Transcript Dams and Water Supply

Dams and Water Supply
• The specification states that in
relation to dams you need to be able
to:
• Interpret the geological factors
affecting the construction and siting
of dams and reservoirs.
Dams
Nature of the underlying
rocks.
• Depth of weathered rock:
– because weathered rock is
not as strong as
unweathered rock.
• Mechanical strength of the
rock/load bearing capacity:
– To support the massive
weight of the dam wall.
• Impermeable rocks are
important, why?
– To stop the water infiltrating
away.
Dams 2
• Suitable seal between
rock and dam.
• Seal could be
improved by grouting.
• Use of a cut off curtain
to stop water leakage.
• Lack of faults – to stop
leaks.
• Lack of jointing – to
stop leaks.
Dams 3
• Strata dip upstream reduces the possibility of
instability of the structure.
• Lack of folds which could
permit leakage due to joints
at the hinge.
Dams 4
• Lack of seismic activity
which could crack the
dam or cause landslips.
• Lack of landslips.
• Lack of volcanic activity.
• Absence of underground
workings or presence of
hidden river channels
which could lead to the
possibility of collapse.
Dams 5
• Suitable building materials
such as hard rock/concrete
for concrete/masonry dams.
• Clay/sediments for earth
dam/aggregates.
Dams 6
• Other obvious features
include:
• A steep sided valley to
capture the water.
• A catchment area that has a
reasonable amount of
rainfall.
• A catchment area with
some impermeable rocks to
allow runoff to the river.
• Lack of sediments in feeder
streams which could lead
to the silting up of the
reservoir.
Water Supply
• The specification states that you need to
be able to:
• Describe water supply in relation to river,
reservoir and underground sources.
• Understand the advantages and
disadvantages of surface and underground
supply.
• Understand that water resources are both
renewable and sustainable if carefully
developed.
Water Supply: Sources
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The 3 main sources are:
Rivers
Reservoirs
Underground or groundwater.
We have already discussed different types
of groundwater aquifers and
reservoirs/dams.
• I think you already know about rivers too.
• Therefore we will move onto the next
section:
Surface v Underground Supplies
Surface good points:
• Easily accessible.
• Can be used for
recreation or
navigation.
• Can be of scenic
beauty.
Surface v Underground Supplies
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Surface bad points:
May be polluted by effluent
or contaminated runoff.
During droughts water may
be lost.
In hot areas evaporation
may remove a large
proportion of the water.
Of no use in arid regions
(central Australia).
Surface v Underground Supplies
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Underground Good Points.
Spring water becomes pure
and drinkable by being
filtered by passage through
sediments.
Reliable/constant - non
seasonal supply.
Accessible even in areas
with no rain.
Maintained hydrostatic
pressure.
Lack of surface pollutants
Surface v Underground Supplies
Underground negative points:
• problem of leachate and
pollution from waste tips.
• problem of recharge and over
pumping.
• spring water becomes
unpalatable if:
– leachates contaminate the flow
– seawater contaminates the flow
Surface v Underground Supplies
• too many salts in artesian
supply makes water saline.
• nitrates/fertiliser contaminate
the water.
• radioactive water from nuclear
waste.
• the water table may fall during
summer months cutting supply.
• the water table may be lowered
by over pumping.
• recharge may be slow.
• hydrostatic pressure falls
through time.
Sustainable Water Supply
• The specification states that you
need to:
• Understand that water resources are
both renewable and sustainable if
carefully developed.
• Water moves through the water cycle
and is just borrowed by humans.
• As long as it is put back into the
system in a reasonably
uncontaminated way then it can be
renewable and it’s use sustained.
• Overuse for irrigation in hot climates
can make the water saline which can
be a problem.