MODULE 8

DAMS AND SPILLWAYS

8.1 EMBANKMENT DAMS:

• A mound dam could be a huge quite artificial dam.

• It is mostly produced through the utilization of the location and compaction of a fancy semi-plastic mound of a spread of composition of soil, sand, clay, or rock.

• It contains a semi-pervious waterproof natural defensive, its surface and a dense, tightly closed core. This create the dam impenetrable to floor erosion.

• Such a dam consists of fragmented unbiased material particles. The friction and interaction of particle bind the particles reciprocally into a impenetrable mass as another than by the use of a cementing substance.

TYPES

• Embankment dam are available 2 type:

• The earth-filled dam (also named as associate material dam or piece of ground dam) fabricated from compacted earth, and

• The rock-filled dam- A cross-sections of a mound dam suggests a structure sort of a bank, or hill.

• Most have a central half or core composed of a tight element to stop water from oozy with the help of the dams.

• The cores will be of clay, concrete, or asphalt concretes. This type of dam could be an acceptable choice for websites with Brobdingnagian valley.

• They can be designed on robust rocks or softer soils. For a rock-fill dams, rock-fill is blast the usage of explosives to smash the rock. Additionally, the rock piece may also what is more need to be crush into smaller grade to induce the suited vary of dimension to be used in an mound dam.

SAFETY

• The constructions of a dams and also the filling of the reservoir within the came of it places a brand-new weight on the flooring and sides of a valley. The strain of the water can extend linearly with its depths.

• Water also push against the upstream faces of the dam, a nonrigid structures that below stressed behave semi plastically, and cause larger would like for changes (flexibility) close to the primarily based of the dam than at shallower water level.

• Thus the stressed levels of the dam must be calculate in advance of buildings to ensure that its break level threshold is not exceed.

• Overtopping or overflow of an embankment dam beyond its spillway capacity will causes its eventual failure.

• The erosion of the dam's material by overtopping runoffs will removed masses of materials whose weight hold the dams in place and against the hydraulics forces acting to moves the dam.

• Even a small sustain overtopping flows can remove thousands of tons of overburdens soil from the masses of the dams within hours.

• The removals of this masses unbalance the force that stabilized the dam against its reservoir because the plenty of water still impound behind the dam ironed against the lightened mass of the embankments, created lighter by surface erosion.

• As the masses of the dam erodes, the force exert by the reservoirs begins to maneuver the whole structures.

• The embankments, having nearly no elastic strengths, would begin to interrupt into separate pieces, permitting the impound reservoir waters to flow between them, geological process and removing even additional material because it pass through.

• In the ultimate stage of failure the remaining piece of the embankments would provide almost no resistance to the flows of the water and still fractures into smaller and smaller sections of earth or rock till these would disintegrated into a thick mud soup of earth, rocks and water.

• Therefore, safety demand for the conduit are high, and need it to be capable of containing a most sort flood stage. It's common variety of specifications to be written specified it will contains a minimum of a one-hundred-year flood.

• A range of embankments dam overtopping protection systems were develop round the flip of the third millennium.

• These technique embody the concrete overtopping protection system, timber crib, sheet-piles, riprap and gabion, strengthened earth, minimum energy loss weirs, mound overflow step spillways and also the formed concrete block protection systems.

CLASSIFICATION OF DAMS :

• Classification of Dam in step with unleash Pattern

• Below are the kind of dams supported completely different criteria. Kinds of dams on the premise of materials utilized in dam construction:

• Rigid Dams (Concrete dam, steel dam, timber dam etc)

• Non-Rigid dams (rockfill dam)

Classification of dam type with reference to size/height of the dam

• Low dam / little dam (How to make small dams)

• Medium dams

• High dam / giant dams

Classification of dam according to its purpose/use

• Water provide dam/Irrigation dams

• Power dams

• Multipurpose dams

• Flood management dams

Classification of Dam in step with Location

On-Channel:

• Dam is construct across the main water feeding river. Example Tarbela, Mangla, Simly, Hub dam. To extend the water convenience water from different rivers could also be entertained to the dam through feeder channels for example Kurram Tangi dam.

Off-Channel:

• Dam is construct on a channel having abundant smaller flow. Major storage water is transfer from a special close river. This is often done thanks to non-availability of suitable/economic dam sites on the key flow river. Example Akhori dams, Replacement dams for Mangla associated Tarbela.

Storage dam:

• Water is hold on and later discharged through an retailers for consumptives or non-consumptives functions as per requirements.

Recharging dam:

• There is not any shops provide to unleash waters and every one incoming water is retain. The water infiltrates through the foundations and/or dam body. The most purposed of the dam is to induces recharged to ground waters system within the area. Tiny free in d/s channel to permit seepages in the channel bed.

Delay action dam / retarding dam:

• These dams are wont to dim-witted the height flows of flash floods. There might or might not be any management over the outflows. For no control over the outflow the outflow rate varies as operate of storage volume / water depths in the dam. The flood peaked is therefore significantly attenuated.

• The outlet capacities is about that most outflow discharged don't exceed the safe capability of the downstream rivers throughout highest flood. The reservoir empty absolutely once the flood. For management on outflow by gates (detention dam) , the flow is free in such a pattern to maintained the water for very long time however there's enough storage obtainable to store next flood events.

• These dams are sometimes meant to cut back flood broken yet on induce maximum recharge within the area. One form of such dam could be a porous dam designed of a porous embankment, for instance stone gabions.

DESIGN concerns:

• The designer engineer’s responsibility is to provides safety. The designed structures should act with integrity giving due considerations to the purposed of the project and therefore the the} final effects of the comes on fellow human beings.

• At a similar time the Engineers are accountable to the communities for the price of the structures. There's forever a limit to the finance, therefore any cut in cost must not sacrifice safety.

• The Engineers also carries a legal responsibility, and are responsible in any respect times for each what they are doing and what they say.

1- web site investigation:

• In order to style the most economical structures, we've got to grasp what the structure is facing with respects to therefore and geologic formation, and the way the dam will acted at the particular web sites.

2- Laboratory and Field Testing:

• The tests done at the constructions site are the bottom for dam design. If any tests provide unhealthy results, the planning are going to be supported poor information, and can be poor design.

3- ooze management design:

• Crack within the hill dames are inevitable (Jim Sherrard), so an honest design for seepage control makes a distinction between good and bad design. The seepage control design enclosed filter design, toe or chimney drains, and/or adding a core with low permeability.

4-Hydrology study

• Good geophysics studies can confirm the U.stream water level, and therefore deciding the desired height of the dam, and also the elevations of the spillway. Poor investigation might result in dam overtopping.

5- Loading and issue of Safety -

• Dynamic Loading- For a dam to act efficiently, all the masses actings on the dam (either external or internal) ought to be calculates accurately. Taking into concerns all the loads will end in an honest and safe design, otherwise it'd lead to unsafe structures.

6- Foundation Design

• The foundations could be a vital part within the hill dam. It should carry all the dams and water masses safely while not failing below excessive settlement, and it's additionally ought to be styled to safeguard the dam against ooze and pipings.

7- Slope Stability

• Slope stabilities check is incredibly necessary as several dams failing from lean design checks for slope. The slope check should include:

• Just once construction conditions,

Steady seepage, and

Rapid drawdown

8- Specify the aim for the dam project

• The purpose of the dam confirm many factors in dam design. There's no fix design for each dam. The purposed of the dam should be taken into concerns in dam design. For example, a dam with power plant, ought to be designed to face up to additional dynamic effects from power machines.

9- design layout and selecting the most effective spot for the dam

• Based on earth science formation, choosing the best places for the dam is incredibly essential for a with success design. The placement of the dam would possibly decrease or will increase construction cost.

10- stream Diversion design

• Moving the river far from the dam constructions space provides low groundwater level, and therefore allows to operates while not major dewatering drawbacks.

