Monthly streamflow forecasting using neuro-wavelet techniques and input analysis     

André Gustavo da Silva Melo Honorato  Gustavo Barbosa Lima da Silva  Celso Augusto Guimarães Santos 《水文科学杂志》2013,58(15-16):2060-2075

ABSTRACT

Combinations of low-frequency components (also known as approximations) resulting from the wavelet decomposition are tested as inputs to an artificial neural network (ANN) in a hybrid approach, and compared to classical ANN models for flow forecasting for 1, 3, 6 and 12 months ahead. In addition, the inputs are rewritten in terms of the flow, revealing what type of information was being provided to the network, in order to understand the effect of the approximations on the forecasting performance. The results show that the hybrid approach improved the accuracy of all tested models, especially for 1, 3 and 6 months ahead. The input analyses show that high-frequency components are more important for shorter forecast horizons, while for longer horizons, they may worsen the model accuracy.  相似文献   

Improvement of streams hydro‐geomorphological assessment using LiDAR DEMs     

Pascale M. Biron  Guénolé Choné  Thomas Buffin‐Bélanger  Sylvio Demers  Taylor Olsen 《地球表面变化过程与地形》2013,38(15):1808-1821

Hydro‐geomorphological assessments are an essential component for riverine management plans. They usually require costly and time‐consuming field surveys to characterize the spatial variability of key variables such as flow depth, width, discharge, water surface slope, grain size and unit stream power throughout the river corridor. The objective of this research is to develop automated tools for hydro‐geomorphological assessments using high‐resolution LiDAR digital elevation models (DEMs). More specifically, this paper aims at developing geographic information system (GIS) tools to extract channel slope, width and discharge from 1 m‐resolution LiDAR DEMs to estimate the spatial distribution of unit stream power in two contrasted watersheds in Quebec: a small agricultural stream (Des Fèves River) and a large gravel‐bed river (Matane River). For slope, the centreline extracted from the raw LiDAR DEM was resampled at a coarser resolution using the minimum elevation value. The channel width extraction algorithm progressively increased the centerline from the raw DEM until thresholds of elevation differences and slopes were reached. Based on the comparison with over 4000 differential global positioning system (GPS) measurements of the water surface collected in a 50 km reach of the Matane River, the longitudinal profile and slope estimates extracted from the raw and resampled LiDAR DEMs were in very good agreement with the field measurements (correlation coefficients ranging from 0 · 83 to 0 · 87) and can thus be used to compute stream power. The extracted width also corresponded very well to the channel as seen from ortho‐photos, although the presence of bars in the Matane River increased the level of error in width estimates. The estimated maximum unit stream power spatial patterns corresponded well with field evidence of bank erosion, indicating that LiDAR DEMs can be used with confidence for initial hydro‐geomorphological assessments. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Isolation parameters for improving the seismic performance of irregular bridges     

José M. Jara  Dorian Villanueva  Manuel Jara  Bertha A. Olmos 《Bulletin of Earthquake Engineering》2013,11(2):663-686

Bridge structures are usually built on irregular topographical surfaces which create substructures with different pier heights and non uniform stiffness distribution. Three irregularity types of typical reinforced concrete (RC) medium length bridges located in a high seismicity zone of Mexico, were analyzed aimed at determining the best strength and stiffness parameters of an isolation system. The isolation system is composed by lead rubber bearings (LRB) located on each pile and abutment. The variation of the bridge characteristics and the isolation parameters produced 169 models that were subjected to ten seismic records representative of the subduction zone in the Pacific Coast of Mexico. A total of 1690 nonlinear time history analyses (NLTHA) were carried out in longitudinal and transverse directions of the structures. The maximum pier drifts, bending moments and shear forces demands were analyzed to identify the best isolation properties for reducing the concentration of damage in one or two elements and for improving the structural behavior of irregular bridges. Additionally, the analysis of the seismic response of the bridges supported on traditional neoprene bearings was carried out.  相似文献   

The changing rotational excitation of C3 in comet 9P/Tempel 1 during Deep Impact     

Máté Ádámkovics  Imke de Pater  Hy Spinrad 《Astrophysics and Space Science》2012,342(2):309-315

The 4050 Å band of C₃ was observed with Keck/HIRES echelle spectrometer during the Deep Impact encounter. We perform a 2-dimensional analysis of the exposures in order to study the spatial, spectral, and temporal changes in the emission spectrum of C₃. The rotational population distribution changes after impact, beginning with an excitation temperature of ～45 K at impact and increasing for 2 hr up to a maximum of 61±5 K. From 2 to 4 hours after impact, the excitation temperature decreases to the pre-impact value. We measured the quiescent production rate of C₃ before the encounter to be 1.0×10²³ s^?1, while 2 hours after impact we recorded a peak production rate of 1.7×10²³ s^?1. Whereas the excitation temperature returned to the pre-impact value during the observations, the production rate remained elevated, decreasing slowly, until the end of the 4 hr observations. These results are interpreted in terms of changing gas densities in the coma and short-term changes in the primary chemical production mechanism for C₃.  相似文献   

