ARKAN IBRAHIM 2015 | GAZIANTEP

DAMS BY:- ARKIAN IBRAHIM

A Report About

SUBMITTED TO: -

Y. Doc.Dr.Mazen KAVVAS

Student Number: -201566108

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Table of Contents DAMS (introduction) .......................................................................................................... 2

Needs For Dam Construction ...................................................................................... 3

Disadvantages Of Dams..................................................................................................... 3 Parts & Structure Of Dams ............................................................................................ 5

Classification Of Dams ....................................................................................................... 6

Planning Of Dams ................................................................................................................ 13 Selection Of Type Of Dams ........................................................................................... 16

Construction Of Dams ...................................................................................................... 17

References .................................................................................................................................. 19

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DAMS

Introduction :-

A dam is a hydraulic structure of fairly impervious material built across a river to create a reservoir on its upstream side for impounding water for various purposes.

Fig.1 .Karakaya Dam/Diyarbakır

Fig. 2. Atatürk Dam/Şanlıurfa

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-A dam and a reservoir are complements of each other. -Dams are generally constructed in the mountainous reach of the river where the valley is narrow and the foundation is good. -Generally, a hydropower station is also constructed at or near the dam site to develop hydropower. -Dams are probably the most important hydraulic structure built on the rivers. They are very huge structure and require huge money, manpower and time to construct. Needs For Dam Construction:

1. Drinking and domestic water supply, 2. Flood control, 3. Irrigation, 4. Industrial water supply, 5. Hydroelectric energy production, 6. Retention and control of sediments,

and Inland navigation, Improvement of water quality, Fish Farming, Recreation facilities.

Disadvantages of Dams: -for construction of a dam we need a lot agriculture land because generally dams are constructed near river so they can collect the water and near to river the land usually found good for agriculture. -sometimes it needs to remove the living population then it becomes hard to relocate them without their will. Ex. In India there are some cases are going on to increase the height of dam but nearby living peoples are not cooperating and so the projects are just in papers. -due to availability of huge amount of water surface there is always a chance of encouraging mosquito breeding. -the mental fear remains in peoples who are living in direction of flow of input water or other side of dam. - imbalances of the ecosystem. - Decreased amount of downstream water, - Reduction in the fertility of farmlands, - Spreading of some water-borne diseases.

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Fig.3. BREAKDOWN by PURPOSE of DAMS in EUROPE

Source: International Commission on Large Dams (ICOLD)

-According to the purpose of dam construction we have: -

SINGLE PURPOSE: When the whole purpose of a project is to produce just electricity for example then such a project is known as a Single Purpose Hydro Power Project.

MULTIPURPOSE: When the water used in hydropower project is to be used for other purposes like irrigation, flood control or fisheries then such a project is known as Multi-Purpose Project.

48.60%

17.40%

12.70%

10.00%

5.30%

0.60% 5.40%

Irrigation

Hydropower

Water Supply

Flood Control

Recreation

Navigation andFishing

Others

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Parts of & Structure of Dams:

Dam body: Body forms the main part of a dam as an impervious barrier,

Reservoir: It is the artificial lake behind a dam body, Water intake structures: is a facility to withdraw water from a

reservoir, Sluice way: An opening in the dam near the ground level, which is

used to clear the silt accumulation in the reservoir side, Diversion facilities: To redirect the streamflow from construction

area, Spillways: It is the arrangement near the top to release the excess

water of the reservoir to downstream side,

Fig. 4. Part of dam

• Heel: contact with the ground on the upstream side, • Toe: contact on the downstream side, • Abutment: Sides of the valley on which the structure of the dam rest, • Galleries: small rooms like structure left within the dam for checking

operations.

