Chapter 8: Dams Flashcards
The purpose of a dam is to
impound (store) water for any of several reasons
The purpose of a dam is to impound (store) water for any of several reasons, e.g.,
flood control, water supply for humans or livestock, irrigation, energy generation, recreation, or pollution control.
Water from rainfall or snowmelt naturally runs
downhill into a stream valley and then into larger streams or other bodies of water
The “watershed system” refers to
the drainage process through which rainfall or snowmelt is collected into a particular stream valley during natural runoff (directed by gravity)
Water from rainfall or snowmelt naturally runs downhill into a stream valley and then into larger streams or other bodies of water. The “watershed system” refers to the drainage process through which rainfall or snowmelt is collected into a particular stream valley during natural runoff (directed by gravity).
Dams constructed across such a valley then impound the
runoff water and release it at a controlled rate.
Dams constructed across such a valley then impound the runoff water and release it at a controlled rate. During periods of high runoff, …………………………………. typically increases
water stored in the reservoir
Dams constructed across such a valley then impound the runoff water and release it at a controlled rate. During periods of high runoff, water stored in the reservoir typically increases, and ……………………………. may occur.
overflow through a spillway
Dams constructed across such a valley then impound the runoff water and release it at a controlled rate. During periods of high runoff, water stored in the reservoir typically increases, and overflow through a spillway may occur. During periods of low runoff, reservoir levels usually
decrease
During periods of low runoff, reservoir levels usually decrease. The owner can normally control the reservoir level to some degree by
adjusting the quantity of water released
During periods of low runoff, reservoir levels usually decrease. The owner can normally control the reservoir level to some degree by adjusting the quantity of water released. Downstream from the dam, the stream continues to
exist
The owner can normally control the reservoir level to some degree by adjusting the quantity of water released. Downstream from the dam, the stream continues to exist, but because the quantity of water flowing is
normally controlled, very high runoffs (floods) and very low runoffs (drought periods) are avoided.
Dams may either be
human-built or result from natural phenomena
Dams may either be human-built or result from natural phenomena, such as
landslides or glacial deposition
Dams may either be human-built or result from natural phenomena, such as landslides or glacial deposition. The majority of dams are
human structures normally constructed of earthfill, rocks or concrete
The majority of dams are human structures normally constructed of earthfill, rocks or concrete. Naturally occurring lakes may also be modified by
adding a spillway to allow for safe, efficient release of excess water from the resulting reservoir.
Dam owners should be aware of:
■ the different types of dams
■ essential components of a dam
■ how the components function, and
■ physical conditions likely to affect a dam.
Human-built dams may be classified according to
the type of construction materials used,
the methods used in construction,
their slope or cross-section,
the way they resist the forces of the water pressure behind them,
the means of controlling seepage, and occasionally, their purpose.
Components of dams
- foundation
- core or membrane
- shell
- transition filter
- internal drain
- toe drain
FOUNDATION
It consists of
earth or rock
FOUNDATION
It consists of either earth or rock and provides a support for
the embankment
. FOUNDATION
It consists of either earth or rock and provides a support for the embankment and resists
both vertical and horizontal loads
. FOUNDATION
It consists of either earth or rock and provides a support for the embankment and resists both vertical and horizontal loads. It also resists
under seepage on the flow of water beneath the dam.
CORE OR MEMBRANE
It holds back
the free water of the dam reservoir
CORE OR MEMBRANE
It holds back the free water of the dam reservoir. It is located either at
the centre or upstream from the centre of the dam.
CORE OR MEMBRANE
It holds back the free water of the dam reservoir. It is located either at the centre or upstream from the centre of the dam. In case of rock fill dams, the core is
provided on the upstream face.
SHELL
It provides
structural support for the core and distributes the load over the foundation.
SHELL
It provides structural support for the core and distributes the load over the foundation. The dams which are constructed of the same materials are called
homogeneous dams.
In core dams, a transition filter between the
core and shell
In core dams, a transition filter between the core and shell is generally provided to
prevent the migration of the fine grained core materials into the pores of the coarse grained shell materials.
An internal drain is provided on
the downstream side of the dam
INTERNAL DRAIN
An internal drain is provided on the downstream side of the dam to
carry away the seepage, and also to prevent the saturation of the upper part of the downstream shell by rain on the dam.
A toe drain is provided at
the downstream face of the shell
A toe drain is provided at the downstream face of the shell. A grating is provided to
cover the upstream face to prevent erosion or wash by waves
Construction Materials— the materials used for construction of dams include
earth, rock, tailings from mining, concrete, steel, and any combination of those materials.
Embankment Dams—embankment dams, the most common type in use
today
Embankment Dams—embankment dams, the most common type in use today, have the general shape shown in Figure 1. Their side slopes typically have
a grade of two to one (horizontal to vertical) or flatter
. Embankment Dams—embankment dams, the most common type in use today, have the general shape shown in Figure 1. Their side slopes typically have a grade of two to one (horizontal to vertical) or flatter. Their capacity for water retention is due to
the low permeability of the entire mass (in the case of a homogeneous embankment) or of a zone of low-permeability material (in the case of a zoned embankment dam).
Embankment Dams—embankment dams, the most common type in use today, have the general shape shown in Figure 1. Their side slopes typically have a grade of two to one (horizontal to vertical) or flatter. Their capacity for water retention is due to the low permeability of the entire mass (in the case of a homogeneous embankment) or of a zone of low-permeability material (in the case of a zoned embankment dam). Materials used for embankment dams include
natural soil or rock obtained from borrow areas or nearby quarries, or waste materials obtained from mining or milling
. Embankment Dams—embankment dams, the most common type in use today, have the general shape shown in Figure 1. Their side slopes typically have a grade of two to one (horizontal to vertical) or flatter. Their capacity for water retention is due to the low permeability of the entire mass (in the case of a homogeneous embankment) or of a zone of low-permeability material (in the case of a zoned embankment dam). Materials used for embankment dams include natural soil or rock obtained from borrow areas or nearby quarries, or waste materials obtained from mining or milling. If the natural material has a high permeability, then
a zone of very low-permeability material must be included in the dam to retain water
Materials used for embankment dams include natural soil or rock obtained from borrow areas or nearby quarries, or waste materials obtained from mining or milling. If the natural material has a high permeability, then a zone of very low-permeability material must be included in the dam to retain water. An embankment dam is termed an
“earthfill” or “rockfill” dam
If the natural material has a high permeability, then a zone of very low-permeability material must be included in the dam to retain water. An embankment dam is termed an “earthfill” or “rockfill” dam depending on
whether it is composed mostly of compacted earth or mostly of compacted or dumped pervious rock.
If the natural material has a high permeability, then a zone of very low-permeability material must be included in the dam to retain water. An embankment dam is termed an “earthfill” or “rockfill” dam depending on whether it is composed mostly of compacted earth or mostly of compacted or dumped pervious rock. The ability of an embankment dam to resist the hydrostatic pressure caused by
reservoir water