BRIEF SUMMARY OF THE PROJECT

A. INTRODUCTION Mawphu Hydro Electric Project, Stage - II is proposed as a run-of-river scheme on the river Umiew in East District of . The proposed dam site is located at about 3.17km downstream of Umduna HEP (90 MW) Power House location and the Power House site is located at about 2km downstream of Thieddieng village on the right bank of the river. The project is being implemented by North Eastern Electric Power Corporation Ltd, a Government of enterprise. Environmental Clearance for pre- construction activities along with approved TOR was accorded by MoEF&CC in September 2014. This clearance was obtained with project installed capacity of 75MW and other associated parameters. EIA/EMP studies have been carried out and completed based on above stated TOR. In the meantime, installed capacity of the project has undergone upward revision to 85MW as per recommendation of CEA. Project parameters have remained unaltered with the above change in installed capacity barring changes in Power House dimensions, Design Energy & Turbine- Generators. Instant PFR has been prepared based on revised installed capacity of 85MW. B. LOCATION OF THE PROJECT Mawphu HEP, Stage - II is located on the Umiew river in East Khasi Hills district of Meghalaya. The proposed dam site is located at latitude 25°18’32”N and longitude 91°38’19”E. The project area can be accessed from Guwahati airport, which is at about 120 km from , the capital of Meghalaya. The nearest rail head is located at Guwahati. State Highway is available from Shillong to reach , which is a small town at about 60km from Shillong. Mawsynram is connected with Thieddieng village through about 6km foot track. Road is also existing from Mawsynram towards Thieddieng for about 4km and the same is under construction. The dam site can be accessed from Thieddieng (at about 2km) through footpath. The power house site is also accessed from Thieddieng village (at about 2km) through footpath.

C. THE PROOSED LAYOUT OF THE PROJECT The proposed civil components of the project are as follows.  A concrete gravity dam of 51m high from the deepest foundation level with low level spillway comprising 6 bays each with radial gate of size 9.00m (W) x 12.00m (H) to pass the design flood of 9970 cumecs.  Temporary river diversion works comprise a Horse Shoe shaped diversion tunnel of 7m diameter, about 384m long on the left bank and 18m (Maximum) high upstream and 6m high downstream cofferdams.  A Power Intake with inclined trash rack on the right bank.  One number of Horse Shoe shaped Head Race Tunnel of 4.8m dia and 2622m long up to Surge Shaft.  One number of restricted orifice type Surge Shaft of 10m dia and 54m high.  One number of circular Pressure Shaft of 3.5m dia and 869m long which bifurcates into 2.5m dia and 32m long pressure shafts to feed two turbine units.  A Surface Power House of 66.0m (L) x 18.0m (W) x 30.5m (H) housing two Vertical Axis Francis Turbines and Generator units of 42.50 MW each.  One tail race channel of 8m wide and 51m long (including recovery bay) to discharge the water into the river. D. HYDROLOGY Available rainfall data at Shillong and along with observed discharge data at Mawphlang dam site from January 1979 to December 1987 was essentially utilized for water availability studies. Proportionate increase of inflow with respect to catchment area with rainfall variability, extension of series using rainfall-runoff relations, withdrawl of water for Greater Shillong Water Supply Scheme etc. were duly taken into account in arriving at a flow series from 1979- 80 to 2004-05. 10-Daily flows during 90 % dependable year (1990-91) have been eventually used for power potential studies. Water availability studies have been examined and approved by CWC vide U. O. No. 4/161/2013-Hyd (NE)/104-05 dated 11/03/14.

Synthetic UG was developed using Sub-Zone 2 (a) report of CWC and convoluted with 1-day PMP given by IMD. From above, design flood (PMF) of 9,970 cumecs has been adopted.

As per IS -14815:2000, diversion flood at Mawphlang comes to 174 cumecs. Transforming this flood using Dicken’s equation, the diversion flood at Mawphu HEP, stage II works out to 375 cumecs.

Since sedimentation observation of Umiew river at the project site or at any other site in the vicinity are not available, sediment rate of 1mm/sq km/yr has been adopted for the studies. From the capacity inflow ratio, trap efficiency from Brune’s curve works out to 0.5%, which indicates that most of the sediment will not be trapped in the reservoir and would flow downstream. Nevertheless, standard sediment mitigation measures have been incorporated in dam configuration.

E. POWER POTENTIAL STUDIES The power potential studies have been carried out based on 26 years (1979-80 to 2004- 05) generated flow series on 10-daily basis at dam site. The net storage capacity of the reservoir between MDDL at EL.464.00 m and FRL at EL.470.00m is 0.50 Mcum. The net head available for the turbine is 230.50m and the design discharge is 40.8 cumecs without overload.

The environment releases as per the Terms of Reference (ToR) of October 2014 mentioned by the Ministry of Environment and Forests and Climate Change (MoEF&CC) as given below have been considered for computing the available discharges for power generation. Sl. No. Period Percentage d ischarge considered

1. Period (June to September) 30% of river discharge

2. Lean Period (December to March) 20% of average discharge

3. Non-Monsoon/Non-Lean Period (April, 25% of average discharge May and October, November)

The proposed installed capacity is 85 MW (2 x 42.50 MW) with 10% continuous overload. The annual energy generation in 90% dependable year with 95% plant availability is 331MU. The plant load factor is 45.12%. F. CLIMATE The proposed dam is near to the village Mawphu (L/B) and the power house is near to Thieddieng village (R/B) in East Khasi Hills District of Meghalaya. The climate of the sub-basin characterized by torrential caused by South West monsoon and 60% to 70% rainfall occurs between June to September. The river flows in deep channel and swells into torrents during the rainy season while during the remaining months it has not much significant flow. The river has floods during June to October with peaks mostly occurring in July to September.

G. ENVIRONMENTAL ASPECTS The submergence area in the reservoir of the project at FRL is 13 Ha. Land will also be required for the project components and the same has been arrived as 97 Ha based on preliminary assessment. Approximately 22 Ha of forest land will be affected by the project. A total provision of Rs.20 crores has been kept towards Environment & Ecology of the project. No significant adverse impact is anticipated on the environment and ecology due to the implementation of this project. The environment releases as per the Terms of Reference (ToR) mentioned by the Ministry of Environment and Forests (MoEF) in October 2014 shall be adopted in the project. H. ESTIMATE OF THE COST The cost of construction of the project has been estimated at April 2016 price level with a construction period of 60 months (including pre-construction activities). The estimated Present Day Cost of the project stands at Rs. 940.20 crore with Rs. 127.39 crore as cost towards IDC and financial charges & Rs. 41.82 crore towards escalation. The completion cost is based on the tentative financial assessment and it may vary based on firm financial package. The levellised tariff has been calculated as Rs. 5.46 /kWh.