting produces wider valleys
Grains are sorted by their size, density, and shape during erosion, transport, and deposition by traction currents.
hydraulic sorting
t or f: downcutting by streams is performed by the stream itself
f (performed by sediments)
sediments in streams physically scrapes or wears away rock in a process called
abrasion
evidence for stream abrasion in solid rock can be seen in
potholes
how does potholes form?
during periods of high discharge when water column develops a swirling motion called an eddy current, causing sediments to rotate and grind holes into the rock
a circular current of water
eddy current
the velocity of a particular stream is controlled by the _______ called ________; also referred to as ____
steepness of the channel ; stream gradient ; grade
is described as the change (loss) of elevation of the stream with distance downstream.
stream gradient
the lowest level to which a stream can erode
base level
this is often referred to as ultimate base level
sea level
why is sea level considered as the ultimate base level?
because the ocean is the end or low point of most rivers
what is the lowest area that is below sea level?
Dead Sea
these form when a streams ability to cut downward is reduced by a resistance rock body, lake, or inland sea
temporary base level
what possibly reduces a streams ability to incise thus forming temporary base levels?
resistance rock body, lake, or inland sea
the ability of running water to transport and deposit sediment is dependent on _____________ and _________
water velocity ; type of particles being transported
describes the fraction of solid particles that is in a suspended state
suspended load
t or f: suspended load moves at the same velocity with the water
t
this is what makes stream appear muddy
suspended load
consists of sediment particles that roll, bounce, or remain stationary on streambed
bed load
highly concentrated bedload layers that are developed beneath and driven by turbulent overlying flows
traction carpet
the geologic process whereby a current transports larger, heavier rocks by rolling or sliding them along the bottom
traction
a sediment transport process that moves grains across the bottom by bouncing or hopping.
saltation
anytime a sediment is in motion, individual particles will undergo _____ causing it to become more ______ and more ______
abrasion; smaller; rounded
t or f: smaller and rounded grains can be transported farther than angular grains
t
the first particles to be removed from the bed load are the _____, ______, and ______-
smallest, least dense, and most angular
the process whereby water separates sediment grains based on their size, shape, and density
hydraulic sorting
hydraulic sorting sorts sediments base on:
size, shape, and density
the combination of ________ and __________ produces relatively pure deposits of sand and clay
hydraulic sorting and chemical weathering
this concentrates high-density particles thereby creating valuable ore deposits
hydraulic sorting
what are examples high-density particles does hydraulic sorting concentrates?
gold, platinum, and titanium
t or f: hydraulic sorting aids in creating placer deposits
t
form when mechanical sorting causes concentration of heavy minerals of economic interest
fluvial placer deposits
the first particles to return to bed load are the _____, _____, ______
largest ; most dense; most round
hydraulic sorting leads to deposits called ____
bars
bars located near the headwaters are often composed of ______ and ___
boulders and coarse gravel
bars located in downstream areas are composed of________
sand-sized materials
t or f: stream gradient in downstream areas is less steep
t
crescent-shaped deposits found on the inside of meander bends
point bars
are mound-shaped channel deposits consisting of sorted material ranging from boulders to coarse gravel to fine sand
bars
crescent-shaped bars
point bars
where does point bar develop?
inside the meander bends
are formed when a river enters a lake or ocean and splits into smaller channels and begins to deposit sediment due to a decrease in velocity
delta
what is the grading of deposition of sediment in a delta?
reverse (prograding)
the weight from the continuous influx of sediment in deltas over time can cause the seafloor to sink and cause ______________
land subsidence
a land subsidence allows deltas to become _______ and _________, thereby creating new land area
thicker and grow seaward
where and how does a delta form?
deltas form at the mouth of a river where velocity decreases therefore, depositing sediments and creating small channels
on what gulf does mississipi river feeds into?
gulf of mexico
alluvium:streams ; ________:hillslopes
colluvium
are large fan-shaped deposits that form where steep mountain streams empty out onto valley floors at the mouth of rivers
alluvium
coalition of alluvial fans
bajada
a channel that is choked with sediment is called a ______
braided streams
streams also transport considerable amounts of dissolved ions (charged atoms) in what scientists refer to as ________
dissolved load
how are alluvial fans formed?
abrupt changes in gradient and velocity causes sediment to deposit, choking the stream
overtime, the stream migrates across the entrance to the valley creating a fan-shaped deposit
flat portion of the valley and the area that is first inundated during flooding
floodplain
erosion on the outside of meander bend produces _______ over time, whereas deposition on the inner banks help build a flat plain on the valley floor called a _____________
wider valleys ; natural floodplain
what is floodplain’s primary role?
periodically store large volumes of water moving through a drainage basin
are pair of ridges that run parallel to the bank which are formed due to the deposition of sediment, commonly sand, at the edge of the bank
natural leeves
are areas on the floodplain that are poorly drained and can remain wet long after a flood
back swamps
are old floodplain left high and dry as river migrates
stream terraces
t or f: back swamps are back portion of natural leeves
t
well-defined stream terraces are often developed in response to
changes in base level due to:
1. sea level drop
2. tectonic uplift
t or f: stream terraces are most likely inundated during a flood
F (less likely)
in a __________ stream clay in in suspension while sand are on bed
low velocity
in a __________ stream, both sand and clay are in suspension
high velocity
t or f: natural leeves are often found along river channels that have well-defined floodplains
t
t or f: flooding causes an abrupt decrease in velocity
t
are developed where floodwaters are unable to return to the main channel
backs swamps
how are natural leeves formed?
formed during flooding where abrupt decrease in velocity causes a deposition of sand-sized particles along the banks
what are deposited on the floodplain during flooding?
finer particles of silt, clay, and organic matter
as flow erodes the banks, it favors the development of a ______________ channel
meandering
abandoned main channel, diverted because of flooding events
oxbow lake
an emptied oxbow lake
meander scar
explain how oxbow lakes are formed
A point bar grows into the river, making the meander more pronounced. As the meander expands, two adjacent concave banks grow closer to one another.
Eventually, continued erosion and high water events like floods or seasonal high water flows can join two concave banks together. The main river channel has changed its course, leaving the riverbend cut off from the main flow of the river.
areas subjected to stream channel migration
meander belt
the part of a valley bottom across which a stream shifts its channel from time to time especially in flood.
meander belt
areas across which the river is prone to move
channel migration zone
belt of meandering
meander “train”
