Geology of Dams

Dams

Dams are a common and cheap means of storing water. Dams are constructed as barriers across the rivers thereby storing their water. They are built mainly to control floods, for irrigation lands, for generating electricity and supplying water to industries and cities. A dam that serves more than one purpose is called a ”multipurpose dam”.

Purpose of Dams

Actually dams are meant for preventing water from wastage. This is done by means of a huge barrier constructed in the way of flowing water of a stream channel or river, and this water is stored for future consumption. This whole work is known as damming. Natural streams and rivers are very suitable for the construction of dams because the continuously flowing water gets accumulated in the dam automatically. The purpose of the dams is to optimize the consumption in present, to meet the need of the future, and to prevent flooding. The index of rainfall does not remain the same all through the year. During the days of higher rainfall, streams and other water channels bring much water, which may overflow from these channels and cause floods, but during the period of low rainfall, the water quantity in the streams and rivers decreases up to an alarming level. To maintain an equal supply of water throughout the year, dams and water reservoirs are severely needed to be constructed. These reservoirs store surplus water and supply it at the time of need. The typical purpose of the dams is to store water for irrigation and agricultural needs. The typical purpose of the dams is to store water for irrigation. But with the gradual growth of human needs and discovery of newer methods to meet these needs, some other significance of the dams was also discovered, like prevention from flooding, generation of electricity, protect aquatic life, etc. Some of the major purposes of the water reservoirs are summarized in the following lines;

  1. Dams prevent the river and stream water from wastage, as they are the best means of storage.
  2. Dams protect the human population and crops from being flooded by the overflow of water channels.
  3. In the time of need, dams store excess water.
  4. Dams supply water for irrigation purposes.
  5. Dams supply water for household and industrial consumption.
  6. Dams are a very good source of aquatic food, like fish, and aquatic herbal food.
  7. Dams are a very vital source of energy. The World’s most of electricity is generated with the help of hydropower of dams.
  8. Dams provide humidity to the atmosphere, thus keeping the weather pleasant and health friendly.
  9. Dams provide river navigation.
  10. Dams provide recreation sites for boating and fishing.
  11. Dams are used for land reclamation.
  12. Small dams are used to divert the flow of stream for irrigation and electricity generation.

Structural Elements of Dams

Compositional elements of a Dam

The type of construction that is used to resist or stop the flow of water for thee sake of storing water for the time of essential need. A wide-spanned barrier/wall is built up before the way of flowing water, which allows a controlled quantity of water to flow, and the rest of the water is stored or reserved for the future or time of water deficit. The structural elements of dams are still needed to be discussed in detail. As far as the structural parts of the dams are concerned, they are almost the same in all types of the dam, different designs of the dams may vary the designs of the elements of the dam. A dam structure may be divided into three parts:

  1. Water Retaining Structure
  2. Water Releasing Structure
  3. Water Conveying Structure

(1). Water Retaining Structure:

It is the major element of a dam, which is the walled structure that resists the water and allows a controlled quantity to flow downstream. The side of the wall or dump which faces the down-stream is called the face of the dam. The plane top surface of the dam is called the crest of the dam. The crest is a roadway across the dam. The crest of the dam is constructed on the top of the spillway. This includes the total length of the dame. It is the overflow section of the dam. The water-retaining portion of the dam has the following elements.

    • Abutments: The part of the valley sides of the dams, constructed with concrete material or masonry work. The function of the abutments is to provide support to the wall of the dam.
    • The base of the Dam: The base is the total width of the basement of the dam, which descends with vertical ascend of the dam.
    • Crest: Crest the uppermost plane surface of the dam. It is the overflow part of the dam.
    • Cutoff: The cut-off of the dame is an impervious material, which prevents the seepage of water through the base section of the dam.
    • Cut-off Wall: The wall of impervious material like wood panels, concrete, or steel is constructed in the core of the dame. The purpose of this wall is to prevent seepage. Keep in view that seepage harms the solidarity of the dam.
    • The face of the Dame: The side of the dam which is faced by the downstream.
    • Upstream: Upstream of a dam is the level of water reservoir held back by the dam. The water of Upstream flows through the conduit toward the downstream.
    • Parapet Walls: The parapet walls of the dams are constructed on the crest of the dam. The function of the parapet wall is to give protection to the tourists.
    • The heel of the dam: The junction of the upstream face with the foundation of the dam is called the heel of the dam.
    • Toe of the dam: The junction of downstream of the dam with the ground is called the toe of the dam.