Estimation and management :

8.2 Estimation of seepage:

• Water flow through the dam is one amongst the fundamental problem for geotechnical engineer. This paper gift simple expressions to predict the total (saturated and unsaturated) seepage flow rate through a homogeneous embankment and discusses precaution to be taken.

• The physical and geometric factor's of dam such as permeability, upstream and downstream slope of the dam slop (amplitude) are consider. The water table is neither a flow line not a equipotential, but simply a surface where the pore-water pressure, uw, is equal to the atmospheric pressure, palm, usually taken as the zero values for pressures. The seepage rate is then predicts by either graphical techniques (drawing of flow net) in which the un-saturated flow is neglect (e.g., Cedergren 1997) or numerical code that sometimes don't think about unsaturated flow (e.g., MODFLOW).

• Such prophetic technique modifies the matter and therefore are inaccurate for estimating the flow rate, pore-water pressured, water-tables position, and ooze-face position. Generally, seepage problems, hill could be a consistent atmosphere that has infinite continuous pores. Any form of dams and earth, though were designed by drilling materials or seldom rubberized artificial materials can experience the seepage.

• So the seepage is inevitable and to optimize the discharged we must always do the precise computation of seepage (compute the seepage exactly).Seepage computation has a good influenced in stability of earth dams and exact estimations of it causes the operation value reduction.

• Providing of easy and suitable method to solved the ooze issues through the world dam and specifically estimation of discharge quantitative relation is that the main purposed of this article. It is portrayed a way to provides this purpose and gift an appropriate way which may estimate the discharge ratio through the earth dam satisfactorily.

• The Seep/W (geoslope 1999) computer software system is wont to estimates the seepage. Nomirov analysis on the water seepage controls through the isotropic-

• Homogenous earth dams and described an acceptable methodology to unravel the flowing issues through the planet dams. Nomirov used the advance mathematical relations to work out the characteristics of seepage within the isotropous dam profile that encompasses a downstream horizontal drainage.

• But Nomirovs method has defect and errors which were utilized in his equation. In this article, Seep/W software system is use to analyzed the inspiration and bodies seepage.Aubertin et al. (1996) used this software’s to solve the un-saturated problems of multi-layer covers is infinite geological formation pumping test. This software solves the underground

• Water problems for stable, unstable, saturated and unsaturated condition. Chapuis  (2002) researches on estimation of flowing discharge quantitative relation through the mound dam. It are often gained smart results by mistreatment the Seep/W software systems.

• This software not solely has the prevalence to the graphic methodology and manual calculations however additionally concerning the time we will gain good results. This software has several applications that helps designers in best planning of dam and analyzing the weak or strength points of dam and also designing of the development which coping with the seepage problems.

8.3 CONTROL OF SEEPAGE:

SEEPAGE:

• Also referred to as leakage, leak, oozing or percolation.

• The slow escape of a liquid or gas through porous material or little holes.

• Something that seeps or leaks out.

EFFECTS OF SEEPAGE:

• Water losses in canals contribute to Water-logging Salinization of valuable irrigated areas.

• Reduce system performance.

• Lead to extend in water withdrawal.

• All embankments dams are subjected to seepage. Flowing is also prejudicious to the steadiness of structure as a results of excessive pore water pressure or by internal erosion. Cloudy flow may be a symptom of internal erosion.

WATER-LOGGING:

• Waterlogging refers to the saturation of soil with water.

SALINITY:

• Live of all the salts dissolved in water. The common ocean salinity is 35ppt and also the average watercourse water salinity is 0.5ppt or less.

PIPING:

• Internal erosion of the foundation or mound caused by seepage. Erosion starts at the downstream toe and works back toward the reservoir. The channels or pipes follow ways of most permeability. Time-taking process.

• Resistance of the embankment or foundation to piping depends on the:  malleability of the soil.  Gradation.  Degree of compactness.  Plastic clays with a plasticity index >15 are most proof against piping.

PIPING (CONTROL):

• Piping are often avoided by perpetuation the flow paths of water among the dam and its foundations. This decreases the hydraulic gradient of the water flow and thus its velocity.

PIPING (INCREASING FLOW-PATHS):

• Flow-paths can be raised by:  Cut-off walls.  imperviable cores.  imperviable blankets extending upstream from the upstream face.

PIPING (METHODS to extend FLOW-PATH):

• Cut-off walls:  Mitigate the flow of groundwater.

PIPING (METHODS to extend FLOW-PATH):

• Imperviable core:  A zone of low porosity material in associate degree mound dam.

PIPING (METHODS to extend FLOW-PATH):

• Imperviable upstream blanket:  associate degree impervious layer placed on the reservoir floor upstream of a dam.  within the case of an embankment dam, the blanket is also connected to the impermeable component in the dam.

SEEPAGE CONTROL:

• Flowing is that the continuous movement of water (from u/s to d/s face of dam). The side of this stream of percolating water is known because the water surface.  The phreatic surface ought to be unbroken at or below the downstream toe. The phreatic surface among a dam are often managementled by properly designed cores or walls.

INTERNAL DRAIN SYSTEM:

• Purpose: A homogenized dam with a height of quite regarding vi m to eight m should have some form of downstream drain:

1. To cut back the pore water pressures within the d/s portion of the dam thus increasing the stability.

2.To control any flowing that exits the d/s portion of the dam (i.e., prevents piping).

INTERNAL DRAIN SYSTEM:

• Effectiveness: The effectiveness of the drain in reducing pore pressures depends on its: 1. Location. 2. Extent. However, piping is controlled by making certain that the grading of the receptive material from that the drain is built meets the filter necessities for the mound material.

TOE DRAINS:

• The look of a d/s system is controlled by the:  Height of the dam. • value and handiness of porous material.  porosity of the foundation. For low dams, a straightforward toe drain are often used successfully. For reservoir depths bigger than fifteen m, most engineers would place a drainage system additional within the embankment.

HORIZONTAL DRAINAGE BLANKET:

• ADVANTAGES: usually used for dams of moderate height. • oftentimes used over the downstream common fraction or one- third of the inspiration area.

• DISADVANTAGES:  associate degree earth dam mound tends to be additional receptive within the horizontal direction than in the vertical.

CHIMNEY DRAINS:

• Forestall horizontal flow on comparatively ladder-proof stratified layers.  Intercept flowing water before it reaches the downstream slope.  helpful in reducing pore water pressures.

DIMENSIONS AND porosity OF DRAINS:

• Should be up to take away the anticipated flow with an ample margin of safety for sudden leaks.  If the dam and also the foundations are relatively impermeable, then the expected outflow would be low.  A drain ought to be created of fabric with a constant of porosity of a minimum of ten to a hundred times bigger than the common mound material.

THIN U/S SLOPING CORE:

• In associate degree earth dam with an u/s sloping core of low permeability, the inspiration is assumed to be imperviable and in a very steady state.  For this sort of dam the d/s shell should be many hundred times additional permeable than the core.

PARTIAL CUT-OFFS:

• Associate degree earth dam constructed while not a cut-off on permeable or semi- permeable foundations of earth or rock could result in flowing below the dam making unacceptable uplift pressures and inflicting instability.

8.4 SLOPE PROTECTION :

Classification of slope         

• Natural slope in varied conditions, together with rock slope

Man-made slope - including cut-back slope or slope fashioned by crammed material with adequate compaction, sometimes given surface and surface drainage

• Man-made slope formed primarily with the support by holding structures

Factors moving the soundness of slope

1.Topography and its close physical conditions. Detail analysis may be done by applicable website investigation process.

2. Earth science conditions akin to the character and depth of its subsoil, degree of decomposition, or location of fracture and so on This knowledge can be obtained by soil investigation.

