Submarine Debris-Flow Runout and Pipeline Risk

Submarine geohazards · Regional simulation · Infrastructure risk

This project links two complementary research layers. The first resolves how submarine debris flows propagate and soften over regional three-dimensional terrain. The second carries the evolving thickness and velocity fields into a distributed model of pipeline impact, segment failure, network capacity, and route-level risk. (Chen et al., 2023; Chen et al., 2022)

TerrainGIS representation of regional three-dimensional seabed topography

HazardRunout, thickness, velocity, and material-strength evolution

RiskPipeline forces, segment failure, network capacity, and mitigation

Research questions

How can regional submarine debris-flow runout be simulated efficiently on complex natural terrain while retaining the effects of progressive material softening?
How do the resulting thickness and velocity fields translate into spatially distributed pipeline impact, network damage, and practical routing decisions?

Layer 1: regional runout with material softening

The runout model solves one-dimensional depth-averaged mass and momentum equations on a GIS grid. Each cell can exchange material through eight directions, allowing the model to follow thickness, velocity, flow direction, cumulative basal shear strain, and evolving yield strength across a regional domain. A Herschel–Bulkley rheology represents plug and sheared layers. (Chen et al., 2023)

\[\tau_y=\tau_{y,\infty}+\left(\tau_{y,0}-\tau_{y,\infty}\right)e^{-\delta\gamma}\]

Interpretation. Yield strength decreases from its initial value $\tau_{y,0}$ toward a residual value $\tau_{y,\infty}$ as basal shear strain $\gamma$ accumulates. The softening factor $\delta$ controls how quickly that loss of strength occurs.

The regional solver was checked against a flume test, two three-dimensional slump tests, and the St Niklausen submarine slide. In the flume comparison, simulated runout was 11.8 m—0.2 m below the experiment—and the mean deposit-thickness difference was 0.013 m. Material softening is neglected in these validation cases. (Chen et al., 2023)

St Niklausen validation: seismic-reflection deposit geometry, a previous CEL result, and the proposed model produce comparable runout and deposit-thickness distributions. Fig. 9 from (Chen et al., 2023).

Four simulated submarine debris-flow deposits showing greater lateral spreading as the material-softening factor increases

An idealized continental-shelf example shows how increasing the modeled softening factor changes the final deposit footprint. Cropped from Fig. 12 in (Chen et al., 2023).

Using a hypothesized initial mass on the Shenhu terrain, the model used 70,069 cells over 28.03 km². The simulated flow largely stopped after about 3,600 s. Across eight monitoring points, maximum velocity ranged from 10.26 to 19.72 m/s and maximum thickness from 8.56 to 34.88 m. Within the tested parameter range, higher yield strength shortened runout, while stronger softening increased both runout and affected area. (Chen et al., 2023)

Layer 2: impact and pipeline-network performance

The distributed pipeline model adds three modules: spatial discretization, regional debris-flow dynamics, and pipeline impact/damage evaluation. Flow direction matters because the radial impact force is generally much larger when the pipeline axis is nearly perpendicular to the moving debris. Segment failures are then propagated through the network according to the remaining transport capacity. (Chen et al., 2022)

\[D_{\mathrm{network}}=1-I_{\mathrm{network}}, \qquad R_{\mathrm{network}}=\sum_{i=1}^{m}P_{f,i}D_{\mathrm{network},i}\]

Interpretation. $I_{\mathrm{network}}$ is the fraction of transport capacity retained after damaged segments are removed. Across $m$ mutually exclusive debris-flow events, scenario risk combines each event's assumed probability with its modeled network-capacity loss.

Time sequence of a simulated submarine debris flow crossing a pipeline network with corresponding impact velocity, radial force, and axial force profiles

A baseline scenario tracks the flow as it crosses four pipeline locations and resolves the associated velocity and force profiles. Cropped from Fig. 5 in (Chen et al., 2022).

What the modeled scenarios show

11.1 m/sMaximum pipeline impact velocity in the baseline network scenario

39.3 kN/mMaximum radial impact force in that scenario, versus 4.9 kN/m axially

0.12 → 0Scenario risk reduced by the most conservative rerouting plan, with 7.1 km of added pipeline

The baseline network scenario produced a damage index of 0.29, corresponding to a modeled loss of 29% of transport capacity. Larger volume, lower yield strength, lower consistency, and interacting flows increased the affected area and network damage. Because terrain controls the path, changing the initiation location could also determine whether the flow intersected the network at all. (Chen et al., 2022)

Within this scenario set, increasing pipe-material yield strength reduced risk from 0.12 to as low as 0.02. Rerouting around slopes steeper than 20° reduced it to 0.03 with 2.6 km of additional pipeline; avoiding slopes steeper than 10° reduced the modeled risk to zero with 7.1 km of additional pipeline. (Chen et al., 2022)

Map comparing the original submarine pipeline network with two rerouting plans that avoid seabed slopes above twenty and ten degrees, accompanied by scenario risk indices

Original network and two rerouting plans evaluated against the assumed debris-flow events; Plan A reduces the simultaneous-event risk index from 0.12 to 0.03, and Plan B to 0. Fig. 14 from (Chen et al., 2022).

