2. OUTLINES
• Introduction
• What is earthen dam?
• Needs for dams construction
• Types of dam
• Construction of dam
• Requirements of earthen dam
• Environmental impacts of dams
• Uses of earthen dam
3. INTRODUCTION
• The first known dam was built in 2900 B.C. across
the Nile River to protect the city of Memphis from
flooding. Dam build was continued into the time
of the Roman empire, after which dam
construction was literally lost until the 1800s.
• Dams are a structure also seen in nature - beavers
build dams to keep the water deep enough to
cover the openings to their homes, protecting
them from predators.
4. • A barrier constructed to hold back water and
raise its level, forming a reservoir used to
generate electricity or as a water supply.
• A dam is a barrier that impounds water or
underground streams.
• The reservoirs created by dams not only suppress
floods but provide water for various needs to
include irrigation, human consumption, industrial
use, aquaculture and navigability.
5.
6. What is earthen dam?
• Earth fill dam, also called Earth Dam, or
Embankment Dam.
• Dam built up by compacting successive layers
of earth, using the most impervious materials to
form a core and placing more permeable
substances on the upstream and downstream
sides.
• A dam built of soil materials (sand, loam, clay,
and so on), with a trapezoidal or nearly
trapezoidal cross section.
7.
8. Needs for Dam Construction
1. Drinking and domestic water supply
2. Flood control
3. Irrigation
4. Industrial water supply
5. Hydroelectric energy production
6. Retention and control of sediments
and Inland navigation, Improvement of water quality, Fish
Farming, Recreation facilities
9. TYPES OF EARTHEN DAM
• Earthen dams are usually of the fixed type (without
the flow of water over the crown); they are commonly
used in many countries because of their simplicity of
construction and maintenance.
• Six main types of earthen dams are distinguished,
depending on the materials used for the body of the
dam and the methods of providing water
impermeability.
• Embankment dams come in two types: the earth-filled
dam (also called an earthen dam or terrain dam) made
of compacted earth, and the rock-filled dam.
10. ACCORDING to HEIGHT of DAM
• High Dam or Large Dam
• If the height of the dam is bigger than 100m
• Medium Dam
• If the height of the dam is between 50m and 100m
• Low Dam or Small Dam
• If the height of the dam is lower than 50m
11. Earth dam
• An earth dam is composed of suitable soils obtained
from borrow areas or required excavation and compacted
in layers by mechanical means.
• Following preparation of a foundation, earth from borrow
areas and from required excavations is transported to the
site, dumped, and spread in layers of required depth.
• The soil layers are then compacted by tamping rollers,
sheeps foot rollers, heavy pneumatic tired rollers, vibratory
rollers, tractors, or earth-hauling equipment.
• One advantage of an earth dam is that it can be adapted to
a weak foundation, provided proper consideration is given
to thorough foundation exploration, testing, and design.
12.
13. • Earthen dams are distinguished according to their
construction method as fill dams, which are built up by dry
pouring of soil, with artificial consolidation and without
consolidation (with pouring of the soil into the water or by
means of a directed explosion), and hydraulic fill dams, the
construction of which is accomplished by the hydro
mechanization method.
• The drainage of an earthen dam is usually made in the form
of a drainage shell or a drainage mattress buried in the
body of the dam.
• Rock fill and paving stone facing covered with concrete or
reinforced-concrete slabs are used to protect the upstream
(pressure) slopes of earthen dams against wave action.
• The downstream slopes are protected by planted grass,
turf, poured gravel, and crushed stone.
14.
15. CONSTRUCTION OF EARTHEN DAM
• Earthen dams may be built on virtually any type of ground
base (except strongly liquescent muddy soil).
• The watertight part of the dam (the baffle and core) is
usually joined to the rocky base by a cutoff or a concrete
joint tongue, under which a grouted cutoff is set in fissured
rock.
• On a non rock base, if the water-resistant material (clay or
rock) is located at an acceptable depth, the impermeable
part of the dam is joined to the water-resistant material by
a positive ground cutoff, a sheet pile bulkhead, or a curtain
(partial cutoff).
• A blanket or partial cutoffs and a sheet pile bulkhead, are
installed for a deep-lying water support.
16.
17.
18. • A cross-section of an embankment dam shows a
shape like a bank, or hill.
