On 22nd August night around 8.30 pm few Tamil Television news channels scrolled the news “ Eight shutters of Upper Anicut collapsed at Mukkombu (Called as Melanai in Tamil) in Tamil Nadu and water is flowing waste to Sea via River Coleroon (Flood Carrier River) without use for Agriculture”(Photo-1 aerial view of the collapsed portion).
Then all the media focused this news and some channels started to show the breached portion of the shutters and also told that no causalities occurred to human and animals. Far past four years, due to insufficient water flow in Cauvery system farmers did not do the agriculture. This time due to magic happened in western ghat area, Mettur Dam of Tamil Nadu has received good inflow to the full capacity. So thousands of farmers belong to delta hold their hands at their heads and many of them literally cried for the little hope of getting water for irrigation has spoiled due to this breach. All Engineers responsible to the system and the Thruichirappali district collector and with minimum police force have assembled at site on the day itself to manage the consequences. This paper high lights what happened at Mukkombu Anicut? And how the State Government managed the disaster event and how they made the River in to resilience for irrigation within 20 days.
- Cauvery River System & the Disaster
The Cauvery River originates at Thalakaveri in Coorg District of Karnataka in Brahmagiri Range of hills in the Western ghats at an elevation of 1341 m. (above MSL) and drains a total area of 81,155 Sq.Kms. of which 34,273 Sq.Kms lies in Karnataka, 43856 Sq.Kms. in Tamilnadu , 2866 Sq.Kms. in Kerala and 160 Sq.Kms in Union Territory of Pondicherry. The total length of the river from the origin to its outfall into the sea is 800 Kms. of which 320 Kms.is in Karnataka, 416 Kms. in Tamilnadu and 64 Kms. forms the common border between the Karnataka and Tamilnadu states. The river crosses the Karnataka state at Billigundu and enters in to Tamil Nadu at Hogenakkal, then touches the Mettur Reservoir located in Salem district and flows down to Erode, Nammakal, Karur, Trichirappally, Thanjavur and Nagapattinam and Cuddalore districts and finally confluence with Bay of Bengal as shown in figure(1) and figure (2).
For more than 4 decades this River has met the man made turbulence (Not supplying the minimum water to Tamil Nadu and Pondichery) between four States. The continues drought and poor rain fall in catchment area from the year 2013 to 2016 not filled the Karnataka dams and subsequently the Mettur Dam which has created severe drought in Cauvery delta area and shattered the hopes of farmers on doing irrigation. The Cauvery system mainly depends on Mettur Reservoir literally called as Stanley Reservoir. This year the south west rain fall has given good yield on Western Ghats around Kudagu hills and Mettur Reservoir level has raised fast towards surplus. Exactly on 1st week of June the south west monsoon should start every year. Due to the effect of Climate change and Global warming the south west rain fall failed in past three to four years. The rain was not so intensive even during the month of June 2018. Even in 10th of July 2018 the Metter Reservoir level is at 65.15” and 15th July 2018 level is 83.20’only against total depth of 120′.But the magic has happened at Kudagu and all-round western ghat. The Cauvery and the tributaries slowly carried more water from the catchment area and the dams of Karnataka raised fast in short spell. From Karnataka, rain water flows from Krishnarajsagar dam (KRS) and Kabini Dams. The KRS receives surplus water from Kabini and Herangi dams
Due to heavy rain fall the Karnataka state has released the surplus water of around 10,000 c/s from all dams. Then it has raised to 20,000, 40,000, 50,000 and to 80,000 c/s on 14th July 2018.Exactly on 22nd July the Mettur reservoir level has touched the full reservoir level 120′ and Government of Tamil Nadu opened the shutters of Mettur reservoir. The flood water flows through Cauvery River and flood warning has announced in all districts of Cauvery River and evacuation from low lying area was done by each district collectors. Flood has also surpluses from Bhavani and Amaravathy dams which are tributaries of Cauvery basin. So the flood capacity has increased to 2.34 lakh c/s with in 21 days. But during the period between 12th August to 18th August of 2018 the flood flow intensity reduced from 2.34 lakh c/s to 68,732 c/s on 22nd August 2018.
