Strategic reserve

| 16/10/2010 | 0 Comments

Abu Dhabi’s plan to create an emergency water reserve has entered its final implementation phase. By Anoop K Menon

Three — that’s the number of days that Abu Dhabi’s water reserves will last, if the emirate’s desalination plants, its primary source of potable water, ceased producing water due to some emergency. If we were to consider just the population, which, at present, is a little over one million, but projected to increase three times by 2030, three days of reserves would seem to be way too little. And an emergency could be anything, from a war or a major oil spill in the Arabian Gulf to natural disasters like cyclones.

Abu Dhabi’s existing water storage capacity (comprising mainly of surface tanks, reservoirs attached to existing desalination plants and water distribution networks) can hold only two million cubic metres of water, which as Peter Menche, Director of Projects of GTZ-IS, a German government-owned technical co-operation organisation, noted, can barely last three days at current consumption rates.

The near-total reliance on desalination for drinking water (Abu Dhabi’s total desalination capacity is 630 MIGD, while water production stands at 0.8 million m³/day) raises questions over water security, the vulnerability of desalination plants to pollution, environmental and natural disasters, disruption caused by maintenance works or even war, and therefore, guaranteed availability of drinking water to tide over such emergencies.

Among the Gulf Co-operation Council (GCC) countries, if we measured emergency water reserves in terms of days, Kuwait’s is the highest, at five days, while for Qatar, Saudi Arabia, Bahrain, Oman and UAE, it is, more or less, two to three days. In such a context, a strategic water reserve can play a critical role in protecting a country from threats to its water supply. It can also, among other things, be useful in managing ‘peak water’ demand and replenish over- exploited ground water resources.

The population of Greater Abu Dhabi City is expected to touch 3.1 million by 2030, three times the existing number, which will increase the pressure on the emirate’s potable water resources. As per official estimates, per capita water use in the emirate stands at 650 litres/day, not taking into account network losses, estimated to be in the range of 25-30%.

The fact that Abu Dhabi’s emergency water reserve of a mere three days would be totally inadequate in a worst-case scenario served as a major impetus to the strategic water reserve project.

The proposal

GTZ, in partnership with Dornier Consulting, a private-sector consulting, engineering and project management services company from Germany, proposed a strategic water-storage project based on Artificial Storage and Recovery (ASR) to the higher authorities of Abu Dhabi for the first time in 1998. Menche pointed out that the proposal owed its origins to a Groundwater Assessment Project (GWAP), covering the entire Abu Dhabi emirate, contracted to the GTZ-Dornier consortium by ADNOC and the Abu Dhabi government in 1995. “After its completion in 2006, we had full-fledged knowledge of everything related to groundwater resources in Abu Dhabi,” explained Menche. “This project, thus, formed the basis for the ASR proposal, submitted to the higher authorities.”

The biggest advantage of ASR is minimal land requirements, as existing ground water layers are recharged with desalinated seawater. This reduces storage costs and minimises environmental impact compared to alternatives, like building massive surface-storage facilities, based on massive concrete or metal storage tanks. “In case of an emergency,” Menche said, “the stored water in the aquifer can be pumped out, with a basic sub-surface storage facility to enable the process. However, if only surface-storage infrastructure was relied on to build the water reserve, the investment cost would be huge, in the region of $4 billion if not more.” He cited the example of six massive water storage tanks in the Mussaffah area of Abu Dhabi, with a capacity of 45,000 m3 each. To store the quantity of recharged water that the ASR project envisaged, at least 600 such tanks of similar capacity would be required. The construction costs apart, one has to consider O&M costs and manpower costs, all of which would take up the total cost by several notches.

According to an Environment Agency Abu Dhabi (EAD) communiqué, issued in 2009, by choosing the ASR route, the cost of storage was reduced significantly. The use of land for surface-storage facilities was reduced from 250 hectares to 15 hectares, the cost of infrastructure needed to store one gallon of water was reduced from Dh 3.5 to Dh0.8, and the cost of operation and maintenance of storage per gallon decreased from Dh1.5 to Dh0.25.

