Sediment Dispersal off a High-Yield River: Observations and Modeling of Gravity-Driven Transport and Deposition

在这笔资金下，PI将通过直接观察和建模，研究hypercnal流的发生，它们的运输和灭绝，以及它们在每年河流洪水产生的沉积物浓度超过20 g/l的环境中的地层记录，这是形成这种流的预期阈值。新西兰怀亚普河是世界上泥沙含量最高的河流之一，年平均悬浮泥沙浓度超过10 g/L，每年洪水泛滥时都会产生高密度水流。 该提案假设每年的怀亚普洪水导致高密度流，由于海底坡度低，在没有波浪的情况下，高密度流将在海岸附近沉降。然而，波浪搅动使这些沉积物流动，并维持悬浮物的密度足以引起进一步的下坡运输。在拟议的研究中，底边界层测量的沉积物重力流，再悬浮，并通过波浪和电流的运输将在一系列的强迫条件下的内部和中间架使用近底三脚架。海底取样和测量将记录最初洪水脉冲造成的沉积以及随后波浪和水流造成的物质重新分布情况，并将研究洪水季节形成的精细地层学以及长期积累和地层特征。所有这些观测结果将用于校准和改进沉积物输运和沉积的分析和数值模拟工作，并评价比现有底部边界层观测结果更长的时间和空间尺度上的扩散模式。

Under this funding, the PIs will study, through direct observations and modeling, the occurrence of hyperpycnal flows, their transport and extinction, and their stratigraphic record in an environment where annual river flooding generates sediment concentrations in excess of 20 g/l, the expected threshold for the formation of such flows. The Waiapu River, New Zealand is one of the most sediment-laden rivers in the world, with an average annual suspended sediment concentration exceeding 10g/L, and routinely generates hyperpycnal flows during annual flooding. This proposal hypothesizes that annual Waiapu floods result in hyperpycnal flows that would settle near shore in the absence of waves due to the low seabed gradient. Wave agitation, however, mobilizes these sediments and sustains suspensions dense enough to cause further downslope transport. In the proposed study, bottom-boundary layer measurements of sediment gravity flows, resuspension, and transport by waves and currents will be made under a range of forcing conditions on the inner and middle shelf using near-bottom tripods. Seabed sampling and measurements will document deposition from the initial flood pulse as well as the subsequent redistribution of material by waves and currents, and will examine both the fine-scale stratigraphy developed over a flood season and longer-term accumulation and stratigraphic signatures. All of these observations will be used to calibrate and refine analytical and numerical modeling efforts for sediment transport and deposition, and to evaluate dispersal patterns over time and spatial scales longer than the available bottom boundary layer observations.