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84 4. SALINE WATER INTAKES AND PRETREATMENT
Onshore intakes in natural or artificial enclosures are typically well protected against wave and wind action and therefore have more consistent water quality. However, one such intake location is that the embayment accumulates silt and sand, and unless the area in front of the intake is dredged periodically, the intake capacity decreases over time. Dredging operations have both cost and source water-quality implications.
The largest seawater RO-desalination plant with onshore open intake is the 155,000 m3/ day (40 MGD) Point Lisas desalination plant in Trinidad. In this case the intake consists of concrete forebay structure located on the shore of industrial port’s ship turning basin (the Gulf of Paria) and is equipped with coarse and fine screens, and vertical turbine pumps.
Another desalination plant that uses source water from an onshore open intake is the 200,000 m3/day (54 MGD) Carlsbad desalination plant in California, which is the largest SWRO desalination facility in the US and the Western Hemisphere. This plant collects most of its source water from the discharge of the Encina Power Station with which it is colocated (Fig. 4.9).
4.3.2 Offshore Open Intakes
Offshore open intakes are the most commonly constructed type of intakes for medium and large seawater desalination plants worldwide. These surface water delivery systems include the following key components: offshore intake structure (velocity-cap-type inlet structure);
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FIGURE 4.9
1. Intake from lagoon
2. Encina Power Station
3. Intake pumps
4. Desalination process
5. Brine discharge
6. Discharge pond
7. Discharge to ocean
8. Purified water to San Diego
Carlsbad Boulevard
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3
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Pacific Ocean
Agua Hedionda Lagoon
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Segment of 600-mm intake collector screen.
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County Water Authority
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