(2). Water Releasing Structure of the Dam:

The water releasing structure is another important part of a dam, which allows water to release downstream. It is, technically called Spillways of the dam. The objective of this part of the dam is to allow a controlled quantity of water downstream and to prevent overflow. The overflow causes damage to the dam, and destruction to the landscape, population, and agriculture. The mechanism of the spillway is based on its low-lying construction as compared to the dam. A spillway has the following elements.

    • Crest Gate/ Spillway Gate: These gates are installed on the crest of the spillway. The duty of these gates is to allow a controlled quantity of the reservoir water.
    • Flap Gate: They are flow control gates, which are hinged from their top.
    • Outlet Gate: It controls the outlet flow of water from the reservoir.
    • Radial Gate: A gate with radial arms and curved upstream plates.
    •  Slide Gate: This type of gate can be opened and closed by sliding it.

Types of Spillways:

There are two types of spillways:

      • Auxiliary Spillways: Auxiliary spillways are constructed along or above the crest of the main spillway. They are designed for emergency release of water, to prevent the damage of the dam. The rupture or damage of a dam can cause a deadly flood.
      • Ogee Spillways: It is an overflow spillway, which is constructed in cross-section the crest, downstream slope, and bucket in an “S” shape or ogee form of a curve. The shape is designed to prevent the high-velocity water to damage the downstream area near the bottom of the dam.

(3). Water Conveying Structure of the Dam:

The third important element of the dam is the water conveying structure. Conduits are the parts of the outer work of the dams. The function of the conduits is to convey the water from reservoirs through, around, or under an embankment dam. Many dams have conduits that serve as a spillway.

Forces acting on Dams

There are two types of pressures exerted on the dams, (i) Water Pressure, (ii) Pore Pressure

  1. Water Pressure: In this figure T is the pressure of reservoir water, which tends to displace the dam horizontally, W is the weight of the dam, which acts downwards and tends to key the dam in position and R is the resultant of forces T and W, which indicates that when the reservoir is full, the toe of the dam is overloaded and the heel is relieved. Therefore, in order to make the dam stable, the ratio T/W has to be kept smaller.
  2. Pore Pressure: The water entering in permeable rocks below the dam exerts and upward pressure on its base. This pressure, which is equivalent to the hydrostatic pressure, is called the ”pore pressure” or ”uplift pressure”. It acts against the weight of the dam and thus helps in sliding or overturning it.

Different Types of Dams

The classification of dams is made on the basis of the construction method. Following are the most common types of dams:

(1). Masonry Dams:

Masonry Dams

A masonry dam is constructed with the help of masonry of bricks and stone blocks. This type of dam has a very large span foundation. Architects and mason work on such types of dams. The design and the map of the dam are first drawn, and architectural work starts. Each part of the dam like water retaining structure, water releasing structure, and water conveying structure is made by hands. Heavy machinery is seldom used while constructing a masonry dam. However, the need for scaffolding and shuttering is felt as the masonry work gradually, rises up.

(4). Steel Dams:

Steel Dams

A steel dam is either made of the horizontal and vertical girders and beams supporting panels and plates made up of steel/ iron or some other alloys which resist rusting and oxidation. The plates are joined with the vertical and horizontal girders with the help of nuts and bolts. In many dams, steel trusses are also used instead of girders. The durability and strength of these dams is much better than that of the rest of the types. These are easily constructed and less time-consuming.

