1. Assoc. Prof. Dr. Tarkan Erdik
Dams
(Barajlar)
Assoc. Prof. Dr. Tarkan Erdik
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 the purpose of drinking water supplies, irrigation, flood control and hydropower generation etc.

3. Drinking water
Navigation
Flood control
Recreational purposes
Irrigation
Hydropower

4. Negative impacts Imbalance of the ecosystem
Decreased amount of downstream water
Spreading of some water-born diseases
Reduction in the fertility of farmlands

5. Purpose Distribution of Dams
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: An artificial channel, especially one for carrying off excess water. It is controlled by a sluice gate. It helps to the spillway discharge. It is used to release water to downstream.
Diversion facilities: To redirect the streamflow from construction area

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

9. Upstream
Reservoir
Dam body
Spillway
Downstream

10. Emergency spillway 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

11. Classification of Dams
According to dams height
If the distance between crest elevation and the river thalweg is greater than 15 m then it can be considered as a Large Dam. Besides, a dam is also said to be large when the height is in between 10m and 15m and at least the one of following criterias are met.
Crest length >500m
Reservoir storage >106 m3
Maximum flood discharge >1000 m3/s
If dam height is less than 10 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:
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 (constructed for flood control)

13. 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
Diemal dam 

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
Rock formations have higher bearing capacity.
Gravel have relatively high bearing capacity, however they have high permeability
Silt and fine sand have low bearing capacity

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 materials

18. F) Project design involves the computation of dimensions of the dam. 1
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.

20. The Failure of a Concrete Dam at Austin in 1911. 

21. The Failure of an embankment dam/ 

22. Dambreak failure in Siciliy/Italy by Tarkan Erdik, Olgay Şen and Pieter van Gelder.

23. 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)

24. 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 to provide dry zone.
see the below figure for two possible ways to divert water:

25. a) Diversion by side tunnel or channel
Cofferdam: small barier employed to divert the river flow or to enclose a dry area during construction. It may be of homogenous or zonned embankment, sheet pile or cellular type (Bowles, 1988).
Important aspects:
Return period of a design flood of a coffferdam shoud be greater than that of a concrete dam. Most of the cofferdams are fill type due to economical reasons. Cofferdams should be constructed druing low flow periods.
a) Diversion by side tunnel or channel
a) Tunnel for deep and narrow valleys and channel for wide valleys.
The minimum diameter is proposed to be 3m (Şentürk, 1988).
b) Two stage diversion

26. 3) Foundation Treatment (Why do we need it?)
Concrete & Rock-fill dams  hard formations
Earth-fill dams  most of soil conditions (because the base widths of earth-fill dams are large which causes the base pressures to be lower than those of other types)
Highly porous foundation  excessive seepage, uplift, settlement “Grouting Operation” is applied to solidify the foundation & to reduce seepage. Water/cement ratio of approximately 5:1 is usually applied. For larger cracks fine sand and fly ash should be added to water/cement ratios (Yanmaz, 2006).

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

28. “Keyways” are built between sections to make the dam act as a monolith
Adjoining blocks should be placed in key-trench manner, termed as keyways.
Waterstops, made of copper and rubber, should be placed to reduce seepage.

29. Porsuk dam (concrete gravity dam)
Upstream face of gravity dams is usually vertical. However, it may be inclined up to a value of 1V:0.1H to increase safety against sliding and overturning under reservoir operating conditions. They are designed such that dams weight resists to the forces acting on them.

30. Karakaya dam (Arch dam)
Arch dams are responsible for transmitting most of the imposed water loads into the valley walls by arch action.

31. Suçatı dam(Roller Compacted Concrete (RCC) Gravity Dam)
RCC should have a minimum amount of cement to maximize economy and minimize internal heat generation. The construction is based on the compaction by heavy static and vibrating rollers.
Roller Compacted Concrete

32. The Daniel-Johnson is a multiple-arch buttress dam on the Manicouagan River. The dam is composed of 14 buttresses and 13 arches in Quebec, Canada. 
Arch 
Butress 

33. Elmalı 2 dam (Butress Dam)
The first butress dam to be built in İstanbul/Turkey. Sloping slab transmits the water thrust to a seriers of butressess at right angles to the axis of the slap. It can be constructed in a wide valley where a dam of medium height is required.

35. Recep YURTAL
Ç.Ü., İnş.Müh.Böl.

38. Recep YURTAL
Ç.Ü., İnş.Müh.Böl.

41. Referances
Sentürk F (1988) Hydraulics criteria for design of dams. DSI Publ., Ankara, Turkey (in Turkish)
Bowles, Joseph E. Foundation analysis and design
Yanmaz, A. Melih. Applied water resources engineering. Metu Press, 2006.