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

本博士论文研究项目将研究热带山地河流的河床输沙，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。热带山地河流的地貌是动态的、复杂的。它们在一个雨季内多次调动粗质河床（砾石到巨石），从而输送大规模洪水。本博士论文研究项目将研究河床的分布和通量，它们在确定这些系统的河道形态方面起着重要作用，因此是系统敏感性的代表。该博士生将通过对哥斯达黎加里约热内卢Pacuare的分析来寻求以下研究问题的答案：(1)与当地地质和沉积物来源相关的下游河道地貌如何变化？(2)各河段输沙速率和年产沙量是多少？(3)下游河床通量是否表达了局部、河段或全系统的地貌连通性？(4)泥沙通量如何响应预测的未来气候变化和蓄水（坝）情景？里约热内卢Pacuare河是进行这类分析的合适河流，因为它是自由流动的，相对容易接近，并且是其他热带山地河流的代表。学生将使用创新的现场技术来绘制和表征沉积物，并创建河段沉积物预算。除了传统的调查方法外，从多张照片中提取地形数据的运动构造方法将适用于粒度分析和颗粒动员识别，以验证沉积物运输估计。水力和泥沙运输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、水力发电、生态和农业）的需求持续稳步增长，但对这些系统的地貌学的研究相对较少。本研究中使用的独特的野外和遥感技术组合将克服热带河流研究的一些突出挑战，包括难以进入、高沉积物通量、快速波动的流量和大颗粒动员。除了扩大对河流地貌学动态，特别是热带河流形态动态的基本理解之外，该项目还可以通过提供公众、科学家、资源管理者和决策者可用的基本信息，帮助热带河流的可持续发展、管理和保护。作为博士论文研究进步奖，该项目将提供支持，使有前途的学生建立一个独立的研究生涯。

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.