1. Dr. S. K. Srivastava Chief Engineer, National Water Academy, Central Water Commission Rajeev Singhal Director, National Water Academy, Central Water Commission

3. KOYNA HYDRO ELECRIC PROJECT STAGE IV EXTENSION OF HRT

5.  It was originally intended to build the dam of a thinner section to store less water (stage-I) and later to thicken it to final section to store more water (stage-II).  But due to the need felt to store the full designed quantum of water much earlier than anticipated initially and thus to complete the dam to full height in one go, a review of the section already constructed indicated that by making the reaming portion of dam towards the top thicker and the raising the top of dam about 3.5M, the resulting modified section would be as safe as the standard section.  Thus the quantity remaining the same there was a technical advantage in eliminating the tricky work of adding fresh concrete on the down stream face and economic advantage in building the dam fully in one go with the existing plant with only one miner modification in the tail tower of the cable ways.  In the overflow section, the same spillway curve has been maintained by suitably cantilevering the top on the upstream side.

6. the main works comprised of the following:  Intake structure, Intake Tunnel with lake tapping arrangement near Navja intake tower.  Head Race Tunnel, Surge Shaft with auxiliary chamber, 4 takeoffs of 4.34M dia. each from surge well to Emergency Valve Tunnel (EVT) hall etc.

7.  Due to no. of planned lift Irrigation schemes, the irrigation water demand on eastward side has increased substantially. Accordingly, Extension of HRT of KHEP Stage IV works was planned to enable KHEP Stage IV work at lower MDDL of Stage IV. Extension of HRT of KHEP Stage IV Scheme envisages construction of 4.5 KM long HRT on the upstream of existing tunnel with a lake tap at lower elevation, thereby lowering the existing MDDL from KRL 630.174m to KRL 618.00m.  To take up the work of lake tapping, it was required to complete the work of connection of operational Koyna Stage IV HRT and new Extension of HRT prior to lake tapping.  This connection work was very difficult, challenging involving lot of risk. For connection work, it was required to dewater the Stage IV HRT completely and for this, the shutdown of Koyna Stage IV power generation was required.  As per the previous planning, about 200 working days after monsoon i.e. from the month of October to June were expected to be required and for this, shutdown of Koyna Stage IV was necessary.

8. Work of connection of Old and New HRT:  This concept was not acceptable to the Power Department and hence the challenge of completing this connection work of 200 days into only 100 days and that too in the monsoon was taken by the Engineers of Koyna Project and completed this almost impossible task successfully.  Along with the old and new HRT connection, the work of connection of Additional Surge Gallery with the old HRT was also completed in the same time limit. Final work of Lake Tapping  After completing the connection work of old HRT and Extension of HRT the planning of Lake Tap work was done and accordingly Lake Tap work was started from August 2011 and finished in time

9.  For Koyna dam only nominal provision for seismic forces was made in the design of Koyna dam(0.05g for 1Sec).  The Dam suffered a devastating EQ of magnitude 6.5 Richter scale on 11 th Dec 1967. This Earthquake was sustained by the dam well though with minor bruises. (Damages to the non-overflow portion of the Dam).  After this Earthquake, experts committee suggested preliminary restorative measures followed by permanent strengthening of NOF portion sealing of upstream more than 0.2mm cracks by epoxy.  Strengthening was done in the form of full backing (from foundation to KRL 1970’) & partial buttress backing(1970’ to 2145’) in rubble concrete. Permanent Strengthening of NOF portion started in February 1969 to be completed in June 1973.

12. Trash Rack work of Kolkewadi Dam IIn Stage III Power House, 4 generators (Units) of 80 MW each are installed. At the entry point of these four penstocks on the upstream side of the dam, trash rack panels are fitted into four independent frames of semi-hexagonal shape. IIn August 2001 it was observed about the threat of detachment of trash racks and entering the same into the turbine, which would damage the turbine. TTo rule out the future need of depletion of Kolkewadi dam for repairs of Trash Racks, it was decided to fix them in a movable and maintainable manner. This work was actually taken in hand by deploying divers in April 2013 and all the trash racks were fixed by January 2014. As a result the Stage III power house is rendered safe.

13. In Koyna Hydro Electric Project, initially the gross storage capacity of project was 98.78 TMC. In due course of time keeping the need for providing irrigation water for agriculture and drinking water for domestic purpose also in consideration, the scope of this project has been enhanced. Accordingly, the storage capacity of this project was increased from 98.78 TMC to 105.25 TMC. For optimizing the usage of the available water, the project has undergone through a series of development with passage of time by way of extension and modernization. Till date, the capacity enhancement of the project in terms of power generation as well as providing irrigation water has been made in four stages. Further in order to enhance power during the peak hours, it is proposed to make some modifications in this project by constructing a pumped storage scheme during the ensuing stage V.

14. THANKS