Applying geomorphological principles and engineering science to develop a phased sediment management plan for Mount St Helens, Washington

Thirty-seven years post-eruption, erosion of the debris avalanche at Mount St. Helens continues to supply sediment to the Toutle-Cowlitz River system in quantities that have the potential to lower the Level of Protection (LoP) against flooding unacceptably, making this one of the most protracted gravel-bed river disasters to date. The Portland District, US Army Corps of Engineers (USACE) recently revised its long-term plan for sediment management (originally published in 1985), in order to maintain the LoP above the Congressionally-authorised level, while reducing impacts on fish currently listed under the Endangered Species Act, and minimising the overall cost of managing sediment derived from erosion at Mount St Helens. In revising the plan, the USACE drew on evidence gained from sediment monitoring, modelling and uncertainty analysis, coupled with assessment of future LoP trends under a baseline scenario (continuation of the 1985 sediment management strategy) and feasible alternatives. They applied geomorphological principles and used engineering science to develop a Phased Sediment Management Plan that allows for uncertainty concerning future sediment yields by implementing sediment management actions only as, and when, necessary. The phased plan makes best use of the potential to enhance the sediment trap efficiency and storage capacity of the existing Sediment Retention Structure (SRS) by incrementally raising its spillway and using novel hydraulic structures to build islands in the NFTR and steepen the gradient of the sediment plain upstream of the structure. Dredging is held in reserve, to be performed only when necessary to react to unexpectedly high sedimentation events or when the utility of other measures has been expended. The engineering-geomorphic principles and many of the measures in the Phased Sediment Management Plan are transferrable to other gravel-bed river disasters. The overriding message is that monitoring and adaptive management are crucial components of long-term sediment-disaster management, especially in volcanic landscapes where future sediment yields are characterised by uncertainty and natural variability

Heterogeneous packing and hydraulic stability of cube and cubipod armor units

This paper describes the heterogeneous packing (HEP) failure mode of breakwater armor. HEP reduces packing density in the armor layer near and above the mean water level and increases packing density below it. With HEP, armor units may move in the armor layer, although they are not actually extracted from it. Thus, when HEP occurs, armor-layer porosity is not constant, and measurements obtained with conventional methods may underestimate armor damage. In this paper, the Virtual Net method is proposed to calculate armor damage considering both armor-unit extraction and HEP. The Cubipod concrete armor unit is then described as a solution to the effects of HEP on conventional cubic block armor. The hydraulic stability of cube and Cubipod armor units was compared in two-dimensional laboratory experiments. Cube and Cubipod armor layers were tested in two wave flumes under nonbreaking and non-overtopping conditions. The hydraulic stability was higher for double-layer Cubipod armor than for single-layer Cubipod armor, which had a higher hydraulic stability tan conventional double-layer cube armor.The authors are grateful for the financial support of CDTI (CUBIPOD Project), SATO Construction Co. (OHL Group), and Puertos del Estado (Convenio de Diques). The authors also thank Debra Westall for revising the manuscript.Gómez-Martín, ME.; Medina, JR. (2014). Heterogeneous packing and hydraulic stability of cube and cubipod armor units. Journal of Waterway, Port, Coastal, and Ocean Engineering. 140(1):100-108. doi:10.1061/(ASCE)WW.1943-5460.0000223S100108140

TNT equivalency analysis of specific impulse distribution from close-in detonations

Detonation of a high explosive close to a structural component results in a blast load that is highly localized and nonuninform in nature. Prediction of structural response and damage due to such loads requires a detailed understanding of both the magnitude and distribution of the load, which in turn are a function of the properties and dimensions of the structure, the standoff from the charge to the structure, and the composition of the explosive. It is common to express an explosive as an equivalent mass of TNT to facilitate the use of existing and well-established semi-empirical methods. This requires calculation of a TNT equivalency factor (EF), that is, the mass ratio between the equivalent mass of TNT and the explosive mass in question, such that a chosen blast parameter will be the same for the same set of input conditions aside from explosive type. In this paper, we derive EF for three common explosives: C4, COMP-B, and ANFO, using an equivalent upper bound kinetic energy approach. A series of numerical simulations are performed, and the resultant magnitudes and distributions of specific impulse are used to derive the theoretical upper bound kinetic energy that would be imparted to a flexible target. Based on the equivalent mass of TNT of each explosive, which is required to impart the same kinetic energy for a given target size and standoff distance as of TNT, the EF is calculated. It is shown that in the near-field, the EFs are non-constant and are dependent on both standoff and target size. The results in the current study are presented in a scaled form and can be used for any practical combination of charge mass, distance from the charge to the target, target size, thickness, and density

