DAMS AND RESERVOIRS

Digley Reservoir, Holmbridge

Factors which affect the location of dams• Areas of high rainfall so the dam is filled naturally.

• Sources of local stone, earth or concrete so that transport costs are not too high.

• A high local water table so that water does not leak away.• Based on impermeable rocks so that water does not leak

out.• Concrete or rock dams need firm foundations so that they

can be safely anchored.• Rocks should dip upstream not downstream so that the

dam does not slide down the valley.• An area which is not earthquake prone, otherwise the

dam could be damaged.• There should be no faults or major joints so that water

does not leak out.• Local rocks do not contain heavy mineral veins, like lead

or zinc which would pollute the water.

Draw a diagram to show the perfect site for a dam and

reservoir.

Quarry to provide rock in large amounts

Area of high rainfall

Dip of rocks

Strong rock foundations for dam supports

reservoir

No faults or major joints

Impermeable rocks underlying reservoir

dam

There are four main types of dams:

•Embankment dams•Arch dams•Gravity dams•Buttress dams

Embankment dams

This dam has a by-pass channel to prevent overtopping of the dam by water.

Butterley dam and reservoir, Marsden

Diagram of an embankment dam.

Diagram from Geology and Environment in Britain and Ireland by Nigel Woodcock

Explain each feature of this dam.

Draw a diagram of an embankment dam.

coreRock or earth fill

Rock or earth fill Cut-off

water

Add a title

Plan and cross

section of Digley Dam,

1947, Holmbridge road

water

reservoiroverflow

Impermeable clay

Stony earth fill to add weight

Earth embankment at Digley, Holmbridge

Earth fill

Road on top of dam

reservoir

High water level

Rip rap is a layer of large rocks which cannot be moved by waves. Rip rap protects the earth dam from erosion.

Stone armour to protect dam from erosion by waves

Digley Dam, Holmbridge

Overflow on Digley DamThis maintains the reservoir level at its maximum height and prevents it overflowing.

Back of Winscar Dam, Dunford Bridge. This dam started to leak in 2000 and was

emptied so that it could be repaired. It was covered by an impermeable membrane to prevent water leaking through cracks in the concrete.

Hoover Dam, R. Colorado,

U.S.A

Strong rock abutments in a narrow valley

Arch dams

Diagram of an arch damExplain each feature of this dam.

The dam will be very firmly anchored to the walls at each side of the valley.

Draw a diagram of an arch dam.

Dam will need firm anchorages at both sides.

Curved shape to brace against weight of water.

reservoir

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Gravity damsGravity dams are kept in place by virtue of their weight with braces them against the weight of

water behind.

Three Gorges Dam, China

Diagram of a gravity dam

Draw a diagram of a gravity dam.

Reservoir

Weight to keep dam stable

Wide base for stability

Made of strong rock or concrete

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Buttress damsButtress dams are similar to gravity dams, but the buttresses at the front of the dam take the weight of the water.

Glen Errochty, Scotland.

Diagram of a buttress dam.

Draw a diagram of a buttress dam.

reservoir

Internal fill of impermeable material

Strong rock sides

Buttress braces dam against the weight of the water

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What type of dam is this?

Butterley Dam, Marsden

What type of dam is this?An embankment dam

What type of dam is this?A buttress dam

Chief Joseph Dam, Washington State, USA

What type of dam is this?A gravity dam

Grand Coulee Dam, Washington State, USA

What type of dam is this?

Kariba Dam, River Zambezi, between Zimbabwe and Zambia

Arch Dam

What type of dam is this?Buttress/gravity dam

Hume Dam, River Murray, Australia

THE END