- India is home to more than 5,000 large dams (over 15 metre high), the third largest number in the world, behind the US and China.
- India has thousands of large dams that are more than 25 yrs old and 164 dams that are more than 100 yrs old.
- Around 15% of India’s land mass is prone to floods, with an average of 1,548 people losing their lives and around eight million hectares getting affected, causing loss of about Rs 5,628 crore every year.
- 36 incidents of dam failure have occurred in the past.In June, the center has introduced a proposal of the “Dam safety bill, 2018” that gives countrywide procedure to ensure safety of the dams.
- Dams are considered vital for: –
- Economic growth
- Generating energy
- Rapid and substantial rural and agricultural growth
Recent Kerala floods: –
- Kerala’s worst flood since 1924.
- According to reports, 35 dams were opened to the already flooded areas of Kerala which let to aggravated loss.
- Though excessive rains filled the dams, experts blamed poor water flow management from the reservoirs for the inundation of the coastal state and many parts of the southern India.
- Water experts are saying that the intensity of Kerala floods could have been reduced if the water from 35 big dams in Kerala was released much earlier. Kerala blamed neighbouring Tamil Nadu for the floods in the Supreme Court, saying the gates of Mullaperiyar dam were suddenly opened without any warning, a claim denied by Tamil Nadu government.
- AK Gosain, professor emeritus at Indian Institute of Technology (IIT), Delhi, agreed with this and said dam management in India works on the principle that at end of the monsoon the reservoirs should be full. “The tendency is not to release water till the last go and this is what has happened in Kerala,” he said.
- Experts say the flooding in downstream areas can be better managed if the India Meteorological Department’s 72-hour forecast is used to create simulation models for water release. Gujarat and Odisha governments use the IMD’s forecast to release water slowing from the dams on Tapi and Mahanadi rivers respectively, helping the two states manage floods. Despite Gujarat receiving substantial rainfall in 2017, Surat city on the Tapi river was not flooded.
How dams/reservoirs contribute in preventing floods: –
Water from snow and rainfall will find its way into stream and rivers and eventually into the sea. After severe storms, or heavy snow or rain over a number of days, the water level in rivers can rise dramatically. Sometimes, the water flows over riverbanks or walls causing flooding of farmland, property, and in the worst cases, loss of life.
A reservoir can be used to control the amount of water flowing in a river after heavy rain. The water level in the reservoir is kept low during the rainier periods of the year. When heavy rain occurs, it is stopped by the dam and held back in the reservoir. When the reservoir gets too full, the floodwater can be passed downstream over a spillway. Sometimes, floodgates are used on top of spillways, and they can be fully or partly opened to control the amount of water let out into the river downstream. Dams such as the Blackwater dam of Webster, New Hampshire and the Delta Works are created with flood control in mind.
Some functions and uses of dams: –
A dam is constructed mainly for power generation, irrigation/water supply or flood prevention. However in most of cases dams have multiple functions: –
- Power generation
The reservoir water is stored at a higher level than the turbines, which are housed in a power station.
Stabilize water flow / irrigation
Dams are often used to control and stabilize water flow, often for agricultural purposes and irrigation.In regions of the world where the climate is very dry for some seasons, the soil becomes so dry that it restricts the growth of vegetation. This problem can be overcome by irrigation, a man-made system for watering the land. Irrigation water can be stored in reservoirs during the rainy season, then in the drier seasons it can be released from the reservoir and distributed over the land through a system of canals.
- Land reclamation
Dams (often called dykes or levees in this context) are used to prevent ingress of water to an area that would otherwise be submerged, allowing its reclamation for human use.
- Water supply of urban areas/ Industrial usage
Many urban areas of the world are supplied with water abstracted from rivers pent up behind low dams or weirs. Examples include London – with water from the River Thames and Chester with water taken from the River Dee.
- Recreational areas
Creating recreation areas or habitat for fish and wildlife, fishing, boating, sports, other activities i.e bird watching.
The construction of a dam across a river forms a reservoir that raises the water level upstream, stores the water, and slows down its rate of flow. This improves the navigation conditions upstream of the dam for ships and boats. Dangerous areas of rocks and sandbanks, previously in shallow water, become well covered, and rapids in the river disappear. Also, water from the reservoir can be released into the river downstream during the drier seasons of the year to make sure that it is deep enough for navigation all the year round.
- Water diversion
A dam can be used to divert all or a portion of the flow of a river from its natural course. The water is diverted into an artificial water course or canal, which may be used for irrigation or return to the river after passing through hydroelectric generators, flow into a different river.
- Self purification
The time the water is held for before it is released is known as the retention time, and is a design feature that allows larger particles and silts to settle out as well as time for the biological treatment of algae and bacteria by plankton-like creatures that naturally live within the water. In general the water quality during storage is improved especially regarding turbidity and there are indications for system’s self purification.
Way forward: –
- Integrated effort is required.
- Improve the rules of water release from Dam.
- Dam management should be seen as an overall system and should be handled accordingly.
- Calculate the factors like velocity of flow of water,etc. and accordingly manage the depletion of water from the dams ensure proper safety measures prior to any mishappening.
- Dams are responsible for controlling floods and at times can also lead to increase in frequency of floods too.
- “Dam safety bill” was recently introduced in the parliament because: –
- Since 1980’s, India is facing dam safety issues and working towards it.
- It ensures giving legal backing to the states to implement already existing policies.
- Lack of few crucial policies has led to introducing this bill.
Dams require special emphasis: –
- Don’t look at dams and human settlements in isolation. Integrated approach is required.
- Village planning and dam management must be seen in coordination.
- Robust information system required.
- Long term planning such as shifting people residing in low lying areas to safer places and government occupying such places in advance to tackle future flooding problems.
- Start taking utmost care of hotspot areas.
- Keep a check on river dredging and sand mining issues.
- Simulation exercises are expected.
- Short term planning should be made binding and time bound.
- Learn our lessons from recent Kerala floods.
- Understand correlations between dam management, dam safety and flooding.
- Proper planning and preventive measures to be taken in advance instead of waiting for the last moment.