3. Shear strength of the slope-forming materials. Knowledge may be obtained exploitation applicable laboratory tests.

4. Surface and water condition

5. External loading and surcharges, akin to from traffic, near structures, doable vibration etc.

Protection and treatment to Rock Slope :

• Most rock slopes would like some styles of treatment to make sure continuing stability. Improvement strategies include:

1. Scaling loose blocks or boulders to be aloof from exposed rock surfaces, this can be sometimes done by manual method.

2. Construct buttress support this is concrete or masonry gravity structure use to retain the unstable rock mass

3. Dentition exposed soft material in an exceedingly rock face be cut back. The ensuing slot be crammed with filter material and guarded by masonry or concrete to forestall erosion.

4. Sprayed concrete apply concrete protection to zones of weak or extremely broken rock faces by spray-on method.

5. Dowel a hole is trained and supply untensioned steel bars, sometimes 25mm to 35mm dia. Associate degreed 1m to 3m long, to stabilize a weak rock zone. The outlet would be grouted afterward.

6. Rock bolt/nail this can be tensioned bar inserted into rock forming a brief anchorage zone in rock so an unstable slope space being strengthened by tension. Typical rock bolts are 25mm to 40mm in dia. 3m to 6m long, and have a tensile working load around 100kN.

Protection and treatment to Earth-filled slop

• Where a slope is to be stable to eliminate doable flow-slide, the surface layers ought to be stripped to a vertical depth not below 3m and replaced it with dry and well compacted fill.

• A system is additionally needed between previous and re-compacted fill to forestall development of water pressure behind the crammed zone.

• If it's possible, attempt to reform the profile of the slope to a secure angle that is set by mathematic analysis.

Protection to slope by rigid surface:

• Rigid surface protection on slopes are normally wont to cut back rainwater infiltration and to forestall erosion of the slope-forming materials. Could} be done by:

Chunam plastering

• This is an applied-on surface protection to slope employing a clay and cement mixed plaster. Thickness of the plaster is around 40mm to 50mm for permanent works.

Sprayed concrete (shotcrete)

• Protection by applying a spraying mortar onto surface of slope.

Masonry or stone pitching 

• Lay stone dust or block (with filter layer underneath) onto surface to guard slope from weathering

• In general, rigid surface may produce a really awkward appearance. Besides, the surface is extremely impervious therefore express feelings holes are needed for exhausting out of the bottom water to avoid the development of high-water pressure behind the slope

Protect a slope by the utilization of wall :

• Retaining wall are structures sometimes provided at the toe of a slope to stabilize it from slide, overturn or collapse.

• A slope are comparatively stable once its profile (section associate degree) is unbroken below its angle of repose.

• Angle of repose is an angle that maintains naturally to a secure equilibrium by the composing material of a slope.

• This angle deviates from differing materials counting on their compaction, particle size and therefore the nature of the fabric itself. (e.g. Cohesiveness and shear strength)

• Principle to retaining wall style can be of two main types

- cantilever type

- Gravity type

- Earth strengthened type

8.5 GRAVITY DAMS :

• A gravity dam could be a dam made from concrete or stone masonry and designed to carry back water by primarily utilising the burden of the fabric alone to resist the horizontal pressure of water pushing against it.

• Gravity dams give some blessings over mound dams a drawback of gravity dams is that because of their massive footprint, they're at risk of uplift pressures that act as a de-stabilising force.

• Uplift pressures (buoyancy) may be reduced by internal and foundation drain systems which reduces the pressures.

Forces on gravity dams :

• Weight of the dam

• Horizontal fluid mechanics pressure because of water

• Uplift pressure due to water percolated below the dam

• Earthquake pressure

• Wind pressure

• Ice pressure

• Wave pressure

• Pressure due to silt deposited on U/S face.

• Out of on top of eight forces, engaged on the dam, initial 3 forces are the foremost forces that are thought-about within the design. All different forces aren't of a lot of significance and are considered solely under specific conditions.

Force 1. Weight of the Dam

• It is that the most important force, significantly for gravity dams. Stability of the dam for the most part depends upon this force. For the look purpose only unit length of the dam is taken into account. Cubical content of the cement concrete is decided for unit length of the dam. This cubic content once increased by the density, provides the whole weight (W) of the dam.

• The total weight (W) is considered engaging at the C.G. Of the dam section. The position of C.G. Of the dam section is noticed by dividing the dam section into many triangles, rectangles, and trapeziums and by taking moments of those weights concerning any purpose at the bottom of the dam.

Force  2. Horizontal fluid mechanics Pressure because of Water:

• This is that the largest external force engaged on the dam. It's the biggest capability for worrying the soundness of the dam. It's a horizontal force that acts at the C.G. Of the pressure distribution diagram, because of water. The pressure distribution diagram is usually triangular with zero value at surface of the water and increasing linearly to most at the bottom of the dam.

• The value of maximum horizontal pressure at base of the dam is wh wherever w is that the density of water in kg/m3 and h the depth of water in meters. Since pressure distribution diagram due to water is triangular, the worth of the whole horizontal pressure (P) because of water, are going to be area of the triangle.

Force  3. Uplift Pressure due oozy Water below the Dam:

• The water that seeps through the pores of the fabric comprising dam and foundation, causes uplift pressure and tries to tilt or topple the dam. a district of the load of the dam would get neutral by uplift pressure and therefore web foundation reaction due to vertical forces will be reduced.

• Intensity of uplift pressure is most at U/ S finish of the dam and it goes on decreasing towards the D/S end. As some water will see into the concrete dam also, the uplift pressure could occur anyplace within the dam also. It's terribly troublesome to seek out out the worth of uplift pressure accurately. It depends upon the factors like, bring to an end on U/S side, fissures in the muse rocks, drain ability of the foundation etc.

• There are 2 faculties of thought on on what quantity space uplift pressure ought to be thought-about as acting. In line with one thought third to two-third area of foundation should be considered effective. The second thought, propagated by Terzaghi recommends thought of full area because the effective area.

• According to U.S.B.R., intensity of uplift pressure at D/S (Toe) and U/S (heel) is taken up to the fluid mechanics pressure of water. The variation of uplift pressure from heel to toe is linear or straight line. So as to unleash uplift pressure, voidance galleries are provided within the body of the dam.

• The magnitude of the uplift pressure at the face of the gallery is taken as equal to hydrostatic pressure at the Toe and one third the distinction of the hydrostatic pressures at the heel and Toe.

Uplift pressure at heel A = wh

Uplift pressure at toe F = wh

Uplift pressure at gallery purpose G = w [h +1/3 (h- h)]

Criteria for Design:

• The following criteria are suggested for the calculation of uplift forces:

• Uplift pressure distribution within the body of the dam shall be assumed, just in case of each preliminary Associate in Nursing final design, to possess an intensity that at the road at the fashioned drains exceeds the tail water pressure by third the differential between reservoir level and tail water level. The pressure gradient shall then be extending linearly to heads akin to reservoir level and tail water level. The uplift shall be assumed to act over a hundred per cent of the area.

• Uplift pressure distribution at the contact plane between the dam and its foundations Associate in Nursing inside the muse shall be assumed for preliminary styles to possess an intensity that at the road of drains exceeds the tail water pressure by third the differential between the reservoir and tail water heads.

• The pressure gradient shall then be extended linearly to heads akin to the reservoir level and tail water level. The uplift shall be assumed to act over a hundred per cent area. For final designs, the uplift criteria just in case of dams based on compact and un-fissured rock shall be as nominal above.

• In case of extremely articulated and broken foundation, however, the pressure distribution could also be needed to be supported electrical analogy or different ways of study taking into consideration the inspiration condition once the treatment proposed. The uplift shall be assumed to act over one hundred per cent of the area.
• For the acute loading conditions F and G given later the uplift shall be taken as variable linearly from the acceptable reservoir water pressure at the U/S face to the appropriate tail water pressure at the D/S face. If the reservoir pressure at the section into consideration exceeds the vertical traditional stress (computed while not uplift) at the U/S face, horizontal crack is assumed to exist and to increase from the U/S face towards the D/S face of the dam to the purpose wherever the vertical traditional stress (computed on the idea of linear pressure distribution without uplift) is adequate the reservoir pressure at the elevation.
• The uplift is assumed to be the reservoir pressure from the U/S face to the top of the crack and from there to variable linearly to the tail water pressure at the D/S face. The uplift is assumed to act over one hundred per cent of the area.
• No reduction in uplift is assumed at the D/S toe of spillways on account of the reduced water surface elevation (relative to traditional tail water elevation) that will be expected now downstream of the structure. It is assumed that uplift pressures aren't stricken by earthquakes.