Reconstruction of a flash flood with large wood transport and its influence on hazard patterns in an ungauged mountain basin

The reconstruction of past flash floods in ungauged basins leads to a high level of uncertainty, which increases if other processes are involved such as the transport of large wood material. An important flash flood occurred in 1997 in Venero Claro (Central Spain), causing significant economic losses. The wood material clogged bridge sections, raising the water level upstream. The aim of this study was to reconstruct this event, analysing the influence of woody debris transport on the flood hazard pattern. Because the reach in question was affected by backwater effects due to bridge clogging, using only high water mark or palaeostage indicators may overestimate discharges, and so other methods are required to estimate peak flows. Therefore, the peak discharge was estimated (123±18 m3 s–1) using indirect methods, but one-dimensional hydraulic simulation was also used to validate these indirect estimates through an iterative process (127± 33 m3 s–1) and reconstruct the bridge obstruction to obtain the blockage ratio during the 1997 event (~48%) and the bridge clogging curves. Rainfall–Runoff modelling with stochastic simulation of different rainfall field configurations also helped to confirm that a peak discharge greater than 150 m3 s–1 is very unlikely to occur and that the estimated discharge range is consistent with the estimated rainfall amount (233± 27 mm). It was observed that the backwater effect due to the obstruction (water level ~7 m) made the 1997 flood (~35-year return period) equivalent to the 50-year flood. This allowed the equivalent return period to be defined as the recurrence interval of an event of specified magnitude, which, where large woody debris is present, is equivalent in water depth and extent of flooded area to a more extreme event of greater magnitude. These results highlight the need to include obstruction phenomena in flood hazard analysis. Copyright © 2012 John Wiley & Sons, LtdWe express our gratitude to the Spanish Ministry of Science and Innovation for financial support. This work was funded by the MAS Dendro-Avenidas project (CGL2010-19274) and the Geological Survey of Spain (IGME). We are grateful to the Tagus Water Authority, Environment Department of Castilla y Leon in avila, Caja avila, Asocio de avila and Navaluenga Council for their collaboration. Our special thanks to forester Jose Luis Galan for his assistance in the field. We would also like to mention Juan Ballesteros, Ignacio Gutierrez, Tasio Fernandez, Leticia Salas, Carolina Guardiola and angel Prieto for contributing suggestions and interesting discussions that significantly improved this paper. Thanks to the contribution of two anonymous reviewers, which improved the quality of the early version of this manuscript.Ruiz-Villanueva, V.; Bodoque, J.; Díez-Herrero, A.; Eguíbar Galán, MÁ.; Pardo-Igúzquiza, E. (2012). Reconstruction of a flash flood with large wood transport and its influence on hazard patterns in an ungauged mountain basin. Hydrological Processes. (9433):1-14. https://doi.org/10.1002/hyp.9433S114943

Influence of the Tunnel Shape on Shotcrete Lining Stresses

Tunnel excavation is frequently carried out in rock masses by the drill and blast method and the final shape of the tunnel boundary can be irregular due to overbreaks. In order to investigate the effects of overbreaks a study of the effect of tunnel boundary irregularity has been carried out. This is done developing a computational tool able to take into account fuzzy variables (i.e., thickness of the beams of the bedded spring approach used for the model). The obtained results show that irregularity effects should be considered when a shotcrete lining is used as the final tunnel lining (for the case where the tunneling procedure does not permit a smooth surface to be obtained). This is crucial to obtain a durable linin

Explicit wave overtopping formula for mound breakwaters with crown walls using CLASH neural network-derived data

Based on the Crest Level Assessment of Coastal Structures (CLASH) Neural Network Overtopping prediction method, a new 16-parameter overtopping estimator (Q6) was developed for conventional mound breakwaters with crown walls, both with and without toe berms. Q6 was built up using the overtopping estimations given by the CLASH Neural Network and checked using the CLASH database. Q6 was compared to other conventional overtopping formulas, and the Q6 obtained the lowest prediction errors. Q6 provides overtopping predictions similar to the CLASH Neural Network for conventional mound breakwaters but using only six explanatory dimensionless variables (Rc=Hm0; Ir; Rc=h;Gc=Hm0; Ac=Rc, and a toe berm variable based on Rc=h) and two reduction factors (g f and g b ). Q6 describes explicit relationships between input variables and overtopping discharge, and hence it facilitates use in engineering design to identify costeffective solutions and to quantify the influence of variations in wave and structural parameters.The authors are grateful for financial support from the Spanish Ministerio de Economia y Competitividad (Grant BIA2012-33967). The first author was funded through the FPU program (Formacion del Profesorado Universitario, Grant AP2010-4366) by the Spanish Ministerio de Educacion, Cultura y Deporte. The authors also thank Debra Westall for revising the manuscript.Molines, J.; Medina, JR. (2016). Explicit wave overtopping formula for mound breakwaters with crown walls using CLASH neural network-derived data. Journal of Waterway Port Coastal and Ocean Engineering. 142(3). https://doi.org/10.1061/(ASCE)WW.1943-5460.0000322S142

Flood realities, perceptions, and the depth of divisions on climate

Research has led to broad agreement among scientists that anthropogenic climate change is happening now and likely to worsen. In contrast to scientific agreement, US public views remain deeply divided, largely along ideological lines. Science communication has been neutralised in some arenas by intense counter-messaging, but as adverse climate impacts become manifest they might intervene more persuasively in local perceptions. We look for evidence of this occurring with regard to realities and perceptions of flooding in the northeastern US state of New Hampshire. Although precipitation and flood damage have increased, with ample news coverage, most residents do not see a trend. Nor do perceptions about past and future local flooding correlate with regional impacts or vulnerability. Instead, such perceptions follow ideological patterns resembling those of global climate change. That information about the physical world can be substantially filtered by ideology is a common finding from sociological environment/society research

A combined risk analysis approach for complex dam-levee systems

[EN] In many areas of the world, dams and levees are built to reduce the likelihood of flooding. However, if they fail, the result can be catastrophic flooding beyond what would happen if they did not exist. Therefore, understanding the risk reduced by the dam or levee, as well as any risk imposed by these flood defences is of high importance when determining the appropriate risk reduction investment strategy. This paper describes an approach for quantifying and analysing risk for complex dam-levee systems, and its application to a real case study. The basis behind such approach rely on the potential of event tree modelling to analyse risk from multiple combinations of load-system response-consequence' events, tested by the authors for a real case study. The combined approach shows how the contribution to system risk of each sub-system can be assessed. It also describes how decisions on risk mitigation measures, at the individual asset scale, can and should be informed in terms of how they impact the overall system risk.This work was supported by Spanish Ministry of Economy and Competitiveness (MINECO) [BIA 2013-48157-C2-1-R].Castillo-Rodríguez, J.; Needham, J.; Morales Torres, A.; Escuder Bueno, I. (2017). A combined risk analysis approach for complex dam-levee systems. Structure and Infrastructure Engineering. 13(12):1624-1638. https://doi.org/10.1080/15732479.2017.1314514S16241638131

Overcoming failure in infrastructure risk governance implementation: large dams journey

[EN] There is ample recognition of the risk inherent in our very existence and modes of social organization, with a reasonable expectation that implementing risk governance will result in enhanced resilience as a society. Despite this, risk governance is not a mainstream approach in the infrastructure sector, regardless of the increasing number of peer-reviewed published conceptualizations, mature procedures to support its application, or public calls to cope with systemic risks in our modern societies. This paper aims to offer a different view on the issue of risk governance, with focus in the analysis of the root causes of its relatively low degree of implementation in the infrastructure sector. We later analyze the impact of such essential causes, which we have grouped and labeled as the ontology, the concerns, the anathemas, and the forgotten, in the specific field of large dams. 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