1.DAMS & RESERVIOR Kaustubh Sane HJD Institute of Technical Education & Research, Kera

2. Dams Dam is a solid barrier constructed at a suitable location across a river valley to store flowing water. Storage of water is utilized for following objectives: Hydropower Irrigation Water for domestic consumption Drought and flood control For navigational facilities Other additional utilization is to develop fisheries 3. Structure of Dam Heel Gallery Toe Spillway (inside dam) Crest NWL Normal water level MWL Max. level Free board Sluice way Upstream Down stream 4. 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. Diversion tunnel: Tunnels are constructed for diverting water before the construction of dam. This helps in keeping the river bed dry. Spillways: It is the arrangement near the top to release the excess water of the reservoir to downstream side Sluice way: An opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side. 5. TYPES OF DAMS Gravity Dams: These dams are heavy and massive wall-like structures of concrete in which the whole weight acts vertically downwards Reservoir Force As the entire load is transmitted on the small area of foundation, such dams are constructe where rocks are competent and stable. 6. Bhakra Dam is the highest Concrete Gravity dam in Asia and Second Highest in the world. Bhakra Dam is across river Sutlej in Himachal Pradesh The construction of this project was started in the year 1948 and was completed in 1963 . It is 740 ft. high above the deepest foundation as straight concrete dam being more than three times the height of Qutab Minar. Length at top 518.16 m (1700 feet); Width at base 190.5 m (625 feet), and at the top is 9.14 m (30 feet) Bhakra Dam is the highest Concrete Gravity dam in Asia and Second Highest in the world. 7. Buttress Dam: Buttress Dam Is a gravity dam reinforced by structural supports Buttress - a support that transmits a force from a roof or wall to another supporting structure This type of structure can be considered even if the foundation rocks are little weaker 8. These type of dams are concrete or masonry dams which are curved or convex upstream in plan This shape helps to transmit the major part of the water load to the abutments Arch dams are built across narrow, deep river gorges, but now in recent years they have been considered even for little wider valleys. Arch Dams: 9. Earth Dams: 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 10. Gravity dam: rigid monolithic structure Trapezoidal cross section Minimal differential movement tolerated Dispersed moderate stress on valley floor and walls Arch dam: high strength concrete wall Convex faces upstream Thin walled structure Relatively flexible Huge stresses imposed on valley walls and floor Earth dams: bank or earth or rock with impermeable core Core of clay or concrete, extended below ground Sand or gravel drains built to cut fluid pressure Low stress applied to valley floor and walls 11. Geotechnical considerations Dam site Topography- a place is selected ideally in narrow gorge or small valley with enough catchment area behind dam is calculated. Technically- a site should have strong, impermeable and stable rock body. Constructionally- site should not be much away from the deposits of material which required for construction. Economical environmental 12. Geological investigation General geology of area- In detailed mapping of the area reveals the facts like Topographic features Natural drainage patterns General characters and structures of rock formation like stratification, folding and faulting Trend and rate of erosion in the area. 13. Lithology- It is the most imp. Factor in dam construction investigation. Lithology in and around area with surface and subsurface lithology is investigated. These studies reveals the composition and textures of rock at site. It gives the idea about the rock type as igneous, sedimentary or metamorphic. It also shows that the area is made up of single thick layer of same rock type or with multiple layers. 14. Structures- These involves detail study of and mapping of planes of weakness like faults, fold, joints, bedding plane etc. Dip and strike: Strength of unfractured stratified rock is greater when stresses are acting normal to the bedding planes . Horizontal beds are stable base Dipping upstream are stable Dipping down stream unstable 15. Fault: The faulted rocks are generally shattered and weak along the rupture surface Unexpected and different rock types may occur on either sides of fault. Faulted land surfaces are the favorable sites for shocks during earthquakes. Small faults and shear zones are treated with some methods Deep and major faults are avoided at construction site. Loading in reservoir may activate previously inactive fault. Dip of faults also plays a major role in selecting a site for dams. 16. Folds: Most notable effect of fold on rocks are shattering and jointing along axial planes stressing of limbs Dams aligned along axial regions would be resting on most unsound rocks. In syncline bends dams placed on the upstream limbs would cause leakage from beneath the dam. 17. Joints: There is no site which is free from jointing. Here nature of jointing, depth of joints are considered. According to the nature are of joints the appropriate engineering technique is used to feel up the joints. 