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Azad Pattan Hydropower Project

History

The project was identified by Montreal Engineering Company, Canada (Monenco) under “Inventory and Ranking Study of Major Hydroelectric Projects” for WAPDA during 1981 to 1984.

During 1992 to 1994, the Project was studied by GTZ-WAPDA and capacity was revised as 222 MW based on design discharge available 50% time of the year. Thereafter no further studies or investigations were carried out until PPIB offered the project to Private sector for its development and a Letter of Interest (LOI) for project capacity of 222MW was awarded to the Alamgir Power in May 2007.

The bankable feasibility study was completed and approved on December 20, 2011 thus fulfilling conditions of LOI and entitling the Company to get tariff approval, issuance of Letter of Support and move foreward to financial closing/construction of the Project with an optimized capacity of 640MW.

 

Location

The Project is located at 33˚44’ N, 73˚38’ E near the village of Muslimabad in district Sudhnoti, Azad Jammu & Kashmir, some 7 km upstream of the Azad Pattan bridge on the river Jhelum, one of the largest eastern tributaries of the river Indus. The river Jhelum, one of the largest eastern tributaries of the river Indus, rises in Kashmir and flows into the Mangla reservoir. Water drawn from the reservoir generates electricity in Mangla powerhouse and after release into the river Jhelum joins the Chenab in district Jhang, merges with River Chenab and thereafter joins River Indus at Mithankot.

The river Jhelum valley, at the Project site, is sparsely populated; deep and narrow valley sides have thick vegetation mainly bushes, with some tress and terraced agriculture. The Project has limited pondage within the river valley without material inundation of fertile land. The area is sparsely populated with approx. 58 households and under 1000 inhabitants in a 22km length on both sides of the valley along the project site. Most of the habitation in the river valley is on the higher slopes and would not be affected by the increased water level after construction of the project. The project site is well connected to a network of all-weather metaled road to Islamabad capital of Pakistan and other parts of AJ&K. The nearest airport and railway connection to the project is at Islamabad/Rawalpindi approx. 90 km (2 hour drive).

 

Project Site


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The Scheme
The Project comprises a run-of-the river pondage scheme with small live storage of 14.3 million m3 which provides an option for 4 hours daily peaking. The final optimized capacity of the Project is 640MW producing net energy of 3064 GWh for delivery to the Grid at a plant factor of about 54%.
The electricity generated will be sold to the Central Power Purchasing Authority (CPPA) under a power purchase agreement with a term of 30 years. A water use charge presently PKR 0.15 per kWh will be paid to the Government of AJ&K providing them a valuable source of revenue.

 

Project Concept
Azad Pattan HPP is one of the projects within the River Jhelum cascade comprising (from upstream to downstream) Chakoti Hattian, Kohala, Mahl, Azad Pattan and Karot. The reservoir capacity and generation potential of each project is influenced by the water levels determined by the Cascade Study commissioned by the PPIB. A normal operating level of 526 m.a.s.l and tailwater level of 461 m.a.s.l. prescribed by PPIB, results in a gross operating head of 65 m. The Jhelum River can be subjected to extreme flood events due to intense monsoon rainfall within the catchment area. A dam with the magnitude and hazard rating of Azad Pattan is required to be designed to pass the PMF without failure. The PMF assessment has estimated at peak flow of 35,650 cumecs.

The general landform within the locality of the project area can be described as Ridge & Trough Plains. This comprises vertically or steeply dipping Murree formation. The sandstone part is resistant to weathering and forms steep, parallel, narrow and long ridges alternating with shallow troughs developed on shales which are easily weathered yielding clayey material.

A notable feature of the Jhelum River is the high suspended sediment load which at Azad Pattan is about 36 million tons annually with a bed load of approx.5 million tons.

The general topography of the area provides a number of challenges to the development of required infrastructure and access to the site. Fundamental issues arise with access to the working areas and disposal of a significant quantity of waste material. The limitation of areas for storage will also result in the requirement for careful planning of the construction phase.

The main components of the scheme comprise:

  • Concrete gravity dam with high capacity spillway incorporated into the dam crest and low level outlets located within the central non-overflow section of the dam;
  • Power generation facilities including U/G powerhouse, with associated headrace tunnels, penstock, tailrace and surge shafts;
  • River diversion facilities.

 

Equipment
The project will use hydropower turbines, driven by flowing water, to rotate an alternator and generate electricity. The technology for Francis turbine is well established and mature and is applicable for heads of 10m to 650m. Developed some 185 years ago it has been installed in many projects over the world since and operates at an efficiency of over 90%.

  • Complete package of hydro-mechanical and E&M equipment on a water-to-wire basis;
  • Hydro-mechanical equipment – power intake gates, spillway gates, stoplogs, draft tube outlets/ gates, powerhouse equipment, cranes, auxiliary systems including fire protection;
  • Hydropower turbines –  4 x Francis type turbine rated at 160 MW each;

 

Electrical Equipment – generators (18 kV), phase isolated bus ducts, single phase transformers (88MVA), gas insulated lines to surface GIS switchgear building and substation, SCADA, auxiliary & control systems.

 

 

Turbines

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Generator

 

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Switchgear

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Project Layout

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Hydraulic Design

Shafts, headrace and pressure tunnels:
From the pressure shafts the pressure tunnels and steel lined penstocks will deliver water from the intakes adjacent to the dam to the turbines in the underground powerhouse. Due to the difference in orientation of the powerhouse and intake structures the tunnels are of varying lengths and surge chambers will be required on the longer tunnels to maintain governing stability of Units 2 and 4 without adding inertia to these units. Tunnel diameter varies from 8 m within the concrete lined sections to 7 m and then 6.5 m in the steel lined sections. The tunnel diameters have been optimized to limit friction and form losses yet be constructible within prevailing ground conditions.

