THE HYDROLOGY AND FLUVIAL
GEOMORPHOLY
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Water has changed little over the past hundred million
years.
Water moves around the world, changes forms, is
taken in by plants and animals, but never really
disappears. It travels in a large, continuous loop.
It is a closed system, meaning it has no other
interferences; what goes in stays in. It does not change
as it evolves. No gains or losses from outside are added
to the system
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The movement of water from the sea through the
air to the land and back to the sea.
HOW DOES IT WORK?
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It is a system of inputs, stores and flows.
Water covers 70% of the earth’s surface
Water exists in three states: liquid, solid and
invisible vapour (gas).
It forms the oceans, seas, lakes, rivers and the
underground waters found in the top layers of the
earth’s crust and soil cover.
In a solid state, it exists as ice and snow cover in
polar and alpine regions.
A certain amount of water is contained in the air as
water vapour, water droplets and ice crystals, as well
as in the biosphere. Huge amounts of water are
bound up in the composition of the different minerals
of the earth’s crust and core.
HOW DOES THE HYDROLOGICAL CYCLE WORK?
The stages of the cycle are:
 Evaporation
 Transport
 Condensation
 Precipitation
 Groundwater
 Run-off
EVAPORATION
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Water is transferred from the surface to the
atmosphere through evaporation, the process by
which water changes from a liquid to a gas. The
sun’s heat provides energy to evaporate water
from the earth’s surface. Land, lakes, rivers and
oceans send up a steady stream of water vapour
and plants also lose water to the air
(transpiration).
Approximately 80% of all evaporation is from the
oceans, with the remaining 20% coming from
inland water and vegetation.
TRANSPORT
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The movement of water through the atmosphere,
specifically from over the oceans to over land, is
called transport. Some of the earth’s moisture
transport is visible as clouds, which themselves
consist of ice crystals and/or tiny water droplets.
Clouds are propelled from one place to another by
either the jet stream, surface-based circulations like
land and sea breezes or other mechanisms. However,
a typical cloud 1 km thick contains only enough
water for a millimeter of rainfall, whereas the
amount of moisture in the atmosphere is usually 1050 times greater than this.
Most water is transported in the form of water
vapour, which is actually the third most abundant
gas in the atmosphere. Water vapour may be
invisible to us, but not to satellites which are capable
of collecting data about it.
CONDENSATION
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The transported water vapour eventually
condenses, forming tiny droplets in clouds.
PRECIPITATION
The primary mechanism for transporting water
from the atmosphere to the surface of the earth is
precipitation.
 When the clouds meet cool air over land,
precipitation, in the form of rain, sleet or snow, is
triggered and water returns to the land (or sea).
A proportion of atmospheric precipitation
evaporates.
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GROUNDWATER
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Some of the precipitation soaks into the ground and
this is the main source of the formation of the waters
found on land - rivers, lakes, groundwater and
glaciers.
Some of the underground water is trapped between
rock or clay layers - this is called groundwater. Water
that infiltrates the soil flows downward until it
encounters impermeable rock and then travels
laterally. The locations where water moves laterally
are called ‘aquifers’. Groundwater returns to the
surface through these aquifers, which empty into
lakes, rivers and the oceans.
Under special circumstances, groundwater can even
flow upward in artesian wells. The flow of
groundwater is much slower than run-off with speeds
usually measured in centimetres per day, metres per
year or even centimetres per year.
RUN-OFF
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Most of the water which returns to land flows
downhill as run-off. Some of it penetrates and
charges groundwater while the rest becomes river
flow. As the amount of groundwater increases or
decreases, the water table rises or falls accordingly.
When the entire area below the ground is saturated,
flooding occurs because all subsequent precipitation
is forced to remain on the surface.
Different surfaces hold different amounts of water
and absorb water at different rates. As a surface
becomes less permeable, an increasing amount of
water remains on the surface, creating a greater
potential for flooding. Flooding is very common
during winter and early spring because frozen
ground has no permeability, causing most rainwater
and meltwater to become run-off.