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Fig. 4.1. Part of dam

Classification Of Dams:

A-ACCORDING to the SIZE of the DAM

1. Large (Big) dam, 2. Small dam, -International Commision on Large Dams, (ICOLD) assumes a dam as big when its height is bigger than 15m. -If the height of the dam is between 10m and 15m and matches the following criteria, then ICOLD accepts the dam as big: If the crest length is bigger than 500m, If the reservoir capacity is larger than 1 million m3 , If the flood discharge is more than 2000 m3/s, If there are some difficulties in the construction of foundation,

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B-ACCORDING to HEIGHT of DAM

1. High Dam If the height of the dam is bigger than 100m. 2. Medium Dam

If the height of the dam is between 50m and 100m. 3. Low Dam or Small Dam

If the height of the dam is lower than 50m. C-ACCORDING to the STATICAL DESIGN of DAM BODY

1. -Gravity Dams 2. -Arch Dams 3. -Butress Dams 4. -Embankment Dams 5. -Composite Dams

Gravity dams:

Gravity dams are satisfactorily adopted for narrow valleys having stiff geological formations. -Their own weight resists the forces exerted upon them. -They must have sufficient weight against overturning tendency about the toe. -The base width of gravity dams must be large enough to prevent sliding. -These types of dams are susceptible to settlement, overturning, sliding and severe earthquake shocks. -Concrete gravity dams area built of mainly plain concrete to take compressive stresses. -Concrete gravity dams have lower maintenance and operation costs compared to the other types of dams. -In the design of these structures, the following criteria should be satisfied: „ Dimensions of the dam are chosen such that only compressive stresses develop under all loading conditions. „ The dam must be safe against overturning, shear and sliding. -In the construction of concrete gravity dams special care is required for the problems due to shrinkage and expansion.

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ADVANTAGES OF GRAVITY DAMS

The gravity dams possess the following advantages:

1. These are more suitable in steep valleys where earth dams may tend to slip.

2. In these dams, surplus water may be discharged through the sluices provided in the body of the dam or over spillway built in a suitable location of the dam.

3. Such dams, when built on strong foundation, may be built up to a maximum practical height.

4. A gravity dam does not fail suddenly. Their failure can be predicted well in advance so that loss of life and property may be saved.

5. Their cost of maintenance is least and benefit of cost ratio is highest. 6. These are found more advantageous in the regions of high rainfall

and heavy snowfalls. 7. In these dams, sedimentation of the reservoir, may be cleared

through deep set sluices.

DISADVANTAGES OF GRAVITY DAMS

The following are the disadvantages of a gravity dam:

1. Their initial cost of construction is high. 2. Their construction period is comparatively more. 3. These require a strong and sound foundation. 4. Dams once constructed, cannot be raised further. 5. For the supervision of concrete dams, skilled labor is required.

Fig.5.Friant Dam, California

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Arch Dams

Arch dams are thin concrete structures. -Stability of an arch dam is based on its self-weight and its ability to transmit most of the imposed water loads into the valley walls. -At the sites of arch dams, the side formations and foundations should be very stiff to resist the applied load. -For effective arching action, the radius of the arch should be as small as possible. -They are formed by concrete blocks. -Reinforcement is not generally required in thick arch dams because it increases the cost drastically. -Arch dams have normally higher structural safety than conventional gravity dams. Types of Arch dams

-Constant-center (variable angle) arch dams are suitable for medium-high dams in U-shape valleys. They have single curvature in plan with vertical upstream face. -Variable-center (constant angle) arch dams are suitable for V-shape valleys. -Variable-center (variable angle) arch dams are composed of the combination of two types described above.

Fig.6.Hoover Dam

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Butress dams:

A buttress dam consists of a sloping slab. - Depending on the orientation of slab, a buttress dam may be classified as „ flat-slab buttress dam, „ multiple-arch buttress dam.

-Buttress dams can also be called Ambursen dams after the American engineer who greatly used this type of dam in the early 20th century,

-Generally, buttress dams are built in wide valleys.

-Originally buttress dams were used in areas requiring irrigation, but where the land was not capable of supporting the size and weight of other types of dams,

Some advantages of buttress dams over conventional gravity dams: -they can be constructed on foundations having smaller bearing capacity than required for gravity dams. So This type of structure can be considered even if the foundation rocks are little weaker, -Since they have thinner slabs, possibility of development of vertical cracks is less, -Flat or curved face, -Problems encountered during the setting of concrete are reduced, -Unless a mat foundation is used, uplift forces are negligibly small because of hollow spaces provided between the buttresses, -Ice pressures are also small as the ice sheet slides up the inclined slab.

