Doctoral Dissertation Research: Geomorphology and Sediment Dynamics of a Tropical Montane River

这项博士论文研究项目将研究热带山地河流的推移质泥沙输送，并估计预测的气候变化和大坝开发情景对其地貌的潜在影响。热带山地河流地貌动态复杂。它们能够在一个雨季内多次调动粗沙(砾石到大卵石)，从而输送大规模洪水。这项博士论文研究项目将研究推移质分布和通量，它们在确定这些系统中的河道形式方面发挥着重要作用，因此是系统敏感度的代理。博士生将通过对哥斯达黎加里约帕夸雷的分析，寻求以下研究问题的答案：(1)与当地地质和泥沙来源相关的下游河道地貌如何变化？(2)每个河段的泥沙输运率和年产沙量是多少？(3)下游推移质流量是否表示局部、河段或系统范围的地貌连通性？(4)泥沙通量将如何随预测的未来气候变化和蓄水(大坝)情景而变化？里约帕夸尔河是一条适合进行这类分析的河流，因为它是自由流动的，相对容易到达，并且是其他热带山地河流的代表。学生将使用创新的实地技术来绘制和描述沉积物，并创建可达范围的沉积物预算。除了传统的调查方法外，从多张照片获得地形数据的结构运动方法将被用于颗粒尺寸分析和颗粒动员的识别，以验证泥沙运移估计。水力和泥沙输送模型将量化泥沙通量，以表征系统对预测的气候变化和蓄水情景的敏感性。对热带河流的研究尤其重要，因为对其资源(淡水供应、水电、生态和农业)的需求继续稳步增长，但对这些系统的地貌研究相对较少。这项研究中使用的野外和遥感技术的独特组合将克服热带河流研究中的一些著名挑战，包括难以进入、高泥沙通量、快速波动的水流和大颗粒动员。除了扩大对河流地貌动态，特别是热带河流地貌动态的基本了解外，该项目还可以通过提供可供公众、科学家、资源管理者和政策制定者使用的基本信息，帮助热带河流的可持续发展、管理和保护。作为博士论文研究改进奖，该项目将为有前途的学生建立独立的研究生涯提供支持。

This doctoral dissertation research project will examine bedload sediment transport of tropical montane rivers and estimate the potential impact of predicted climate change and dam development scenarios on their geomorphology. Tropical montane rivers are geomorphically dynamic and complex. They convey large-magnitude floods with the capacity to mobilize coarse bedload (gravels to large boulders) multiple times during a single rainy season. This doctoral dissertation research project will examine bedload distribution and flux, which play an important role in defining channel form in these systems and therefore are a proxy of system sensitivity. The doctoral student will pursue answers to the following research questions through an analysis of the Rio Pacuare, Costa Rica: (1) How does channel geomorphology vary going downstream in relation to local geology and sediment sources? (2) What are the sediment transport rates and annual yields of each reach? (3) Does downstream flux of bedload express local, reach, or system-wide geomorphic connectivity? (4) How will sediment flux change in response to predicted future climate change and impoundment (dam) scenarios? The Rio Pacuare is an appropriate stream for these kinds of analyses because it is free-flowing, relatively accessible, and is representative of other tropical montane rivers. The student will use innovative field techniques to map and characterize sediment and to create reach-scale sediment budgets. In addition to traditional survey methods, the Structure from Motion approach, which derives topographic data from multiple photographs, will be adapted for grain-size analysis and identification of grain mobilization to validate sediment transport estimates. Hydraulic and sediment transport models will quantify sediment flux to characterize system sensitivity to projected climate change and impoundment scenarios. Research on tropical rivers is particularly important because demands on their resources (freshwater supply, hydroelectricity, ecology, and agriculture) continue to increase steadily, but relatively little research has been done on the geomorphology of these systems. The distinctive mix of field and remote sensing techniques used in this research will overcome some of the noted challenges of tropical river research, including difficult access, high sediment flux, rapidly fluctuating flows, and large-grain mobilization. Beyond expanding basic understanding of the dynamics of fluvial geomorphology, and especially the dynamics of tropical river morphology, this project may assist in the sustainable development, management, and conservation of tropical rivers by offering fundamental information that is usable by the public, scientists, resource managers, and policy makers. As a Doctoral Dissertation Research Improvement award, this project will provide support to enable a promising student to establish an independent research career.