Much work awaits to get Medigadda back into shape

The ultimate salvation of the Medigadda barrage, the most damaged of the three Kaleshwaram lift irrigation scheme (KLIS) barrages, could lie in what could tantamount to a huge undertaking with the option of constructing diaphragm walls – huge cement concrete walls going deep into the river bed and protect the foundations – being considered as the only possible option to ensure long term safety of the structure.The barrage was built on a design that rests on contiguous secant piles which form a cut-off wall. This was supposed to protect the barrage from possible under-the-foundation erosion but failed to do that, something that the National Dam Safety Authority (NDSA) had pointed out.Now, amidst hectic consultations with experts, design consultants, and irrigation engineers, it has emerged that Medigadda, if it is to be saved, will need diaphragm walls along its length, and this option is learnt to have come up for discussion at a high-level meeting chaired by irrigation minister N. Uttam Kumar Reddy on Sunday.It is learnt that AFRY India, the design consultant for rehabilitation designs for Medigadda, was of the opinion that ultimately, only a diaphragm wall would save the barrage. Sources familiar with Medigadda’s engineering designs, said that such a wall could go fairly deep, some 40 metres or so, once the geophysical and geotechnical test results are available. This could mean a long and fairly expensive undertaking, but once done, the barrage could be put back to work, but only after the other component of design deficiency – that of short stilling basin – is addressed.The stilling basin, a structure designed to slow down the speed of water flowing downstream, was practically non-existent at Medigadda with only a downstream apron structure followed by a series of cement concrete blocks that were meant to dissipate the energy from the flow, one of the fatal flaws that was also pointed out by the NDSA.It is now believed that a proper stilling basin with baffles in between and extending up to some 60 metres will be designed to ensure that flowing water will not damage the river bed which otherwise could contribute to seepage from under the barrage foundations, as had been the case with Medigadda.The irrigation department, determined to begin works at the barrage, is learnt to have set itself a October/November deadline this year to start works on the stilling basin, and has also drawn up a schedule for not just Medigadda, but also for Sundilla and Annaram barrages to start this work, with the major repairs to follow. Meanwhile, a major exercise is being mounted to start drilling around 1,000 boreholes at the three barrages for geological studies of the riverbed, the results of which could help in preparing barrage repair designs.What lies aheadDrilling awayBarrage – Boreholes needed – Rigs* being mobilisedMedigadda – 504 – 35Sundilla – 230 20Annram – 281 20*25 additional rigs to be on standbyA tight deadlineRigs mobilisation –April 10 to 26Boreholes drilling –April 20 to June 10Borehole specimen analysis –April 30 to July 15Medigadda 2d model study – June 1 to July 31Annaram/Sundilla 2 D model study – July 21 to Oct 30Rehabilitation designs – Aug 1 to Oct 20Design completion – By Oct 31Engineering drawings –Nov 16 to Nov 30



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