Collaborative Research - Processes Controlling Depositional Signals of Environmental Change in the Fly River Sediment Dispersal system:Rates and Mechanisms of Floodplain Deposition

EAR-0203577威廉·E·迪特里希该项目关注两个基本问题：1)通过低地洪泛平原系统的水流和泥沙路线如何缓和向近海沉积环境输送泥沙的短期和长期变化？2)是什么控制了河流淤积在滩地上的泥沙比例？本文假设在全新世海平面上升期间，滩地的泥沙净流失量最大，在海平面接近稳定后，滩地的泥沙淤积比例逐渐下降。这两个基本问题通过比较来解决这两个基本问题，并通过比较中飞河和下游斯特里克兰河的泥沙流失比例来解决这两个基本问题。从历史上看，斯特里克兰携带的负荷大约是苍蝇的7倍，据推测，更大的负荷导致了更大的航道动力，更陡峭的坡度，更粗糙的河床，更高的泛滥平原，以及可能比苍蝇更低的诱捕效率。目前正在开发一种数值模型，该模型具有足够的机械性，可以解决事件和季节尺度上的衰减和捕获效率问题，但也足够简化，可以模拟共同演变的河床粒度、河道坡度和泛滥平原地形，这是理解捕获效率随时间演变的关键能力。尽管雄心勃勃，但该模型的许多部分在之前的研究中已经组装好了。水动力模型考虑了滩地地貌和水文的影响。泥沙输移考虑了河道迁移的影响，并考虑了泥沙在颗粒大小上的淤积和侵蚀。为了记录洪水波的阻尼率、斯特里克兰河和飞来河的泥沙截留效率，并对数值模型进行参数化，正在进行一个现场程序。目前正在通过地形测量和遥感图像分析来量化洪泛区的地貌。对流速和悬浮泥沙场的密集测量被用来激励水力学和泥沙输送模型并将其参数化。浅层岩心记录了滩涂沉积的短期和长期(不到100年)的速度。中飞的OK Tedi矿业有限公司和斯特里克兰的Porgera合资企业正在提供大量的水流和泥沙监测数据。以前对苍蝇河的研究使研究的重点放在斯特里克兰河上。

EAR-0203577 William E. Dietrich This project focuses on two fundamental questions: 1) How does flow and sediment routing through a lowland floodplain system moderate short and longer-term variations in sediment delivery towards offshore depositional environments? and 2) What controls the proportion of a river's sediment load that is deposited on its floodplain? It is hypothesized that net sediment loss to the floodplains was highest during Holocene sea-level rise and, after near stabilization of sea level, the proportion of the sediment load deposited in the floodplain has progressively declined.These two basic question are being addressed by comparing the flow and sediment routing processes, and the proportion of sediment lost to floodplains on the middle Fly and lower Strickland Rivers. Historically, the Strickland carried about 7 times the load of the Fly and it is hypothesize that this larger load has led to greater channel dynamics, steeper slopes, coarser bed, more elevated floodplain and possibly a lower trapping efficiency than the Fly. A numerical model is being developed that is sufficiently mechanistic that it can address the questions of damping and trapping efficiency on the event and seasonal scale, yet simplified enough that it can also model the co-evolving bed grain size, channel slope and floodplain topography, a crucial capability for understanding the time evolution of trapping efficiency. Though ambitious, many parts of the model have been assembled in previous research. The hydrodynamic model accounts for the effects of floodplain morphology and hydrology. The sediment routing includes effects of channel migration and accounts for the deposition and erosion of sediment by grain size.A field program is being conducted to document the flood wave damping rates, the sediment trapping efficiency of the Strickland and Fly Rivers, and to parameterize the numerical model. Quantification of floodplain morphology is being done through topographic surveys and analysis of remote sensing imagery. Intensive surveys of the velocity and suspended sediment fields are used to motivate and parameterize the hydraulics and sediment transport model. Short and longer-term (less than 100 years) rate of floodplain deposition is being documented from shallow cores. Extensive flow and sediment monitoring data are being provided by Ok Tedi Mining, Ltd. on the Middle Fly and by Porgera Joint Venture on the Strickland. Previous research on the Fly River enables the research focus to be on the Strickland River.