Numerical modelling of river and floodplain responses to environmental change

世界上许多大河都受到一系列自然和人为干扰的威胁，包括气候变化、大坝建设、采矿、农业集约化、城市化、污染和过度开采水资源。这些现象促使河流流态和泥沙负荷发生变化，进而促进河流的不稳定性以及输洪能力和生态功能的变化。数值模型是预测未来环境变化和人类活动下河流演变的重要工具。然而，尽管它们在这方面很重要，但大多数现有的数值模型都不能代表控制河流演变的关键过程。缺少的关键过程包括植被对水流和泥沙输送过程的影响、河岸侵蚀和泛滥平原的发展。此外，现有的河流演变模型倾向于将植被视为必须指定的东西(作为模型输入条件)，而不是作为河岸和泛滥平原景观的紧急特征，后者是一系列相互竞争的植被类型建立、生长和死亡的产物。本研究将开发新的方法来表示河流和泛滥平原演变的地形动力学模型中的植被和植被效应。这些模型将利用现有的实地、实验室和遥感数据集，并借鉴其他学科(例如气候科学)使用的动态植被模型中使用的方法来开发。新的模型将在几十年到几个世纪的时间段内，在具有不同植被类型的一系列环境环境中应用和评估河流，以证明模拟在这些不同环境中发现的各种河流样式的可行性。在评估了新的模型之后，它们将被用来回答一系列与河流环境中植被的作用和意义有关的关键问题。这些问题将包括：(1)植被和植被反馈在控制河流对人类活动(如修建大坝)的反应方面起什么作用？(2)对比的河流景观对未来气候变化的敏感性如何，植被在控制这种敏感性方面发挥了什么作用？(3)在河流演变模型中，表示植被影响所需的最低复杂程度是多少，忽略植被影响对数值模型的准确性和敏感性有何影响？

Many of the worlds large rivers are under threat from a range of natural and anthropogenic disturbances, including climate change, dam construction, mining, agricultural intensification, urbanisation, pollution and over-abstraction of water resources. These phenomena drive changes in river flow regimes and sediment loads, which in turn can promote river instability and changes in flood conveyance capacity and ecological functioning.Numerical models are essential tools for predicting the evolution of rivers in the face of future environmental change and human activities. However, despite their importance in this regard, most existing numerical models fail to represent key processes that control river evolution. Key missing processes include the effects of vegetation on flow and sediment transport process, bank erosion and floodplain development. Moreover, existing models of river evolution tend to treat vegetation as something that must be specified (as a model input condition) rather than as an emergent characteristic of the riparian and floodplain landscape that is a product of the establishment, growth and mortality of a range competing vegetation types.This studentship will develop new methods of representing vegetation and vegetation effects within morphodynamic models of river and floodplain evolution. The models will be developed using existing field, laboratory and remote sensing datasets, and by drawing on approaches used in dynamic vegetation models used in other disciplines (e.g. climate science). The new models will be applied and evaluated for rivers across a range of environmental settings with contrasting vegetation types, over time periods of decades to centuries, in order to demonstrate the feasibility of simulating the wide range of river styles found in these different environments. Having evaluated the new models, they will be used to answer a set of key questions relating to the role and significance of vegetation in riverine environments. These questions will include: (1) What is the role of vegetation and vegetation feedbacks as controls on river responses to anthropogenic activities (e.g., such as dam construction)?; (2) How sensitive are contrasting riverine landscapes to future climate change, and what role does vegetation play in controlling this sensitivity?; (3) What is the minimal level of complexity required to represent the effects of vegetation in models of river evolution, and how does the neglect of vegetation effects impact on the accuracy and sensitivity of numerical models?