• Most have a central section or core composed of
an impermeable material to stop water from
seeping through the dam.
• The core can be of clay, concrete, or asphalt
concrete.
• For a rock-fill dam, rock-fill is blasted using
explosives to break the rock.
• Additionally, the rock pieces may need to be
crushed into smaller grades to get the right range
of size for use in an embankment dam
19. Small earth dam design:
A typical design of a small earth-fill dam is shown in Figure 8. For stability, the upstream slope
must be a minimum of 3:1. Erosion protection is required to protect the dam from wave action.
This protection can be achieved with a combination of smaller and larger rocks (or other suitable
material).The downstream slope requires a minimum 2:1 slope, seeded with native grasses to
prevent surface erosion. The top or crest of the dam should be a minimum of 2m feet wide for a
stable embankment structure. The crest elevation should be a minimum of 0.5m above the Full
Supply Level (FSL) of the reservoir. The dam should be fenced to prevent livestock traffic, as
this traffic can be a major cause of slope and crest degradation. A textbook perfect dam
embankment structure would look like the one in Figure 9. The crest width and the slope of
embankments can be designed according the guidelines in Table 2 and 3.
Figure 8: Typical earth dam layout. (Ignore riparian pipe for our purpose)
Table 2: Crest width based on different dam embankment height
20.
21. Requirements of earthen dam
• b. Basic requirements of an embankment dam.
Dams are a critical and essential part of the
Nation’s
• infrastructure for the storage and management
of water in watersheds.
• To meet the dam safety requirements, the
design, construction, operation, and modification
of an embankment dam must comply with the
following technical and administrative
requirements:
22. • (1) Technical requirements.
• The dam, foundation, and abutments must be
stable under all static and dynamic loading
conditions.
• Seepage through the foundation, abutments,
and embankment must be controlled and
collected to ensure safe operation.
• The intent is to prevent excessive uplift
pressures, piping of materials, sloughing
removal of material by solution, or erosion of
this material into cracks, joints, and cavities.
• In addition, the project purpose may impose
a limitation on allowable quantity of seepage.
23. • The design should include seepage control
measures such as foundation cutoffs,
adequate and non brittle impervious zones,
transition zones, drainage material and
blankets, upstream impervious blankets,
adequate core contact area, and relief wells.
• The freeboard must be sufficient to prevent
overtopping by waves and include an allowance
for settlement of the foundation and
embankment.
• The spillway and outlet capacity must be
sufficient to prevent over-topping of the
embankment by the reservoir.
26. ENVIRONMENTAL IMPACTS of CONSTRUCTION
PHASE of DAMS
• River pollution
• Erosion
• Loss of aesthetic view
• Air pollution
• Noise pollution
• Dust
27. ENVIRONMENTAL IMPACTS of RESERVOIRS
• Loss of land
• Habitat Destruction :
• The area that is covered by the reservoir is destroyed, killing whatever
habitat existed there beforehand.
• Loss of archeological and histrorical places
• Loss of mineral deposits
• Loss of special geological formations
• Aesthetic view reduction
• Sedimentation
• Change in river flow regime and flood effects
• Reservoir induced seismicity
• Change in climate and plant species
28. EFFECTS of DAMS to WATER QUALITY
• Change in temperature
• Turbidity
• Dissolved gases in the water
• Water discharged from the spillway contains 110-120% saturated
nitrogen. This amount may be destructive for fish life.
• Eutrophication
• It means increase in vegetation. If moss and other plants exist in
water, quality of that water gets worse.
29. Uses of earthen dam
• Generation of hydroelectricity .
• Irrigation.
• These are often diversion dams, which stop a
river’s natural course so that water can be
sent off to a different place.
• Control flooding.
• These are called detention dams, which are
constructed to either stop or slow the amount
of water in a river.
30. • This dam type is a good choice for sites with wide
valleys.
• Since they exert little pressure on their
foundations, they can be built on hard rock or
softer soils.
• Hydropower is often used in conjunction with
dams to generate electricity.
• A dam can also be used to collect water or for
storage of water which can be evenly distributed
between locations.
31. • Modern mechanical excavation methods make
possible the construction of earthen dams to
heights of 150 m or more.
• Dams generally serve the primary purpose of
retaining water, while other structures such
as floodgates are used to manage or prevent
water flow into specific land regions.