Moreover, storing water in storage tanks or ground reservoirs for long periods is also fraught with risks from the water becoming stagnant. The water would need to be recycled within the network, or disinfected and refreshed. On the other hand, ASR systems enable multi-year storage and recovery of water in good quality and quantity.

Another alternative considered was the GCC Water Grid, which relies on a network of three large desalination plants, but would cost a whopping $5.3 billion, if not more. Also, the desalination plant network that underpins this grid would be exposed to the same environmental and operational risks, the kind of risks that a strategic water reserve would need to be avoid or insulated against; and one cannot dismiss the huge amounts of energy expended to desalinate the seawater.

Successful pilot

The proposal submitted by the GTZ-Dornier consortium recommended a feasibility study, followed by a pilot. After getting the go-ahead, the consortium carried out the feasibility study during 2001-02, in terms of hydro-geological assessment, water demand analysis, selection of the project site and the planning of the pilot. Following a successful feasibility study, a pilot project was implemented in the western region of Abu Dhabi from 2002 to 2004. In his paper, Strategic Water Reserve: New Approach for Old Concept in GCC Countries, Dr Mohamed Dawoud of EAD writes that a shallow-to-medium-deep aquifer, north of the Liwa Crescent, was selected for the pilot on the basis of the following attributes:

  1. Existence of a large natural fresh groundwater lens (salinity less than 1,500 ppm, partly meeting the TDS-limit of the World Health Organisation (WHO) drinking water standard (1,000 ppm)
  2. Sufficient lateral extension and aquifer thickness
  3. Sufficient depth of groundwater table
  4. Relatively homogenous lithology
  5. Far from already existing well fields
  6. Favourable hydro-chemical conditions.

“The pilot project lasted two years; the first year for planning and constructing the facilities and the second year for testing,” Menche said. Among other things, the consortium successfully tested storage and recovery techniques and evaluated recovery efficiency and reservoir response.

Two basic recharge/recovery schemes were tested — the Well Gallery Scheme (dual purpose wells where water is injected through wells into the sub-surface and, later on, pumped out from the same wells) and the Infiltration Basin Scheme (comprising infiltration basin constructed in the sand and recovery wells. The desalinated water was percolated through infiltration basins into the sub-surface and, finally, into the ground water layer, relying on gravity instead of pumps). In the case of an emergency, extraction is done through normal water wells.

“The pilot project lasted two years; the first year for planning and constructing the facilities and the second year for testing,” Menche said. Among other things, the consortium successfully tested storage and recovery techniques and evaluated recovery efficiency and reservoir response.

Two basic recharge/recovery schemes were tested – the Well Gallery Scheme (dual purpose wells where water is injected through wells into the sub-surface and, later on, pumped out from the same wells) and the Infiltration Basin Scheme (comprising infiltration basin constructed in the sand and recovery wells. The desalinated water was percolated through infiltration basins into the sub-surface and, finally, into the ground water layer, relying on gravity instead of pumps). In the case of an emergency, extraction is done through normal water wells.

The pilot demonstrated that recharging an existing freshwater aquifer with desalinated water and efficient recovery of the same was feasible on a large scale. Based on the results of the pilot project, it was decided that the Infiltration Basin scheme best served Abu Dhabi’s requirements.

“We found the Well Gallery Scheme to be very complicated, needing tremendous amount of maintenance, spare parts and repair, as well as a highly educated and trained staff, which is a tough proposition even worldwide,” Menche explained. With Infiltration Basins, the energy and maintenance requirements were less, as gravity does the bulk of the work; pumps are needed only for taking out the water during an emergency. Because the extraction is done through normal wells, there is no need to invest in dual-purpose wells. “We found Infiltration Basins to be more reliable as a long-term proposition and therefore, sustainable,” Menche said.

In the implementation phase

After extensive discussions, a tender for large-scale artificial recharge was put into the market during 2007-2008. Last month, a joint venture (JV) between Arabian Construction Company (ACC) and POSCO Engineering & Construction Company (POSCO E&C) was awarded the Dh1.6 billion contract for the engineering, procurement and construction (EPC) of a Strategic Water Storage and Recovery System in Liwa.