DRAINAGE BASINS
 Geomorphologist
and hydrologists often
view streams as being part of drainage
basins. A drainage basin is the
topographic region from which a stream
receives runoff, throughflow, and
groundwater flow. Drainage basins are
divided from each other by topographic
barriers called a watershed .A watershed
represents all of the stream tributaries
that flow to some location along the
stream channel.
THE FOLLOWING IMAGE SHOWS THE NESTED NATURE OF DRAINAGE BASINS
AS DETERMINED FROM A TOPOGRAPHIC MAP SHEET. THE RED LINES DESCRIBE
THE WATERSHEDS FOR THE DRAINAGE BASINS OF FIRST ORDER STREAMS. THE YELLOW
LINES DEFINE THE WATERSHEDS FOR TWO DRAINAGE BASINS FROM LOCATIONS
FURTHER UPSTREAM.
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Drainage basins are commonly viewed by scientists as
being open systems.
Inputs to these systems include precipitation, snow
melt, and sediment. Drainage basins lose water and
sediment through evaporation, deposition, and
streamflow.
A number of factors influence input, output, and
transport of sediment and water in a drainage basin.
Such factors include topography, soil type, bedrock
type, climate, and vegetation cover. These factors also
influence the nature of the pattern of stream channels
HYDROGRAPHS:A HYDROGRAPH MAY BE USED TO SHOW HOW THE WATER FLOW
A DRAINAGE BASIN (PARTICULARLY RIVER RUNOFF) RESPONDS TO A PERIOD OF
RAIN.
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This type of hydrograph is known as
a storm or flood hydrograph and it is
generally drawn with two vertical
axes. One is used to plot a line graph
showing the discharge of a river in
cumecs (cubic metres per second) at
a given point over a period of time.
The second is used to plot a bar
graph of the rainfall event which
precedes the changes in discharge.
The scale on the horizontal axis is
usually in hours/days and this allows
both the rain event to be recorded
and the subsequent changes in river
discharge to be plotted
SHAPE
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The shape of the hydrograph varies according to a number
of controlling factors in the drainage basin but it will
generally include the following features.
The baseflow of the river represents the normal day to day
discharge of the river and is the consequence of
groundwater seeping into the river channel. The rising
limb of the hydrograph represents the rapid increase in
resulting from rainfall causing surface runoff and then
later throughflow. Peak discharge occurs when the river
reaches its highest level. The time difference between the
peak of the rain event and the peak discharge is known as
the lag time or basin lag. The falling limb (or recession limb
as it is sometimes known) is when discharge decreases and
the river’s level falls. It has a gentler gradient than the
rising limb as most overland flow has now been discharged
and it is mainly throughflow which is making up the river
water.
INFLUENCE OF BASIN SHAPE
A number of factors
(known as drainage basin
controls) influence the way
in which a river responds
to precipitation and have
an effect on the shape of
the hydrograph.
 The size, shape and relief
of the basin are important
controls.
Water
takes
longer to reach the trunk
stream in a large, round
basin than in does in a
small, narrow one
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INFLUENCE OF STEEPNESS
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Where gradients are
steep, water runs off
faster, reaches the river
more quickly and causes
a steep rising limb.
Prolonged heavy rain
causes more overland
flow than light drizzly
rain
DIFFERENCES
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Areas of permeable rocks
and soil allow more
infiltration and so less
surface run off.
WATER BALANCE
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A general water balance equation is:
P = Q + E + ΔS
Where : P is precipitation
Q is runoff
E is evapotranspiration,
ΔS is the change in storage (in soil or the bedrock)
A water balance can be used to help manage water supply
and predict where there may be water shortages. It is also
used in irrigation, flood control and pollution control.
The water balance can be illustrated using a water balance
graph
which
plots
levels
of
precipitation
and
evapotranspiration often on a monthly scale.
Several monthly water balance models had been developed
for several conditions and purposes. Monthly water balance
models had been studied since the 1940s.
RIVER CHANNEL PROCESSES &
LANDFORMS, FLOOD &
MANAGEMENT
(1) RIVER PROCESSES.
(2) DEPOSITION & SEDIMENTATION (HJULSTROM
CURVE)
(3) VELOCITY & DISCHARGE
(4) PATTERNS OF FLOW
(5) CHANNEL TYPES
(6) CHANNEL LANDFORMS
(7) FLOOD (CAUSES, IMPACT AND MANAGEMENT)
RIVER PROCESSES:
Three river processes:
1.
