Mechanisms and Countermeasures on Sediment and Wood Damage in Sediment Retarding Basins

Improvements in sediment retarding basin design are required to mitigate flood damage caused by bed load and wood debris outflow in lower river reaches. We used a scaled sediment retarding basin model to optimize our basin design, with the goal of improving sediment and wood debris transport and capture. Changes to the structural dimensions and elements of the sediment retarding basin were assessed under experimental debris flow conditions. The results obtained from the experiments and simulations were in good agreement regarding sediment flow and containment. The proposed one-dimensional model is useful for showing the effects of flow conditions within a sediment retarding basin on sediment transport.

Potential Source Analysis of Macrodebris in Untung Java Island by Using Trajectory Particle Modelling

Untung Java is one of the small islands in Thousand islands. One of the most highlighted problems on this island is the accumulation of macrodebris that occurs in the coastal and mangrove ecosystems. The purpose of this study is to determine the most potential source point for distributing debris to Untung Java Island by using a hydrodynamic model and particle trajectory model of MIKE 21. The scenario of the simulation is using pre-reclamation condition in 1999 and 2019. The estuary in Jakarta Bay is illustrated as the starting point for debris transport. Five other estuaries as potential source assumption are selected, namely Cisadane, Citarum, Muara Angke, Ciliwung and Cikeas. The validation data model used tidal data from Intergovernmental Oceanographic Commission (IOC) Sea Level Monitoring by utilizing Root Mean Square Error (RMSE) method. The RMSE is calculated up to 0.49-12.78%. The tidal current of Jakarta Bay is simulated up to 0.015-0.375 m/s. The Cisadane estuary is the most potential source as a supplier of macrodebris to Untung Java Island due to its debris movement pattern and the nearest distance to the island.

Glacial processes and landforms

From 1965-2000 glacial geomorphology became increasingly specialised and developed significantly due to technological improvements, particularly in remote sensing, surveying and field-based glaciological process studies. The better understanding of basal thermal regimes in ice sheets and glaciers led to the development of concepts such as spatial and temporal migration of ice divides in dynamic ice sheets that could overprint subglacial landform assemblages, debris entrainment processes related to polythermal glacier systems, and glacier and ice sheet beds composed of cold and warm based mosaics. Process observations at the ice-bed interface led to the discovery of the third glacier flow mechanism, substrate deformation, which provided the impetus to reconstruct the genesis of subglacial bedforms such as drumlins and to evaluate the origins and potential flow law for till. Numerical evaluations of glacial erosion led to a better understanding of abrasion and quarrying as well as the erection of genetic models and erosion rates for larger scale features such as U-shaped valleys and cirques. Linkages were made between debris transport pathways and moraine construction in supraglacial environments, with the role of glacier structure being linked to specific landforms, such as medial, lateral, hummocky and ice-cored moraines as well as rock glaciers. Our appreciation of the erosional and depositional impacts of glacifluvial systems was enhanced significantly with the advent of process observations on the hydrology of modern glaciers as well as the final vindication of J.H. Bretz and his proposed jökulhlaup origins of the Channelled Scablands and the Missoula Floods. In addition to the increasing numbers of studies at modern glacier snouts, the embracing of sedimentology by glacial geomorphologists was to result in significant developments in understanding the process-form regimes of subglacial, marginal and proglacial landforms, particularly the recognition of landform continua and hybrids. Advances resulting from this included the recognition of different modes of moraine and glacitectonic thrust mass development, lithofacies models of the varied glacifluvial depositional environments, and the initial expansion of the sediments and depo-centres of glacimarine settings, the latter being the result of glacial research taking to submersibles and ice-strengthened ships for the first time. A similarly new frontier was the expansion of research on the increasingly higher resolution images returning from Mars, where extraterrestrial glaciations were recognised based on comparisons with Earth analogues. Holistic appreciations of glaciation signatures using landform assemblages were developed, initially as process-form models and later as glacial landsystems, providing an ever expanding set of templates for reconstructing palaeoglaciology in the wide variety of topographic and environmental settings, which also acknowledge spatial and temporal change in glacier and ice sheet systems.

Inter-Model Comparison for Tsunami Debris Simulation

Assessing the risk of tsunami-driven debris has increasingly been recognized as an important design consideration. The recent ASCE/SEI7-16 standard Chapter 6 requires all the areas included within a 22.5° spreading angle from the debris source to consider the debris impact. However, it would be more reasonable to estimate the risks using numerical simulation models. Although a number of simulation models to predict tsunami debris transport have been proposed individually, comparative studies for these simulation models have rarely been conducted. Thus, in the present study, an inter-model comparison for tsunami debris simulation model was performed as a part of the virtual Tsunami Hackathon held in Japan from September 1 to 3 in 2020. The blind benchmarking experiment, which recorded the transport of three container models under a tsunami-like bore, was conducted to generate a unique dataset. Then, four different numerical models were applied to reproduce the experiments. Simulated results demonstrated considerable differences among the simulation models. Essentially, the importance of accurate modelling of a flow field, especially a tsunami front, was confirmed to be important in simulating debris motion. Parametric studies performed in each model and comparisons between different models also confirmed that a drag coefficient and inertia coefficient would influence the simulated debris trajectory and velocity. It was also shown that two-way coupled modelling to express the interaction between debris and a tsunami is important to accurately model the debris motion.

