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.