Ord River and Cambridge Gulf hydrodynamics and sediment movement study, Western Australia

In August 1999, a preliminary field trip was undertaken to study the sediment dynamics of the East and West Arms of Cambridge Gulf. A self-logging Analite nephelometer was deployed for 6 days during spring tides, attached near low tide level at a pile of the Wyndham Harbour jetty in the West Arm. Tide gauges were bottom deployed for 2 days at 3 stations in the East Arm during spring tides and Analite nephelometers were also deployed at two of these stations for the same period. In the thalweg of both the West and East Arms, vertical profiles of currents, temperature, salinity and suspended sediment concentration were obtained hourly from a small boat at anchor for 13 h in the West arm and 10 h in the East Arm. In the West Arm, a Seabird CTD with Analite nephelometer attached was bottom deployed along the sloping banks during the passage of a tidal bore. Photographs of flocs of suspended matter in near surface waters were obtained during CTD stations in both the West and East Arms. Two additional samples were collected in King River estuary south of Wyndham. Floc size data for near bottom waters were also obtained during the 13 h tidal station in the West Arm. The bathymetry of cross-sections of the East Arm was measured using an echo sounder. Two aerial surveys were completed, once during low tide and once over the tidal bore.In December 1999, tide gauges were deployed in the East Arm for two days at 2 sites, which were last surveyed in 1969. The bathymetry of a cross-section of the estuary, which was also last surveyed in 1969 was resurveyed using an echo sounder.In June 2000, work continued in the East Arm, with several cross-sections across the estuary completed in upstream locations. Two Aanderaa tide gauges were also deployed to study the tidal bore observed on a previous trip.In September/October 2000 (dry season), four moorings were deployed in the East Arm and in Cambridge Gulf. Various instruments were attached to these, which included nephelometers, InterOcean S4 current meters, Dataflow temperature and salinity loggers and tide gauges. CTD casts were made at moorings and other locations within the estuaries. From the 24th October to 6th November 2000, a second field trip was undertaken to retrieve instruments and additional CTD casts were made. During this trip two frames, with a similar range of instruments were deployed for 5 days.In December 2000, a CTD survey of the King River and the West Arm was carried out.In January 2002 (wet season), in a similar program to September/October 2000, a further 5 moorings were deployed in the West Arm and in Cambridge Gulf. The instruments were recovered approximately 1 month later. CTD casts were also done.
This field and model study of the water and fine sediment dynamics of both the West and East Arms of the Cambridge Gulf was undertaken to determine the impacts of increased sediment runoff due to land clearing and the suppression of river floods by damming of the Ord River on the physical features of the Ord River estuary. At the time that this research was undertaken, the Marine Parks and Reserves Authority of Western Australia had identified Cambridge Gulf and its adjoining estuarine systems as worthy of investigation for suitability as a marine reserve.
Cambridge Gulf has two estuaries, the West and East Arms. The West Arm, is the estuary of the mostly undisturbed Durack, Pentecost and King Rivers. The East Arm is the estuary of the Ord River and flows are affected by land clearing and two dams constructed between 1969 and 1972. The only natural river flow in the East Arm is from the Dunham River, a small tributary of the Ord River, downstream of the dams. The bathymetry of the West Arm during the last 111 years was obtained from bathymetric charts of the Royal Navy before 1900, of the Royal Australian Navy before 1960 and after that from annual surveys by the Western Australia Department of Transport.

1999年8月，为研究剑桥湾（Cambridge Gulf）东西两支的沉积物输运动力学，开展了初步野外考察。本次考察在西支温德姆港（Wyndham Harbour）码头的桩柱近低潮位处布设一台自记式Analite浊度计（nephelometer），在大潮期间连续运行6天。大潮期间在东支的3个站位布设了底置式潮位计（tide gauge），持续运行2天；同时在其中2个站位同期布设了Analite浊度计。在西支和东支的深泓线（thalweg）处，通过锚泊小艇每小时获取一次海流、温度、盐度及悬浮泥沙浓度的垂直剖面数据：西支观测时长13小时，东支为10小时。在西支的潮汐涌潮（tidal bore）过境期间，沿倾斜岸线布设了一台搭载Analite浊度计的Seabird温盐深仪（CTD, Conductivity Temperature Depth），采用底置式部署。在西支和东支的CTD观测站位处，获取了近表层水体悬浮絮凝体（flocs）的照片。在温德姆以南的金河（King River）河口额外采集了两份样品。在西支13小时的潮位观测站位处，同时获取了近底层水体的絮凝体粒径数据。采用测深仪（echo sounder）测定了东支各断面的水深地形。完成了两次航空勘测：一次在低潮时段，另一次在潮汐涌潮过境期间。

1999年12月，在东支最后一次勘测于1969年的2个站位布设潮位计，持续运行2天；同时采用测深仪对该河口最后一次勘测于1969年的某一断面进行了重测。

2000年6月，东支的野外工作持续开展，在河口上游区域完成了多条断面的勘测；同时布设2台Aanderaa型潮位计，用于研究此前考察中观测到的潮汐涌潮。2000年9月至10月（旱季），在东支及剑桥湾内布设了4套锚系观测站（moorings），搭载的仪器包括浊度计、InterOcean S4型海流计、Dataflow型温盐记录仪及潮位计；在锚系站位及河口内其他点位开展了CTD站次观测。2000年10月24日至11月6日，开展第二次野外考察以回收仪器设备，并额外开展了CTD站次观测；本次考察中还布设了2套搭载同类仪器的观测架，持续运行5天。2000年12月，对金河河口及西支开展了CTD勘测。

2002年1月（雨季），参照2000年9-10月的考察方案，在西支及剑桥湾内额外布设了5套锚系观测站，仪器约1个月后完成回收；同时开展了CTD站次观测。

本次针对剑桥湾东西两支水体及细颗粒泥沙输运动力学的野外与数值模拟研究，旨在明确土地开垦导致的悬浮泥沙径流增加，以及奥尔德河（Ord River）筑坝拦洪对奥尔德河河口物理特征的影响。本研究开展期间，西澳大利亚海洋公园与保护区管理局已将剑桥湾及其毗邻河口系统列为评估海洋保护区适宜性的重点调查对象。

剑桥湾包含两个河口分支：西支与东支。西支为基本未受干扰的杜拉克河（Durack River）、五旬节河（Pentecost River）及金河的河口系统；东支为奥尔德河河口，其径流受土地开垦及1969年至1972年间修建的两座水坝影响。东支仅存的天然径流来自奥尔德河大坝下游的小型支流邓纳姆河（Dunham River）。

西支近111年的水深地形数据来源如下：1900年前采用英国皇家海军的海图，1960年前采用澳大利亚皇家海军的海图，1960年后则采用西澳大利亚州交通运输部的年度勘测数据。