Modelled flood plumes - central and northern Great Barrier Reef

MECCA - a verified 3-dimensional hydrodynamic model was used to simulate river plume dynamics.Model simulations were compiled to examine the intensity, duration and frequency of different lower salinity events. Return periods were then calculated from the annual frequency of such events.The model was forced using daily river discharge data and time-series wind observation data. A mixing parameter was used to simulate tidal forcings. Use of computer simulation to understand the fate of riverine water as it mixes and moves around with the currents and winds.Used to quantify the connectivity between coastal runoff and the central and northern GBR.The simulations demonstrate a range of common spatial patterns and unusual events that can be expected from a dynamic process. Using this information a risk assessment using return period analysis of the frequency of different impact events can be undertaken to identify 'high-risk' regions or reefs.Environmental managers can use analyses based on the model for risk assessment on implications for dilutions and residence times of dissolved and suspended material carried within catchment runoff, as well as identifying potential plume pathways and travel times for the runoff and its contents to reach reefs. The model has been used for flood plume analyses on the Burdekin River (1966 - 1995); the Burdekin, Herbert, Tully, Johnstone, Russell, Barron, Daintree, Endeavour, Jeannie and Normanby Rivers (1969 - 1998); and the GBR lagoon.The database for analysis by the model created includes information on the duration of exposure to fresh water (exceedance), the minimum salinity and the return periods for the modelled domain.Wind data (recorded every 3 hours) was obtained from the Mackay weather station (just south of model domain) for the period 1966-1991, and from the AIMS weather stations for the period 1992-1998. Daily discharge data from the rivers was obtained from the Queensland Water Resources Commission. Tidal influences were included implicitly via the mixing parameters based on the work of King and Wolanski (1996). Thus these data can be applied to the model to simulate any of the major flood events of the rivers in this region over the last 30 years. The model has subsequently been run for the 2008 flood period.本研究采用经过验证的三维水动力模型MECCA模拟河流羽流动力学。通过整理模型模拟结果，分析不同低盐度事件的强度、持续时长与发生频率，并基于此类事件的年发生频率计算其重现期。该模型以逐日河流径流数据与时序风速观测数据作为强迫场，并通过混合参数模拟潮汐强迫作用。本研究借助计算机模拟，探究河流水体在流场与风场作用下混合、运移的归宿过程，可用于量化沿海径流与中北部大堡礁（Great Barrier Reef, GBR）之间的连通性。模拟结果揭示了该动力过程下常见的多类空间分布模式与异常事件。基于上述结果，可通过对不同影响事件的频率开展重现期分析完成风险评估，从而识别“高风险”区域或珊瑚礁。环境管理人员可依托该模型的分析结果开展两类风险评估：一是评估集水区径流携带的溶解态与悬浮态物质的稀释过程与滞留时间的影响；二是识别径流及其携带物质抵达珊瑚礁的潜在羽流运移路径与传播时长。该模型已被用于以下区域的洪水羽流分析：1966年至1995年的伯德金河；1969年至1998年的伯德金河、赫伯特河、塔利河、约翰斯通河、拉塞尔河、巴伦河、丹特里河、恩迪沃弗河、珍妮河与诺曼比河，以及大堡礁潟湖。本研究所构建的模型分析数据库，涵盖模拟区域内淡水暴露时长（超标时长）、最低盐度以及各事件重现期等信息。1966年至1991年的每3小时一次的风速观测数据来自模型区域南侧的麦凯气象站，1992年至1998年的数据则来自澳大利亚海洋科学研究所（Australian Institute of Marine Science, AIMS）气象站；逐日河流径流数据由昆士兰州水资源委员会提供。本研究基于King与Wolanski（1996）的研究成果，通过混合参数隐式引入潮汐影响。因此，上述数据集可输入模型，模拟该区域过去30年间该区域河流发生的任一大型洪水事件；后续该模型还被用于2008年洪水时段的模拟。