GEOLOGY OF DAMS AND RESERVIORS

Presented by:K TARUN KUMARSTRUCTURAL ENGINEERINGINSTITUTE OF AERONAUTCAL ENGINEERING

Types of Dams:

Based on purpose1. Storage Dam Or Impounding Dam2. Detention Dam3. Diversion Dam4. Coffer Dam5. Debris Dam

1. STORAGE DAM:

• It is constructed to create a reservoir to store water during periods when there is huge flow in the river (in excess of demand) for utilization later during periods of low flow. 

• Water stored in the reservoir is used for irrigation, power generation, water supply etc.

2. DETENTION DAM:• It is primarily constructed to temporarily detain all or part of the

flood water in a river and to gradually release the stored water later at controlled rates

• So that the entire region on the downstream side of the dam is protected from possible damage due to floods.

• It may also be used as a storage dam.

3. DIVERSION DAM:

• It is constructed to divert part of or all the water from a river into a conduit or a channel.

• For diverting water from a river into an irrigation canal, mostly a diversion weir is constructed across the river

4. COFFER DAM:

• It is a temporary dam constructed to exclude water from a specific area.

• It is constructed on the u/s side of the site where a dam is to be constructed so that the site is dry.

• In this case, it behaves like a diversion dam.

5. DEBRIS DAM:

• It is constructed to catch and retain debris flowing in a river.

Based On Structural Behaviour• Gravity Dam• Arch Dam• Buttress Dam• Embankment Dam

A typical dam has following parts – • Crest – The top of dam. In some cases, this provides a roadway

or walk way.

• Parapet walls – Low protective walls on the either side of the road way on the crest.

• Abutments – The valley slopes on the either side of dam wall to which it is keyed.

• Free board – The space between the highest level of water in the reservoir and crest of the dam.

• Heel – The upstream portion of the dam in contact with the river bed or foundations.

• Toe – The downstream portion of the dam wall for the discharge of surplus water from the reservoir.

• Spillway – The passage in the dam wall for the discharge of surplus of water from the reservoir.

• Gallery – Level or gently sloping tunnel like passage transverse or longitudinal within the dam wall with drains in the floor for seepage water

SELECTION OF DAM SITE:

Selection of site – The selection of dam site across a river is to impound water behind the dam. Following points are required that –

Topographically, a place which is most suitable for the purpose is selected. Ideally it should be narrow or a small valley with enough catchment areas available behind so that when a dam is placed there it would be easily store a calculated volume of water in reservoir created upstream.

Technically, the site should be as sound as possible, strong, impermeable and stable. Strong rocks for design, impermeable for inventory of stored water and stability with references to seismic failures.

• Constructionally, the site should not be far from deposits of materials which would be required for construction.

• Economically, the benefits arising out of a dam is proposed to be placed at a particular site should be realistic and justified in terms of land irrigated , power generated and water stored i/c floods averted.

• Geological investigations – Following geological characters of the area should be

investigated for particular site selected for dam – Geology of area comprising of main topographical features, natural drainage patterns, general characters and structures of rock formations, the trend and type of weathering and erosion of area.

• Geology of site i.e. types of rocks of the area where dam will be built, properties of rocks i.e. chemical composition, texture and hardness of rocks, porosity and permeability of rocks.

• Structural features of the rock i.e. dip, strikes, outcrop etc. Structural defect of rocks i.e. folds, fissures, faults etc.

• Crushing and shearing strength of rocks, extent of weathering of rocks.

• Thickness of the bedding planes. • Zones of fractures and weaknesses. • Water table in the area

• The ideal foundation should be built over a uniform formation.• The underlying rocks should be strong enough to bear weight

of dam and to withstand resultant thrust of pressure of the impounded water and weight of dam itself.

RESERVIOR:

• A reservoir is a storage space for fluids. These fluids may be water or gas.

• A reservoir usually means an enlarged natural or artificial lake, storage pond or impoundment created using a dam or lock to store water.

• Reservoirs can be created by controlling a stream that drains an existing body of water.

• They can also be constructed in river valleys using a dam.

TYPES BASED ON PURPOSE:

Storage reservoirs:• These are designed to increase downstream river

discharge during the dry season. • Accordingly a portion of the rainy season flood water

mass is stored behind the dam and then released more or less uniformly during the duration of the dry season to provide a reliable and adequate year round water supply for downstream users

(i.e. hydroelectric power plants, irrigation, municipal water supply, navigation).

Flood control reservoirs• These are designed to decrease the magnitude of the

peak flood discharge during the rainy season in order to protect downstream areas from flood damage.

• They fill rapidly during the rainy season.• Once the flood wave has passed, the stored water is

released. • Water level and surface area experience a large annual

fluctuation. 

Multi purpose reservior:• Multipurpose reservoirs may be managed to balance some or all

of the following activities:• Water supply• Flood control• Soil erosion• Environmental management• Hydroelectric power generation• Navigation• Irrigation

GEOPHYSICAL STUDIES

• Gravity and magnetic methods can be directly related to physical properties of rocks, i.e. the density and the susceptibility, and are very useful to field geologists and geophysicists in the mapping and identification of various rock types.