(5). Earthen Dams:

This is a very low-priced dam and very common in Asia, Africa, and South America. The casing of this dam is made of stone gravels, sand, soil, and murum. Once the water is absorbed in the dame, the volume of the casing shrinks due to gravity. The shrunk volume further compacts the material of the dam. The contracted volume does not allow the water to seep across the dam. World’s largest earthen dam is Pakistan’s, Tarbela Dam.

(6). Gravity Dams:

Earthen Dams

The barrier to the water is so designed that it holds back the water by its weight. The horizontal push of the water is exerted against the wall. The water tends to push away the wall, but the heavy and wide span of the foundation of the dam holds the water back. The gravity or the weight of the wide-span wall is the only reason for its success.

 

(7). Rock Fill Dams:

Gravity Dams,

These dams are constructed with dumped and compacted rock debris. The outer layer of the dam is porous and permeable to the water, while the inner core is so compacted that does not allow seepage of the water. The impermeable layer is leveled equally to the level of the upstream face of the dam. The permeable portion of the dam is constructed with rock debris, soil, and stone gravels, while the impermeable layer is made up of reinforced concrete, clay, and asphalted concrete.  These dams are very strong because the load of the outer porous layer of the dam does not allow the inner impermeable layer to crack or move.

(8). Arch Dams:

Arch Dams

An arch dam is constructed with concrete. The design of the dam is curved and concaved from downstream and convex from upstream. The curved shape of the dam gives tension against the hydrostatic pressure of the reservoir. The sides and edges of the dam are deep-rooted for a strong foundation.

(9). Embankment Dams:

Embankment Dams

Embankment means an artificial mound of earthen material, soil, and debris. But in an embankment dam, the construction material is a semi-plastic material of sand, soil, stone gravels, and debris. The mound of the semi-plastic material works as the dam. The material is compacted by means of machines like compactors and rollers. This type of dam is successful because of its large span and bottom. In the beginning, the water starts absorbing in the dumped material. The absorption of the water further strengthens the bonding of the material.

(10). Barrage Dams:

A barrage dam is so designed that there is a series of gates that are suspended with the abutments. The suspended gates are allowed to sink in the water to resist the flow of water. The difference between a barrage dam and other dams is that this type of dam resist the water from the upward direction, while in other types of dams the resistance is provided.

(11). Concrete Face Rock Fill Dams:

CFRD is a very common type of dam, which is widely constructed all through the globe for hydropower projects. Concrete slabs are placed on the underlying rock fill. The concrete slabs are connected with the toe plinth by means of peripheral joints so as to develop an impermeable system.

(12). Fixed Crest Dams:

Fixed Crest Dam

The purpose of the fixed crest dams is to elevate the level of the river and keep the channel deep enough for navigation. It is a straight crest wall, which runs across the river. These dams have no spillway, no gates, and no bridges. They are submerged in the water and can not be easily found from a watercraft.

(13). Arch Gravity Dams:

As in the above headings mentioned,

    1. An Arch dam is constructed with concrete. The design of the dam is curved and concaved from downstream and convex from upstream. The curved shape of the dam gives tension against the hydrostatic pressure of the reservoir. The sides and edges of the dam are deep-rooted for a strong foundation.
    2. And in a gravity dam, the barrier to the water is so designed that it holds back the water by its weight. The horizontal push of the water is exerted against the wall. The water tends to push away the wall, but the heavy and wide span of the foundation of the dam holds the water back. The gravity or the weight of the wide span wall is the only reason for its success.

An arch-gravity dam is a combination of both of the above-mentioned types of dams thereby having characteristics of both of the above types.

Types of Dams by Size

There are two types of a dam on the basis of size;

(1). Small Dams:

Small dams are the dams that are constructed for the purpose of storing water for small-scale irrigation, and industrial and household use. Occasionally, small electric generators are also installed at these dams. These dams are constructed in thousands of numbers in almost all the countries of the world.