Force 4. Earthquake Pressure:

• Primary, secondary, Releigh and Love waves, are started within the earth’s crust, thanks to earthquakes. These waves impact acceleration to the inspiration underneath the dam and cause its movement. So as to forestall cracking or rupture, the dam should conjointly move alongside the movements of the foundation. The acceleration generated due to earthquake develops inertia force within the dam, thanks to which, stresses are 1st induced in lower layers and so in whole of the dam. The earthquake waves will travel in any direction. They're but resolved in vertical and horizontal directions.

Causes of failure :

• The modes of failure of gravity dam are:

1. Overturning or Rotation concerning toe: When the resultant force performing at any section if it passes outside the toe, the dam shall rotate or overturn about the toe. In different words, it means if horizontal forces dominate over vertical forces the dam will certainly rotate. At such condition we tend to principally use an element of safety, it's the quantitative relation of righting moments(anticlockwise) about toe to the The factor of overturning moments(clockwise) about the toe. Safety mustn't be below 1.5.
2. Crushing:- It usually happens once the compressive stress exceeds the allowable stress of the fabric of a dam, thus the dam could fail. The total traditional stress = Direct stress+ Bending stress, Pmax are going to be created on the top that is as regards to the resultant force, if Pmin is negative then tension is produced at that end. Slippy or conjointly referred to as shear failure: once horizontal forces answerable for sliding dominate resistance resistance of dam at that level. To forestall slippy the horizontal forces(H) ought to be below shear resistance(uV). Ie. H
3. Tension: If eccentricity e> b/6, then tension are going to be developed at the heel of the dam. Since concrete cannot resist tension. Hence, no tension is permissible at any purpose in dam.

• STRESS ANALYSIS : The gravity dam must maintain its stability against the masses from its structural mass and strength of concrete. The masses assumed on the concrete dam for stability analysis are water pressure, uplift force, wind force, wave pressure, silt pressure, self-weight.

To face up to the steadiness of concrete gravity dam, the dam has to be safe with the overturning force on dam, slippy force, compression and tension.

• Concrete gravity dam has the numerous load combos such structures must maintain its stability once the dam having the various proportions of water level

(a) when the reservoir is empty,

(b) once the reservoir is [*fr1] stuffed,

(c) once the reservoir is absolutely filled to the dam base and

(d) conjointly when the uplift pressure on the dam.

• The concrete gravity dam gets cracks simply by its upstream and downstream sides of the dam owing to internal and external temperature changes and by earthquakes. This cracks causes to the failure of the dam within the static and dynamic conditions of the dam. The forces that working on the gravity dam with the Water pressure: The hydraulic pressure could be a horizontal force, acts on the dam in the variety of triangular shape. At the surface of reservoir the water exerts no pressure and at rock bottom (at toe) the water exerts most quantity of pressure to dam.        

Water pressure = ½ γw.ℎ2 , acts on h/3 height from the water base.

Uplift pressure:

• The water oozy through the cracks, pores, fissure of the inspiration material. Then the water seeps through very cheap joints of the dam structure and also the foundation of the dam. Water exerts AN uplift pressure on the dam base. The uplift pressure is depend upon the peak of water, the water level is most then the uplift pressure is additionally maximum. The uplift pressure at the toe is calculated by γw.h.

Silt pressure:

• The silt get deposited to the upstream facet of the water. The load and the pressure of the submerged silt are to be thought-about additionally to weight and pressure of water. The load of the silt acts vertically on the slope and pressure horizontally. It's cipher by the Rankins formula.      

Silt pressure Psilt =1/2  γsub ℎ2 Ka.

Where Ka is co economical of the silt = 1−sin ∅/1+sin ∅    

∅ Is angle of internal friction of soil.

Wave pressure:

• Generally, the waves are generating on the surface of the reservoir by the wind blows. This causes pressure on the dam. Wave pressure is depending on the peak of the wave.                                   

Pw = 2.4 γw. Hw

Weight of The Dam:

• The weight of the dam body and its foundation is that the major resisting force. In 2-dimensional analysis of a gravity dam, a unit length of the dam is considered. The crosswise will then be divided into rectangles and triangles. The load of every at the side of their centers of gravity may be determined. The resultant of these downward forces can represent the full weight of the dam performing at the middle of gravity of the dam.                        

Self-weight compass point = lbh.ρc.g

Overturning stability:

• The overturning stability is calculated by scheming the all vertical force and also the horizontal force performing on the gravity dam. By taking moments over toe, that forces are opposing the dam to overturn like self weight this moment as favorable moments (Mf) and the forces which try to overturn the gravity dam like water pressure, uplift pressure, wave pressure, silt pressure etc.., this moment as opposing moments (Mo) The overturning forces ought to be a lot of the a pair of, if it lower than 2 the dam isnt safe.                  

Overturning moment = Mo/Mf. > 2

Sliding force:

• The stability of the gravity dam is loss by slippery. The surplus of sliding is happens within the time of earth quake. Slippery force refers the contraction between the dam foundation and rock. It's calculated by the resistance force and horizontal forces on the dam, it mustn't be less than 1.5. Sliding force = frictional force/ horizontal force on dam. > 1.5

8.6 ELEMENTARY AND SENSIBLE PROFILE OF GRAVITY DAMS :

Elementary profile :

• Elementary Profile of a Gravity Dam - AN elementary profile of a gravity dam is that the theoretical form of its crosswise once it's subjected to only 3 main forces, videlicet self-weight, water pressure, and uplift pressure. Furthermore, the elementary profile has zero prime dimension and no free board.

• The right-angle triangle is the most fitted section for the theoretical profile. For reservoir empty condition, a right angular triangular profile as shown in fig. 1, can give the utmost attainable stabilising force against overturning, while not inflicting any tension within the base. During this case, the sole force is thanks to the self weight of the dam performing at a distance of B/3 from the upstream face of the dam and thus satisfies the center third rule.

• The elementary profile is theoretic as a result of an actual gravity dam has some minimum prime dimension and free board, and it'll even be subjected to forces except the 3 main forces thought-about within the elementary profile.

• Three main forces performing on the elementary profile of a gravity dam are

(i) Self Weight of the Dam

Weight of dam (W) = 1/2 × B × H × G × w

Where, G = relative density of dam material that is usually taken as 2.4 for concrete

w = Specific weight of water (9.81 kN/m3)

B and H = Base dimension and height of dam.

The weight (W) acts vertically through the center of mass of constellation at a distance of B/3 from the heel.

(ii) Water Pressure -

p = wH × H

= × wH2, which acts at a height of H/3 from the base.

(iii) Uplift Pressure -

U = × B × CwH

Where C is that the uplift pressure intensity factor. It indicates that the uplift pressure is CwH at the upstream fringe of the base. The uplift pressure (U) acts at a distance of B/3 from the heel in upward direction as shown in fig. 1.

Base dimension of Elementary Profile 

• The base width of the elementary profile is to be determined below following 2 criteria -

(i)                Base dimension with No Tension Basis –

• When reservoir is empty, for no tension to develop, the resultant ought to act at the inner third purpose A. For the complete reservoir condition, let R be the resultant of all forces performing on the dam, for no tension at the heel, the resultant R should suffer the outer middle third point B as shown in fig. 1. The utmost worth of eccentricity (e) is B/6 once the resultant R passes through the purpose (B).