• They are also used for the detection of minerals with large contrast in density and susceptibility compared to country rock.

Gravity method:

• Gravity surveying measures variations in the Earth’s gravitational field caused by differences in the density of sub-surface rocks.

• Gravity methods have been used most extensively in the search for oil and gas, particularly in the twentieth century.

• Hydrocarbon exploration • Regional geological studies • Isostatic compensation determination • Exploration for, and mass estimation of, mineral deposits • Detection of sub-surface cavities (microgravity)

• Location of buried rock-valleys • ƒDetermination of glacier thickness • Tidal oscillations • Archaeogeophysics (micro-gravity) • Shape of the earths (geodesy) • Military (especially for missile trajectories) • Monitoring volcanoes.

Magnetic method:

• The magnetic method is a very popular and inexpensive approach for near-surface metal detection.

• Engineering and environmental site characterization projects often begin with a magnetometer survey as a means of rapidly providing a layer of information on where utilities and other buried concerns are located

Common uses of magnetometers include: • Locating buried tanks and drums • Fault studies • Mineral exploration • Geothermal exploration • Mapping buried utilities, pipelines • Buried foundations, fire pits for archaeological studies

Siesmic method:• Seismic techniques are commonly used to determine site geology,

stratigraphy, and rock quality. • These techniques provide detailed information about subsurface

layering and rock geo mechanical properties using seismic acoustical waves.

• Reflection and Refraction are the most commonly used seismic techniques.

• These methods determine geological structure and rock velocities by either refracting or reflecting waves off boundaries between rock units with different seismic velocities or impedance.

• Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies.

• The field also includes studies of earthquake environmental effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions).

• A related field that uses geology to infer information regarding past earthquakes is paleo seismology.

Radiometric method:

• The radiometric method is a geophysical process used to estimate concentrations of the radio elements potassium, uranium and thorium by measuring the gamma-rays which the radioactive isotopes of these elements emit during radioactive decay.

• Airborne gamma-ray spectrometric surveys estimate the concentrations of the radio elements at the Earth's surface by measuring the gamma radiation above the ground from low-flying aircraft or helicopters.

Geothermal Method:

• Geothermal resource exploration, development, and production draw on the techniques of both the mining and oil/gas industries.

• The geologic setting of geothermal resources is similar to deposits of metal ores, and geothermal systems are thought to be the modern equivalent of metal ore-forming systems.

• Hence, exploration draws most heavily on the techniques of the mining industry.

• Development of the resource and its production as hot fluid uses the techniques of the oil/gas industry with modifications because of the high temperatures and the much higher flow rates needed for economic production.

GROUTING:

• Grout is a particularly fluid form of concrete used to fill gaps. It is used in construction to embed rebar's in masonry walls, connect sections of pre-cast concrete, fill voids, and seal joints such as those between tiles.

• Grout is generally a mixture of water, cement, sand, often color tint, and sometimes fine gravel (if it is being used to fill large spaces such as the cores of concrete blocks).

•  Finer particle sizes let the grout penetrate more deeply into a fissure.

• Portland cement is the most common cementing agent in grout.Portland cement-based grouts come in different varieties depending on the particle size of the ground clinker used to make the cement, with a standard size of around 15microns, microfine at around 6–10 microns.

Grout varieties include tiling grout, non-shrink grout, structural grout.

• Tiling grout is often used to fill the spaces between tiles or mosaics, and to secure tile to its base.

• Tiling grout is also cement-based, and comes in sanded.• The sanded variety contains finely ground silica sand. • Unsanded is finer and produces a non-gritty final surface.

• Non-shrink grout is used beneath metal bearing plates to ensure a consistent bearing surface between the plate and its substrate.

• Often used as a transfer medium between load-bearing members.

• Structural grout is often used in reinforced masonry to fill voids in masonry housing reinforcing steel, securing the steel in place and bonding it to the masonry.

IMPROVEMENT OF GROUTING AT SITES:

Some of these areas of expertise include:

1. Permeation2. Jet Grouting3. Hot Bitumen Grouting

PERMEATION GROUTING:• Permeation Grouting consists of injecting grout under

controlled, low pressure in order to permeate the strata without causing fracturing.

• It can be applied in both soil and rock.

JET GROUTING

• Jet Grouting creates in-situ columns of grouted soil using very high pressure grout injection.

• Grouting is performed by pumping high velocity jets of grout (or sometimes grout and air or grout, water and air) through the side of a grout monitor, attached at the end of the drill string.

HOT BITUMEN GROUTING:

• Hot Bitumen Grouting is a special type of grouting where melted bitumen is used as grouting material.

• The major feature of hot bitumen grout is its temperature dependent viscosity. The bitumen is first preheated up to approximately 200° Celsius.

TUNNELING:

• A tunnel is an underground or underwater passageway, dug through the surrounding soil/earth/rock and enclosed except for entrance and exit, commonly at each end.

• A pipeline is not a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods.

• A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal.