Collaborative Research: Fate of Irrawaddy and Salween River Sediment: Relative Importance of Oceanographic and Tectonic Controls

5亿人生活在河流三角洲上，由于地面沉降加剧、增长率下降和海平面上升加速，其中许多地区现在被认为处于危险之中。这些沿海地区的土地下沉大大增加了风暴潮和洪水的威胁。 例如，2008年，纳尔吉斯飓风席卷缅甸伊洛瓦底江三角洲，造成138，000多人死亡，2015年同一地区的季风大雨导致低洼地区洪水泛滥，造成20万人流离失所。为了了解和预测河流三角洲的未来演变，有必要了解河流中的沉积物是如何被输送到三角洲的陆上和海上区域的，因为这是三角洲形成的物质。 该项目将提供对缅甸伊洛瓦底-萨尔温江（I-S）三角洲的了解，这可能是地球上最后一个我们缺乏完整图片的主要三角洲系统。 具体而言，该项目将研究控制沉积物输送的构造和海洋学因素，以及三角洲增长的目前模式和速度。 这项研究的结果将为5000万人居住的敏感三角洲的未来发展提供信息，并增加我们对全球三角洲的一般知识。 该项目还将包括对美国本科生和研究生的指导和培训，并将吸引缅甸科学家和学生，为培训和与美国同行合作提供机会。I-S系统每年携带的约6亿吨河流沉积物中，有很大一部分被输送到安达曼海北方的广阔大陆架，该大陆架受到强潮汐，季风条件，和周期性的旋风;然而，这种材料的命运是未知的。现有的测深数据和稀疏的初步调查暗示，在一种模式的水下三角洲的发展在大陆架上形成鲜明对比，从其他以前研究的主要三角洲。特别是，大陆架表现出显着的双边（东西）不对称的表面形态和沉积物的纹理：一个轻轻倾斜的桑迪坡道的伊洛瓦底江东部的嘴，和泥泞的内部到中间的大陆架斜坡在邻近的西部海湾的Martaban。基于实地和建模的实验将使研究团队能够对比海洋分类，运输过程和底层构造在创造这种不寻常的三角洲表达中的相对作用。地球物理观测、取芯和实验室研究将详细说明结构，并量化全新世和最近沉积物在大陆架上的积累量、来源和分布。为了探索沉积物从河流源到沉积汇的迁移路径，将使用一个数值模型来说明河流输入、波浪、潮汐和风力驱动的水流对河流沉积物在沿海海洋内扩散的影响。 模型运行将代表在东南和西北季风期间的条件，并在高排放时间。该模型还将用于探索在大风暴期间利用气旋产生的波浪和风场的表示来增强传输的潜力。

Half a billion humans live on river deltas, and many of these areas are now considered at risk as a result of increasing land subsidence, decreasing growth rate, and accelerating sea-level rise. Sinking land in these coastal areas greatly increases the threat from storm surge and flooding. For example, Cyclone Nargis tracked across the Irrawaddy delta in Myanmar in 2008 resulting in over 138,000 fatalities, and heavy monsoon rains in this same area in 2015 displaced 200,000 people as a result of flooding in low lying areas. To understand and predict the future evolution of river deltas, it is necessary to know how sediment from the river is transported and delivered to the onshore and offshore regions of the delta, as this is the material from which deltas arise. This project will provide an understanding of the Irrawaddy-Salween (I-S) delta in Myanmar, perhaps the Earth's last remaining major delta system for which we lack a complete picture. Specifically, the project will examine the tectonic and oceanographic factors that control the delivery of sediment, and the present pattern and rates of delta growth. This results of this study will inform the future development of a sensitive deltaic setting home to 50 million people, and add to our general knowledge of deltas worldwide. The project will also involve the mentoring and training of US undergraduate and graduate students, and will engage Myanmar scientists and students, providing opportunities for training and collaboration with US counterparts.Much of the estimated 600 Mt of river sediment carried by the I-S system annually is delivered to a wide continental shelf in the northern Andaman Sea that is influenced by strong tides, monsoon conditions, and periodic cyclones; however the fate of this material is unknown. Existing bathymetric data and sparse initial surveys hint at a mode of subaqueous delta development on the shelf which contrasts markedly from other previously studied major deltas. In particular, the shelf exhibits a dramatic bilateral (east-west) asymmetry of the surface morphology and sediment texture: a gently sloping sandy ramp off the eastern mouths of the Irrawaddy, and a muddy inner- to mid-shelf clinoform in the adjacent western Gulf of Martaban. Field- and modeling-based experiments will enable the research team to contrast the relative roles of oceanographic sorting, transport processes, and underlying tectonics in creating this unusual deltaic expression. Geophysical observations, coring and laboratory studies will detail the architecture and quantify the amounts, source, and distribution of Holocene and recent sediment accumulating on the shelf. To explore transport pathways of sediment from the fluvial source to depositional sinks, a numerical model will be used to account for the effects of river input, waves, tidal- and wind-driven currents on the dispersal of river sediment within the coastal ocean. Model runs will represent conditions during the SE and NW monsoons, and during times of high discharge. The model will also be used to explore the potential for enhanced transport during large storms using representations of the cyclone-generated wave and wind field.