12. reserviors, Dams and hydropower Flashcards
what is a reservoir
man made lakes used for storing water
two types of reservoirs
impounded lakes
dammed rivers
exampoe of single purpose reservoir
industry relater-town water supply,
example of multipurpose
water supply irrigation silt retention transportation electricity recreation flood mitigation
different types of dams
arc dam butteress (seires of vertical supports) gravity (resist by own weight) Timber Embankment (rock or earth)
what is an earth dam
trapezoidal embankment
what does an earth dam design ensure
impermeable enough
settlement must not be excessive so as to reduce freeboard
upstream must withstand waves
downstream must withstand rain
bond to foundation to prevent seepage paths
what is piping
internal erosion of foundation or embankment due to seepage, starts at reservoir toe and works pack through most permeable route
avoid seepage by
increasing flow paths
how to increase flow paths
cut off walls (under dam)
impermeable core
blankets upstream and downstream
chimeny drains
what is that top flow path called again
the phreatic surface
and where should the phreatic surface be
below the downstream toe
types of earth filled dams
homogeneous
hydraulic fill (shell gets placed by sedimentaiton)
thic core, thin core, inclined core, rolled rockfill core
concrete deck
asphalt concrete deck
notes on soil placement for earth dam
course-larger than 200 sieve
fine-smaller than 200 sieve
layers should be less than 15cm thick after compaction
pore pressure issue
in rockfill damns, during compaction , pore pressure become greater than uplift from a filled reservoir, meaing construction is less stable
environmental impacts of dams
land inundation moves people threat to wildlife beauty river regiem effects of storage on water quality water bourne diseases induced earthquakes air noise pollution etc
additional structures required
coffer dams-built upstream for construction fish ladders gates power plants locks spillway tunnels valves, vaulve vaults
what is an engineers responsibiity to saftey
-act with integrity-to ultimate effects of human and nature
responsibke fore the cost of the structure
liable to community first, then client
what is live storage made up off
inactive and active storage
types of turbines
Kaplan
Pelton
Francis
cross flow
what is kaplan
reaction, high flow low head
what is pelton
impulse, low flow high head
what is francis
in between
parts of a hydro system
intake
forebay -must be able t cope with largest flow)
penstock - keep short
powerhouse-should be close to settlement
trailrace-empty into natural water course
parts of the powerhouse
control
generator
coupling
trubine
who made a sedimentery trap model
Brune
three depositional zones in reservoir
topset bed
foreset bed
bottomset bed
what is topset bed
coarse (delta deposits )
foreset bed
face of the delta deposits (steeped slope, decrease in grain size)
bottomset bed
fine, by turbididty , floods can bring larger
consequence of reservoir sedimentation
loss of storage upstream:loss of navigable depths downstream:degredation fo channel:loss of land hydropower: abrasion of trubines loss of coast lines
5 elements of sediment management
1 reduce sediment inflow 2 route sediment 3 sediment removal 4 proved large storage volume 5 sediment placement, deposit it where it can be removed or doesnt matter
routeing sediment techniques
drawdown during flods
off stream reservoirs
sediment bypass
venting
