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Rainfall recharge

Middle East

Water is at a premium in the UAE, but a series of dams is helping the farming community.

The mountains of the Northern Emirates are about as far from the sophistication of Dubai as it is possible to be.

Not geographically; it takes only a few hours to drive from Dubai to the mountain settlement of Hatta or even to the Emirate of Fujairah on the Gulf of Oman on the far side. But landscape and atmosphere are totally different as, more importantly, is the weather.

Between November and March it rains. Downpours, often highly localised, cause water to flow through the wadis with tremendous force, bringing down man-sized boulders with them. In 1996 an entire village was washed away.

In former times farmers living high up in the mountains would warn the villagers below with a series of rifle shots as the wadis began to run. Nowadays there is a sophisticated weather forecasting system. But, as Dutco Balfour Beatty Construction Group Civil and Roadworks divisional manager Wail Farsakh reminisces, evacuating an entire earthmoving fleet from the bed of wadi in just one hour still presents a certain challenge when the rainfall is forecast to render the protective bunds ineffective.

The contractor has been working in the area since the end of 2001 constructing a series of recharge dams (25 in all) designed to trap the precious water. The dams are being financed by the Ruler of Abu Dhabi, His Highness Sheikh Zayed bin Sultan al Nahyan, president of the UAE.

Designated client is the Agriculture & Fisheries Ministry of the UAE which is responsible for upkeep and maintenance.

The beneficiaries are the local farming communities who pump the groundwater to irrigate their land which is highly fertile thanks to the silt brought down by the water flow. Design has been carried out by Ingema, the consultancy arm of Morocco's General Directorate of Water Engineering.

The five dams built by the group near Hatta in the Emirate of Al Khaimah are straightforward earthfill structures with a concrete crest and rock armour facing. Capacity of the largest, Al-Quor is 584,000m 3and Al Tawa 520,000m 3.Loss and Munai were variations to the original three dam contract. Villagers had dumped material across the beds of the wadis to form makeshift bunds which have now been fully engineered.

All materials were won locally with earthmoving equipment and a grizzly installed in the bed of the wadi. Much of it proved to be of excellent quality Farsakh reports. Rock armour was supplied by a local quarry.

In addition to the dams, the contractor constructed access roads, some of which were extended to serve local communities. Mechanical work was subcontracted and a network of observation wells linked by satellite allows the Agriculture Ministry to monitor the system.

The structures may be simple, but the standard of finish is high.

All access areas are block paved with contrast detailing, sometimes incorporating the name of the dam in Arabic or English.

Work on the Al Khaimah dams was completed by September 2002, three months ahead of schedule. An indication of just how valuable the dams are was given a few months later when two hours of rainfall filled Tawa to a depth of 2.5m.

The team has now moved to the Emirate of Fujairah where it is in the final stages of its latest contract for four dams. These include the area's first rollcrete structure - which nestles elegantly in its picturesque mountain location. There were also two barriers. One is a simple concrete structure, while the other is stepped and L-shaped and built completely from gabions placed as accurately as if a straight edge had been used.

This was particularly labourintensive, says project manager Tarek Hatahet. At one stage there were 500 men placing and filling the gabion baskets.

Part of the current work addresses concerns that water trapped by the dam at Wadi Ham (one of the largest wadis in the region) might be channelled towards the sea, and thus lost to the local farmers.

After a number of tests, concrete outflow channels are being constructed to ensure first that all the water was available for agriculture and secondly that there was no chance of the dam overtopping in freak weather conditions.

The channels direct surplus water to two further recharge facilities, 950m away in one direction and 1,300m in the other. A cover will reduce evaporation, which can be as much as 100mm/day during August, Hatahet explains, and protect it from falling rock and scree.

Port paving

Expanding the container terminal at Jebel Ali port, Dutco Balfour Beatty Construction Group is back at the site where the two companies first worked together. The contractor moved on site in the middle of September 2002 and was due to hand over 50% of the new area to the client, Dubai Ports Authority, by the end of January 2003, completing the whole extension by 26 May.

The contract involves 225,000m2 of block paving and a 325m extension of the quay wall crane rail gallery, plus the placing of 9km of RTG ground beams for the rubber tyred gantry cranes.

'It's nothing really difficult or technically sophisticated, ' says project manager Bert van Dokkum. The problems, he says, lie with the tight time scale (effectively less than nine months) and the logistics of supplies.

The quay wall is a mass concrete gravity structure backed by rockfill. Extending the usable area involves demolishing the top block of the wall and casting a new one with a services gallery running immediately behind, plus providing foundations for the rails on which the dock cranes run.

Van Dokkum has devised a travelling shutter for the services gallery which has speeded up the operation, with further mechanisation in the form of two specialist block laying machines. Ground preparation involved a sizeable muckshift with 190,000m3 of excavation and 125,000m3 of backfill.

Machine block laying is rare in the region, but the group's investment in two German Optimas units has proved highly successful. Preparation involved intensive discussions with block suppliers and the client's engineer, Scott Wilson Kirkpatrick about the way the blocks were to be positioned on the delivery pallets. For technical reasons, Scott Wilson Kirkpatrick wanted to avoid the use of L-shaped blocks. An acceptable solution was eventually found but four blocks still have to be removed by hand from every pallet.

Some hand laying is still required and with no storage on the dock, deliveries are on a just in time basis.

Even so, some 1,500m 2of paving is being laid every day, brought into use for container storage almost as soon as it is completed, so great is the demand for space in the port.

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