MUHAMMAD ZUBAIR  - Neelum-Jhelum Hydro-electric Project is a flagship mega project of immense national importance. The Project is located in Muzaffarabd district in the state of Azad Jammu and Kashmir (AJ&K) at an approximate latitude 34°20’N and longitude 73°40’E, between elevation of 600m and 1100m above sea level. It envisages the diversion of Neelum River water through a tunnel and after producing power, out-falling into the Jhelum River.

The Project utilises a gross head of about 420m by diverting the Neelum River at Nauseri by construction of Composite Dam (Gravity + Rock fill), to the lowest reach of the Jhelum River at Zaminabad through a 52 km long tunnel system including Tailrace Tunnel. A Composite Dam, 160 m long and 60 m high is being constructed on Neelum River at Nauseri 41km north east of Muzaffarabad. 39.2km of the Headrace Tunnel is twin tunnel having dia of about 8.5m each.

The remaining 8.94 km tunnel is a single tunnel of dia 9.6 m. About 10 km stretch of the twin tunnels will be constructed through Tunnel Boring Machines having dia of 8.5m. The Headrace Tunnel is accessed by eight (8) Adits for removal of excavated spoil and other works. The Headrace Tunnel crosses Jhelum River approx. 200m below its bed level. The Power House of the Project is located near Chattar Kalas, 22 km south of Muzaffarabad. Neelum-Jhelum Hydroelectric Project has an installed capacity of 969 MW and will generate 5.15 Billion units of electricity annually.

The Neelum-Jhelum Hydro-electric Project is located in tectonically active mountains of north-western part of the Himalayas, which is separated into three distinct units by a series of parallel and sub-parallel regional thrust faults like, SRT (Salt Range Thrust), MBT (Main Boundary Thrust), MCT (Main Central Thrust), MMT (Main Mantle Thrust).

The initial detailed seismic hazard analysis done for Neelum-Jhelum Hydroelectric Project was based on:

Report on Seismic Hazard Analysis for the Neelum-Jhelum Hydroelectric Project by WAPDA in association with GTZ, HEPO No 148, 1991. ICOLD Bulletin 72: Selecting Seismic Parameters for Large dams, 1989.

The seismic parameters adopted for the tender design on the basis of this study were as follows:

SURFACE INSTALLATIONS

 OBE - 0.16 g peak ground acceleration (rock site)

 MCE - 0.45 to 0.60 g peak ground acceleration (rock site)

Underground works

 OBE - 0.11 g peak ground acceleration

*  MCE - 0.30 to 0.40 g peak ground acceleration

A powerful Earthquake (EQ) of October, 2005 with a magnitude of Mw = 7.6 struck the project area and caused widespread damage in Azad Kashmir & adjoining areas. The origin of this EQ was attributed to the movement on three segments of a thrust fault system, including; Balakot - Bagh Fault, Muzaffarabad Fault, Himalayan Frontal Thrust (HFT), Tanda Fault and Murree Fault.

This devastating Earthquake prompted a critical review of the adopted seismic parameters used for the tender design. The values adopted in tender stage design, were considered low based on the work done after October, 2005 event. The review of latest seismic hazard/risk maps for Pakistan was developed by (USGS) Earthquake Hazard Programme and the Building code of Pakistan (Seismic Provision - 2007).

* Seismic hazard map for Pakistan developed by the USGS Earthquake Hazards Programme, indicates a PGA for the Project area in the range of 0.24g to 0.32g.

The Seismic Zoning Map of Pakistan given in the Pakistan Building Code Seismic Provisions (2007) placed the Project area in Zone 4 with Peak Ground Acceleration (PGA) > 0.32g for 500 years return period.

After the October 2005 earthquake, the seismic design parameters adopted for the tender design of the Project were thoroughly reviewed, and seismic design of the Project structures was appropriately revised to account for the following updated seismic parameters which also indicated that the seismic hazard for various parts of the Project is of different level. The updated seismic parameters adopted by project consultants are;

FOR DAM SITE

Operating Basis Earthquake (OBE) 0.34 g peak ground acceleration

Maximum Credible Earth-quake (MCE) 1.16 g peak ground acceleration

FOR POWERHOUSE SITE

 Operating Basis Earthquake (OBE) 0.25 g peak ground acceleration

Maximum Credible Earth-quake (MCE) 0.62 g peak ground acceleration

FOR UNDERGROUND WORKS

Operating Basis Earthquake (OBE) 0.17 g peak ground acceleration

Martin Wieland (Member of Panel of Experts) ensured that “for Neelum-Jhelum Hydro-electric Project adequate estimates of seismic design parameters have been made which ensure that the project fully complies with today’s seismic safety standards for a hydropower plant in a highly seismic region. He further stated that, the prediction of strong earthquake, which would include time, magnitude and location, is still impossible and hardly any progress has been achieved within the last 40 years.

 Since it is not possible to accurately predict the time, magnitude and location of future earthquakes, but it has been ensured by experts that the revised design of project is based on the seismic parameters, which are as per world-wide standards, can sustain high intensity seismic activity in the project area. The writer is CEO of Neelum-Jhelum Hydroelectric Company.