An earthen dam or an embankment dam is a type of dam that was an old and simple practice of building a dam that still exists nowadays.
A homogeneous material is used to construct the embankment and a gate is provided to control the flow of water.
Here we will learn about earthen dam, types of earthen dams & much more.
Introduction to earthen dam:
An earthen dam is a dam in which a large embankment is built across the river with a central impermeable layer, catchments are possible to accumulate most of the soil, foothills or elsewhere.
This dams are constructed from earthen materials such as gravels sand, silt and clay.
Following are the various condition favoring an earth dam as follows:
- When funding is low, the construction of an earth dam is appropriate.
- When the foundation strut is not sufficiently strong.
- In this situation, when sufficient spillway space is not available.
- When there is the availability of local material and sufficient quarry material near the dam site, construction of an earth dam is suitable and economical in such a situation.
- If the river is perennial (i.e. flows continuously throughout the year), then in such a situation, the earth is more favourable for dam construction.
- When the construction of a large dam is not possible.
Types of earthen dams:
Types of earth dams based on methods of construction are as follows:
1.Homogeneous Earthen dam:
It type of earthen dams with simple earthen embankments, built in a single material so it is homogenous.
When only one type of material is available locally and which is economical, a purely homogeneous section is used.
Such a homogeneous section is used for low to medium high dams and also for levees.
A purely homogeneous section creates the major problem of seepage and the section has to be made into a larger section or a larger section to make the entire structure safe against piping, stability, etc.
2.Diaphragm Earthen dam:
This type of embankment dam has an impermeable core called diaphragm which is surrounded by earth or rock.
The dominant core or diaphragm is made of impermeable clay, wood, concrete, steel or any other suitable material.
The diaphragm acts as a barrier or water barrier to avoid seepage through the dam.
The diaphragm is located in the center of the dam section or upside down or located like a blanket.
3.Zoned Earthen dam:
This type of embankment have a central impermeable core covered by a transition zone that surrounds the previous outer zone, central core is useful to check seepage.
The transition zone is useful to prevent piping through cracks that may be likely to be installed in the central core.
The outer zone provides stability to the central impermeable filler and distributes the load over a large area of the foundation.
Clay is highly impermeable but sometimes it does not form the best core, if it expands and shrinks substantially.
So the soil is mixed with fine gravel or fine sand to form the most suitable material for the central core.
Advantages of Earthen Dam:
Following are the advantages of earth dam as follows:
- It can be constructed on any type of foundation strut which includes soil, gravel, earth murm, rock etc.
- This type of dam is suitable for places where there are very wide valleys.
- Earth dam can be constructed with the use of locally available natural materials, hence reduces the cost of transportation.
- The design of such a dam is flexible so that a wide variety of materials can be used for the construction.
- There is a continuous process of manufacturing with a highly mechanized system.
Disadvantages of earthen dams:
Following are the various limitations of an earth dam as follows:
- An earth dam requires a complementary structure to a spillway.
- Excessive leakage and foundation erosion are more likely.
- Inadequate capacity of the spillway causes dam structure failure as there is potential for over-exploitation of the dam.
- Burrowing animals can damage the dam’s structure.
Unlike gravity dams, earthen dams can be built on relatively soft earth foundations instead of hard rock, however these dams are more susceptible to failure than gravity.
It is normally formed by the placement and compaction of a complex semi-plastic mound of varied compositions of soil, sand, clay or rock.