The characteristics of the Mocoa compound disaster event,Colombia

A rainfall-induced compound disaster happened in Mocoa in the pre-dawn hours of 1 April 2017. More than 300 people were killed, and a large number of houses and roads were destroyed in the worst catastrophe in the history of Mocoa. To investigate this disaster, a detailed interpretation was carried out using high-resolution images. Analysis of disaster characteristics based on satellite image revealed that the disaster could be identified as a consequence of compound mountain hazards including landslides, debris flows, and mountain torrents. The mountain hazards converged in the mountain watershed, which amplified the disaster’s effects. Analysis considers that this disaster is the result of heavy rainfalls. Moreover, in-depth interpretation of rainfall data and satellite images spanning over 16 years reveals that the previous El Niño event (2014–2016) also played an important role, which caused reduced rainfall and vegetation coverage. The long period of drought brought by El Niño affected the growth of vegetation and reduced the ability of vegetation to cope with heavy rainfalls. The results reveal that both antecedent rainfalls and climate impact need to be taken into consideration for mountain hazard analysis.     

Study on laterally loaded piles with rectangular and circular cross sections

The conventional approach in the design of laterally loaded piles with rectangular cross section involves the simplification of converting the rectangular cross section of the pile to an equivalent circular cross section. An analysis to determine the response of laterally loaded rectangular or circular piles in elastic soil is presented in which this simplification is not required. The analysis is based on the solution of differential equations governing the displacements of the pile–soil system derived using energy principles. The pile geometry and the elastic constants of the soil and pile are the input parameters to the analysis. Using this analysis, comparisons are made between the response of rectangular and circular piles in elastic soil. Based on the proposed solution scheme, a user-friendly spreadsheet program (LATPAXL) was developed that can be used to perform the analysis. In addition, simple equations obtained by regression analysis of the pile head deflection and bending moment profiles are proposed. Examples illustrate the use of the analysis.     

New impact equation using barrier Froude number for the design of dual rigid barriers against debris flows

Landslides - In the design of multiple rigid barriers, the height of the first barrier governs the impact dynamics of debris flow on the next barrier in a channel. However, current design...     

Assessment of debris flow multiple-surge load model based on the physical process of debris-barrier interaction

Debris-flow impact load is one of the key parameters for design of engineering countermeasures. The multiple-surge load model is a remarkable progress in estimating the debris-flow impact load, which clearly delineates the contribution of each surge to the total impact load and the corresponding acting points. In order to better understand the impact process of channelized debris flow against flexible barrier, a series of medium-scale flume experiments with varying debris-flow volumetric solid concentration (0.40/0.50/0.55) were conducted. Especially, surge impact behavior is focused so that the predictability of the multiple-surge load model could be assessed. The flume and model flexible barrier were instrumented so that both the barrier dynamic response and the debris-flow properties (flow regime) could be correlated to facilitate the assessment. The results show that multiple-surge load model well predicts the total impact load. However, due to the simplification in the impact process, the interaction between the mobile phase (surge) and the deposited phase is ignored, resulting in discrepancy in the load distribution between the model prediction and experimental result. The remixing of deposited debris by the subsequent surges leads to downward momentum transfer to the lower section of barrier, which should be regarded as an adverse scenario of the design of flexible-barrier anchor capacity.

     

Effects of particle size of mono-disperse granular flows impacting a rigid barrier

Understanding the interaction between complex geophysical flows and barriers remains a critical challenge for protecting infrastructure in mountainous regions. The scientific challenge lies in understanding how grain stresses in complex geophysical flows become manifested in the dynamic response of a rigid barrier. A series of physical flume tests were conducted to investigate the influence of varying the particle diameter of mono-dispersed flows on the impact kinematics of a model rigid barrier. Particle sizes of 3, 10, 23 and 38 mm were investigated. Physical tests results were then used to calibrate a discrete element model for carrying out numerical back-analyses. Results reveal that aside from considering bulk characteristics of the flow, such as the average velocity and bulk density, the impact load strongly depends on the particle size. The particle size influences the degree of grain inertial stresses which become manifested as sharp impulses in the dynamic response of a rigid barrier. Impact models that only consider a single impulse using the equation of elastic collision warrant caution as a cluster of coarse grains induce numerous impulses that can exceed current design recommendations by several orders of magnitude. Although these impulses are transient, they may induce local strucutral damage. Furthermore, the equation of elastic collision should be adopted when the normalized particle size with the flow depth, δ/h, is larger than 0.9 for Froude numbers less than 3.5.     

Assessment of the governance system for the management of the East Sea-Jung dumping site,Korea through analysis of heavy metal concentrations in bottom sediments

As with many countries, the Korea government has made a variety of efforts to meet the precautionary principle under the London Convention and Protocol acceded in 1994 and 2009. However, new strategies for the suitable marine dumping of waste materials have since been developed. In this study, the distribution and contamination of heavy metals including Al, Fe, Mn, Li, Co, Cr, Ni, Cu, Zn, As, Cd, Pb and Hg in bottom sediments were analyzed and compared to various criteria in order to evaluate the effectiveness of the management of the East Sea-Jung (ES-Jung) dumping site by the Korea government. The results indicate that the average metal concentrations were significantly lower than Effects Range Low (ERL) values, and generally similar to or lower than the Threshold Effect Levels (TEL) from the Sediment Quality Guidelinces (SQGs). According to analyses of various metal contamination indexes (Enrichment Factor: EF, Pollution Load Index: PLI and the Index of Geoaccumulation: Igeo), most areas were found to be uncontaminated by heavy metals with the exception of several moderately contaminated stations (ESJ 33, 54, 64 and ESJR 20). Heavy metal concentrations in areas grouped as G1, G2, DMDA, N-Ref and S-Ref which showed similar characteristics between 2007-2013 and 2014, were compared. Unexpectedly, most concentrations in the northern reference area (N-Ref) were much higher than those in the actual dumping areas (G1 and G2), may be due to the influences from nearby cities to the west of the ES-Jung site, rather than from the dumping site itself. Additionally, heavy metal concentrations in the dredged material dumping area (DMDA) were found to be low although they have slightly increased over time and those in the southern reference area (S-Ref) were found to have gradually decreased with year. The concentrations of most metals in the East Sea-Jung dumping site were similar to or less than those in the Earth’s crust and approximately the same as those in continental sediments. As a result, this site can be considered as uncontaminated or slightly contaminated. This implies that the efforts made by the Korea government to manage and govern the dumping site through various policies, including ‘the focal point system’, ‘the responsibility zones system’ and ‘the principle of pollution causing party liability’, have been successful.     

Evaluation of a regional ocean reanalysis system for the East Asian Marginal Seas based on the ensemble Kalman filter

Ocean Science Journal - This study introduces the East Asian Marginal Seas (EAMS) reanalysis system and evaluates its products from 1982 to 2006. The EAMS reanalysis system consists of an ocean...