The Cauvery system at Coleroon is divided in to three portion as Cauvery with 41 vent openings ,Coleroon South with 45 vent openings and Coleroon North with 10 vent openings as shown in figure (3). The flood water come through the River Broad Cauvery (Aganda Cauvery), diversion takes place at Upper Anicut Mukkombu. One is in to the River Coleroon and other is in to River Cauvery. The Coleroon again divided in to South Coleroon and North Coleroon. The Coleroon totally carries around 2.50 lakh c/s flood and Cauvery river flood carrying capacity is around 1.00 lakh c/s.
From July 24th onwards minimum flood quantity of 40,839 c/s to maximum of 2,34,200 c/s was flown on 18th August 2018 at Upper Anicut and it continued till end of August 2018 . On 16th of August the flow in River was 37,604 c/s..The total flow in Broad Cauvery is 68,372 c/s on 22nd August 2018 and in Cauvery was 31,322 c/s and in Coleroon was 37,410 c/s. Suddenly on 22nd August 2018 around 7.30 pm to 8.30 pm the piers 6th to 15th vents of Coleroon south were settled towards down streamside and the gates were collapsed which is shown in photo (2).
Disaster Management Plan
As already explained after the broad Cauvery area below Kulithalai and Pettaivaithalai, the river divided in to two portion as Coleroon for flood carrier and Cauvery for regular irrigation supply to Grand Anicut (Kallanai in Tamil). Major portion of the irrigation supply is regulated from the Grand Anicut area. At Grand Anicut water is regulated through four major vents as furnished below. The figure (4) shows the major irrigation pattern at Grand Anicut.
Coleroon as usual for flood carrier and irrigation supply to lower Anicut of carrying capacity of 1.00 lakh c/s. This Coleroon joins with upper Anicut Coleroon at south east downstream side of Grand Anicut.
- Cauvery River for irrigation of capacity 10,000 c/s
- Vennar River for irrigation of 11,000 c/s
- Grand Anicut canal for irrigation of capacity 3500 c/s
The damaged shutters paved the ways for draining more water in Coleroon. If more water goes in Coleroon, then the irrigation supply is inadequate in Cauvery River at Grand Anicut. So the water flowing through damaged openings is to be totally stopped or reduced. During the disaster day the flow is less than 37,410 c/s only. Total flow required at Grand Anicut for all irrigation is around 24,000 c/s. Since the flow is more in Coleroon at Mukkommbu as 12,536 c/s on 24th August 2018 and flow in Cauvery is 11,064 c/s only. So the flow in Cauvery has reduced due to the collapse of 9 gates.
On 24th August 2018 around 8.00 am to 11.00 am Honorable Chief Minister of Tamil Nadu and other ministers and officials team have visited the damaged area (Photo-3) and enquired the responsible officials when it has happened and how it has happened? He was very keen that there is no life causalities happened during the incident. After the field visit, preliminary meeting were conducted at field itself with the, the Principal secretary of Public Works Department (PWD), the Engineer in Chief (Water Resources Department), Chief Engineer Trichy region, Superintending Engineer Middle Cauvery system, the Executive Engineers and Assistant Executive Engineers, Assistant Engineers and the Senior retired Engineers from specially formed.
Tamil Nadu Water Resources Development Cell PWD Tamil Nadu. Honorable CM has discussed the various possibilities of reducing the water flow through Coleroon and also either to bring back the old structures to the original position or going for new construction at downstream side of the present structure since the old structure was constructed during the year 1886. The main direction from the Chief Minister was close the breached portion as early as possible as war footing basis and to increase the flow in Cauvery for irrigation. The goals and objectives of the disaster management system was planned to fulfill the following goals.
To close the breached portion of the shutters area by providing the sand bags coffer dam in upstream side as quick as early
To clear the sand shoal made in the upstream side of Cauvery so that water shall be easily drained to Cauvery River.
