Modeling Selected Water Quality Parameters at Jebel

MARAQA, M. A., ALI, A. and KHAN, N., 2007. Modelling Selected Water Quality Parameters at Jebel Ali Harbour, Dubai-UAE. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 794 – 799. Gold Coast, Australia, ISSN 0749.0208 Jebel Ali Free Zone in Dubai has the largest man-made harbour in the world. Several factors may affect water quality in the harbour, including discharge of treated wastewater, navigational activities, and nearby projects in the Arabian Gulf. The main objective of this study was to simulate the level of BOD and some nutrients in the harbour water under existing and potential future conditions. Modeling of water quality was carried out using the ECO Lab coupled with the advection-dispersion modules in the MIKE21 modeling system. The results showed that the input rates of BOD, ammonia, nitrate and phosphate associated with the discharged treated wastewater are not sufficient to simulate the observed levels of these parameters in the harbour water. Additional input rates of 600 times for BOD and 144 times for nitrate are needed to adequately describe the observed levels of these parameters. An assimilation capacity analysis of BOD in the harbour water revealed that the BOD starts to build up when the BOD loading rate reaches 2.88 g/m/d, which is about 20% higher than the estimated loading rate under the current conditions. Simulations further showed that increasing the organic loading into the harbour will reduce DO and increase ammonia, but will not significantly affect nitrate and phosphate levels in the harbour water. ADDITIONAL INDEX WORDS: Simulation, BOD, Nutrients, MIKE21 ECO Lab INTRODUCTION Jebel Ali Free Zone (JAFZ) in Dubai is a growing industrial park with over 4500 trading, manufacturing, service, and distribution companies. Currently, Jebel Ali Harbour receives discharge consisting of several treated industrial and sewage effluents. Water discharged into the harbour must adhere to the effluent quality criteria set out in the Environmental Requirements established by JAFZ Authority. However, a further expansion of industrial activities may increase discharge flow rates into the harbour. This, in addition to port activities and ongoing and planned projects in the vicinity of the harbour, may increase pollutant loading beyond the capacity of the harbour. Furthermore, future harbour water quality may be negatively affected by the bottle-like nature of the harbour, in which limited mixing takes place. Assessment of harbour water quality is necessary to protect marine life and to minimize the impact of industrial activities on the surrounding ecosystem. In 2004, Maraqa and co-workers started a project to assess the water and sediment quality of Jebel Ali Harbour. MARAQA et al. (2006) developed a hydrodynamic model using MIKE21 (DHI, 2003a) to describe the circulation pattern in the harbour. The authors concluded that the main flow regime in the harbour follows alternate paths during flooding and ebbing, creating eddy-like circulations in net flow distribution. MARAQA et al. (2006) further developed an advection-dispersion model using MIKE21 (DHI, 2003b) to describe the transport of solutes in the harbour. The authors found that the flushing time of a conservative tracer discharged into the harbour varies from a few months to several years depending on the discharge location. This study expands on the work of MARAQA et al. (2006) and uses the ECO Lab module of the MIKE21 modeling system (DHI, 2003c) to assess harbour water quality. One of the objectives was to investigate the ability to simulate selected water quality parameters with respect to input rates from the known discharge locations. Another objective was to use the developed water quality model of Jebel Ali Harbour to determine changes in water quality parameters when the loading rate of discharged organic matter increases or decreases.