Dams

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Dams
(Barajlar)

• Mehmet Özger

Department of Civil Engineering, I.T.U
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What is a dam?

• A dam is a barrier built across a stream, river
  or estuary to hold and control the flow of water
  for such uses as drinking water supplies,
  irrigation, flood control and hydropower
  generation etc.

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Negative impacts

1. Imbalance of the ecosystem
2. Decreased amount of downstream water
3. Spreading of some water-born diseases
4. Reduction in the fertility of farmlands

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Purpose Distribution of Dams
Source International Commission on Large Dams
(ICOLD)
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Worlds registered dams
Source International Commission on Large Dams
(ICOLD)
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Parts of a dam

• Dam body Body forms the main part of a dam as
  an impervious barrier
• Reservoir It is the artificial lake behind a dam
  body
• Spillway is that part of a dam to evacuate the
  flood water from reservoir.
• Water intake structures is a facility to
  withdraw water from a reservoir.
• Sluiceway Gerektiginde baraj gölünü tamamen
  bosaltmak, dolusavak kapasitesini azaltmak,
  akarsu mansabina birakilacak suyu salmak amacina
  yönelik tesisler.
• Diversion facilities To redirect the streamflow
  from construction area

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Parts of Dams
Reservoir
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Upstream
Reservoir
Dam body
Spillway
Downstream
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Right abutment
Downstream slope
Upstream slope
Principal chute spillway
Spillway training walls
Berm
Top of dam
Riprap
Toe drain outlet
Toe of embankment
Left abutment
Emergency spillway
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Classification of Dams

• According to dams height
• If crest elevation and foundation level is
  greater than 15 m then it can be considered as a
  Large Dam.
• If dam height is less than 15 m then Small Dam.
• If dam height is greater than 50 m then High Dam

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Classification of dams

• Dams are classified on several aspects, some of
  the important aspects are as follow
• Based on Hydraulic Design
• Over flow dams (e.g. concrete dams)
• Non over flow dams (e.g. embankment dams)
• Based on Structural Design
• Gravity dams
• Arch dams
• Buttress dams
• Based on Usage of Dam
• Storage dams
• Diversion dams
• Detention dams

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Classification of dams

• Based on Construction Material
• Concrete / Masonry dams
• Earthfill dams
• Rockfill dams
• Earthfill rockfill dams
• Concrete faced rockfill dams (CFRD)
• Based on Capacity
• Small dams
• Medium dams
• Large dams

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3.3 Planning of Dams

• Three steps
• - Reconnaissance survey
• (infeasible alternatives eliminated)
• - Feasibility study
• - Planning study

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3.3.1 FEASIBILITY STUDY

• A) Determination of water demand
• Estimate various types of demands through the
  life time
• B) Determination of water potential
• From available sources and available past data
• C) Optimal plans
• ? Check out the relation D versus S.

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• D) Determination of dam site
• ? Factors should be taken into consideration
• Topography
• Geology and dam foundation
• (faults and weak geologic formations should be
  avoided)
• Type of soil affects the overall stability of dam
  body
• Available of construction materials
• Flood hazard
• Seismic hazard
• Spillway location and possibilities
• Construction time
• Climate (earth fill dam is not appropriate for
  rainy climates)
• Diversion facilities
• Sediment problem
• Water quality
• Transportation facilities
• Right of way cost

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e) Determination of dam location

• Characteristics of dam location
• Geologic formation
• Spillway location and capacity
• Diversion conditions
• Sediment condition
• Transportation facilities
• Structural design
• Availabilty of meterials

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• f) Project design
• ? involves the computation of dimensions of the
  dam.
• 1. Hydrologic design (max. lake elevation
  spillway cap. crest elevation)
• 2. Hydraulic design (static dynamic loads
  spillway profile outlet dimensions)
• 3. Structural design (stress distribution
  required reinforcement)

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• Failure of the dam ? Dam Break
• It is rapid for a concrete dam. See the
  textbook for the examples.

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3.3.2 PLANNING STUDY

• ? Followings need to be done, since dimensions
  are already determined
• Topographic surveys (15000 scaled map)
• Foundation study (seepage permeability, bearing
  capacity etc. tests)
• Materials study (quantity of materials)
• Hydrologic study (measurements of hydrologic
  parameters)
• Reservoir operation study (is to be performed
  periodically)

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3.4 Construction of Dams

• Four principal steps are followed during the
  construction
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• 1) Evaluation of Time Schedule and
  Equipments
• ? a work schedule is prepared using CPM.
•   2) Diversion
•  ? before the construction, river flow must be
  diverted from the site
• see the below figure for two possible ways to
  divert water

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• 3) Foundation Treatment
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• ? Concrete Rock-fill dams ? hard formations
• Earth-fill dams ? most of soil conditions
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• ? Highly porous foundation ? excessive seepage,
  uplift, settlement
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• Grouting Operation is applied to solidify the
  foundation
• to reduce seepage

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• 4) Formation of the Dam Body
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• For Concrete Gravity dams
• ? Low-heat cements ? to reduce shrinkage problem
• ? Concrete is placed in blocks

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• Keyways are built between sections to make the
  dam act as a monolith

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• Waterstops are placed near upstream face to
  prevent leakage

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