Walwhan dam is one of the dams in the chain of reservoirs constructed to supply water to Khopoli Hydro Power Station of Tata Power Company Limited. Water from Walwhan reservoir is carried through a 7 km long open channel up to Khandala forebay wherefrom it is led to Khopoli Power house through a system of penstocks. The dam, 1.3 km long constructed between year 1911 to 1916 is a gravity dam constructed in rubble masonry has a maximum height of around 26 m with a storage capacity of 72.55 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 59 in number are 9 m thick and 14 m wide. The buttresses have been designed for raised FRL of the dam by another 0.6 m.
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 now been designed to cater to probable maximum flood (PMF) by modifying existing spillway. The proposed new spillway arrangement is 72 m long and provided with 13 automatic tilting gates each of size 5 m x 1.4 m each.
TCE Scope of Work
1. Checking structural stability of the existing dam for raised Full Reservoir Level (FRL) and seismic forces.
2. Engineering for field investigation and tests.
3. Planning and detailed design of buttresses (59 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 new overflow section and energy dissipation arrangement.
6. Design and detailing review of new automatic tilting gates.
7. Technical assistance in obtaining approval of the proposed modifications from Statutory agencies like CDO Maharashtra.
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 (13 numbers, each of size 5 m x 1.4 m) and inspection of installation works at site.
13. Submission of as-built drawings and manual for operation and maintenance of gates.