The Challenge

The Government of Punjab appointed SMEC in 2015 as part of a joint venture with National Engineering Services Pakistan (NESPAK) to provide construction supervision services on the Trimmu Barrage Improvement Project.

The main challenge for the team was to rehabilitate the barrage converting century old foundations to modern standards in a river where discharge could vary from 6,000 cusecs to its flood capacity of 645,000 cusecs and beyond.  Thirteen additional bays needed to be constructed adjacent to the existing barrage without destabilising the century old foundations of the existing barrage.

Another key directive of the project was to implement construction without disrupting the water flow for irrigation. During the design and construction, the team also had to contend with accumulation of sediment upstream and different hydraulic conditions which affected each side of the barrage.  High flow season and irrigation canal closures added additional constraints to planning. The scope of services for the project included:

• Conducting surveys and investigations
• Reviewing the detailed design of all civil, mechanical, and electric works and updating as required
• Construction supervision; contract management and provision of all working drawings
• Maintaining quality of construction
• Ensuring compliance with the Resettlement Plan and Environmental Management Plan
• Certification of completed works.

The Solution

The project demanded very precise planning of time, scope, and quality. Construction of the 13 additional bays resulted in the driving of steel sheet piles and dismantling of the existing guide bank along with canal head regulator which controls the flow of water. To maintain river flow without disruption, the existing barrage was rehabilitated in two stages.

In the first stage, half of the barrage was barricaded by constructing coffer dams and diverting river water to the other half of the barrage. The barrier wall was constructed to separate two flows with different hydraulic conditions. A sub weir was built on the right half of the wall to regulate the flow, while the left half had an unregulated flow. A hammer head was also constructed to provide additional support to the sub-weir during flood flows.

Extensive hydraulic simulations were conducted to understand the risks of shoaling and sediment build up. This impacted the construction and operation of the gate systems. Operators were trained how to use integrated SCADA systems, adjusting the gates accordingly to control and manage incoming suspended sediment. The introduction of a SCADA system was a significant step in modernising the systems, to monitor and control water levels, gates, pumps, and turbines.

Over the course of the construction over seven million Cubic feet of concrete installed. The concrete batching required installation of a chiller plant to maintain suitable temperatures to preserve the quality of the cement mix.  In the hottest months of the year ice flakes were used to keep temperatures below 21C.  Transit mixer’s drums were also covered with an insulation sheet/hessian cloth to protect the concrete from heat during transportation to the site. Sprinkling systems were also deployed over the aggregate yard for cooling and washing of the aggregates.

The Impact

Trimmu Barrage Rehabilitation successfully upgraded century old infrastructure.  Key impacts include the provision of reliable irrigation water to 1 million hectares through three canals, directly benefitting 395,000 farming families.  The new barrage significantly reduces the risk of floods, protecting an estimated 150,000 people.

Irrigated agriculture is crucial for generating higher incomes and attaining Punjab’s targeted growth rate. The irrigation infrastructure of Punjab has an estimated replacement value of USD $20.0 billion, while the estimated cost to upgrade the system to modern standards was completed at a fraction of the cost at USD $3.5 billion. SMEC has enabled the government to focus on improving the current infrastructure rather than replacing it entirely.