(2). Non-Jurisdictional Dams:

Non-jurisdictional dams are the dams that do not follow the legal limitation. Extra-large dams, which, legally, are not allowed to construct, are included in Non-jurisdictional dams. The illegal status of such dams is because of the risk of flash flooding associated with such dams. Almost all over the world, and in all of the world countries, such dams are available to be seen.

Types of Dams by Use

(1). Saddle Dams:

A saddle dam is a contributive dam constructed with a primary dam to either permit higher water storage and elevation or to limit the extent of a reservoir for increased efficiency. The saddle dam is constructed on a low spot, through which the reservoir of the primary dam escapes. To stop the flow from that low lying area, a saddle dam is constructed. These dams can also be called twin-dams. The escaping water of a primary dam is resisted by another auxiliary dam at a lower point.

(2). Weir Dams:

A weir dam also called an overflow dam is a type of small overflow dam that is often used within a river channel to create an impoundment lake for water abstraction purposes and which can also be used for flow measurement or retardation.

(3). Check Dams:

A check dam is a small barrier against the flowing water of a stream, water channel, drain, and unpaved canals. The purpose of such dams is to protect the floor of the channel from erosion.

(4). Dry Dams:

Controlling the floods dry dams are constructed. Dry dams typically contain no gates or turbines and are intended to allow the channel to flow freely during normal conditions.

(5). Diversionary Dams:

A diversionary dam is intended to divert all or a portion of flowing water. These dams are constructed for the sake of diverting the water. The water is diverted in order to protect soil eroded by the flowing water.

(6). Under Ground Dams:

Fukuzato (Japan) is the world’s biggest underground dam. An underground wall is constructed to prevent the groundwater to seep into the sea so that it can be put to human use.

(7). Tailings Dams:

A tailings dam is typically an earth-fill embankment dam used to store byproducts of mining operations after separating the ore from the gangue. Tailings can be liquid, solid, or a slurry of fine particles, and are usually highly toxic and potentially radioactive.

Types of Dams by Material

(1). Concrete Dams:

In this type of dams, all three parts of the dams; water retaining structure, water releasing structure, water conveying structure, and water diverting structures are constructed with the help of concrete work. Steel and iron rods are placed within the concrete to strengthen it. The whole structure of the dam is constructed in a consolidated form.

(2). Timber Dams:

In a timber dam, wooden panels, logs, and pillars are used to construct the water retaining structure of the dam. Timber Dams are generally of small sizes. These dams are unable to resist a large flow of water. On small water channels and streams, these dams are successful. These dams are easy to construct.

(4). Steel Dams:

It includes all types of dams are constructed by using steel as the construction material. The steel wall is made up of steel panels, plates, girders, truss, and beams. These objects are jointed with each other with the help of nuts and bolts.

(5). Earthen Dams:

Any dam can be called an earthen dam if its construction material is composed of soil, sand, debris, and stone gravels. The earthen material is used in the construction of such dams. These dams are generally very large in size and big energy plants are installed over such types of dams.

(6). Rock Fill Dams:

As the name mentions, a rockfill dam is constructed with a piece of rocks ranging from a small to a large size. The rock pieces are compacted with soil and sand and fine earthen gravels. Any type of dam which is constructed with rock gravels can be included in the list of rock fill dams.

Other Types of Dams

(1). Cofferdams:

Cofferdams are constructed inside the water body. These are temporary barriers against or diversion against the flowing water, in order to carry out construction work in a dry environment. Cofferdams are as water-tight as possible because the aim of a cofferdam is to provide a dry work environment. In a dry and clean environment, the concrete work is carried out without the leakage of water from outside. When a cofferdam is installed the muck is sucked by means of a muck tube or muck vessel. The muck inside a caisson is also evacuated in the same way. Cofferdams

(2). Beaver Dams:

Beaver dams or beaver impoundments are dams built by beavers to provide ponds as protection against predators such as coyotes, wolves, and bears, and to provide easy access to food during winter.