Publics were not allowed to see the ongoing works. Farmers were allowed to visit the damaged area and to have discussed with the Engineers about the time of completion of the rehabilitation works.
The public park at Mukkombu area is totally banned up to the completion of restoration works
Planned to invite the IIT Civil department professors to check with the type of work carrying out now is enough and to have new Barrage across the Cauvery just 200 m below the present damaged barrage.
This temporary rehabilitation works shall also be with stand any flood flow at Upper Anicut for future three to four years up to the completion and operation of new barrage to be constructed. So this rehabilitation works are not temporary but semi permanent. Accordingly the disaster management plans was designed and executed with in short time to full fill the farmers need of irrigation water.
The engineers assembled at field on 22d night and 23rd morning itself. The works like collection of empty sand bags and thousands of tons of sand were started on the next day 23rd August 2018 itself. Filling the sand bags were also started on the second day of the incident that was on 23rd of August 2018. After the visit of Honorable Chief Minister of Tamil Nadu on 24th August 2018 to the site the above the management plan was finalized. The sand bags coffer dam was fixed at 10 m upstream side from the shutters alignment. But during the execution after three days it was found that advancing with the sand bags were difficult to stop the flow in Coleroon. Near the right bank water depth is less and so sand bags were placed layer by layer after erecting the guide stems using casuarinas poles. While going towards centre of breached portion it was found that the wooden poles were not able to with stand in the speedy flow. The progress was very slow for three days and the entire team found difficult to keep up the progress. Again the Engineers and the officers discussed the issues and decided to add some new technologies in the action plan. The photos of visit of TNCM and sand bag cofferdam are shown in photos(4 to 5).
- Changes in the action plan
Then after the detailed analysis and discussion it has decided to go for the cofferdam with granite boulders to be provided as semicircular way at just above the damaged alignment and just below the sand bags coffer dam as shown in figure( 5).
Now between sand coffer dam and the boulders coffer dam has become vacuum area where the water is stagnated with slow velocity of spiral movements on surface area. Later the vaccum area was also filled with sand loads and sand bags. Progress of various stage of construction of the sand and boulders coffer dams are shown in photos (6to 9)
So on the eighteenth day, that was on 9 th of Sep 2018 able to reduce the flow in Coleroon and increased the flow in Cauvery. More than 6.5 lakh sand bags were placed in the coffer dam. More than 3700 numbers of boulders load were dumped in the Granite cofferdam alignment. Initially it was fixed as 1: 1 slope with 4 to 5 m width on top surface. Later after joining with the left end the coffer dam was strengthened and widened for 7m and 1; 1.5 slope. Around 1000 c/s seepage was found on downstream side through the coffer dam which is again required at lower Anicut for irrigation. But this temporary structure shall be with stand for another two to three years up to the proposed new barrage shall be completed. On 2nd Sep Indian Army Engineer Er. Arvind from Bangalore center visited the Mukommbu dam area to help the TN engineers. They spent almost 4 hours at Mukkombu and expressed their happiness that the technology adopted and progresses shown are good to full fill the objectives. The photos (10-11)
Between sand bags coffer dam and boulders coffer dam huge quantity of sand loads and again the small size boulders were dumped to stop the seepage oozing out at downstream side. Exactly after 18th day the required water is diverted to Cauvery and from the Grand Anicut the irrigation water was released in all three ways as per their requirement.
- Progress towards achieving the goals.
Since the objectives were fixed clearly, the implementation was so arranged that daily 300 – 500 number of laborers were worked at site as per the priorities.
The irrigation in delta is already delayed for ten days due to some local issues like not desilting the canals and degradation of canals. Implementation of Disaster management plan could have been done after three weeks after reduced the Stanly Dam level to around 110′ and in that case works were also easily executed. But the primary objective of releasing water to Cauvery River for irrigation could have been delayed months together.
The first priority is fixed as connecting the damaged portion from the pier 6th to 15th pier using boulders coffer dam. There are many quarries operating within 100 km radius from the site as like Pudukottai, Perambalur and Karur. More than 60 lorries of capacities from 20 MT to 45 MT were engaged and worked day and night. Working conditions were not comfortable due to continuous flow of water. The existing mud road for emergency use from Sri Rangam to Upper Anicut was repaired and leveled as war footing basis for operating the Lorries.