Main disadvantage of buttress dams: -May have comparable costs, because of increased formwork and reinforcement . -The multiple arch dam pictured below is the Bartlett dam and it is the tallest dam constructed from concrete in the United States. It consists of 10 arches, 9 buttresses, and 2 gravity wing dams. The top of the dam is 287 feet high.

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Fig.7.Butress dam

Embankment Dam

An embankment dam is a massive artificial dam. It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock,

Earth or rock, Weight resists flow of water, They are trapezoidal in shape. Earth dams are constructed where the foundation or the

underlying material or rocks are weak to support the masonry dam or where the suitable competent rocks are at greater depth.

Earthen dams are relatively smaller in height and broad at the base.

They are mainly built with clay, sand and gravel, hence they are also known as Earth fill dam or Rock fill dam

They composed of fill of suitable earth materials at the dam site, -Coarse-grained soils (gravel and coarse sand), -relatively pervious, -easily compacted, -resistant to moisture, -Clay is considered as a core material (impermeable), -unstable when saturated (expands due to wetting, hard compact), -Therefore, clay mixed with sand and fine gravel is used as a core, -Core must be compacted in thinner layers with fairly accurate

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moisture control, -Compacted asphalt may also be used as an economical core material in case of loose foundations. -Asphalt can absorb earthquake shocks effectively.

-Embankment dams are usually safer against deformations and settlements. Body volume of embankment dams is relatively greater than the other types of dams. -Normally cheaper than the other types where there is enough fill material in the close vicinity. -Fill dams comprise more than 70% of the dams in the world and 90% in Turkey.

Fig.8. Embankment Dam

Fig.8.1 Embankment Dam

D-ACCORDING TO THE FUNCTION OF DAM 1. Storage dams: They are constructed to store water during the rainy

season when there is a large flow in the river. 2. Diversion dams: A diversion dam is constructed for the purpose of

diverting water of the river into an off-taking canal (or a conduit). 3. Detention dams: Detention dams are constructed for flood control

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4. Debris dams: A debris dam is constructed to retain debris such as sand, gravel, and drift wood flowing in the river with water

5. Coffer dams: It is an enclosure constructed around the construction site to exclude water so that the construction can be done in dry.

E-Based on Hydraulic Design: 1. Over flow dams (e.g. concrete dams), 2. Non over flow dams (e.g. embankment dams).

Planning of Dams: Three steps:

- Reconnaissance survey (infeasible alternatives eliminated), - Feasibility study, - Planning study,

RECONNAISSANCE STUDY

1. Evaluation of the data having at archives, 2. Field investigation for limited time (Reconnaissance Study), 3. Some maps in small scale, for example 1/25.000 or 1/50.000, 4. Some hydraulic data about

a. Basin, b. Precipitation area, c. Runoff, maximum discharge {Q=R/t (m3/s)}, d. Modulus of Runoff (R/t/m2 ~ R/t/km2),

5. Some approach to the reservoir area, dam site and type of dam and height of dam...etc

6. Photogeological studies 7. A preliminary report

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, 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.

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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

-Characteristics of dam location:

Topographic surveyings, Geologic formation. Hydrogeological studies, Underground explorations Boreholes, adits....etc, Spillway location and capacity, Diversion conditions, Sediment condition, Transportation facilities, Structural design, Availabilty of meterials, Slope stability analysis,

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),

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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).

ENVIRONMENTAL IMPACTS of CONSTRUCTION PHASE of DAMS

River pollution, Erosion, Loss of aesthetic view , Air pollution, Noise pollution, Dust.

ENVIRONMENTAL IMPACTS of RESERVOIRS

Loss of land, Habitat Destruction, The area that is covered by the reservoir is destroyed, killing whatever

habitat existed there beforehand, Loss of archeological and histrorical places, Loss of mineral deposits, Loss of special geological formations, Aesthetic view reduction, Sedimentation, Change in river flow regime and flood effects, Reservoir induced seismicity, Change in climate and plant species.

