Dams and Water Supply

1
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.

2
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.

3
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.

4
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.

5
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.

6
Dams 5

• Suitable building materials such as hard
  rock/concrete for concrete/masonry dams.
• Clay/sediments for earth dam/aggregates.

7
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.

8
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.

9
Water 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

10
Surface v Underground Supplies

• Surface good points
• Easily accessible.
• Can be used for recreation or navigation.
• Can be of scenic beauty.

11
Surface 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).

12
Surface 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

13
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

14
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.

15
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 its use sustained.
• Overuse for irrigation in hot climates can make
  the water saline which can be a problem.