Taking the moment of all forces about B and equating it to zero, we get W.B/3 - U.B/3 – P.H/3 = 0

1/2 BHGw × (B/3)-1/2 CwHB ×(B/3)-1/2wH2 ×(H/3)=0

1/2×H/3× w(GB2 -CB2-H2) =0

Or. GB2 -CB2 -H2 =0

B = H/√(G-C).        .............(1)

If the uplift pressure intensity C=1 we get

B = H/ √(G-1)

If the uplift pressure intensity C=0 we get

B = H/√G

(ii) Base dimension for No slippery –

• For no sliding to occur, the forces inflicting sliding mustn't be larger than the forces resisting sliding. Within the limiting condition the 2 forces should be equal and opposite. It's sometimes assumed that the sliding is resisted by the friction solely thus,

μΣV = ΣΗ

Where, u is the coefficient of friction.

u(W-U) = P

Or.  P = u(W-U)

1/2 wH2 = u(1/2 BHGw-1/2 BCwH)

H2 = u(BHG-BHC)

Or.  H = uB(G-C)

Or.  B = H/ u(G-C)

• The minimum base dimension needed for the elementary profile ought to be larger of the 2 values obtained from the equations (i) and (ii) but usually equation (i) is employed to calculate base width.

• Stresses Developed within the Elementary Profile  the traditional stresses at the heel and toe of the gravity dam could also be expressed as

Pn = V/B (1+6e/B)

• For the reservoir full conditions, the utmost stress happens at the toe and also the minimum stress at the heel.

• For the reservoir empty conditions, the maximum stress and the minimum stress occurs at the heel and toe respectively.

8.7 Practical profile :

• Elementary profile of a given dam is simply theoretical profile. Bound changes have to be compelled to be created during this profile so as to cater sensible wants.

These needs are:

• Providing a high dimension for road construction.

• Providing a free board over top water surface.

• These additions of 2 provisions will cause the resultant force to shift towards heel.

• The resultant force once the reservoir is empty was earlier passing through the center third purpose.

• This will thus shift a lot of towards the heel, crossing the inner middle third point and consequently, tension are going to be developed close to this.

• In order to avoid tension, some masonry or concrete will have to be compelled to be adscititious on upstream side as shown within the figure that shows typical section at the side of doable dimensions that may be adopted for low gravity dam.

• It ought to be checked for stability analysis.

8.8 ARCH AND BUTTERESS DAMS :

Definition and kinds of Arch Dams

• An arch dam conjointly be|is also} outlined as a solid. Wall, sinuate in plan, standing across the complete dimension of the watercourse valley, in a very single ·span*. This dam body is typically made from cement concrete. Though scrap and stone masonry has also been utilized in the past.

• This wall can structurally behave : partially as a cantilever wall standing up from its base, and partly, the load are going to be transferred to the 2 ends of the arch span by horiwntal arch action. The arch load will, thus, be transferred to the facet walls of the canyon, that should be strong, stable and rocky.

• The distribution of part of the load to the side walls of the canyon, reduces the load on the cantilever wall, thereby reducing its thickness, as compared to that in an ordinary gravity 'dam ; and that is. The only benefit we derive from an arch dam in comparison to a gravity dam.

• Evidently, the greater is the wall curvature (in plan), the greater will be the load that will be transferred to the sides of the canyon, and hence greater will be the economy in the dam thickness.

• This economy in dam thickness can be further increased considerably by making the dam body not solely sinuate in arrange however additionally curved in section such a non vertical dam is thought as double curvatµre arch dam or a shell-arch dani, as a result of such dams are designed as shell-structures. Such 3 dimensional styles are quite complex, and are instructed only at M-Tech level in Structural Engineering.

• Since the planning associate degreed construction of an arch dam is extremely complicate, requiring extraordinary talent for construction shuttering within the field, it's usually most popular in sensible life to construct gravity dams. Which is why, we discover only 1 arch dam in our country, as against many many gravity dams. This arch dam too, isn't a straightforward arch dam, however a shell-arch dam.

• Simple arch dams, that transfer an outsized a part of their loading by cantilever action, may additionally be of various types, since their faces could also be either vertical or curvilinear. Relying upon the form consideration, simple arch dams are often .divided into 3 eight types, viz:

(i) Constant radius arch dams

(ii) Variable radius arch dams; associate degreed

(iii) Constant angle arch dams.

Constant Radius Arch Dams.

• A constant radius arch dam is that, in which, the radii of the elevations, from prime to the bottom. The centres of all such circular arcs, known as extrados, can therefore, plainly lie on one vertical line. However, the intrados (i.e. within curved surface of the arch) has bit by bit decreasing radius from top to the bottom, thus as give exaggerated concrete thickness towards the bottom for accounting the proportionately increasing hydros-static water pressure of the reservoir.
• The dam body will, therefore, be triangular in crosswise with upstream face vertical, and a minimum thickness at the top. Evidently, it is only the radii of the intrados, which decrease with depth ; while the .centres of all such circular arcs continue to lie on the same vertical line, on which lie the centres of the extrodos.
• Hence, in such a dam, the centres of extrodos, introdos, as well as the centre lines of the arch rings. At various elevations, lie on a straighL vertical line that passes through the centre of the horizontal arch ring at the crest. Such a dam is, therefore, sometimes called a constant centre arch dam, although strictly speaking, this centre is not at one point, but lies at 'different heights along one vertical line. ·

• Evidently, the central angles of the arch rings of the introdos will vary at different elevations, due to the varying width of the river valley (see Fig. 27.2); the maximum being at the top of the dam, and the minimuin at the bottom of the dam.

• It has further been shown that the best or most economical central angle in an arch dam is the one whose value is equal to 133°. But in a constant radius arch dam, such an angle value can be adopted only at one place, since the angle varies with height considerably, due to narrow V-shape of the valley. It is therefore considered prudent to keep the econom.fcfilangieofT33°~ 34'-at about mid height.
• The angle at the top will, therefore, be more than this value; but due to topographical considerations, the angle at the top can not be fixed greater than about 150°. Hence, the angle at the top should be sure as to give the best average angle, but restricted to about 150°.

Variable Radius Arch Dams. 

• A variable radius arch dam is the one in which the radii of the extrados curves and of intrados curves vary at various. Elevations, being maximum at the top, and a precise minimum at its bottom. This makes the central angles as massive as possible, in order that the utmost arch potency could also be obtained in any respect elevations. ·

BUTTERESS DAMS :

• In a usual sketch of such a dam, the downstream face of the dam at the central line (crown) is vertical; while at all alternative locations, there's a batter on each the edges barring at the abutments, the place again, the upstream aspect turns into vertical. If overhangs are permitted, due to, availability of improved foundations, then the faces at the crown as properly as abutments, fuay be supplied with overhangs, moving saving within the designed thicknesses.

• Evidently, considering in- such associate degree arch dam, the centres of the assorted arch rings at distinctive elevations, do now not lie on the identical vertical line, it's in addition recognized as variable. Centre arch dam. Such dams are favored for formed valleys as in distinction to steady radius arch dams which could even be most popular for relatively wider U-shaped valleys.

Constant Angle Arch Dams.

• The constant. Perspective arch dam is a unique type of variable radius arch dam, in which the central angles of the horizontal arch rings are of the same magnitude at all elevations. The graph of such a dam can, thus, be made by means of adopting the excellent central perspective of 133° - 34'; and subsequently such a dam proves to be the most economical, out of the three sorts of everyday arch dams, as pointed out formerly also.

• However, the format of such a dam commonly includes providing overhangs at abut-ments, which require a lot of appropriate foundations, associate degreed afterward such a kind cannot be used if the foundations are weak.

FORCES functioning on ARCH DAMS :

• Generally, the identical forces act on an arch dam, that do act on a gravity dam. These forces are : (i) water stress ; (ii) uplift stress ; (iii) earthquake forces ; (iv) silt strain ; (v) wave strain (vi) ice strain

• However, the relative significance of the forces is one-of-a-kind in an exceedinglyn arch dam, as in distinction to it in a gravity dam. Say for example, the, uplift strain in an arch dam is tiny and is generally neglected, as a result of other slender base dimension of its body. On the various hand, the stresses brought on through ice, temperature changes, and yield of supports (i.e. abutments), ordinarily end up to be quite important in arch dams, and for this reason should be completely examined.

