Dams Mehmet Özger (Barajlar) Department of Civil Engineering, I.T.U

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.

Drinking water Navigation Flood control Recreational purposes Irrigation Hydropower

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

Purpose Distribution of Dams Source: International Commission on Large Dams (ICOLD)

World’s registered dams Source: International Commission on Large Dams (ICOLD)

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: Gerektiğinde baraj gölünü tamamen boşaltmak, dolusavak kapasitesini azaltmak, akarsu mansabına bırakılacak suyu salmak amacına yönelik tesisler.   Diversion facilities: To redirect the streamflow from construction area

Parts of Dams Water intake structures Flow Sluiceway Dam body Spillway Reservoir

Upstream Reservoir Dam body Spillway Downstream

Upstream slope Riprap Top of dam Principal chute spillway Spillway training walls Downstream slope Right abutment Emergency spillway Left abutment Toe of embankment Berm Toe drain outlet

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 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 less than 15 m then Small Dam. If dam height is greater than 50 m then High Dam If dam height is greater than 50 m then High Dam

Classification of dams: Dams are classified on several aspects, some of the important aspects are as follow: 1) Based on Hydraulic Design:  Over flow dams (e.g. concrete dams)  Non over flow dams (e.g. embankment dams) 2) Based on Structural Design:  Gravity dams  Arch dams  Buttress dams 3) Based on Usage of Dam:  Storage dams  Diversion dams  Detention dams Dams are classified on several aspects, some of the important aspects are as follow: 1) Based on Hydraulic Design:  Over flow dams (e.g. concrete dams)  Non over flow dams (e.g. embankment dams) 2) Based on Structural Design:  Gravity dams  Arch dams  Buttress dams 3) Based on Usage of Dam:  Storage dams  Diversion dams  Detention dams

Classification of dams: 4) Based on Construction Material:  Concrete / Masonry dams  Earthfill dams  Rockfill dams  Earthfill rockfill dams  Concrete faced rockfill dams (CFRD) 5) Based on Capacity:  Small dams  Medium dams  Large dams 4) Based on Construction Material:  Concrete / Masonry dams  Earthfill dams  Rockfill dams  Earthfill rockfill dams  Concrete faced rockfill dams (CFRD) 5) Based on Capacity:  Small dams  Medium dams  Large dams

3.3 Planning of Dams   Three steps:   - Reconnaissance survey (infeasible alternatives eliminated)   - Feasibility study   - Planning study

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

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

e) Determination of dam location e) Determination of dam location  Characteristics of dam location: Geologic formation Geologic formation Spillway location and capacity Spillway location and capacity Diversion conditions Diversion conditions Sediment condition Sediment condition Transportation facilities Transportation facilities Structural design Structural design Availabilty of meterials Availabilty of meterials

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)

 Failure of the dam  “Dam Break”  It is rapid for a concrete dam. See the textbook for the examples.

Recep YURTALÇ.Ü., İnş.Müh.Böl.

3.3.2 PLANNING STUDY   ◘ Followings need to be done, since dimensions are already determined:   Topographic surveys (1:5000 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)

3.4 Construction of Dams   Four principal steps are followed during the construction:     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:

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

  4) Formation of the Dam Body     For Concrete Gravity dams:   ◘ Low-heat cements  to reduce shrinkage problem   ◘ Concrete is placed in “blocks”

  “Keyways” are built between sections to make the dam act as a monolith

  “Waterstops” are placed near upstream face to prevent leakage

Recep YURTALÇ.Ü., İnş.Müh.Böl.

Recep YURTALÇ.Ü., İnş.Müh.Böl.