DamsDams

Mehmet ÖzgerMehmet Özger

((BarajlarBarajlar))

Department of Civil Engineering, Department of Civil Engineering, I.T.UI.T.U

What is a dam?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 impactsNegative impacts

1.1. IImbalance of the ecosystemmbalance of the ecosystem2.2. Decreased amount of downstream waterDecreased amount of downstream water3.3. Spreading of some water-born diseasesSpreading of some water-born diseases4.4. Reduction in the fertility of farmlandsReduction in the fertility of farmlands

Purpose Distribution of DamsPurpose Distribution of Dams

48.60%

17.40%

12.70%

10.00%

5.30%0.60% 5.40%

Irrigation

Hydropower

Water Supply

Flood Control

Recreation

Navigation and Fishing

Others

Source: International Commission on Large Dams (ICOLD)

World’s registered damsWorld’s registered dams

Source: International Commission on Large Dams (ICOLD)

Parts of Parts of a da damam 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 DamsParts of Dams

Water intake structures

Flow

Sluiceway Dam body

Spillway

Reservoir

Upstream

ReservoirDam body

Spillway

Downstream

Classification of Dams Classification of Dams

According to dams height According to dams height If crest elevation and foundation level is greater If crest elevation and foundation level is greater

than 15 m then than 15 m then it can be considered as a it can be considered as a Large Large Dam.Dam.

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

If dam height is greater than 50 m then If dam height is greater than 50 m then High High DamDam

Classification of dams: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

Classification of 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

3.3 Planning of Dams3.3 Planning of Dams Three steps: - Reconnaissance survey (infeasible alternatives eliminated) - Feasibility study - Planning study

3.3.13.3.1 FEASIBILITY STUDYFEASIBILITY STUDY

A) Determination of water demand A) Determination of water demand Estimate various types of demands through Estimate various types of demands through

the life timethe life time B) Determination of water potentialB) Determination of water potential

From available sources and available past From available sources and available past datadata

C) Optimal plansC) Optimal plans◘ ◘ Check out the relation D versus S.Check out the relation D versus S.

D) Determination of dam site◘ Factors should be taken into consideration:TopographyGeology and dam foundation

(faults and weak geologic formations should be avoided) Type of soil affects the overall stability of dam body

Available of construction materialsFlood hazardSeismic hazardSpillway location and possibilitiesConstruction time Climate (earth fill dam is not appropriate for rainy climates)Diversion facilitiesSediment problemWater qualityTransportation facilitiesRight of way cost

e) e) Determination of dam location Determination of dam location Characteristics 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 meterialsAvailabilty 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” Failure of the dam “Dam Break” It is rapid for a concrete dam. See the It is rapid for a concrete dam. See the

textbook for the examples.textbook for the examples.

Recep YURTALRecep YURTAL Ç.Ü., İnş.Müh.Böl.Ç.Ü., İnş.Müh.Böl.

3.3.23.3.2 PLANNING STUDYPLANNING 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 Dams3.4 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 YURTALRecep YURTAL Ç.Ü., İnş.Müh.Böl.Ç.Ü., İnş.Müh.Böl.

Recep YURTALRecep YURTAL Ç.Ü., İnş.Müh.Böl.Ç.Ü., İnş.Müh.Böl.