dam lecture

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

2. 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.

3. Drinking water
Navigation
Flood control
Recreational purposes
Irrigation
Hydropower

4. 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

5. Purpose 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)

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

7. 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

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

9. Upstream
Reservoir
Dam body
Spillway
Downstream

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

11. 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

12. 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

13. 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

14. 3.3 Planning of Dams
 Three steps:
 - Reconnaissance survey
(infeasible alternatives eliminated)
 - Feasibility study
 - Planning study

15. 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.

16. 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

17. 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

18. 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)

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

21. Recep YURTAL Ç.Ü., İnş.Müh.Böl.

22. 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)

23. 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:

25.  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

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

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

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

33. Recep YURTAL Ç.Ü., İnş.Müh.Böl.

36. Recep YURTAL Ç.Ü., İnş.Müh.Böl.