Numerical modelling: a useful tool to simulate collapsing volcanoes     

Solène Pouget  Tim Davies  Ben Kennedy  Karim Kelfoun  Hervé Leyrit 《Geology Today》2012,28(2):59-63

Since the nineteenth century scientists have tried to reproduce natural events in order to study and understand them through the technique of modelling. However, technology has evolved rapidly in the past two decades and now sophisticated numerical models are widely used to reproduce past events or simulate new scenarios. These models are particularly useful to reproduce the large scale and complexity of geological events. To illustrate the use and potential of numerical modelling in geological sciences, we describe a simulation of a large debris avalanche caused by the collapse of the north flank of the Taranaki volcano in New Zealand and the value of this information in the context of disaster planning.  相似文献   

A 70 Ma record of suprasolidus conditions in the large,hot, long‐duration Grenville Orogen          下载免费PDF全文

François Turlin  Clara Deruy  Aurélien Eglinger  Olivier Vanderhaeghe  Anne‐Sylvie André‐Mayer  Marc Poujol  Abdelali Moukhsil  Fabien Solgadi 《地学学报》2018,30(3):233-243

Petrochronology of magmatic monazite and apatite from a single paragneiss leucosome derived by in situ partial melting documents the thermal evolution of the Allochthonous Belt of the central Grenville Province. Monazite records suprasolidus metamorphism from ca. 1080 to 1020 Ma under high temperature up to 850°C. Apatite from the same leucosome yields an age of 960 Ma, consistent with cooling of this crustal segment down to subsolidus conditions of ca. 450°C. A pegmatitic granite dyke, with lobate contacts, previously dated at ca. 1005 Ma (Turlin et al., 2017 ) is interpreted to intrude the paragneisses at a temperature of ca. 650°C close to the wet‐solidus. These data document slow cooling at a rate of 2–6°C/Ma for the middle crust of this part of the Grenville hinterland marked by protracted suprasolidus conditions for at least 70 Ma. It supports the definition of the Grenville Orogen as a large, hot, long‐duration orogen.  相似文献   

Geomorphic and stream flow influences on large wood dynamics and displacement lengths in high gradient mountain streams (Chile)          下载免费PDF全文

Andrés Iroumé  Virginia Ruiz‐Villanueva  Luca Mao  Guillermo Barrientos  Markus Stoffel  Gastón Vergara 《水文研究》2018,32(17):2636-2653

Understanding large wood (LW; ≥1 m long and ≥10 cm in diameter) dynamics in rivers is critical for many disciplines including those assessing flood hazard and risk. However, our understanding of wood entrainment and deposition is still limited, mainly because of the lack of long‐term monitoring of wood‐related processes. The dataset presented here was obtained from more than 8 years of monitoring of 1,264 tagged wood pieces placed in 4 low‐order streams of the Chilean mountain ranges and was used to further our understanding of key factors controlling LW dynamics. We show that LW displacement lengths were longer during periods when peak‐flow water depths (H_max) exceeded the bankfull stage (H_Bk) than in periods with H_max ≤ H_Bk and that these differences were significantly higher for smaller wood pieces. LW length and length relative to channel dimensions were the main factors governing LW entrainment; LW displacement lengths were inversely related to the ratio of piece length to H_15% (i.e., the level above which the flow remains for 15% of the time) and to the ratio of H_15% to bankfull width. Unrooted logs and LW pieces located at the bankfull stage travelled significantly longer distances than logs with attached rootwads and those located in other positions within the bankfull channel. A few large logjams were broken during the period of observation, and in all occasions, LW from these broken logjams did not travel over longer distances than other pieces of LW moved in the same periods and in the same stream segments. Most importantly, our work reveals that LW dynamics tend to be concentrated within a few reaches in each stream and that reaches exhibiting high wood dynamics (extensive entrainment, deposition, or repositioning of LW) are significantly wider and less steep than less dynamic reaches.  相似文献   

On viscoplastic regularisation of strain-softening rocks and soils     

René de Borst  Thibault Duretz 《国际地质力学数值与分析法杂志》2020,44(6):890-903

Constitutive models for rocks and soils typically incorporate some form of strain softening. Moreover, many plasticity models for frictional materials use a nonassociated flow rule. Strain softening and nonassociated flow rules can cause loss of well-posedness of the initial-value problem, which can lead to a severe mesh dependence in simulations and poor convergence of the iterative solution procedure. The inclusion of viscosity, which is a common property of materials, seems a natural way to restore well-posedness, but the mathematical properties of a rate-dependent model, and therefore the effectiveness with respect to the removal of mesh dependence, can depend strongly on how the viscous element is incorporated. Herein, we show that rate-dependent models, which are commonly applied to problems in the Earth's lithosphere, such as plate tectonics, are very different from the approach typically adopted for more shallow geotechnical engineering problems. We analyse the properties of these models under dynamic loadings, using dispersion analyses and one-dimensional finite difference analyses, and complement them with two-dimensional simulations of a typical strain localisation problem under quasi-static loading conditions. Finally, we point out that a combined model, which features two viscous elements, may be the best way forward for modelling time-dependent failure processes in the deeper layers of the Earth, since it not only enables modelling of the creep characteristics typical of long-term behaviour but also regularises the initial/boundary-value problem.  相似文献