Under the system, designed by the GTZ-Dornier partnership, an existing ground water layer will be recharged with seven MIGD (over 31,000m³/day) of desalinated seawater through three infiltration basins, over a period of 27 months, resulting in surplus water of 5,753 MIG (26.15 million m3). The recovery rate, in an emergency scenario, would be 40 MIGD or 181,000 m³/day for a period of 90 days, with the total volume recovered being 3,600 MIG or 16.4 million m3, translating into an availability of 182 litres per capita per day.

The desalinated water will be transferred from the Al Mirfa desalination plant situated on the Abu Dhabi coast, transported through a 1,200-diameter pipeline to an existing pumping station in Madinat Zayed, and further pumped down to a location south of Madinat Zayed, from where it will be pumped into the infiltration basin. The total length of all the pipelines constructed for the project will be 161 kilometres.

Apart from the pipelines, other key components of the project include:

  • Three recharge/recovery schemes, consisting of:
    • Three recharge basins
    • 326 recovery wells
    • 117 groundwater monitoring wells for tracking ground water levels, temperature, quality.
  • Pumping stations and treatment facilities
  • Independent process control and instrumentation system

Menche elaborated: “To monitor the hydro-chemistry, all three schemes are surrounded by a ground water monitoring system. We have proposed that the area be demarcated as ground water protection zone. This aspect forms an important part of the initial evaluation process. Are there any industrial or oil & gas activities near the site? Is there scope for agricultural or human interference? This location is pure desert and, hence, very ideal.” The system will also enable close monitoring of the incoming water and the mixing process, so that operators have a complete picture of what is happening with regard to water quality in the sub-soil.

Menche noted that a certain amount of mixing between native water and injected water is expected. He explained: “Water lens or water barrier is not static; it is moving. The water in the aquifer is very salty at the bottom, getting sweeter as you move up. And on the top lies a small lens of drinking water quality. We are essentially topping up the lens.”

Following the award of the contract, the construction and implementation phase is expected to last 30 months, which will be followed by a two-year, operation-and-maintenance phase. “We did the entire planning and design for the project and will supervise all the work till the project is handed over to the client,” Menche said. “It is important to ensure high-quality performance from the contractor, as the three re-charge/recovery schemes constitute the heart of the project.”

Project moments

The feasibility and pilot project stages had their moments. For example, in the course of carrying out GWAP and the ASR pilot, the consortium drilled nearly 10,000 shallow-to-very-deep ground water exploration wells all over the emirate. “The shallowest well was 20 metres deep while the deepest one measured 1000 metres,” Menche said. Extensive ground water modelling was another highlight. “We also developed, in what may be a first for this region, a suitability- evaluation catalogue for selecting an area for ASR projects, factoring in natural resources as well as human, agricultural industrial aspects,” Menche added.

Answering a question of whether the project will go into hibernation once the 27-month re-charge phase is completed, Menche said: “We have proposed to the client that parts of the water could be used for meeting the water needs of the Liwa Crescent area. In such a scenario, the recharging process can be extended beyond 27 months. Internally, we regard this project only as Stage 1 because there is tremendous scope for increasing the aquifer storage capacity through additions.”

Menche pointed out that similar ASR projects have been implemented in other parts of the world on a smaller scale, most notably in Amsterdam, where a coastal aquifer is being recharged, in this case with recycled wastewater. He continued, “We studied experiences from all over the world and tried to optimise them for Abu Dhabi’s environment. The ASR project in Liwa can be replicated in the eastern region, where a pilot had already been implemented. Also, the Liwa project is being closely observed by neighbouring countries, especially Saudi Arabia and Qatar.”

Menche also sees tremendous scope for recharge projects using recycled wastewater in the region. “You can use the ASR method to create sub-surface storage facilities for supply of recycled wastewater to agriculture,” he said. “There is tremendous scope for smaller, isolated recharge projects using recycled wastewater in the MENA region.”

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Category: Features, Water

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