dams and water supply the specification states that in relation to dams you need to be able to:...
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Dams and Water SupplyDams 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.
DamsDamsNature 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 2Dams 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 3Dams 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 4Dams 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 5Dams 5
• Suitable building materials such as hard rock/concrete for concrete/masonry dams.
• Clay/sediments for earth dam/aggregates.
Dams 6Dams 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 SupplyWater 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: SourcesWater Supply: Sources
• 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 SuppliesSurface v Underground Supplies
Surface good points:• Easily accessible.• Can be used for
recreation or navigation.
• Can be of scenic beauty.
Surface v Underground SuppliesSurface v Underground Supplies
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 SuppliesSurface v Underground Supplies
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 SuppliesSurface 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 SuppliesSurface 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 SupplySustainable 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.