18. RESERVOIR A reservoir is a large, artificial lake created by constructing a dam across a river. 19. Types of reservoir Single purpose Multipurpose 20. Depending upon the purpose served, reservoirs may be classified as under: 1. Storage or conservation reservoirs, - formed by constructing a dam across a river. - to store water in the rainy season and to release it later when flow is low. - primarily used for supply Of water for irrigation, development of hydroelectric power and domestic and industrial water supply 2.Flood control reservoirs, - is constructed for the purpose of flood control. - to protect the area lying on its D/S side from the damages due to floods. - it holds some of the flood waters of a river during the rising flood and releases them gradually at a safe rate when the flood recedes. - It is of two types: a) Retarding reservoirs: It is the one which is provided with outlets and spillway not controlled by gates or valves. spillway is provided with the dam at such a level and capacity that the flood discharge through it is safe for the D/S areas. It stores a portion of the flood when the flood is rising and releases it later when the flood is receding .it means the high flood discharge is retarded and it takes long time for the flood water to flow completely towards the downstream area. The flow stops when the water level falls below the crest of the spillways. 21. b) Detention Reservoir: A detention reservoir is the one which is provided with outlets and spillway controlled by gates or valves. - stores excess water during flood and releases it after the flood . - spillways with adjustable gates are provided with the dam so that the flood water may be detained for sometimes and then released according to the situation of the D/S area by operating the gates of the spillways. 3. Distribution reservoirs: It is a small storage reservoir used for water supply in a city. Water is continuously pumped in to the reservoir at a constant rate and is supplied to the consumers. - It is rarely used for the supply of water for irrigation. It is not formed by constructing a dam across a river it is constructed of masonry work or concrete work in the form of a rectangular or circular tank at suitable places near the town. 22. Investigation for reservoir planning: 1. Engineering surveys: The area of the dam site and reservoir basin should be surveyed throughly to prepare topographical map and contour map. From the contoured plan the storage capacity and the water spread area of the reservoir at the various elevations are determined. The reservoir capacity or the volume of storage, corresponding to a given water level in the reservoir may be determined either by trapezoidal formula or by prismoidal formula. 2. Geological surveys: geological investigations of the dam and reservoir site are required to determine the following items: I. Suitability of foundation for the dam, II. Water tightness of the reservoir basin, III. Location of the quarry sites for the construction materials 23. 3. Hydrological investigations: study of runoff pattern of the river at the proposed dam site to determine the storage capacity of the reservoir corresponding to a given demand. Determination of the hydrograph of the worst flood to determine the spillway capacity and design. 24. SELECTION OF SITE FOR A RESERVOIR: The topography, At the site river valley should be narrow so the length of the dam to be constructed is less, Basin should be watertight and free from fissures, cracks, so that there is no loss of water due to percolation. The site should be such that as far as possible minimum land and property is submerged in the reservoir, It should be such that it avoids water from the tributaries which carry usually high content of sediment, The site must be such that adequate reservoir capacity is available for the desired purpose, The site should be such that a deep reservoir may be formed so that the land costs per unit of capacity are low, evaporation loss is less and there is less likelihood of weed growth, The soil and mass at the reservoir site should not contain any objectionable soluble minerals and salts which may get dissolved in water and deteriorate water quality. 25. The quality of water stored in the reservoir must be satisfactory available for its intended use, The site should be easily accessible by road or railway, The construction materials for the dam should be available in the vicinity of the site. The site should be such that the costs of associated works such as roads, rails, housing colonies for workers and staff, etc. should be low. 26. ZONES OF STORAGE: The storage capacity of a reservoir is designated by several zones by certain water surfaces or pool levels in the reservoir as indicated below: Normal pool level: It is the maximum elevation of the water surface which is to be stored in the reservoir during ordinary operating conditions. This water level is also known as full reservoir level (F.R.L). Minimum pool level: It is the lowest elevation to which the water is drawn from the reservoir under normal conditions. This level is fixed by providing outlets in the dam. Maximum pool level: It is the maximum elevation to which the water surface will rise in the reservoir during the peak flood. I t is also known as maximum water level (M.W.L).