Irrigation Schemes Offer Big Construction Opp...

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Irrigation Schemes Offer Big Construction Opportunities
Governments and international lending agencies are pouring billions of dollars into irrigation灌溉冲洗 construction and rehabilitation, hoping for a payoff in jobs, energy, and economic revival.
In addition to the new projects, contractors are also at work rehabilitating older, sometimes ancient, irrigation systems in the third world. PRC Engineering, New York, USA, has a $9.8-million contract to supervise and monitor rehabilitation and maintenance planning on the Indus River basin scheme, in Pakistan. It is one of the largest systems in the world, with 58,500 km of canals.
High Hopes
Despite the fact that megaprojects大型项目 have generally fallen from favor under questioning about such factors as costs, environmental impact, and real benefits, some of the ambitious 费力projects in progress or planned in the world today are irrigation related.
Work began in 1984 on construction of the Great Man-Made River Project, in Libya, with the award of a $3.3-billion contract.
The giant Mahaweli project, in Sri Lanka, is now well advanced. Although most early attention has focused on its electricity generating capacity, its four new storage reservoirs will open up over 100, 000 ha of dry land for farming by more than 100,000 new settlers.
Indonesia's second irrigation sector project requires a $195-million investment in Sumatra's Simalungun district for both new construction and system rehabilitation. The seven-years of employment, according to the Asian Development bank, which has approved an $85-million loan for the scheme. Work includes rehabilitation of 124 weirs and 4500 canal运河管道structures; extensive of 584 km of main and 293 km of secondary canal extension; tertiary facilities covering nearly 40,000 ha; and the establishment of a central water management training center.
Type of work
Rehabilitation of major schemes, some extremely ancient, others only a decade or two old, is also a growing source of work for contractors. and a look at such a project demonstrates clearly the wide variety of construction activities and opportunities created by irrigation projects.
The Indus system was built in the 1950s by Pakistan's Water and Power Development Authority (WAPDA) and turned over to four provincial irrigation districts (PIDs) for operation. Inadequate funding and a shortage of trained workers led to maintenance inadequacies. The World Bank and the Agency for International Development are now funding the program to redesign segments of the canals, and to implement a training program to provide management skills for the Pakistanis.
Glenn Tarbox, PRC's Project Manager, said that because WAPDA is the major constructor on the project, PRC's work is largely operation and maintenance. However, just maintaining a very large system requires major construction activities. One problem is that none of the canals is unlined; they behave like alluvial channels, or natural streams.
The water out of the Indus River is heavily laden with sediment. Sometimes contractors have been able to dredge the canals, and maintain the original trapezoidal cross section. But other times they have just built up the canal banks, creating perched waterways above the land. Failures and floods overtop the banks. One of the major construction activities in maintaining the canal system is to rehabilitate these banks. Tarbox said.
"The PIDs are responsible for utilizing earthmoving equipment, taking materials and hauling them to the site, and putting them in place. One example is the small portable Mud Cat™ dredge which has been selected as the best device available worldwide for restoring the canals. Our responsibility is to assist them in their understanding of equipment, and construction management. We do have teams which are working with the Pakistanis, assisting them in running the new equipment, and developing inventory control systems. They had maintenance workshops, but they have fallen into a state of disrepair, so we are rehabilitating them."
Structural work
All the original structures need maintenance, said Tarbox. "The original structures, the major diversion headworks, that control the flow of water into the system are made of reinforced concrete. We're talking about concrete repair protective coating for gates, seals, and their replacement. If we have any settlement, then you have a alignment problems. These things are typical. No unusual problems-it's just that it's such a massive system."
Design evaluation
PRC is also taking a look at the original design of the system to see whether the whole flow regime could be more efficient. "Rehabilitation... is a second chance. Rather than just put the canal bank in place it might be advisable to change some elevations, slopes, or cross sections"
Reprinted from World Construction Magazine


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