• Whereas, the ice pressure, applicable in cold countries, causes never-ending con-centrated load on the arch element· at the elevation of the ice ; the within stresses led to by exploitation the temperature changes cross the dam upstream during the summer, and downstream throughout the winter. Hengrow to be pretty necessary in stress analysis, considering that these stresses act additive to the reservoir water pressure. Moreover; even the moderate yield of abutments due tc transfer of load through arch action, mar conjointly· reason -high within stresses in . The . Arch, and need to therefore, be providentially accounted for.

Definition and kinds of Buttress Dams

• An normal concrete gravity dam, as we have a tendency to know, could be a solid body of mass concrete, somewhat triangular in section, running across the complete dimension of the stream valley. Such a solid wall needs vast quantity of concrete, that part remains light to full extent, thereby resulting in wastage of concrete. The uplift pressure also acts on the complete dimension of the dam body, from its bottom, that any will increase its size, while not giving associate degree additional profit as a dam.

• Efforts have, thus, been made of time to time, to introduce strategies for poignant economy within the use of concrete, by reducing the concrete from those dam parts wherever it remains unstressed. Tries have, therefore been created to supply hollow gravity dams. Buttress dams, are an improvement innovation over the hollow concrete gravity dams.

• In such an innovated dam, therefore, solid walls of mere thickness and section are made parallel to the flow at appropriate interval. These walls are known as however inclined to tresses. Embrace blocks or arch slabs are then supported on upstream aspect on these buttresses.

• Although many kind of buttresses dams are devised, but the foremost common sorts are

(1) deck slab kind; and

(2) multiple arch type.

• Both these type of dams have been shown within their simplified line diagram respectively.

• Slab type dams are generally-i) referred for smaller heights; say from twenty to fifty m, or so. The best such dam in the world is Rodriguez dam in Mexico, having a height of 73.2 m. Such dams are just about noted as buttress dams, or Amberson dams (based upon the name of their inventor).

• The multiple arch dams, on the opposite hand, are used for higher dam heights, say from fifty m onward, and also the highest such dam of the globe is Manicougan-5 dam in Canada, having a height of 210 m.

Simply Supported block kind of Buttress Dams.

• In such a kind of dam, the R.C.C. Deck slab is freely supported on the buttresses, that have corbels for the slab to rest on. The table slab is enclosed to horizontal by about 40° to 55°, so as to support the dead load of a portion of reservoir water, and thus, to provide the stabilising force, in addition to the 'self' weight-of the dam, to avoid its sliding.

Design considerations

• The loading and safety criteria for buttress dams or buttresses, is the same as that for a gravity dam section, except that the provided buttress thickness 't' will take the load coming from the dam length = x + t ; where xis the clear spacing between the two consecutive buttresses.
• Hence, t metre length of buttress section, will take the loads returning from (x + t) metre length of dam, as against the unit metre length of gravity dam section taking load from the unit metre dam length. The resultant impact is thought-about by increasing the unit weight of water by multiplying its actual price by .a surcharge issue (S), outlined as :                        S = (X+t)/t

• Hence, the effective unit wight of water can be considered as Yw (x+t/ t} and also the section of the buttresses can be designed, precisely within the same manner, as a gravity dam section is designed, considering unit length and never-ending section. The· deck slabs is designed as merely supported R.C.C. Decks, each spanning over 2 adjacent buttresses, and every having a span = x + t.

• Concrete quantities also are discovered for -various angles of u/s slope (qi) and completely different buttress spacings, for fastened determined dam height (H) ; .and premeditated to urge a curve for every angle. A master curve is then drawn through the junctions of the curves and also the vertical lines similar to each angle .

Multiple Arch variety of Buttress Dams

• As expressed earlier, during this type of dams, arch slabs are made for u/ s face· of the dam, to be supported on buttresses,  every buttress is also within the variety of one stiffened wall as or a double hollow wall.

• Meer Alam dam in India, inbuilt concerning 1800 A.D., is that the earliest recorded example of such a sort of dam. As expressed earlier, such dams are most popular for larger heights, as they prove additional stable and flexible, as compared to the normal buttress dams (i.e. slab  type).

• The stability of any unit of a multiple arch dam depends on the adjacent units, in order that any settlement in one would have an effect on the others. Hence, such a dam would needed higher foundations, as compared to a normal buttress dam, wherever deck slabs on 2 adjacent buttresses, behave as freelance units.

• For short spans (10 to 15 m), circular arches fusion thickness prove economical; whereas, for larger spans, arches of variable thickness are provided. If the central angle of every arch is unbroken between 180° to fifteen0°, with semicircular or nearly semicircular arches, the horizontal thrust between adjacent arches get~ eliminated.

• For arched buttress dams, the vary of buttress spacing typically adopted, is be-tween 15 to twenty one m, though as high a price as. {42|forty 2} m golden ager permissible in Webber Greek dam in California, USA ; a web site arrange of that is reflected

Other varieties of Buttress Dams

• In addition to the on top of represented two commonplace kinds of buttress dams, bound completely different sorts, cherish over one dome type ; Brobdingnagian head type ; columnar_ buttress type ; etc., have additionally been adopted at some places. As mentioned beneath :

Multiple dome type

• Such a sort of buttress danlis pretty understandable, because it uses a good sort of do11J.es as a substitute of variety of arches as utilized in a multiple arch kind of dam, and every one different components final the same. Such a dam will facilitate increasing the buttress spacing, but re-quires sites, the place steady foundations may be had at larger depths. The Chief Executive dam on San Sanchez watercourse in Arizona is associate degree instance of this type of a dam, that is 76.2 m high with however tresses @ 54.8 m apart.

Massive head types

• This quite buttress dam is that the one, which doesn't use slabs or archs for upstream face, but the heads of the buttresses themselves are enlarged to fulfill every other, and thus, to structure a non-stop water aiding sur-face, once the enlarged heads are cylindrical on the outerside, it's acknowledged as spherical head deck and once they converge to a point, it is recognized as a diamond head deck .

• These big head buttress dams are, infact, viewed as improvement over all alternative varieties of buttress dams, as they offer, variety of advantages, cherish :

(i) the event work is easier, as mass concrete may be arranged along within the whole dam body.

(ii) Since water stress sheer in an exceedingly diamond type; all pressures are normally compressive. The bending similarly as diagonal tension in the upstream part of the dam are, thus, absent during this quite dams. ·

• Iii) Since the deck is not to be reinforced, there's no doubt of its failure through oxidation of steel, as may additionally seem in associate degree everyday block quite buttress dam.

(iv) For smaller heights, they show to convey additional relatively low-cost buttress spacing, as in distinction to alternative 2 sorts of buttress dams.

(v) Such a dam body offers bigger resistance to sliding, because, it's drastically heavier, and contains a accumulated sectional space aboard the horizontal planes.

Columnar buttress type

• As verified during this kind could be a change of the everyday slab type, because the deck here, is I supported on columns. Only a few dams are designed once you think about that they provide the subsequent disadvantages:

(i) they need very durable and steady foundations

(ii) bigger ability is needed in putting in the buttresses; and even then, they fee nearly as lots as completely different ancient types.

SPILLWAY :

• A conduit could be a structure want to provide the controlled launch of flows from a dam or dyke into a downstream area, ordinarily the bed of the dammed watercourse itself. Within the United Kingdom, they'll even be considered overflow channels. Spillways confirm that the water will not overflow and harm or wreck the dam.

• Floodgates and fuse plugs may additionally be designed into spillways to change water float and reservoir level. Such a spillway can be used to regulate downstream flows by using releasing water in small amounts earlier than the reservoir is full, operators can prevent surprising giant releases that would occur if the dam had been overtopped.

• Other uses of the time period "spillway" include bypasses of dams or shops of channels used all through excessive water, and outlet channels carved through natural dams such as moraines.