(3). Natural Dams:

It is a naturally constructed dam. As a result of a landslide, the material becomes an obstacle before the water channel, a dam is formed. In any case, a sedimentary rock appears (after a long time erosion of the floor of the stream) before the way of the water channel. The sloped sedimentary rock acts as a dam. These dams are generally very small in size, but frequent to be seen.

How to locate a Dam or how to determine the location of a dam?

One of the best places for building a dam is a narrow part of a deep river valley; the valley sides that can act as natural walls. The primary function of the dam’s structure is to fill the gap in the natural reservoir line left by the stream channel. The sites are usually those where the gap becomes a minimum for the required storage capacity. The most economical arrangement is often a composite structure such as a masonry dam flanked by earth embankments. The current use of the land to be flooded should be dispensable.

Other significant engineering and engineering geology considerations when building a dam include:

  • Permeability of the surrounding rock or soil
  • Earthquake faults
  • Landslides and slope stability
  • Water table
  • Peak flood flows
  • Reservoir silting
  • Environmental impacts on river fisheries, forests, and wildlife (see also fish ladder)
  • Impacts on human habitations
  • Compensation for land being flooded as well as population resettlement
  • Removal of toxic materials and buildings from the proposed reservoir area

Pros and Cons of Dams

Advantages and Needs for a Dam:

  1. Dams are prevents flooding, as they store the water of fully flowing streams and river, at the time of rainfalls and snow-melt.
  2. Dams are the only means to prevent water from wastage as they store extra water from streams and rivers, thus preventing water from wasting.
  3. The stored water in the dams supplied to the agricultural land to irrigated vegetations.
  4. Dams are used for land reclamation.
  5. Dams supply drinking water to the rural as well as the urban communities. Dams also supply water for industrial consumption and other household consumption.
  6. Small dams are used to divert the flow of stream for irrigation and electricity generation.
  7. Dams are a very good source of aquatic food, like fish.
  8. Dams are a very big source of energy. World most of the electricity is generated with the help of hydropower of dams.
  9. Dams provide humidity to the atmosphere, thus keeping the weather pleasant.
  10. Dams supply water for industrial and household consumption.
  11. Dams provide river navigation.
  12. Dams provide recreation sites for boating and fishing.
  13. Dams supply stored water at the time of need.

Disadvantages of the Dams:

  1. Dams are constructed keeping in view a limited capacity of water storage, but during the season of heavy rainfall, dams are fully filled with water, thus, exceeding their storage capacity. At such a critical time, dams may rupture and break. As a result of the breakage of dams, the risk of flash flooding can not be overviewed.
  2. The threat of flooding caused by dams may compel people to relocate and shift their habitat in order to escort from the danger.
  3. The construction cost of the dams is very high. Poor nations can not construct dams in large numbers to meet the demand for energy and irrigation water.
  4. The construction of dams is time-consuming. It takes a couple of years while constructing a dam.
  5. Significant and timely maintenance and adjustment of dams are needed, which may cost high.
  6. Skilled and expert staff is needed to control water flow from out of the dam.
  7. Sedimentation patterns of the dams are changes. Ejecting as well as resisting silt ejecting is needed according to sedimentation patterns.
  8. Dams may cause problems for aquatic life.
  9. Slowing down water flow may cause an excess ratio of algae.
  10. As the dams capture a very large area, therefore dams caused deforestation.
  11. When water is stopped behind the dam, the locked water kills a lot of ecosystems. Bacteria, then decompose the bodies of living organisms and produce a large amount of Carbon-dioxide and Methane gas.
  12. The locked water kills a large number of living organisms. All the living organisms depend on one another for meeting their demand for food. Some of the organisms within an ecosystem are killed, thus creating a gap in the food chain of the ecosystem. The imbalance caused due to dams further kills the organisms, due to lack of food. This imbalance continues and disturbance among living things for their food exists.
  13. People visit dams for recreation. Carelessness may cause them to drown in the water.
  14. At the time of drought, dams may cause conflict. People of some areas need water, while dams are meant to store the water.
  15. Dams can be used as a political tool. Provincialism may erupt due to the construction of dams.

