Damns Flashcards
name 4 types of damn
gravity
buttress
arch
embankment
embankment dam
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.
gravity damn
massive impermeable rock structure with sufficient weight o resist load from reservoir. Requires a lot of concrete
buttress damn
inclined face on upstream side + buttress supports on downstream side. Uses less concrete but puts a greater load on foundations.
arch damn
impermeable concrete shells. Arch shape in plan + cross section so is thin + uses less concrete but is strongest. Vulnerable to earthquakes
consequences of building a damn x5
floods land river level changes stops migration reservoir silts up- clear water erosion heavy rainfall= flooding
how can you reduce leakage from a damn? x3
grouting porous+ permeable rocks + fault lines
lining base with clay
cut off curtain- trench dug into rock + filled with concrete
how can you ensure strong foundations for a damn?x4
deep foundations to reach bedrock
draining and artificially compacting rock
grouting rock- injecting concrete to increase LBS
piles driven into bedrock
why should the beds under a damn dip upstream?
to prevent leakage under the damn
what happens if the beds dip into the valley?
landslides due to weight of water entering rock and acting as a lubricant
syncline under a damn pros and cons
stronger rocks at centre due to compression
leakage occurs as water flows along permeable beds under damn
cons of an anticline under a damn x2
weaker rock due to tensional joints on outside of fold
joints on crest weaken rock and cause leakage
problems with faults x3
water leak down fault line
rocks with different load bearing strength brought together
move in an earthquake= collapse
why should the sedimentation rate in a damn be low?
otherwise reservoir will silt up and reduce in volume
Why is a large steep sided valley the best place for a reservoir? x2
large volume of water storage
only a small damn is required
what rocks are most suitable for a damn foundation rock?
igneous and crystalline sedimentary rocks as they have a high LBS
what may happen to the rocks surrounding the reservoir due to the increased weight of water? x3
subsidence, slumping, landslips
what should the depth of bedrock and weathered rock be?
bedrock should be close to the surface
depth of weathered rock should be low
what are the problems with deeply weathered rock?
weakens bed rock, enhances joints and fractures= collapse or leakage under damn
what should the porosity and permeability of the rock be?
low to prevent leakage so max amount of water is held
unjointed limestone or igneous rock is ideal
why should joints, fractures and solution channels be avoided? x3
leakage
reduces LBS=collapse
joints in valley side= landslips into reservoir
why should underground mine working be avoided?
water leaks away
subsidence
collapse
problems with hidden infilled river channels
water leaks along permeable sand and gravels. They’re poorly cemented= low LBS
what will happen to the height of the water table when the reservoir is filled? x4
surrounding aquifers rise
position of springs change
valley sides become saturated and slip
minor earthquakes due to increased hydrostatic pressure which weaken rock
damn
a man-made barrier across a river which is built to hold back water in an artificial lake called a reservoir
