Water movement in Exmouth Gulf

Water movement, due to tides and surface waves, is the basic forcing mechanism for nutrient fluxes, sediment dynamics and the fate of pollutants within the Exmouth Gulf. The dominant hydrodynamic process in this shallow basin is tidal motion, with a predominant semi-diurnal constituent. Large surface waves are only generated during tropical cyclones but their development is limited by water depth and bottom friction. Therefore, our hypothesis is that long-term water mass balance is predominantly governed by tidal motion and wind-induced currents. To estimate the water mass balance within the Gulf, field observation and numerical modelling were carried out in parallel. During the first stage of the field study, waves, wave-induced velocities and tidal elevations were measured at various locations in the Gulf. This study revealed that outside of cyclone episodes, wind-generated waves are only important at the entrance to the Gulf and wind-induced velocities are less than 0.5 m sec-'. The second stage of the field study involved measuring water velodties along sixteen transects widely distributed throughout the Gulf. Both vertical and horizontal velodties were recorded from the surface to the bottom at a resolution of 0.25 metres, every 10 seconds. Tidal elevations were aiso observed at two locations. The data collected during the field studies are now used for calibration of a computer model of tidal circulation in the Gulf. It is expected that this model will provide a long-term water mass balance for the Gulf and quanhfy the net fluxes of various suspended organic and non-organic substances into and out of the Gulf. The distribution of water flow intensity, also provided by the model, will indicate areas of potential erosion and areas vulnerable to potential pollution.

受潮汐与表面波浪驱动的水体运动，是埃克斯茅斯湾（Exmouth Gulf）内营养盐输运、沉积物动力学过程以及污染物归宿的核心强迫机制。该浅海盆地的主导水动力过程为潮汐运动，其以半日潮分潮为主要分量。大型表面波浪仅在热带气旋期间生成，但其发展会受到水深与底摩擦的限制。据此，本研究提出假设：埃克斯茅斯湾的长期水团平衡主要由潮汐运动与风致海流主导。为估算海湾内的水团平衡，本研究同步开展了现场观测与数值模拟工作。现场研究第一阶段，团队于海湾内多个测点开展了波浪、波浪诱导流速以及潮位的观测。本阶段观测结果显示，在非气旋事件期间，风生波浪仅在海湾入口处具有显著影响，且风致流速小于0.5 m·s⁻¹。现场研究第二阶段，团队沿遍布海湾的16条断面开展了水体流速观测，观测覆盖从表层至底层的垂向与水平流速，采样间隔为10秒，垂向分辨率为0.25米。研究团队同时在两个测点开展了潮位观测。现场观测获取的全部数据，现已用于校准海湾潮汐环流的数值模型。预期该模型可输出海湾的长期水团平衡结果，并量化各类悬浮有机与无机物质进出海湾的净输运通量。模型同时输出的水流强度分布，可用于识别潜在侵蚀区域与易受污染影响的敏感区域。