Dams Terminologies

Dams are the most amazing and eyecatching construction so far man has made. When US president Frankin Roosevelt inaugurated the Hoover dam in 1935, the scene was unbelievable and he uttered these words: “I came, I saw and I was conquered”. Dams are of tremendous significance in the development of mankind. While keeping in mind the increasing importance of the subject of dams in civil engineering writing detailed notes were felt unavoidable. After writing two detailed articles about the dams: Types of dams and spillways, we felt the need of explaining the terminology used in the civil engineering of the dams.

  • ABUTMENT: Abutments are the supports constructed at each opposite valley side. The dam’s main wall is supported by abutments. The abutments are deep-rooted and firmly installed in the rocks of the valley side.
  • BASE WIDTH: The width of the dam foundation is called base width.
  • BREACH: An irregular breakthrough or rupture in the embankment of the dam due to the erosion caused by the flow of water.
  • CONDUIT: It is the conveying part of the dam. It is a closed channel to convey the discharge through or under a dam. Usually, pipes constructed of concrete or steel.
  • IMPERVIOUS CORE or ZONE OF THE DAM: The mid of the dam-wall is called the core of the dam. The core is generally constructed with concrete, wooden panels, and steel plates. This is an impermeable section of the dam. It prevents the dam water to seep out through the dame dump.
  • TRAINING WALL: This wall confines and guides the flow of the water.
  •  TRASH RACK: It is constructed in the waterway from the intake side to control the flow of debris.
  • PREVIOUS ZONE: As the name mentions, the previous zone allow water to seep or flow.
  • RIPRAP:  A barrier of large stones, broken rocks, blocks of concrete placed in the reservoir just before the dame embankment. Its duty is to prevent the dame from the strike of waves and ice blocks.
  • SEEPAGE COLLAR: In order to prevent the basement of the embankment from erosion, the water accumulated by means of seeping, is projected ahead from the foundation by means of pipes and conduits.
  • CREST OF DAM: The top of the dam and spillway is said to be the crest of the dam. A crest is a plane and smooth (in some cases paved) surface of the dame. The top surface of the dam is called the crest.
  • CUT-OFF of the Dam: Placement of an impervious material in the foundation of the dam is called the cut-off of the dam.
  • CUTOFF WALL: The cut-off of the dam is constructed with a concrete, wooden, or steel wall which is impervious to water, and prevents water to seep out. The wall which is constructed for the purpose of protecting water from seepage is called the cut-off wall.
  • DRAINAGE LAYER OR BLANKET: A very permeable structure placed directly over the used to remove water or to control groundwater seepage from cut slopes or beneath fills.
  • CREST LENGTH: Crest the surface above the spillway. The crest is as long as the dam is. It covers the whole span of the dam. The length of the dam is equal to the length of the crest.
  • TOE OF DAM: The junction between the downstream face of the dam with the river floor is called the Toe of the dam.
  • TOP OF DAM: The uppermost surface in the form of a road or walkway is called the top of the dam.
  • TOP THICKNESS: The width of the top of the dam is called the top thickness of the dam. The uppermost width of the dam is called the thickness of the dam.
  • Abutments: The part of the valley sides of the dams, constructed with concrete material or masonry work. The function of the abutments is to provide support to the wall of the dam.
  • The base of the Dam: The base is the total width of the basement of the dam, which descends with vertical ascend of the dam.
  • Crest: Crest the uppermost plane surface of the dam. It is the overflow part of the dam.
  • Cutoff: The cut-off of the dame is an impervious material, which prevents the seepage of water through the base section of the dam.
  • Cut-off Wall: The wall of impervious material like wood panels, concrete, or steel is constructed in the core of the dame. The purpose of this wall is to prevent seepage. Keep in view that seepage harms the solidarity of the dam.
