dams mehmet Özger (barajlar) department of civil engineering, i.t.u
TRANSCRIPT
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.
Negative impactsNegative impacts
1.1. IImbalance of the ecosystemmbalance of the ecosystem
2.2. Decreased amount of downstream waterDecreased amount of downstream water
3.3. Spreading of some water-born diseasesSpreading of some water-born diseases
4.4. 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)Source: International Commission on Large Dams (ICOLD)
World’s registered damsWorld’s registered dams
Source: International Commission on Large Dams (ICOLD)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
Upstream slope
Riprap
Top of dam
Principal chute spillway
Spillway training walls
Downstream slopeRight abutment
Emergency spillwayLeft abutment
Toe of embankment
Berm
Toe drain outlet
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
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.
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”