EFFECTS of DAMS to WATER QUALITY

Change in temperature, Turbidity, Dissolved gases in the water, Water discharged from the spillway contains 110-120% saturated

nitrogen. This amount may be destructive for fish life.\, Eutrophication,

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It means increase in vegetation. If moss and other plants exist in water, quality of that water gets worse.

Selection of Type of Dams:

1. Topography and valley shape, 2. Geology and foundation conditions (Bearing capacity of the underlying

soil, Foundation settlements, Permeability of the foundation soil), 3. Availability of construction materials, 4. Overall cost, 5. Spillway size and location, 6. Earthquake hazards, 7. Climatic conditions & Diversion problems, 8. Environmental considerations, 9. Roadway, 10.Length and height of dam, 11.Life of dam, 12.Miscellaneous considerations, 13.Safety, 14.Qualified labour. Geological Investigation for a Concrete Dam 1. Rock should be sound and resistant to static and dynamic forces. 2. Valley slopes should be stable. 3. Dam foundation should be safe from sliding. 4. The foundation rocks should be of same geological properties. 5. Reservoir should be free from seepage/leakage. 6. Rocks should be resistant to corrosion, erosion, solution, drying and

wetting. 7. Reservoir drainage and overburdens should be resistant to erosion and

sliding. 8. In case of arch dams, the abutments should be extremely strong. 9. The site should have a permissible (a) spillway and (b) diversion tunnel

and/or outlet works, if any. 10. Construction material should be economically available. 11. Overall economy and safety.

Safety requirement for earth dams: 1. There is no danger of overtopping – sufficient freeboard and spillways. 2. The seepage line is well within the downstream face. 3. The upstream slope is safe from sudden draw down (rip-rap).

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4. The upstream and downstream slopes are flat enough that, with the materials utilized in the embankment, they will be stable and show a satisfactory factor of safety by recognized methods of analysis.

5. The upstream and downstream faces of the dam are flat enough that the shear stresses induced in the foundation is enough less than the shear strength of the material in foundation to ensure suitable factor of safety.

6. Water which passes through and under the dam, when it reaches the discharge surface has a pressure and velocity so small that it is incapable of moving the materials of which the dam or its foundation is composed.

7. The upstream face is properly protected from the wave action and the downstream face is protected against action of rain.

8. Clay core and a filter at the toe to regulate the flow from upstream to downstream.

Construction of Dams:

Four principal steps are followed during the construction:

1) Evaluation of Time Schedule and Equipment

Items to be considered: -the characteristics of dam site, -the approximate quantities of work, -the preservation of construction equipment and materials, -diversion facilities and urgency of work.

2) Diversion before the construction, river flow must be diverted from the site,

1-Typical cross-section of earth cofferdams -f: free board f=0.2(1+h) - h: flow depth (meters) -G=z/5 + 3 (meters) 2-Cofferdams should be constructed during the low flow season. 3-For fill type dams, embankment cofferdam may be kept in place as part of the embankment, 4- For concrete dams, embankment cofferdam should be demolished after the dam has been constructed.

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Fig.10.Diversion tunnel

3) Foundation Treatment - to achieve less deformation under high loads, -to decrease permeability and seepage, -to increase shearing strength, and -to satisfy slope stability for the side hills.

4)Formation of the Dam Body

Ex: For Concrete Gravity dams:

Low-heat cements to reduce shrinkage problem, Concrete is placed in “blocks”.

Conclusion Studying this report gives the idea that most of water resource projects are require mostly the same kind of data with different duration and detail according to the importance of the project, thus it shows that the more detailed study we make at the data collection, the better choice will be made and the project serves its function more properly and efficiently.

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References:

1. -https://www.google.com.tr/webhp?sourceid=chrome-instant&rlz=1C1AVNE_enTR664TR664&ion=1&espv=2&ie=UTF-8#q=types%20of%20dams%20ppt

2. https://en.wikipedia.org/wiki/Embankment_dam 3. http://theconstructor.org/water-resources/classification-types-of-

dams/4439/ 4. Reference: http://seminarprojects.com/Thread-a-presentation-on-

classification-of-dams-and-spillways-ppt#ixzz3qQwPIlKx 5. http://physdams.tripod.com/physics24/id4.html .