Proposed broader research framework

A 2024 review of hydrate-exploitation and marine-environment geohazards identifies monitoring data, multiphase and multifield coupling, multiscale analysis, susceptibility and vulnerability data, and engineering risk standards as research needs. It proposes a multi-scale, multi-spatial-temporal “digital triplet” framework for geohazard risk management in the Qiongdongnan Basin. (Jiang et al., 2024)

Conceptual digital-triplet framework proposed for multi-scale geohazard sensing, numerical analysis, intelligent decision-making, and risk control in the Qiongdongnan Basin

Conceptual multi-scale and multi-spatial-temporal digital-triplet framework proposed by the review paper. Fig. 12 from (Jiang et al., 2024).

Scientific contribution

Regional efficiency with process detail. Depth-averaged dynamics and GIS routing resolve evolving flow over large natural terrain without treating runout as a single empirical distance. (Chen et al., 2023)
Material evolution matters. The strength-softening law explains why a fixed-strength analysis can underestimate the affected area in the modeled scenarios. (Chen et al., 2023)
Hazard fields connect to network function. Thickness, velocity, and direction are converted into impact forces, segment failures, and remaining transport capacity. (Chen et al., 2022)
The model supports engineering choices. Material upgrades and alternative routes can be compared with the same network-level risk measure. (Chen et al., 2022)

Scope and limitations

In the Shenhu runout application, the terrain is derived from regional data, while the initiation area and debris-flow properties are assumed. The runout model simplifies ambient-fluid effects, does not capture debris-flow-generated waves, and does not include geotechnical or geological uncertainty; the authors also call for additional flume and field datasets. (Chen et al., 2023)

The pipeline application uses a hypothetical production network and assumed potential debris-flow locations. It treats the debris flow as a one-phase mixture, ignores inherent pipeline movement and interaction between the pipelines and sliding material, models pipeline elements as suspended members with simple supports, and measures consequences through transport-capacity loss. The semi-empirical impact-force equations also have a stated range of applicability in terms of the non-Newtonian Reynolds number. (Chen et al., 2022)

The development and utilization of deep-sea oil and gas is a crucial solution to our energy challenges. The submarine geological hazards are likely generated by natural factors(earthquake, et al.) and human being activities(exploitation, et al.), threatening the safety of major engineering and existing facilities. This work reviews the existing research status of the generation mechanism and multi-scale evolution pattern of marine geological hazards. Moreover, it also summarizes the vulnerability of marine geological hazards, engineering facility, and the current status of risk assessment. According to the literature, the research on geological hazards faces several challenges. Firstly, there is a scarcity of monitoring data and a lack of targeted multi-field/multi-phase coupling analysis methods and multi-scale numerical analysis methods; Secondly, the existing basic data, evaluation models, and accuracy of studying geological hazard susceptibility and vulnerability are insufficient to meet the existing demand; Thirdly, the evaluation index system used in risk assessment is not objective and scientific, and lacks systematic theoretical methods and software suitable for engineering practice, as well as relevant norms and standards for risk control standards and response measures of seabed geological hazards. This paper proposes several solutions to address the challenges faced in the research of geological hazards in the Qiongdongnan Basin. These solutions encompass exploration technology of reservoir, macro and micro constitutive models of sediment, multi-scale numerical simulation, and the dynamic theory of landslide impact force. Furthermore, it suggests that risk identification, risk assessment, and mitigation measures should be integrated to achieve controllable risk development. At the same time, with the help of new methods such as artificial intelligence, this paper proposes a multi-scale and multi-spatial-temporal coupling digital triplet framework, which provides the reference for geological hazard research of large hydrate reservoir(Qiongdongnan Basin, et al.)exploitation in the next step.

Evaluation of regional submarine debris flows is critical for quantitative assessment of vulnerable areas and reasonable design of geohazard mitigation measures. In this article, an efficient numerical model for kinematics of regional submarine debris flows is developed. The proposed model can simulate the runout process and morphological evolution of submarine debris flows over natural 3D terrain by solving 1D depth-averaged governing equations in a geographic information system (GIS). A strength softening equation is introduced to capture the degradation of sliding material strength during the runout process. The model is validated by a flume test, two slump tests, and a real case history of submarine debris flow (St Niklausen slide). Applications to Shenhu area, South China Sea, are presented to demonstrate the ability of the proposed model over complex natural terrain and the importance of considering material softening. Results show that the proposed model is capable of simulating the whole debris flow process and tracking the propagation of the sliding material. Simulation of submarine debris flow without material softening will underestimate the disaster consequences. In addition, the influences of the ambient fluid and the yield strength of the sliding material on its runout behavior are also discussed.

This paper proposes a distributed model for assessing the damage to a submarine pipeline network induced by regional debris flows. The model consists of three components: a spatial discretization module, a regional submarine debris flow dynamics module, and an impact force and damage evaluation module for the pipeline network. The model is applied to the Shenhu area in the northern South China Sea to investigate the responses of a pipeline network subjected to regional submarine debris flows. The proposed model can capture the impact forces and damage level of the pipeline network during the debris flow process. The influence of the properties and initial location of a potential debris flow on the pipeline network damage and the effect of multiple debris flows on the pipeline network are investigated. The risk mitigation measures for a complex submarine pipeline network in extreme disaster scenarios on a regional scale are compared. The proposed model represents a feasible solution for assessing the responses of a pipeline network subjected to regional submarine debris flows and can facilitate risk-informed decision-making for the planning and optimization of pipeline routes.

Research questions

Layer 1: regional runout with material softening

Layer 2: impact and pipeline-network performance

What the modeled scenarios show

Proposed broader research framework

Scientific contribution

Scope and limitations

References

2024

2023

2022