Transportation
2.
Deposition
3.
Erosion
RIVER TRANSPORTATION
The load is transported by 4 ways:
(i)
Saltation: when pebbles, sand and gravel (bedload) are lifted
up by current and bounced along the bed in a hopping motion.
(ii)
Traction: when largest boulders and cobbles (bedload) roll or
slide along the bed.
traction
saltation
(iii)
Suspension: very fine particle such as clay and silt (suspended
load) are dislodged and carried by turbulence in a fast flowing
river.
(iv)
Solution: water flowing within a river channel contains acids
(e.g. carbonic acid from precipitation) dissolve the load such as
limestone in running water and removed in solution.
solution
suspension
RIVER DEPOSITION
Deposition:
When velocity begins to fall, it has less energy and no
longer had competence and capacity to carry all its load
so largest particles, materials begins to be deposited.
When occur?
1.
Low discharge during period of low precipitation
2.
Less velocity when river enter sea or lake.
3.
Shallow water occurs on inside of a meander.
4.
The load suddenly increase (debris from landslide)
5.
River overflow its bank so velocity outside channel is
reduced. (resulting in floodplain)
RIVER EROSION.
Erosion: wearing away of river bed and bank.
There are four main process of erosion:
(i)
Corrasion: occurs when the river picks up materials and rubs
it along its bed and banks, wearing them away by abrasion,
effective during flood. Major method by which river erodes
both vertically and horizontally.
Landforms: potholes. (turbulent eddies in the current can swirl pebbles
around to form potholes that are hollows in river bed and pebbles are
likely to become trapped)
potholes
(ii)
Attrition: As bedload moved downstream, boulders collide with
other material and the impact may break the rock into smaller
pieces. In time angular rocks become increasingly rounded.
(iii)
Solution/corrosion: This process in independent of river
discharge and velocity. It is related to chemical composition of
water e.g. concentration of carbonic acid and humid acid.
(iv)
Hydraulic action: The sheer force of the water as the turbulent
current hits banks (outside of meander) pushes water into
cracks. The air in cracks compressed, pressure increased and
in time bank will collapse.
Cavitation: is a form of hydraulic action caused by bubbles of
air collapsing.
HJULSTROM CURVE
HJULSTROM CURVE
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The Hjulstrøm curve is a graph used by hydrologists to determine
whether a river will erode, transport or deposit sediment. The graph
takes sediment size and channel velocity into account.
The curve shows several key ideas about the relationships between
erosion, transportation and deposition.
The Hjulstrøm Curve shows that particles of a size around 1mm require
the least energy to erode, as they are sands that do not coagulate.
Particles smaller than these fine sands are often clays which require a
higher velocity to produce the energy required to split the small clay
particles which have coagulated.
Larger particles such as pebbles are eroded at higher velocities and very
large objects such as boulders require the highest velocities to erode.
When the velocity drops below this velocity called the line of critical
velocity, particles will be deposited or transported, instead of being
eroded, depending on the river's energy.
Velocity and Discharge:
Discharge: is the amount of water originating
as precipitation which reaches the channel
by surface runoff, throughflow and baseflow.
Q=AXV
(Q: discharge, A: cross-sectional area and
V: velocity)
VELOCITY:
1. Velocity: speed of a river (m/s)
2. Velocity of a river is influence by 3 factors:
(i)
Channel shape in cross-section.
(ii)
Roughness of the channel’s bed and banks.
(iii) Channel slope.
PATTERNS OF FLOW
As water flows downhills under gravity, velocity decreases.
This is not only due to friction found along river bed and
banks, but also internal friction of water and air resistance
on the surface. There are two patterns of flow:
1.Laminar flow : horizontal movement of water
(rarely found), common in lava flow.
2. Turbulent: a series of erratic eddies, both vertical and
horizontal, in a downstream direction.
3. Helicoidal flow: a corkscrew movement, in a meander.
It is responsible for moving material from the
outside of one meander bend and depositing
on the inside of the next bend.