 

Diversion Tunnels:

  • 2 concrete lined tunnels 415 metres and 495 metres long with finished span of 12.5 metres and height of 14 metres
  • Capacity just full 3,100 cumecs

 

Head Race Tunnels:

  • 4 concrete lined headrace tunnels with a total length of under 1 km, finished diameter of 8 metres (excavation 9.5 m span and 10 m height) and individual lengths of 169, 211, 255 and 299 meters

 

Tailrace Tunnels:

Water from the turbines will be discharged into four 8 m dia steel lined draft tube tunnels that will combine, below the tailrace surge chambers, into two short concrete lined tailrace tunnels of 11 m finished dia, and length of 80 m and 110m, to return the water to the river.
Spillway:

  • The main spillway is of asymmetric layout. The operating philosophy is discussed with combinations of gate openings for different flood conditions.

 

Discharge capacity:

  • 20,000 cumecs at FSL
  • 35,650 cumecs at MFL
  • LLO capacity 3,000 cumecs at FSL

 

Power Waterways:

Due to the narrow operating range of the reservoir the inlet structure is placed at a high level. Each turbine has a dedicated headrace tunnel. Each inlet has two wheeled bulkhead gates to isolate each headrace tunnel. There are no stoplogs given that it is possible to rapidly lower the reservoir level by opening the spillway gates in case of an emergency.

  • Design flow 300 m3/s per unit
  • Friction and form losses - 4 to 4.4 m

 

River Diversion:

River diversion is required to provide access to the dam foundation and construction of the tailrace outfall; an all season diversion with capacity of twice the mean annual flow has been selected which will keep the works area dry throughout the construction period. Two D shaped tunnels of 12.5 m wide and 14 m wide will provide diversion for the 1:2 to 1:3 year flood events. Greater floods, characterized by short duration, will be planned to overtop the concrete coffer dam and it was considered that clean up after such an event would also be short and would not impact the project schedule.

 

RCC Gravity Dam
The dam is placed in a V-shaped valley with a base of 50m. The foundation conditions comprise the Murree Formation which comprises alternating sequence of sandstone and siltstone and claystone bands with some incidence of conglomerate. Within the river reach of the proposed scheme there are massive bands of sandstone at intervals along the river. Between each band are thinner bands of sandstone intercalated with siltstone, claystone and broader bands of siltstone and claystone.

It is considered that the foundation conditions would be suitable for the founding of a concrete gravity dam. In addition use of roller compacted concrete would result in significantly lower cost compared with a conventional concrete gravity structure. The dam form and design would enable construction of an integrated spillway structure and low level outlets for control of sedimentation.

 

  • 90m gravity dam has been design following USACE design guidelines and international best practice.
  • The dam is curved in plan therefore it has been necessary to carry out stress and stability analysis for a trapezoidal shaped foundation footprint for each gravity block.
  • Foundation parameters have been assessed using Hoek Brown and Barton Bandis methods.
  • Factor of safety against sliding / overturning has been calculated for all load cases – usual, unusual and extreme.
  • Full account has been taken of the exceptionally high tail-water levels for major floods.

 

Underground Works
The U/G PH cavern was heavily influenced by prevailing ground conditions and the whole U/G works arrangement comprises compact short tunnel lengths and galleries to house transformers, main inlet valves, powerhouse cavern and other subsidiary tunnels and galleries including cable access, power routing shaft, busbar galleries and drainage gallery etc.

  • Design methodology has been to use rock mass classification to estimate rock support for tunnels and initial assessment of design requirements for the larger caverns. Hoek Brown method used to derive strength parameters, Bartons Q method used to assess support requirements.
  • Precedent experience is provided from Ingula HPP and Drakensburg HPP in South Africa (mudstones / sandstones).
  • Studies for the Neelum-Jhelum found stronger rock but more tectonically disturbed than at Azad Pattan. Studies for the Kohala project found weaker rock, more tectonically disturbed.

Numerical modelling undertaken to investigate interaction between the main cavern and adjacent galleries and surge chambers.

 

Underground Structures

Sufficient modelling has been completed to determine that the support of the powerhouse is feasible with a combination of rock bolts and cable bolts. 
Detailed modelling required with validation of design parameters during initial construction.
It is likely that future design development will result in greater spacing between the main cavern and galleries.

Description: report1

 

The construction activities will be entrusted, on a competitive basis, to a selected experienced and competent EPC Contractor. Proper, sound and internationally accepted construction practices will be followed to ensure safety and minimum environmental degradation during construction which, amongst others, would endeavour to limit soil erosion, noise, tree removal ensure that proper procedures, safety measures and methodology for tunnel excavation and blasting are adopted.

After completion of the project the plant operation & maintenance activities will be entrusted to a selected experienced and proficient O&M operator who will maintain and operate the plant in accordance with international standards and practices including accepted norms of health, safety and the environment practices. The provisions for manpower, training, health, safety, environment and emergencies will be adequately covered in the EPC contract during the construction phase and in the O&M contract during the operational phase.

 

Hydrology

A preliminary assessment of the project hydrology has been undertaken as follows: the daily discharge data for Azad Pattan and Karot gauging stations were collected from Surface Water Hydrology Project WAPDA for the period 1970 to 2004. The data has been processed and mean annual flows at Azad Pattan site are presented as follows:

 

Mean Annual Flows at Azad Pattan


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Monthly flows at Azad Pattan in 2001


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Based on the daily flow data from 1970 to 2004, a flow duration curve has been developed as presented below. It shows that a discharge of 1200 m3/sec is available about 30% of the time, and the 550 m3/s on which the 222 MW scheme is based is available 50% of the time.

 

Flow-Duration Curve for Jhelum River at Azad Pattan

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Project Salient Features