Shirawata dam is one of the storage dams constructed to store water for generating power at Khopoli Hydro Power Station of Tata Power. This is largest dam in terms of storage and length in the chain of Khopoli dams and was constructed during December 1912 to June 1920. It is a gravity structure having upstream and downstream face walls constructed in lime concrete. The dam, 38.7 m high, 2.3 km long, has a gross storage capacity of 196.6 Mm3.

When constructed, the dam was not designed for earthquake forces and uplift pressures. In view of the recent seismic activity in this region, the dam has been strengthened to cater to earthquake forces as well as uplift pressures. Strengthening has been carried out by construction of buttresses in colgrout masonry at the downstream face of this dam. The buttresses 72 in number are 15 m thick and 12 m wide. The buttresses have been designed for raised FRL of the dam by another 1.0 m considering future requirements. The spillway capacity of the dam was designed on the basis of the empirical flood formulae. As required by current design standards, the spillway capacity has been designed to cater to probable maximum flood (return period of 10000 years) by modifying existing spillway. The proposed new spillway arrangement is provided with 18 automatic tilting gates, each of size 5.0 m wide x 2.4 m height.

TCE Scope of Work

1. Checking structural stability of the existing dam for proposed raised Full Reservoir Level (FRL) and seismic forces.
2. Engineering for field investigation and tests.
3. Planning and detailed design of buttresses (72 Nos.)
4. Flood estimation and flood routing as per current codes to assess hydrological safety considering the revised spillway design flood.
5. Hydraulic and Structural design of overflow section and energy dissipation arrangement duly assessing the hydrological safety / design flood.
6. Design and detailing review of new automatic tilting gates.
7. Technical assistance in obtaining approval of the proposed modifications from Statutory agencies.
8. Preparation of Tender Document; enquiry specifications and Bill of quantities for civil works.
9. Strengthening measures like grouting, pointing, shotcrete, guniting, etc., of dam for reducing the seepage/permeability.
10. Detailed construction drawings for modifications to existing Non-overflow section, buttresses, modifications to overflow section, bridge above the spillway and stilling basin.
11. Construction supervision of rehabilitation & strengthening works.
12. Inspection of fabrication of automatic tilting gates (18 numbers) and inspection of installation works at site.
13. Submission of as-built drawings and manual for operation and maintenance of gates.