The hydrodynamics of Dickson Inlet, Port Douglas, north Queensland

The major part of this study was carried out in the wet season, during a very high spring tide period (14-17 February, 1989). A further, more limited study was carried out in the dry season (October 11-13, 1989).In February 1989, the AIMS research vessel, RV Harry Messel, was moored on two piles near pile No 14 (on the edge of the deep channel), about 100 m upstream from the marina near the mouth of Dickson Inlet. Water depth at low tide was 3.2 m under the research vessel. The following oceanographic equipment was deployed, suspended from a boom pointing towards the thalweg of the main channel:1. a bottom-mounted Aanderaa sea level recorder. Sea level and water temperature were recorded every 5 minutes.2. two Inter-Ocean model S4 vector-averaging current meters, suspended 0.8 and 2.5 m below the surface, recording every 5 minutes. 3. a string of 6 Analite optical fiber nephelometers recording averaged turbidity at each sensor every 2 minutes. The nephelometers were spread uniformly from the surface down to 3.2 m below the surface. 4. a very high-frequency (210 kHz) Deso 10 acoustic sounder. This instrument was turned on for a few minutes every half hour during the sampling period.Vertical profiles of temperature, salinity and turbidity (using the AIMS 'mud probe')were obtained hourly for one tidal cycle (the largest tidal range during the study) at the mooring site. Approximately 50 profiles of turbidity, salinity and temperature were obtained along the estuary and its principal drainage creeks at high and low water. The high frequency Deso 10 acoustic sounder was also used during some of these observations. The datum for tidal data was obtained by comparison of observations with those of the Department of Harbours and Marine from their tide gauge for the high tide (2.84 m) of 17 February 1989 am. Depth was measured on 30 cross-sections across Dickson Inlet and its main drainage creeks, with surveys spanning from bank to bank. These data were referred to datum.At high tide on 16 February 1989 a survey of temperature, salinity and turbidity in Muddy Creek north of Dickson Inlet was undertaken. It was not possible to study this creek at low tide because its mouth is blocked by a sand bar.During the dry season field study a boat was moored in the main channel across the current. Two Inter-Ocean vector-averaging current meters were deployed at mid-depth from the bow and the stern of the boat for one tidal cycle at site W1. At half-hourly intervals during that tidal cycle, vertical profiles were obtained of temperature, salinity and turbidity using the AIMS 'mud probe'.Near slack high tide and slack low tide, when currents were minimal, vertical profiles of salinity, temperature, turbidity and dissolved oxygen were measured at 11 stations (W1-W11) along Dickson Inlet and two mangrove creek tributaries. Each survey took almost exactly one hour, so that the measured, distributions of these parameters were essentially synoptic. While the CTD allowed for measurements of temperature and salinity all the way to the bottom, the dissolved oxygen probe had only a 3 m long lead so that dissolved oxygen profiles could be measured to 3 m depth only. This restriction means that at high tide bottom waters could not be sampled. However, at low tides all the water column in Dickson Inlet could be readily sampled for dissolved oxygen except only at the bottom of some of the occasional deep holes in Dickson Inlet.Tidal data were taken from tidal predictions. The current meter data were decomposed into the longitudinal current (along the channel axis) and the transverse current (perpendicular to the bank; hence reflecting the secondary circulation in a cross-section). The aim of the wet season sampling was to collect data on the tides, currents, water temperature, salinity and turbidity in Dickson Inlet, so that the hydrodynamics could be modelled and predictions made about the influence of mangrove forest removal on sedimentation patterns. In addition, the approximate residence time of water in the Inlet could be calculated, and predictions made of the effect of pollutants in the creek/forest system.The dry season field study was aimed at obtaining current meter data to verify the numerical model and measuring the distribution of salinity, temperature, turbidity and dissolved oxygen in Dickson Inlet, to assess trapping and possible pollution impact of mangrove land reclamation. This study of the hydrodynamics of Dickson Inlet was undertaken as part of the Marine and Estuarine Studies section of the Port Douglas and Environs Planning Study, in accordance with the brief from the Premier's Department, through Environment Science and Services. Survey data in the swamps were obtained from Mr Ben Cropp, who obtained water data along the new road to the Mirage spoil dump, at slack tide during the very high spring tide (3.1 m) a week before our trip. We were also given access by Mr Cropp to an earlier detailed survey map showing some bathymetric contours in the mangroves. These data were referred to datum.

