Damns

Question 1

name 4 types of damn

Answer 1

gravity
buttress
arch
embankment

Question 2

embankment dam

Answer 2

Made from sediment + rock. Broad based + require large volumes of suitable earth and rock to fill. Faced with thin layer of concrete or stone on reservoir side to stop erosion.

Question 3

gravity damn

Answer 3

massive impermeable rock structure with sufficient weight o resist load from reservoir. Requires a lot of concrete

Question 4

buttress damn

Answer 4

inclined face on upstream side + buttress supports on downstream side. Uses less concrete but puts a greater load on foundations.

Question 5

arch damn

Answer 5

impermeable concrete shells. Arch shape in plan + cross section so is thin + uses less concrete but is strongest. Vulnerable to earthquakes

Question 6

consequences of building a damn x5

Answer 6

floods land
river level changes 
stops migration 
reservoir silts up- clear water erosion 
heavy rainfall= flooding

Question 7

how can you reduce leakage from a damn? x3

Answer 7

grouting porous+ permeable rocks + fault lines
lining base with clay
cut off curtain- trench dug into rock + filled with concrete

Question 8

how can you ensure strong foundations for a damn?x4

Answer 8

deep foundations to reach bedrock
draining and artificially compacting rock
grouting rock- injecting concrete to increase LBS
piles driven into bedrock

Question 9

why should the beds under a damn dip upstream?

Answer 9

to prevent leakage under the damn

Question 10

what happens if the beds dip into the valley?

Answer 10

landslides due to weight of water entering rock and acting as a lubricant

Question 11

syncline under a damn pros and cons

Answer 11

stronger rocks at centre due to compression

leakage occurs as water flows along permeable beds under damn

Question 12

cons of an anticline under a damn x2

Answer 12

weaker rock due to tensional joints on outside of fold

joints on crest weaken rock and cause leakage

Question 13

problems with faults x3

Answer 13

water leak down fault line
rocks with different load bearing strength brought together
move in an earthquake= collapse

Question 14

why should the sedimentation rate in a damn be low?

Answer 14

otherwise reservoir will silt up and reduce in volume

Question 15

Why is a large steep sided valley the best place for a reservoir? x2

Answer 15

large volume of water storage

only a small damn is required

Question 16

what rocks are most suitable for a damn foundation rock?

Answer 16

igneous and crystalline sedimentary rocks as they have a high LBS

Question 17

what may happen to the rocks surrounding the reservoir due to the increased weight of water? x3

Answer 17

subsidence, slumping, landslips

Question 18

what should the depth of bedrock and weathered rock be?

Answer 18

bedrock should be close to the surface

depth of weathered rock should be low

Question 19

what are the problems with deeply weathered rock?

Answer 19

weakens bed rock, enhances joints and fractures= collapse or leakage under damn

Question 20

what should the porosity and permeability of the rock be?

Answer 20

low to prevent leakage so max amount of water is held

unjointed limestone or igneous rock is ideal

Question 21

why should joints, fractures and solution channels be avoided? x3

Answer 21

leakage
reduces LBS=collapse
joints in valley side= landslips into reservoir

Question 22

why should underground mine working be avoided?

Answer 22

water leaks away
subsidence
collapse

Question 23

problems with hidden infilled river channels

Answer 23

water leaks along permeable sand and gravels. They’re poorly cemented= low LBS

Question 24

what will happen to the height of the water table when the reservoir is filled? x4

Answer 24

surrounding aquifers rise
position of springs change
valley sides become saturated and slip
minor earthquakes due to increased hydrostatic pressure which weaken rock

Question 25

damn

Answer 25

a man-made barrier across a river which is built to hold back water in an artificial lake called a reservoir