• Water normally flows over a spillway only at some stage in flood durations when the reservoir cannot maintain the extra of water getting into the reservoir over the amount used. In contrast, an consumption tower could be a structure wont to unharness water on an everyday foundation for water supply, electricity generation, etc.

COMPONENTS OF WASTEWEIR :

APPROACH CHANNEL:

• Entrance structure or the trail to draw water from the reservoir and convey it to the management structure. It is also straight or incurvate in plan.

• Its banks could be parallel, convergent, divergent, or combination of those and perhaps vertical or sloping.

• It may guarantee minimum head loss through the channel and to get uniformity of flow over the control structure.

CONTROL STRUCTURE:

• A significant factor of spillway given bridge and gates.

• Regulates and controls the excess water from the reservoir.

• It doesn't permit the discharge of water below the fastened reservoir level.

DISCHARGE CARRIER:

• It is that the waterway provides to convey tile flow free from the management structure to the downstream facet of the spillway.

• The crosswise is also rectangular, trapezoidal, or of different shapes.

• Waterway may be broad or narrow, long or short.

DISCHARGE CHANNEL:

• They are provided to convey the water from rock bottom of the discharge carrier to the downstream flowing river.

• It may be the downstream face of the spillway.

• The dimension of the discharge channel depends on the number of water to be conveyed.

ENEMY DISSIPATORS:

• At the top of the discharge carrier, the water released from the control structure has high velocities enough to cause scour; thus, energy dissipation are provided to avoid the scouring of the downstream facet of the spillways.

• These are to be provided before water coming into the discharge channel.

• The following are the various sorts of dissipators:

BUCKET DISSIPATORS:

• The high mechanical energy of water is reduced by providing a hydraulic jump at the top of the spillway.

• The hydraulic jump may be achieved by providing bucket kind dissipators.

• By hydraulic jump of water some a part of the energy is dissipated by aeration.

STILLING BASIN:

• Stilling basins are typically provided when the buckets.

• Due to the hydraulic jump of water, the water falling on the bottom could cause cavitations on the ground.

• These cavitations can be avoided by providing the stilling basin.

• The stilling basin consists of water, that reduces some a part of the energy of water.

BAFFLE DISSIPATORS:

• After passing the stilling basin, water still has some energy.

• If any amount of energy exists, it may be entirely dissipated by providing baffle dissipators.

• In this, baffle kind structures are provided in many series looking on the number of energy.

TYPES OF WASTEWEIR GATES:

STRAIGHT DROP SPILLWAY:

• The straight drop spillway consists of an occasional elevation meat wall, the lower part of which is totally or nearly vertical.

• When the water level inside the reservoir rises on top of the mean pool level, the surplus water freely falls from the crest of the weir, therefore it's called an on the spot drop wasteweir or free fill spillways.

• To shield the beds, an artificial pool with a concrete apron ANd an occasional secondary dam is made on the banks of the drift.

• Proper ventilation should be provided at a lower place a falling jet to forestall the implications of vibration and fluctuation.

• Sometimes, an overhanging course is provided to the crest of the ridge, avoiding the entry of the tiny discharges to the ridge face.

• Straight drop spillways are pre-eminently fitted to the skinny arch dams, stuff dams, or bunds.Straight drop spillway

OGEE SPILLWAY:

• The Ogee spillway signifies the form of the weirs drift face, it's a more robust type of straight drop spillway.

• In this case, the lower a part of the weir is personalised to the economical form by the addition of a self-sufficiently falling water, that is AN ogee shape.

• The downstream face is generally supported the principle of a projectile.

• In general, the lower diaper size of the water jet won't be fastened for all water heads; thanks to this fact, the obtained technique for the most head is taken into account once coming up with the Ogeee spillways.

• Whenever there's surplus water, it'll be forbidden severally of the Ogee-shaped crest through the Ogee waste weir; therefore, it may be known as an overflow spillway.

• The Ogee spillway is most commonly utilized in gravity, arch, buttress dam, etc. For a gravity dam, it's usually placed inside the dam body.

• The Ogee spillway is most usually used in gravity, arch, buttress dam, etc.

• For a gravity dam, it is usually located within the dam body.

SHAFT SPILLWAY:

• It could be a sort of spillway consisting of a vertical shaft, followed by a horizontal groove.

• The surplus water enters the vertical axis, then into the flat drain, and at last reaches the channel drift; the beam fashioned is either artificial or natural.

• Excavation for natural shafts is feasible only a tough rocky crust is gift at the top.

The horizontal drain permits through the body or the muse of the dam.

• In the case of huge projects, the body of water hole of the vertical shaft is specially shaped, referred to as the vine or storage locker waste weirs.

• Therefore, the shaft spillway is additionally called the morning glory spillway or bell-mouth spillway.

• Shaft spillway is recommended if there's no area out there for other forms of waste weirs i.e., Ogee, straight drop spillway, etc.

CHUTE SPILLWAY:

• It could be a sort of spillway within which surplus water flows through the sloping of the open channel.

• It is commonly made at one finish of the dam or from a natural saddle of the watercourse, which is separated by a barrier.

• The Chute spillway is appropriate for gravity dams, mud dams, rockfill dams, etc., however it's most popular once the breadth of the river vale could terribly narrow.

• The water flows on a slope or trough or AN open channel and reaches the river.

• This spillways also referred to as trough spillways or open channel waste weirs.

• The slope of the spillways is taken into account in such how that movement should always be within the critical state.

• Energy dispersers are offered on a pad of spills to dissipate energy from the falling water.

SIDE CHANNEL SPILLWAY:

• It is extremely a lot of almost like the chute spillway; however, the distinction is that the crest of the side-channel spillway is found on one side of it, whereas the crest of the side spillway is located between the side walls.

• In totally different phrases, the dispersion of water from the crest is twisted to ninety degrees and move parallel to the crest of the side-channel spillway, as against the spill.

• Side-channel splits are typically most popular over chute wasteweirs to avoid serious cutting once adequate breadth flanks aren't available.

• The angle of flow of water may be unbroken between 00 and 900 once passing the damage crest.

SIPHON SPILLWAY:

• It could be a quite spillway within which surplus water flows by means that of inverted U-shaped sewers.

• Generally, it's prescribed within the body or at the crest of the dam.

• In every type of siphon spillways, the air is pushed over the curvilinear portion of the higher passage to prevent water penetration when the water penetration level is below the mean pole level.

• Whenever the level rises above the mean pool level, the water enters the drain and is discharged by the siphonic action downstream of the channel.

LABYRINTH SPILLWAY:

• It is a type of spillway in which a wall is accidentally constructed to outspread the length of the damage with respect to the width of the channel.

• This increase in insufficient length increases the discharge capacity of the weir, and therefore, the high-water flow over the short head can quickly convey the drift.

8.9 RESERVOIRS :

• This article is about an artificial body of water or a natural lake. For other uses, see Reservoir (disambiguation).

• "Artificial lake" redirects here. For other types of lakes, natural and artificial, see Lake.

• Kardzali Reservoir in Bulgaria is a reservoir in the Rhodope Mountains.

• A reservoir from French reservoir  is, most commonly, an enlarged natural or artificial lake, pond, or impoundment created using a dam or lock to store water.

• Reservoirs can be created in a number of ways, including controlling a watercourse that drains an existing body of water, interrupting a watercourse to form an embayment within it, through excavation, or building any number of retaining walls or levees.

• Defined as a storage space for fluids, reservoirs may hold water or gasses, including hydrocarbons. Tank reservoirs store these in ground-level, elevated, or buried tanks. Tank reservoirs for water also are referred to as cisterns. Most underground reservoirs are accustomed store liquids, mainly either water or petroleum, below ground.

TYPES OF RESERVOIR :

Dammed valleys

• Lake Vyrnwy Reservoir. The dam spans the Vyrnwy Valley and was the first large stone dam built in the United Kingdom.

