High-Resolution Ocean Model Simulations of the Dispersion of Desalination Discharge Brines from Multiple, Large-Scale, Coastal Facilities Located in Relatively Close Proximity

In recent years Israel has become a world leader in the technology and use of desalination to supplement the meager and dwindling natural fresh water supplies which are further stressed due to increasing population as well as the projected warming and drying of the region. Today nearly 50% of the water consumed in Israel is supplied from desalination. Five desalination facilities located in a 90 km section along the coast produce nearly 90% of this amount through desalination of seawater (currently ~600 MCM/yr, but expected to increase to over 700). A roughly equivalent amount of reject brine with salinity nearly twice that of the intake seawater is discharged back into the sea. In order to assess the dispersion and potential long term, cumulative effects of the discharge brine, a series of high spatial resolution simulations were conducted with a three dimensional ocean circulation model run for a period of five years. Three of the five outfalls are subsurface and located ~1.5 km offshore. The other two surface discharges are mixed with cooling water from adjacent power plants and diluted in ratios of between 4:1 and 8:1. The model domain covers a 200 km section of the coast and extends seaward to include the entire continental shelf and slope as well as part of the adjacent deep sea. The horizontal resolution is ~450 m and the entire water column is divided into 30 unevenly spaced sigma-layers. Surface forcing is extracted from the 6 hourly NCEP CFSR reanalysis while the initial and lateral boundary conditions are taken from the daily Copernicus/MyOcean Mediterranean Sea reanalysis. Our preliminary results indicate that: (1) multiple discharges can potentially cause a small, gradual but noticeable increase in the near bottom salinity in the southern half of the inner shelf; (2) in summer the brine is mainly transported to the north following the prevailing along slope current; (3) in winter and in the transition seasons the brine is more likely to be transported across the shelf and downslope: and (4) discharges diluted with cooling water from power plants appear to mix and disperse more effectively than the subsurface brine discharges.