本研究的主体工作于湿季开展，时段覆盖1989年2月14日至17日的极高春汛期间。另有一项规模有限的补充研究于干季进行，时段为1989年10月11日至13日。

1989年2月，澳大利亚海洋科学研究所(AIMS)的"Harry Messel"号研究船(RV Harry Messel，RV为Research Vessel的缩写，即研究船)系泊于14号桩附近的两根桩柱上，站位紧邻深槽边缘，距离迪克森湾(Dickson Inlet)河口附近的游艇码头上游约100米。该研究船下方的低潮水深为3.2米。本次研究布设了以下海洋观测设备，均通过指向主航道深泓线的吊臂悬挂部署：
1. 海底式安德拉海平面记录仪(Aanderaa sea level recorder)：每5分钟记录一次海平面与水温数据。
2. 两台Inter-Ocean S4型矢量平均海流计(Inter-Ocean model S4 vector-averaging current meters)，分别悬挂于水面下0.8米与2.5米处，每5分钟采集一次数据。
3. 一套由6台Analite光纤浊度计(Analite optical fiber nephelometers)组成的观测链，均匀布设于水面至水下3.2米的深度区间内，每2分钟记录各传感器的平均浊度值。
4. 超高频率（210 kHz）Deso 10型声学剖面仪(Deso 10 acoustic sounder)：采样时段内每半小时开机运行数分钟。

在锚泊站位，于本研究期间最大潮差的一个潮汐周期内，每小时获取一次温度、盐度与浊度的垂直剖面数据，数据采集采用AIMS"泥浆探针"设备。在高潮与低潮时段，沿迪克森湾及其主要排水溪流共获取约50组浊度、盐度与温度剖面数据。部分此类沿岸调查中，也使用了前述高频Deso 10型声学剖面仪。

潮汐数据的基准面通过比对本研究观测结果与港口与海事部门潮位站数据确定，该站1989年2月17日上午的高潮位为2.84米。研究团队对迪克森湾及其主要排水溪流的30条断面开展了全断面水深测量，测量覆盖从一岸至另一岸的全部水域，所有水深数据均以该基准面为参照。

1989年2月16日高潮时段，研究团队对迪克森湾北侧的马迪溪(Muddy Creek)开展了温度、盐度与浊度调查。因该溪流河口被沙洲阻塞，无法在低潮时段开展该溪流的观测工作。

干季野外研究中，一艘船只系泊于主航道内横对海流的位置。在W1站位，于一个潮汐周期内，从船首与船尾的中深度位置各部署一台Inter-Ocean矢量平均海流计。该潮汐周期内每半小时，采用AIMS"泥浆探针"获取一次温度、盐度与浊度的垂直剖面数据。

在涨憩潮与落憩潮（潮流流速极小的时段），沿迪克森湾与两条红树林溪流支流的11个站位（W1至W11）测量了盐度、温度、浊度与溶解氧的垂直剖面数据。每次调查耗时恰好约1小时，因此测得的各参数分布基本为同步的瞬时观测结果。尽管温盐深仪(CTD，Conductivity, Temperature, Depth)可测量从表层至海底的温度与盐度，但溶解氧探头的缆线仅长3米，仅能获取至3米深度的溶解氧剖面。这一限制意味着高潮时段无法采集底层水样，但在低潮时段，迪克森湾内除少数偶发深洞的底层水域外，整个水柱均可便捷地采集溶解氧样本。

潮汐数据取自官方潮汐预报值。海流计数据被分解为纵向海流（沿航道轴线方向）与横向海流（垂直于岸线方向，反映断面内的次级环流）。

湿季采样的核心目标为收集迪克森湾的潮汐、海流、水温、盐度与浊度数据，以便构建水动力模型并预测红树林移除对沉积模式的影响。此外，还可计算该湾内水体的近似滞留时间，并预测溪流-森林系统内污染物的扩散影响。

干季野外研究的目标为获取海流计数据以验证数值模型，并测量迪克森湾内盐度、温度、浊度与溶解氧的分布，以评估红树林围垦活动的淤积效应与潜在污染影响。

本迪克森湾水动力学研究作为《道格拉斯港及周边区域规划研究》中海洋与河口研究部分的内容开展，依据昆士兰州总理府通过环境科学与服务部门提出的任务要求实施。沼泽区域的调查数据来自本·克罗普(Ben Cropp)先生，其于我们行程前一周的极高春汛（潮位3.1米）憩潮时段，沿通往米拉奇废料堆放场的新道路沿线采集了水体数据。克罗普先生还允许我们使用其早年获取的一份详细测绘地图，该地图标注了红树林区域内的部分水深等深线。所有此类数据均以前述基准面为参照。