Why are beach wells sometimes preferred over open intakes for seawater desalination?

Beach wells are sometimes preferred over open intakes for seawater desalination primarily because they provide a natural pre-filtration mechanism, resulting in higher feedwater quality and reduced pre-treatment requirements. Open intakes directly draw seawater from the ocean, which can contain high levels of suspended solids, organic matter, algae, and other contaminants. This requires extensive and costly pre-treatment processes, such as screening, coagulation, flocculation, and filtration, to protect the desalination membranes from fouling. In contrast, beach wells extract seawater that has naturally filtered through the sand and gravel aquifer beneath the beach. As seawater percolates through the subsurface, the porous media act as a natural filter, removing a significant portion of the suspended solids and organic material. This natural filtration reduces the turbidity and Silt Density Index (SDI) of the feedwater, which are critical parameters for RO membrane performance. Lower turbidity and SDI mean less fouling of the RO membranes, leading to longer membrane life, reduced cleaning frequency, and lower operating costs. Additionally, beach wells can provide a more stable water temperature compared to open intakes, which are subject to seasonal temperature fluctuations. Stable temperature improves the consistency and efficiency of the desalination process. Furthermore, beach wells often have a lower environmental impact on marine life compared to open intakes, which can entrain or impinge marine organisms, especially larvae and small fish. Beach wells draw water from the subsurface, minimizing direct impacts on marine ecosystems. However, the suitability of beach wells depends on the local hydrogeology and the availability of a sufficient aquifer with adequate hydraulic conductivity to supply the required feedwater flow rate.