CHANNEL TYPES
(a) Straight channel
(b) Braided channel
(c) Meander channel
STRAIGHT CHANNELS
BRAIDED CHANNEL
What? A braided stream has islands/ eyots of deposited material within the
channel.
Description:
Overall channel is straight with eyots and smaller channels.
It rapidly and frequently change position.
When?
It occurs when the load contain high proportion of coarser sands and gravel.
Area:
Semi-arid environment.
Braided reach of Lillooet River,
southwestern British Columbia.
WHAT? Bends in course of a river channel.
MEANDER
HOW OCCUR?
1. Begin when a river approaches its middle course & gradient channel
is less steep.
2. It results from helicoidal flow with faster current spirals downstream in
corkscrew fashion. Movement result in erosion on outside bend of meander to
form river cliff and deposit on inside bend called slip off slope.
CHARACTERISTICS:
1. River cliff on outside of bend and gentle
sloping slip- off slope called point bar on
inside of bend of meander.
RIFFLE AND POOLS
Riffles: deposition of a coarse material that create
areas of shallow water.
Pools: areas of deeper water between riffles.
Pools and riffles developed in section along river channel
which create different gradient of channel.
Coarse pebbles create steeper gradient than eroded
pools.
This is a Profile of a River-Middle, Upper and Lower Stages:
o
o
o
In the upper course of the river, there are many features.
The river channel is narrow and fast, with interlocking spurs and
v-shaped valleys
Steep drops in the river with extremely fast flows are waterfalls,
with retreating gorges of recession, ending with a plunge pool.
FLUVIAL LANDFORMS
Effects of fluvial erosion:
1.
(a)
V-shaped valleys
A river erode vertically by traction or saltation which resulted in a
steep- sided valley called a V-shaped valley.
Steepness of valley sides depend of factors such as:
(i)
Climate: valley are steeper where there is sufficient rainfall.
(for mass movement and allow river to transport bedload and
erode vertically)
(ii)
Rock structure: resistant, permeable rocks such as limestone
produce vertical sides.
(iii)
Vegetation: it helps to bind soil together and keep the hillslope
more stable.
Vertical
erosion is
dominant
The river cuts downwards like a saw.
This happens in the upper part of the river and makes the valley go
deep.
Rain erodes the edges to make it wider at the top.
Interlocking spurs
It forms because the river is forced to follow a winding course
around the protrusions of the surrounding highland, resulting
in spurs interlock.
Interlocking spur.
2. Water fall:
A waterfall form when a river, after flowing over relatively hard
rock meets a band of less resistant rock flow over the edge of a
plateau. Over a period of years, the edges of this shelf will
gradually break away and the waterfall will steadily retreat
upstream, creating a gorge of recession.
Havasu fall, Arizona.
Middle course of the river has more energy and a high volume of water. The
gradient here is gentle and lateral (sideways) erosion has widened the river
channel. The river channel has also deepened. A larger river channel means there
is less friction, so the water flows faster:
o
As the river erodes laterally, to the right side then the left side, it forms large
bends, then horseshoe-like loops called meanders.
o
The formation of meanders is due to both deposition and erosion.
o
The force of the water erodes and undercuts the river bank on the outside of the
bend where water flow has most energy.
o
On the inside of the bend, where the river flow is slower, material is deposited.
o
Over time the horseshoe become tighter, until the ends become very close
together. As the river breaks through and the ends join, the loop is cut-off from
the main channel. The cut-off loop is called an oxbow lake.
EFFECT OF FLUVIAL DEPOSITION.
Deposition of sediment takes place where there is a decrease in energy
or an increase in capacity which makes the river less competent to
transport its load.
It can occur anywhere from upper course, where boulders may be left,
to the mouth where fine clays may be deposited.
FLUVIAL LANDFORMS:
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Floodplains:
A floodplain is a mostly flat area of land bordering a river subjected to
periodic flooding. It is made of silts and sands which have been
deposited over many years by the river.
Levees
When river overflows its banks, the increase in friction produced by
the contact with the floodplain causes material to be deposited.
The coarsest material is dropped first to form a small, natural
embankment (levee) alongside the channel. During subsequent
periods of low discharge, further deposition will occur within main
channel causing bed of the river to rise and the risk of flooding to
occur.