The other constraints were water flow has not reduced, water depth at upstream side has increased at center of the damaged portion due to scouring, lorries with load were operated one by one due to single route that too from Sri Rangam. After unloading the loads the Lorries were allowed through the barrage road in the River Cauvery.
The loads were brought through one route and empty vehicles sent out through other route. If the vehicles reached the site, the unloading activities of boulders for coffer dam took more than one hour due to single way operation at site. After unloading the boulders only that lorry was sent away and the next lorry was allowed. So totally per day for 24 hours around 60 to 70 trips only allowed to operate.
The flow from Stanly dam was not reduced due to continuous inflow from Karnataka. At the same time the inflow to Upper Anicut was able to divert only 3000 c/s to irrigation out of 37400 c/s.
Finally on 10th September 2018 the irrigation water required at Grand Anicut was regulated from upper Anicut and the minimum seepage flow 1250 c/s through Coleroon was allowed since this water is required at downstream side.
The boulders coffer dam was completed up to the shutter number 17 and the sand bags cofferdam was completed after 30 days that was on 24th of Sep 2018.
After one month the seepage flow through Coffer dam at breached portion is well controlled to within 300 c/s. The complete closure of construction of sand coffer dam and boulders coffer dam are shown in photos (12-13).
Tamil Nadu state assembly Hon opposition leader M.K Stalin and other Member of legislative assembly were visited the site. The grouting firm also visited the site to explore the grouting technology to stop the seepage as shown in Photo (14-15)
The climate and Global warming have its own effect on water resources. This has been warned often by many international organizations like United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC) working on climate change. The conventional method of monitoring the old irrigation structures due to want of finance and other reasons logics are to be changed. So the good old structures shall be thoroughly inspected before pre monsoon period and if any cracks or damage found immediate attention shall be given to rectify it. This shall be adopted as mandatory rule in all water related works.
Even if anything happened at site beyond our human knowledge, the top level decision making leader shall not be panic about the disaster. Instead of panic they shall trust the engineers and administrators to carry out the work early since the persons involved in that project must have knowledge on the system. If new engineers or administrators posted it will take three to four weeks to study the system and stabilize to start the work. So in this incident our Hon Chief Minister has accepted the ground reality and trusted our Engineers and given solid direction to execute the plan.
The technologies recommended to execute in site may have need some changes during execution. So our Hon Chief Minister requested the Army engineers to visit the site for their opinion. The Army engineers after their visit and detailed analysis expressed their happiness that the works being carried out by the TN PWD engineers were in right direction. This statement has strengthened the confidence of the engineers and after the visit of Army Engineers the progress was very fast. Even though the Tamil Nadu Engineers can well handle the flood management works effectively with the available forces, it was the extra ordinary incident that the damaged portion shall be closed quickly and to regulate the water through Cauvery. So the visit of experts from Department of Civil Engineering IIT Madras has suggested and their few meaning full suggestions to erect the 8 “dia pipes for supporting the sand bags coffer dam has paved the way for easy and stable erection.
Above all the Engineering team, the Contractors team with energized labour forces under the able guidance of our Honorable Chief Minister and Principal Secretary the whole disaster management plans were execute well within three weeks. The water to be released in Cauvery system has supplied and the farmers also happy after solved all the issues even though they raised some unhappiness about the disaster. The involvement and the field execution are always enriching our knowledge, courage and the boldness to face the disaster works. The existing Government department officials can do the best, because of their credibility and accountability. So the lapses in the departments shall be solved and vacancies such as Irrigation Assistant at gross root level shall be filled to improve the efficiency in water management.
My heartiest congratulation to the Honorable Chief Minister Government of Tamil Nadu for trusted the engineers and Secretaries. My wishes to the Principle secretaries, engineers, contractors, farmers and the labours who executed this disaster management plan within time frame.