Numerical Simulation of Supraglacial Debris Mobility: Implications for Ablation and Landform Genesis

Supraglacial debris does not remain fixed atop ablating ice, but can move across the ice surface as supraglacial topography evolves. This active debris movement (distinct from passive movement due to underlying ice motion) affects landform genesis as well as the rate and spatial distribution of ablation. While observations of debris transport across evolving supraglacial topography are abundant, models of these coupled processes over timescales of decades and longer are few. Here I adapt a numerical model of coupled ablation and downslope debris transport to simulate the evolution of an idealized debris-covered glacier on the timescale of complete de-icing. The model includes ablation that depends on supraglacial debris thickness and a hillslope-scale debris transport function that scales non-linearly with slope angle. Ice thickness and debris distribution evolve with model time, allowing complete simulation of de-icing and landform construction in an idealized glacier test-section. The model produces supraglacial relief that leads to topographic inversions consistent with conceptual models of hummocky landform genesis. Model results indicate that the relief of the glacier surface and postglacial hummocks depend on the relationship between characteristic timescales for ablation and debris transport, which is defined as an index of debris mobility. When debris mobility is high, topographic inversions are rapid and supraglacial and postglacial relief are subdued. When debris mobility is low, more pronounced supraglacial relief is produced, but postglacial relief remains subdued. An intermediate mobility appears to optimize both postglacial relief and the rate of de-icingcompared with both highly-mobile and immobile debris. This enhancement of de-icing due to debris mobility could contribute to the observed anomalous rates of ablation in some debris-covered glaciers.

Modelling steady states and the transient response of debris-covered glaciers

Debris-covered glaciers are commonly found in alpine landscapes of high relief and play an increasingly important role in a warming climate. As a result of the insulating effect of supraglacial debris, their response to changes in climate is less direct and their dynamic behaviour more complex than for debris-free glaciers. Due to a lack of observations, here we use numerical modelling to explore the dynamic interactions between debris cover and geometry evolution for an idealized glacier over centennial timescales. The main goal of this study is to understand the effects of debris cover on the glacier's transient response. To do so, we use a numerical model that couples ice flow, debris transport, and its insulating effect on surface mass balance and thereby captures dynamic feedbacks that affect the volume and length evolution. In a second step we incorporate the effects of cryokarst features such as ice cliffs and supraglacial ponds on the dynamical behaviour. Our modelling indicates that thick debris cover delays both the volume response and especially the length response to a warming climate signal. Including debris dynamics therefore results in glaciers with extended debris-covered tongues and that tend to advance or stagnate in length in response to a fluctuating climate at century timescales and hence remember the cold periods more than the warm. However, when including even a relatively small amount of melt enhancing cryokarst features in the model, the length is more responsive to periods of warming and results in substantial mass loss and thinning on debris-covered tongues, as is also observed.

Modeling Supraglacial Ponding and Drainage Dynamics: Responses to Glacier Surface Topography and Debris Flux Conditions

Supraglacial ponds play a significant role in the mass loss of many debris-covered glaciers in the Himalaya. Glacier surface topography and debris flux conditions are thought to govern supraglacial ponding and drainage. Existing studies, however, have not adequately investigated the relationships and feedbacks between meltwater production, debris transport, topographic evolution and ponding, because field measurements are limited in time and space, and most existing models either neglect these processes or use oversimplified assumptions. Such limitations restrict our understanding of supraglacial hydrology and introduce uncertainties in our assessments of glacier sensitivity to climate forcing. This study develops a more comprehensive numerical model to provide insights into the couplings between topographically-controlled surface ablation, meltwater drainage, ponding, and gravitational debris transport under radiative forcing. We investigate supraglacial ponding and drainage dynamics in response to different topographic and debris flux conditions through numerical simulations based on Baltoro Glacier in the Karakoram and several hypothetical scenarios. Results suggest that: 1) Supraglacial ponds make a significant contribution to the total ice loss (more than 20 %) in the lower-mid ablation zone over one ablation season, which elevates the glacier's nonlinear response to radiative forcing. 2) Gravitational debris transport has a non-negligible control on the growth rate of supraglacial ponds by governing debris thickness and ablation rates on the ice-cliffs around ponds. 3) Glacier surface gradient and local topographic depressions control pond formation by affecting supraglacial water storage and drainage. Our simulations provide a possible explanation to the abundance of ponds in the mid ablation zone where slope is gentle and more local depressions are present. These findings may contribute to more accurate predictions of future glacier changes in response to climate change.

Degradable Loss Control System for Coiled Tubing Interventions

Coiled tubing (CT) milling and cleanout interventions depend heavily on the circulation of fluids and debris throughout a wellbore. When these interventions are performed on lateral wells which are subhydrostatic or are not able to sustain a stable column of fluid during the operation, they pose unique challenges. This is mostly due to the inability of the well to support a column of fluid, which consequently causes circulation over long distances and along narrow annular spaces to be difficult or impossible, particularly when a thief zone is present. The many consequences of poor to nonexistent fluid circulation can be severe, ranging from poor hole cleaning and formation damage to inducing a stuck pipe scenario. Over the years, many mechanical and chemical solutions have been employed to improve fluid circulation in subhydrostatic wells, but each comes with its own set of challenges and can be costly to implement. Two methods commonly used today to improve debris removal from a low-pressure wellbore include the use of nitrogen and the creation of an underbalanced condition in the wellbore by flowing formation fluids. The former is expensive, time consuming, and requires advance bottomhole assembly (BHA) planning whereas the latter can lead to significant formation damage or a reduction in fracture conductivity through the removal of proppant from the near-wellbore area. A fiber- and particulate-laden degradable loss control system (LCS) is proposed as an improvement on the current techniques used to improve circulation in subhydrostatic wells. The LCS temporarily prevents losses to the reservoir and enables the circulation of debris out of the well. The system was applied to low-pressure wells in North America to demonstrate its effectiveness in addressing the reduction or loss of circulation throughout the wellbore and improving debris transport to surface.