Floodplains and levees.
Delta:
It is composed of fine sediment which is deposited when a river
losses energy and competence as it flows into an area of slow
moving water such as a lake or sea. The shape resembled that
of delta, the fourth letter of the Greek alphabet (
)
Delta provide world’s fertile land, while shallow and frequently
changing river channels hinder navigation.
There are three types:
(a)
Arcuate (fan-shaped delta) : having rounded, convex outer margin e.g.
Nile.
(b) Cuspate (tooth’s delta) : where material brought down by a river is
spread out evenly on either side of its channel. E.g. Tiber
(c ) Bird’s foot: where the river has many distributaries bounded by
sediment and which extent out to sea like the claws of a bird’s foot.e.g.
the Mississippi.
Arcuate delta e.g. River Nile.
Bird’s foot e.g.Mississippi river.
Cuspate delta e.g. Tiber.
FLOOD
Causes
 Impact
 Management
 Case studies
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FLOODING
CAUSES (Human and physical factors)
(I) PHYSICAL FACTORS:
When does flooding occur?
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Water overflows river banks onto surrounding area.
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Occur when water available is more than infiltration capacity.
When does water overflow?
1.
Intense precipitation
Prolong rainfall in saturated soil.
i.e. clay prone to overlandflow (smaller pores)
Soil already saturated thus reduce infitration capacity. (prone to flood)
2.
3. Sudden increase in temperature (rapid snow melt)
(II) HUMAN FACTORS:
1.
Dam burst
2.
Land use (drainage system, digging ditch, ploughing up and down slope)
3.
Urbanisation (land made impermeable in road building)
4.
Deforestation.
HYDROLOGY & FLUVIAL
GEOMORPHOLOGY
EXERCISES!!!!
Look at the diagram:
1. List down input & output
2. Which are the storage &
flow.
3. How does water from
surface storage reaches
groundwater storage?
4. Name the flow marked A
and B.
5. Define terms shown in
diagrams.
Catchments of rivers X & Y
hydrographs over
24 hours of the two rivers.
Using both diagram explain why the
discharge of the two rivers are different
Explain how each of these influence
storm hydrograph:
Drainage basin shape, geology,
rainfall intensity, drainage density
Describe the differences between
the discharges of rivers X and Y in
response to the rainfall
1. Name the flows shown
as A, B & C.
2. Describe what is meant by
percolation.
3.Describe and explain the
occurrence of the flows A,
B and C.
Flow of water in a cross section of soil and bedrock
WATER
BALANCE
Briefly define
the term water
balance.
2. Describe one reason
why water balance
may vary over
time.
1.
RIVER PROCESS
1.
2.
3.
Briefly describe the processes by which rivers can
erode their channels.
[8]
Briefly describe laminar, turbulent flow and
helicoidal flow and draw them.
[6]
Name four methods by which rivers transport their
load and briefly describe these methods.
[8]
HJUSTROM CURVE.
1. Name the type of sediment that requires the
lowest velocity to be eroded. [1]
2. Name the type of sediment that is likely to be
transported at all velocities. [1]
3. Describe and explain the relationship between
water velocity and the erosion of clay
and sand particles. [4]
4. Explain the variation in water velocity that is
required to transport and to deposit
sediments of different particle diameter. [4]
5. Describe what is river deposition and what
are the condition needed for it to occur.
LANDFORMS
1. Draw a labelled diagram to show each of the following
landforms & explain how they are formed:
(a)
Meandering
(b)
Flood plain and levees.
(c)
Delta
(d)
Ox-bow lake
(e)
Water fall
(f)
Braided channel.
FLOOD
Explain how river floods might be predicted.
Giving examples, describe the methods which
may be used to reduce the effects of flooding.
 Describe the main features of river flood plains
and explain why flood plains may present
problems for human settlements.
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HUMAN ACTIVITIES
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ON FLOW
Suggest how human activities might affect flows
within a river channel.
How can changes in land use affect flows and
stores in a drainage basin?
How can the abstraction (removal) and the
storage of water by humans affect flows and
stores within a drainage basin.
Explain how urbanisation
channel flows.
can
affect
river