Abstract
The Kingdom of Saudi Arabia is the largest producer of desalinated water with about 13% of the global desalination capacity. Most of these desalination plants use the open-ocean intakes to deliver raw seawater to the desalination facility. Recently, some of the private desalination plants have shifted to subsurface intake systems, either wells or galleries, in order to obtain better water quality with a minimal environmental impact (e.g. minimal entrainment and impingement). The use of these intake types has improved the raw seawater quality extracted from the Red Sea and Arabian Gulf, providing better protection for the membrane component by eliminating/reducing algae, bacteria and organic matter concentrations from the seawater source. One of these desalination plants is located south of Jeddah city which is the second largest city in Saudi Arabia. The plant shifted from an open-ocean intake to beach wells to improve the water quality at the site. Currently, the plant employs 10 vertical wells to extract enough water to produce 10,000m(3)/d of product water via the reverse osmosis process. Studies show that quality of seawater significantly improved after shifting to the well system. The use of a larger capacity well system or a seabed gallery intake was investigated at this site for a proposed additional 20,000m(3)/d future expansion of the facility. More than 60 sediment samples were collected from the seabed along five different transects in an area of 25,000m(2), starting from shoreline and moving seaward. Grain size analyses, hydraulic conductivity and mud percentage were analyzed in order to determine the characteristic of marine sediments at the studied site. The marine bottom at the selected site contains carbonate sediments which have a high potential of reducing the natural organic matter concentration in the raw seawater. In this study, the laboratory measurements showed that this site has low mud content and moderately high hydraulic conductivity, which make it feasible for seabed gallery construction as an intake. It is concluded that use of a seabed gallery intake for the future expansion will overcome the problem of limited water capacity produced by individual wells, but additional alignments of wells is also technically feasible.