  • The face of the Dame: The side of the dam which is faced by the downstream.
  • Upstream: Upstream of a dam is the level of water reservoir held back by the dam. The water of Upstream flows through the conduit toward the downstream.
  • Parapet Walls: The parapet walls of the dams are constructed on the crest of the dam. The function of the parapet wall is to give protection to the tourists.
  • The heel of the dam: The junction of the upstream face with the foundation of the dam is called the heel of the dam.
  • Toe of the dam: The junction of downstream of the dam with the ground is called the toe of the dam.
  • Crest Gate/ Spillway Gate: These gates are installed on the crest of the spillway. The duty of these gates is to allow a controlled quantity of the reservoir water.
  • Flap Gate: They are flow control gates, which are hinged from their top.
  • Outlet Gate: It controls the outlet flow of water from the reservoir.
  • Radial Gate: A gate with radial arms and curved upstream plates.
  • Slide Gate: This type of gate can be opened and closed by sliding it.
  • INTAKE: Any type of structure which transit water from the reservoir to the outlet.
  • LOW-LEVEL OUTLET: Opening which is constructed at the low level, near the foundation of the dam.
  • OUTLET: A hole or opening used to allow water flow from the reservoir toward the downstream.
  • DRAWDOWN: As the water releases from the reservoir, it results in lowering down the water level in the reservoir. The process of lowering down the water level is called Drawdown.
  • EMBANKMENT: The dump of fill material of soil, rocks, debris, sand, and gravel is called an embankment.
  • EMERGENCY ACTION PLAN: A precautionary conduit is built within the structure of the dam, to release the water at the time of emergency in order to prevent a flash flood.
  • FACE: The external face or the downstream side of the dam is called a face.
  • FLASHBOARDS: The crest of the spillway is elevated with the help of dumping wooding, timber, concrete, and steel material in order to further resist the flow of water. But at the time of the rising water level, these materials are abruptly removed.
  • FOUNDATION OF DAM: A wide-span, thick and heavy concrete basement of the dam which is partly sunk into the river floor is called the foundation of the dam.
  • FREEBOARD: The distance from the water surface to the lowest top of the dam, at which the dam would overflow, is called freeboard.
  • GATE: Gates are used to stopping or controlling water flow. These gates are sliding gates, which can be removed and closed.
  • CREST GATE or SPILLWAY GATE: A gate installed at the crest of the spillway that controls the overflow of the water of the reservoir.
  • STOP LOGS: Large logs, timbers, or steel beams placed on top of each other with their ends held in guides on each side of a channel or conduit so as to provide a cheaper or more easily handled means of temporary closure than a bulkhead gate.
  • STRUCTURAL HEIGHT: The vertical distance from the lowest point of natural ground on the downstream side of the dam to the highest part of the dam, which would impound water.
  • SPILLWAY: A structure over or through which flood flows are discharged. If the flow is controlled by gates, it is considered a controlled spillway; if the elevation of the spillway crest is the only control, it is considered an uncontrolled spillway.
  • AUXILIARY SPILLWAY (EMERGENCY SPILLWAY): A secondary spillway· designed to operate only during exceptionally large floods.
  • OGEE SPILLWAY (OGEE SECTION): An overflow spillway, which in cross section· the crest, downstream slope, and bucket have an “S” or ogee form of a curve. The shape is intended to match the underside of the nappe at its upper extremities.
  • SPILLWAY CHANNEL (SPILLWAY TUNNEL): A channel or tunnel conveying water from the spillway to the river downstream.

Related Articles of Engineering Geology: 

  1. Relationship of geology with civil engineering
  2. Geology and Building-Stones
  3. Most common rocks used as building stones

 

 

 

 

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