Developing the UK national centre of excellence for geohazards through quantification of field-scale turbidity current hazard

我们的总体目标是更好地了解被称为浑浊流的强大海底水流对用于开采石油和天然气的管道和其他海底基础设施的影响。浑浊水流对昂贵的海底设施构成严重危险，特别是在深水环境中。这些沉积物流动特别危险，因为它们可能非常强大(移动速度高达20米/S)，并可以长距离(100公里)流动，对大片海底造成破坏。以~1-2米/S的速度移动的水流即使较弱，也会严重损坏海底设备，或折断具有重要战略意义的海底通信电缆，而有些水流的速度已维持在5米/S以上数百公里。这使得通过对管道进行局部改道来减轻灾害变得困难。在海底地形崎岖的地方，许多运营商在峡谷内铺设管道；然而，这些都是浑浊水流活动的焦点。减少浑浊当前的地质灾害，特别是在峡谷内，可能会对工业产生非常重大的成本影响--每公里额外的深水管道布线成本约为300万美元。据预测，在刚果峡谷下方铺设管道的缓解成本为20亿美元，那里的浑浊水流危害被认为很高。或许同样重要的是，管道漏油可能会导致重大的声誉损害。鉴于对用于回收石油和天然气的建筑物发生事故的担忧，对地质灾害的关注也与NERC的环境责任相一致。浑浊流最值得注意的方面是，来自水流的直接测量非常少，部分原因是它们损坏了放置在海底的监测设备。有几条证据表明，在浑浊洋流底部存在一个泥沙浓度较高的区域。这些致密的底层非常重要，因为：(I)它们正好位于大多数潜艇基础设施所在的底床上方；(Ii)由于密度大，它们携带的动量最大。然而，在这些层中从来没有直接测量过泥沙浓度。物理实验、数值模拟和古代沉积为这些流动提供了有价值的见解；但迫切需要监测实际行动中的全面流动。这一项目是及时的，因为它将开发创新的基于现场的技术，以成像近床层流动结构和现场含沙量的垂直变化。目的：(1)我们的第一个目标是开发一种新的近床层致密遥感技术并进行现场试验。(2)我们的第二个目标是更好地理解近床层致密层的性质。(3)我们的第三个目标是将对致密近床层的更好的理解嵌入到工业用来评估浊流对油气管道的影响的数值模型中。(4)该项目还将有助于在英国国家海洋学中心建立一个国际海底地质灾害研究示范中心。在这里，我们建议对位于加拿大豪湾的Squamish三角洲夏季河流流量上升期间每天出现的部分浑浊洋流的致密基底层进行直接测量。我们将使用创新的四点系泊装置将船舶和悬浮仪器有效载荷稳定地保持在主动航道系统上方，同时使用Chirp亚海底剖面仪观察致密的基底层。低频和宽带(1.5-13.0 kHz)Chirp源确保穿透致密的近床层，分辨率为~10厘米的层。这些野外观测将有助于了解近床层的基本特征及其形成的情况。

Our over-arching aim is to better understand the impact of powerful submarine flows, called turbidity currents, on pipelines and other seabed infrastructure used to recover oil and gas. Turbidity currents pose a serious hazard to expensive seabed installations, especially in deeper-water settings. These sediment flows are particularly hazardous because they can be exceptionally powerful (travelling at speeds of up to 20 m/s), and can flow for long distances (100s km), causing damage over vast areas of seafloor. Even weaker flows travelling at ~1-2 m/s can severely damage seafloor equipment, or break strategically important submarine telecommunication cables, while some flows have maintained speeds in excess of 5 m/s for hundreds of kilometres. This makes hazard mitigation by local re-routing of pipelines difficult. Where seafloor topography is rugged, many operators route pipelines within canyons; however, these are focal points for turbidity current activity. Mitigating against turbidity current geohazards, particularly within canyons, can have very significant cost implications for industry - additional deepwater pipeline routing costs ~ $3 million per km. Mitigation costs of $2 billion are predicted to route pipelines under the Congo Canyon, where turbidity current hazard is deemed to be high. Perhaps just as importantly, pipeline oil spills could lead to major reputational damage. Given concern over accidents to structures used to recover oil and gas, a focus on geohazards is also aligned with NERC's environmental responsibility. The most remarkable aspect of turbidity currents is how few direct measurements there are from flows, in part because they damage monitoring equipment placed on the seafloor. Several lines of evidence point to the existence of a region of high sediment concentration at the base of turbidity currents. These dense basal layers are of key important because of: (i) their location just above the bed where most submarine infrastructure is located; and (ii) they carry most momentum due to their large density. Yet, sediment concentration has never been measured directly measured in these layers. Physical experiments, numerical modeling and ancient deposits provide valuable insights into these flows; but there is a compelling need to monitor full-scale flows in action. This project is timely because it will develop innovative field-based techniques for imaging near bed flow structure and vertical changes in sediment concentration in situ.Aims: (1) Our first aim is to develop and field test a novel technique for remote sensing of dense near bed layers. (2) Our second aim is to better understand the nature of near bed dense layers. (3) Our third aim is to embed improved understanding of dense near-bed layers into numerical models used by industry to assess impact of turbidity currents on oil and gas pipelines. (4) The project will also help to establish an international centre of excellence for submarine geohazard research at the UK National Oceanography Centre. Here we propose to make direct measurements of dense basal layers that form part of the turbidity currents occuring daily during the elevated summer river discharge on the Squamish Delta, located in Howe Sound, Canada. We will use an innovative four-point mooring to hold a vessel and suspended instrumentation payload stable above an active channel system, while we observe the dense basal layer with a Chirp sub-bottom profiler. The low frequency and broad bandwidth (1.5 -13.0 kHz) Chirp source guarantees penetration through dense near-bed layers, resolving layers with ~10 cm resolution. These field observations will help to understand the fundamental character of near bed layers, and the situations in which they form.