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

在这笔资金的资助下，pi将通过直接观察和建模，研究在每年河流洪水产生的沉积物浓度超过20克/升（这是形成此类流的预期阈值）的环境下，超潮流的发生、运输和灭绝，以及它们的地层记录。新西兰的怀亚普河是世界上含沙最多的河流之一，年平均悬浮泥沙浓度超过10g/L，在每年的洪水期间经常产生超峰流。这一建议假设，每年的怀亚普洪水会导致高旋流，由于海床梯度低，在没有波浪的情况下，这些水流会在海岸附近沉降。然而，波浪的搅动搅动了这些沉积物，并维持了足够密集的悬浮物，从而导致进一步的下坡运输。在提议的研究中，将使用近底三脚架，在一系列强迫条件下对内大陆架和中间大陆架进行底边界层沉积物重力流、再悬浮和波浪和洋流运输的测量。海底取样和测量将记录最初洪水脉冲的沉积以及随后由波浪和水流重新分配的物质，并将检查在洪水季节形成的精细地层和长期积累和地层特征。所有这些观测结果将用于校准和完善泥沙运输和沉积的分析和数值模拟工作，并评估比现有底边界层观测结果更长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.