Author(s): Aaron C. Chow; E. Eric Adams; Bader Al-Anzi; Khawla Al-Shayji; Tanuspong Pokavanich; Yousef Al-Osairi; Robin Morelissen; Wilbert Verbruggen
Linked Author(s): Robin Morelissen
Keywords: Desalination; Dilution; Far field; Arabian gulf; Puff modeling; Delft3D
Abstract: Brine discharges in the Arabian Gulf from desalination plants are challenging from the point of view of dilution because the Arabian Gulf is a shallow (mean depth of about 35 m), reverse tidal estuary with only one outlet available for exchange flow (the Strait of Hormuz), located up to 1000 km downcoast from the discharge. Brine discharges typically contain excess salinity (up to 70,000 ppm), excess temperature (about 5 - 15 degrees Celsius warmer than ambient seawater for multistage flash desalination plants), and contaminants such as heavy metals and organophosphates. We present three far field dilution models, of increasing complexity, to analyse the potential dilutions achievable from discharge locations in the Northern Arabian Gulf, with a focus on an offshore discharge location near Kuwait (located about 900 km from the Strait of Hormuz). The first and simplest far field model is a box model that assumes that the discharge is well mixed over a tidal excursion, and assumes a constant depth and a contaminant with one first order decay coefficient. The second model of intermediate complexity is a reverse Gaussian puff model which simulates the discharge over multiple tidal cycles, using time series data spanning about a month from a single moored current meter. Again, a water body of constant depth and a contaminant with one first order decay coefficient are assumed. The third model – the most complex – is a 3-dimensional finite difference hydrodynamic model (Delft3D) that uses measured bathymetry data, meteorological and tidal forcings, as well as freshwater riverine inflows into the Gulf to simulate circulation patterns in the Gulf. The simulated circulation patterns within the Gulf are employed to determine the spatial concentrations distributions (and therefore dilutions) of brine discharges from a selected number of discharge locations. We compare the predicted far field dilutions within the Arabian Gulf) from the three models described. The comparison is used for two objectives: the first is to identify ambient conditions (such as the relative magnitudes of the residual and the tidal currents) that have the greatest impact on the far field dilution. The second is to determine conditions (e.g., distance offshore) under which the simpler models (that are computationally much cheaper) may be used to adequately predict the local dilution.