The migration of large-scale bed forms in an estuarine environment: observation and parameterisation for coastal area modelling

上下文在2025年海洋方案中，该提案的主题涉及：大陆架和沿海过程：13“利物浦湾和邻近河口的形态建模”。它主要适用于WP 3.5“海岸形态动力学和水深演变”，同时也有助于WP 9.1“评估和提高陆架海模型的准确性”。此外，该奖学金将为NERC资助的FORMOST项目增加重要价值（NE/E015123/1，2008-2010年，涉及班戈尔大学和POL），其目的是（一）扩大POL在泥沙输运研究方面的实地观测能力，（二）根据班戈尔的泥沙输运模型，这将在两个沿海地区模型（Telemac和POLCOMS）中实施。Telemac系统已经升级，包括班戈尔模型的参数化版本，这将通过FORMOST作为数据解释的工作工具提供给学生。此外，FORMOST期间将在POL海岸观测站范围内的迪河口外航道获得新的实地数据，为学生提供背景资料。背景大规模沉积特征（沙波、岸和沙坝）的迁移对海底的形态演变有重大贡献。这些特征在沿海沉积物输运模型中没有得到解决，从而导致形态结果的不确定性。该项目将侧重于迪河口大规模河床特征的流动性和迁移，主要从观测角度研究关键的物理过程，但包括一个建模元素，可以对实验结果进行知情解释。从气候变化背景下的管理观点来看，了解迪伊河等河口作为移动的沉积物的源或汇的作用至关重要。2007年夏季，使用POL的X波段雷达进行了一项试点研究（班戈尔大学理学硕士项目，由POL联合监督），研究结果表明，大规模的沙特征正在向位于希尔布尔岛和维拉尔大陆之间的潮间带的迪河口推进。更一般地说，POL的雷达能够监测半径为4公里的河床形态的运动，它揭示了大的沙子特征也正在向更深的水域进入河口。然而，目前尚不清楚的是，各大河床形态对迪河口沉积物收支的相对贡献。该奖学金的具体目标是：（i）跟踪希尔布雷岛附近潮间带的沙丘，从而阐述2007年试点研究的结果。这将突出波浪和水流对净沉积物输送的作用。对结果的解释将包括现场测量条件的Telemac模拟。(ii)利用X波段雷达跟踪河口中部深水区沙洲和沙丘的运动。将通过现有/新的ADCP数据和模型进行解释。Telemac（可能还有POLCOMS）将用于建立负责形态变化的“驱动程序”。(iii)以货车Rijn（2005年）的粗糙度公式为起点，建立一种在沿海地区模型中纳入大尺度河床特征的方法，将其引入Telemac，并严格测试其对Dee河床形状的影响。最终用户。博士课程将与关心Dee管理问题的最终用户相关。例如，威尔士农村委员会（CCW）以及环境局（EA）将出席FORMOST项目会议，学生将为此做出贡献。这项研究还将直接为流域和沿海研究中心作出贡献，该中心是阿伯里斯特威斯大学和班戈尔大学之间伙伴关系项目的一部分。

CONTEXT. The topic of this proposal relates within Oceans 2025 to: Shelf and coastal processes: 13 'Morphological modelling in Liverpool Bay and adjacent estuaries'. It fits mainly under WP 3.5 'Coastal morphodynamics and bathymetric evolution', while contributing also to WP 9.1 'Assessing and improving the accuracy of shelf sea models'. In addition, this studentship will add significant value to the NERC-funded FORMOST project (NE/E015123/1, 2008-2010, involving Bangor University and POL) which aims to (i) extend POL's field observational capabilities in sediment transport research, and (ii) develop new parameterizations of local sediment transport, based on Bangor's Sand Transport Model, that will here be implemented in two coastal area models (Telemac and POLCOMS). The Telemac system has already been upgraded to include a parameterised version of the Bangor model, and this will be available to the student via FORMOST as a working tool for data interpretation. In addition, new field data will be obtained during FORMOST in the outer channels of the Dee Estuary, within the area of POL's Coastal Observatory, providing background information for the studentship. BACKGROUND. The migration of large-scale sedimentary features (sand waves, banks and bars) contributes significantly to the morphological evolution of the seabed. Such features are not resolved within coastal sediment transport models, giving rise to uncertainty in morphological outcomes. This project will focus on the mobility and migration of large-scale bed features in the Dee Estuary, examining the key physical processes largely from an observational standpoint, but including a modelling element that will allow an informed interpretation of the experimental outcomes. An understanding of the role of estuaries like the Dee in acting as sources or sinks for mobile sediment is essential from a management viewpoint against a background of climate change. The results of a pilot study carried out using POL's X-band radar during summer 2007 (MSc project, Bangor University, jointly-supervised by POL) indicate that large-scale sand features are advancing into the Dee Estuary in the intertidal area between Hilbre Island and the Wirral mainland. More generally, POL's radar, which is capable of monitoring the movement of bed forms over a 4 km radius, has revealed that large sand features are also advancing into the estuary in deeper water. However, what is unknown is the relative contribution of the respective large bed forms to the sediment budget of the Dee Estuary. The DETAILED AIMS of the studentship are to: (i) track sand dunes in the inter-tidal area near Hilbre Island, thus elaborating the results of the 2007 pilot study. This will highlight the role of waves and currents on net sediment transport. Interpretation of the results will include Telemac simulations for the conditions measured on site. (ii) track using X-band radar the movement of sand banks and dunes in deeper water in mid-estuary. Interpretation will be provided both by available/new ADCP data and modelling. Telemac (and possibly POLCOMS) will be used to establish the 'drivers' responsible for morphological change. (iii) establish a methodology for the inclusion of large-scale bed features in coastal area models, taking as a starting point Van Rijn's (2005) roughness formulation, introducing this into Telemac, and critically testing its effect with regard to the bed forms in the Dee. End users. The PhD programme will be of relevance to end users concerned with management issues in the Dee. For example, the Countryside Commission for Wales (CCW) as well as the Environment Agency (EA) will be in attendance at FORMOST project meetings to which the student will contribute. The study will also contribute directly to the Centre for Catchment and Coastal Research, part of the Partnership Project between Aberystwyth and Bangor Universities.