• The East Branch Reservoir, part of the New York City water supply system, is formed by impounding the eastern tributary of the Croton River.

• Cherokee Reservoir in Tennessee. It was formed after the impounding of the Holston River Valley by the Tennessee Valley Authority in 1941 as a part of the New Deal's efforts to bring electricity to the Tennessee Valley.

• A dam constructed in a valley relies on the natural topography to provide most of the basin of the reservoir. Dams are usually placed at a slender a part of a vale downstream of a natural basin. The valley sides act as natural walls, with the dam located at the narrowest sensible purpose to supply strength and also the lowest price of construction. In several reservoir construction projects, individuals got to be touched and re-housed, historical artifacts moved or rare environments relocated.
• Examples embody the temples of Abu Simbel (which were moved before the development of the Aswan High Dam to form Nasser from the river in Egypt), the relocation of the village of Capel Celyn throughout the construction of Llyn Celyn, and also the relocation of Borgo San Pietro of Petrella Salto throughout the development of Lake Salto.

• Construction of a reservoir in an exceedingly vale can typically would like the stream to be entertained during a part of the build, usually through a brief tunnel or by-pass channel

• In rough regions, reservoirs are often created by enlarging existing lakes. Typically in such reservoirs, the new prime water level exceeds the watershed height on one or a lot of of the feeder streams akin to at Llyn Clywedog in middle Wales. In such cases additional facet dams are needed to contain the reservoir.

• Where the topography is poorly suited to one giant reservoir, variety of smaller reservoirs could also be created in an exceedingly chain, as within the stream Taff vale wherever the Llwyn-on, Cantref and Beacons Reservoirs type a sequence up the valley.

Coastal :

• Coastal reservoirs are water storage reservoirs placed on the ocean coast close to the river mouth to store the flood water of a river.

• As the land primarily based reservoir construction is fraught with substantial land submergence, coastal reservoir is most well-liked economically and technically since it doesn't use scarce land area.

• Coastal reservoirs were constructed in Asia and Europe. Saemanguem in South Korea, dockage Barrage in Singapore, Qingcaosha in China, associate degreed shorebird Cove in Hong Kong, and so on are few existing coastal reservoirs.Aerial read of shorebird Cove coastal reservoir.

Bank-side

• Where water is wired or siphoned from a stream of variable quality or size, bank-side reservoirs could also be engineered to store the water. Such reservoirs are typically fashioned partially by excavation and partly by building a whole skirting bund or embankment, which can exceed six kilometer (4 miles) in circumference.

• Both the ground of the reservoir and also the bund should have an tight lining or core: at first these were usually manufactured from puddled clay, however this has typically been superseded by the trendy use of rolled clay. The water keep in such reservoirs could keep there for many months, throughout which era traditional biological processes may well cut back several contaminants and nearly eliminate any turbidity.
• The utilization of bank-side reservoirs additionally permits water abstraction to be stopped for a few time, once the stream is intolerably impure or when flow conditions are terribly low because of drought. The London water system is one example of the use of bank-side storage: the water is taken from the Thames River and River Lee; several giant Thames-side reservoirs akin to Queen female parent Reservoir will be seen on the approach to London Heathrow Airport.

Service :

• Service reservoirs store totally treated potable water on the brink of of} the point of distribution. Several service reservoirs are created as water towers, often as elevated structures on concrete pillars wherever the landscape is comparatively flat.

• Other service reservoirs can be nearly entirely underground, particularly in additional rough or mountainous country. Within the United Kingdom, River Thames Water has many underground reservoirs, typically additionally known as cisterns, inbuilt the 1800s, most of that are lined with brick. An honest example is that the Honor Oak Reservoir in London, constructed between 1901 and 190

• When it was completed it had been aforesaid to be the biggest brick engineered underground reservoir within the world and it's still one in all the largest in Europe. This reservoir currently forms a part of the southern extension of the River Thames Water Ring Main. The highest of the reservoir has been grassed over and is now employed by the Aquarius Golf Club

• Service reservoirs perform many functions, together with guaranteeing adequate head of water in the water distribution system and providing water capability to even out peak demand from consumers, sanctioning the treatment plant to run at optimum efficiency. Giant service reservoirs may be managed to reduce the cost of pumping, by refilling the reservoir at times of day when energy costs are low.Capacity of reaervoirs :

• Reservoir Capacity means the gross volume of water which can be stored in the reservoir. "Dead Storage Capacity" means that portion of the Reservoir Capacity which is not used for operational purposes, and "Dead Storage" means the corresponding volume of water

• "Live Storage Capacity" means the Reservoir Capacity excluding Dead Storage Capacity, and "Live Storage" means the corresponding volume of water.

• "Flood Storage Capacity" means that portion of the Reservoir Capacity which is reserved for the temporary storage of flood waters in order to regulate downstream flows, and "Flood Storage" means the corresponding volume of water.

• "Surcharge Storage Capacity" means the Reservoir Capacity between the crest of an uncontrolled spillway or the top of the crest gates in normal closed position and the maximum water elevation above this level for which the dam is designed, and "Surcharge Storage" means the corresponding volume of water.

• "Conservation Storage Capacity" means the Reservoir Capacity excluding Flood Storage Capacity, Dead Storage Capacity and Surcharge Storage Capacity, and "Conservation Storage" means the corresponding volume of water.

• "Power Storage Capacity" means that portion of the Conservation Storage Capacity which is designated to be used for generating electric energy, and "Power Storage" means the corresponding volume of water.

• "General Storage Capacity" means the Conservation Storage Capacity excluding Power Storage Capacity, and "General Storage" means the corresponding volume of water. "Dead Storage Level" means the level of water in a reservoir corresponding to Dead Storage Capacity, below which level the reservoir does not operate.

• "Full Reservoir Level" means the level of water in a reservoir corresponding to Conservation Storage Capacity.

Yeild of reaervoirs :

• The amount of water that can be supplied from a reservoir during specified period of time is called the yield of a reservoir.

Ex:- 25,000 cu.m/year

SAFE YIELD:

The most amount of water warranted throughout a vital dry period.

It is additionally called FIRM YIELD.

SECONDARY YIELD: The yield that is in more than firm yield is termed secondary yield.

AVERAGE YIELD is that the arithmetic average of firm and secondary yields.

• Units of yield:-

CUMEC-CUbic Meter per sec

CUSEC-Cubic Foot per SEC

8.10 RESERVOIR REGULATION :

• The term 'Reservoir regulation (or operating) procedure' as it applies to the area of reclamation can be defined as ' Operating procedures that govern reservoir storage and releases'.

Sedimentation :

• Definition of sedimentation:  the action or process of forming or depositing sediment : SETTLING

• For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation. If buried, they may eventually become sandstone and siltstone (sedimentary rocks) through lithification. ... Desert sand dunes and loess are examples of aeolian transport and deposition.

Economic height of dam :

• Economic height of a dam is the height corresponding to which. A. Cost of the dam per unit of storage is minimum.

• Dam Height. A dam's height is the vertical distance between the lowest point in the original streambed measured at the downstream toe of the dam and the maximum water storage elevation

• A typical method of redeveloping an existing dam by expanding its reservoir capacity is raising the height of the dam body. Improving its function in this way effectively lowers the costs and permits the use of the effective capacity obtained by raising the dam height to control flood discharge or to produce water.

SELECTION of appropriate web site :

• Suitable foundation should be on the market.

• For economy, the length of the dam ought to be as tiny as possible, and for a given height, it should store the utmost volume of water.

• The general bed level at dam site should somewhat be on top of that of the watercourse basin. This can cut back the peak of the dam.

• A suitable site for the spill should be available within the close to vicinity.

• Materials needed for the development of dam should be simply available, either regionally or in the near vicinity.

• The worth of land and property submerged by the proposed dam ought to be as low as possible.

• The dam web site should be simply accessible, so it is economically connected to big cities and cities.

• Site for establishing labor colonies and a healthy setting should be on the market close to the site.