From UPSC perspective, the following things are important :
Prelims level : Rate of siltation
Mains level : Paper 3- Ageing dams and challenges associated with it
Ageing dams threaten India’s water security, affect farmers’ income and increases the frequency of flooding.
What is a dam?
- A dam is a barrier that stops the flow of water and results in the creation of a reservoir. Dams are mainly built in order to produce electricity by using water. This form of electricity is known as hydroelectricity.
- Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability.
Types of Dams
There are many dams in India, and hence there is a need to know about them as there are questions based on the dams of India. The Bank Exams like IBPS or SBI contains questions from this section.
Based on the structure the types of dams are as mentioned below:
- Arch Dam: An arch dam is a concrete dam that is curved upstream in the plan. It is designed so that the hydrostatic pressure (force of the water against it) presses against the arch, causing the arch to straighten slightly and strengthening the structure as it pushes into its foundation or abutments. An arch dam is most suitable for narrow canyons or gorges with steep walls of stable rock to support the structure and stresses.
- Gravity Dam: Dams constructed from concrete or stone masonry are Gravity dams. They are designed to hold back water by using only the weight of the material and its resistance against the foundation to oppose the horizontal pressure of water pushing against it. These are designed in such a way that each section of the dam is stable and independent of other section.
- Arch-Gravity Dam: This dam has the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water pressure against the canyon rock walls. The inward compression of the dam by the water reduces the lateral (horizontal) force acting on the dam.
- Barrages: A barrage is a type of low-head, diversion dam which consists of a number of large gates that can be opened or closed to control the amount of water passing through. This allows the structure to regulate and stabilize river water elevation upstream for use in irrigation and other systems.
- Embankment Dams: An embankment dam is a large artificial dam. It is typically created by the placement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay, or rock. It has a semi-pervious waterproof natural covering for its surface and a dense, impervious core.
- Rock-Fills Dams: Rock-fill dams are embankments of compacted free-draining granular earth with an impervious zone. The earth utilized often contains a high percentage of large particles, hence the term “rock-fill”.
- Concrete-face rock-fill dams: A concrete-face rock-fill dam (CFRD) is a rock-fill dam with concrete slabs on its upstream face. This design provides the concrete slab as an impervious wall to prevent leakage and also a structure without concern for uplift pressure.
- Earth-fill dams: Earth-fill dams, also called earthen dams, rolled-earth dams or simply earth dams, are constructed as a simple embankment of well-compacted earth. A homogeneous rolled-earth dam is entirely constructed of one type of material but may contain a drain layer to collect seep water.
Major Dams in India
The major dams in India have helped the inhabitants in a number of ways like:
- Providing adequate water for domestic, industry and irrigation purposes.
- Hydroelectric power production and river navigation.
- These major dams in India and their reservoirs provide recreation areas for fishing and boating.
- They have helped in the reduction of floods.
Some facts about the issue of ageing dams
- India is ranked third in the world in terms of building large dams.
- Of the over 5,200 large dams built so far, about 1,100 large dams have already reached 50 years of age and some are older than 120 years.
- The number of such dams will increase to 4,400 by 2050.
- This means that 80% of the nation’s large dams face the prospect of becoming obsolete as they will be 50 years to over 150 years old.
- The situation with hundreds of thousands of medium and minor dams is even more precarious as their shelf life is even lower than that of large dams.
Impact on the storage capacity
- As dams age, soil replaces the water in the reservoirs technically known as silt or sediment.
- Therefore, the storage capacity cannot be claimed to be the same as it was in the 1900s and 1950s.
- To make matters worse, studies show that the design of many of our reservoirs is flawed.
- Almost every scholarly study on reservoir sedimentation shows that Indian reservoirs are designed with a poor understanding of sedimentation science.
- The designs underestimate the rate of siltation and overestimate live storage capacity created.
- Therefore, the storage space in Indian reservoirs is receding at a rate faster than anticipated.
- When soil replaces the water in reservoirs, supply gets choked.
- The net sown water area either shrinks in size or depends on rains or groundwater, which is over-exploited.
- Crop yield gets affected severely and disrupts the farmer’s income.
- The farmer’s income may get reduced as water is one of the crucial factors for crop yield along with credit, crop insurance and investment.
- It is important to note that no plan on climate change adaptation will succeed with sediment-packed dams.
- The flawed siltation rates demonstrated by a number of scholarly studies reinforce the argument that the designed flood cushion within several reservoirs across many river basins may have already depleted substantially due to which floods have become more frequent downstream of dams.
Consider the question “Ageing dams poses several challenges for India. Identify these challenges and suggest the measures to deal with these challenges.”
The nation will eventually be unable to find sufficient water in the 21st century to feed the rising population by 2050, grow abundant crops, create sustainable cities, or ensure growth. Therefore, it is imperative for all stakeholders to come together to address this situation urgently.