Experimental investigation of the vertical pullout cyclic response of bucket foundations in sand

A series of 1 g model tests was conducted to investigate the accumulated vertical pullout displacement and unloading stiffness of bucket foundations embedded in dry and saturated sands. The foundations were subjected to vertical pullout cyclic loading with different load amplitudes. Cyclic load was applied up to 10⁴ cycles. Test results showed that the accumulated vertical pullout displacement increased with the increase in the number of load cycles and cyclic load amplitudes. The unloading stiffness of the bucket foundations decreased with the increase in load amplitude and number of cycles. Empirical equations were proposed based on the test results to evaluate the accumulated vertical pullout displacement and unloading stiffness of the bucket foundations in saturated sand. These equations can be used for the preliminary design of single or tripod bucket foundations.     

A regime shift in sediment export from a coastal watershed during a record wet winter,California: Implications for landscape response to hydroclimatic extremes

Small, steep watersheds are prolific sediment sources from which sediment flux is highly sensitive to climatic changes. Storm intensity and frequency are widely expected to increase during the 21st century, and so assessing the response of small, steep watersheds to extreme rainfall is essential to understanding landscape response to climate change. During record winter rainfall in 2016–2017, the San Lorenzo River, coastal California, had nine flow peaks representing 2–10‐year flood magnitudes. By the third flood, fluvial suspended sediment showed a regime shift to greater and coarser sediment supply, coincident with numerous landslides in the watershed. Even with no singular catastrophic flood, these flows exported more than half as much sediment as had a 100‐year flood 35 years earlier, substantially enlarging the nearshore delta. Annual sediment load in 2017 was an order of magnitude greater than during an average‐rainfall year, and 500‐fold greater than in a recent drought. These anomalous sediment inputs are critical to the coastal littoral system, delivering enough sediment, sometimes over only a few days, to maintain beaches for several years. Future projections of megadroughts punctuated by major atmospheric‐river storm activity suggest that interannual sediment‐yield variations will become more extreme than today in the western USA, with potential consequences for coastal management, ecosystems, and water‐storage capacity. The occurrence of two years with major sediment export over the past 35 years that were not associated with extremes of the El Niño Southern Oscillation or Pacific Decadal Oscillation suggests caution in interpreting climatic signals from marine sedimentary deposits derived from small, steep, coastal watersheds, to avoid misinterpreting the frequencies of those cycles. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.     

Estimation of phosphorus loads with sparse data for agricultural watersheds in the Czech Republic

Abstract

Agricultural watersheds in the Czech Republic are one of the primary sources of non-point-source phosphorus (P) loads in receiving waters. Since such non-point sources are generally located in headwater catchments, streamflow and P concentration data are sparse. We show how very short daily streamflow and P concentration records can be combined with nearby longer existing daily streamflow records to result in reliable estimates of daily and annual P concentrations and loads. Maintenance of variance streamflow record extension methods (MOVE) can be employed to extend short streamflow records. Constituent load regressions are used to predict daily P constituent loads from streamflow and other time varying characteristics. Annual P loads are then estimated for individual watersheds. Resulting annual P load estimates ranged from 0.21 to 95.4 kg year^-1 with a mean value of 11.77 kg year^-1. Similarly annual P yield estimates ranged from 0.01 to 0.3 kg ha^-1 year^-1 with an average yield of 0.07 kg ha^-1 year^-1. We document how short records of daily streamflow and P concentrations can be combined with a national network of daily streamflow records in the Czech Republic to arrive at meaningful and reliable estimates of annual P loads for small agricultural watersheds.

Citation Beránková, T., Vogel, R. M., Fiala, D. & Rosendorf, P. (2010) Estimation of phosphorus loads with sparse data for agricultural watersheds in the Czech Republic. Hydrol. Sci. J. 55(8), 1417–1426.     

移动荷载作用下土体动力反应数值模拟

在研究轨道振动荷载的产生机理基础上,归纳出一个能够涵盖速度、线路不平顺、轮重、轨枕对轮载的分散作用等因素在内的轨道荷载解析表达式,以此作为输入施加到土体模型上,利用ANSYS模拟地基土在轨道移动荷载作用下的三维瞬态弹塑性反应。通过计算得到土体不同位置位移和加速度时程曲线,并得出如下结论:荷载刚施加时地面位移会有一个突变,但是随着荷载的移动会达到一个稳定值,并随着水平面内远离轨道,该值逐渐衰减;荷载刚刚施加时加速度会有一个突变值,随着荷载的移动逐渐趋于零。轨道机车速度对竖向方向的位移和加速度影响不大。     

Non-linear channel–shoal dynamics in long tidal embayments

The dynamics of finite-amplitude bed forms in a tidal channel is studied with the use of an idealized morphodynamic model. The latter is based on depth-averaged equations for the tidal flow over a sandy bottom. The model considers phenomena on spatial scales of the order of the tidal excursion length. Transport of sediment mainly takes place as suspended load. The reference state of this model is characterized by a spatially uniform M₂ tidal current over a fixed horizontal bed. The temporal evolution of deviations from this reference state is governed by amplitude equations: these are a set of non-linear equations that describe the temporal evolution of bed forms. These equations are used to obtain new morphodynamic equilibria which may be either static or time-periodic. Several of these bottom profiles show strong similarity with the tidal bars that are observed in natural estuaries. The dependence of the equilibrium solutions on the value of bottom friction and channel width is investigated systematically. For narrow channels (width small compared to the tidal excursion length) stable static equilibria exist if bottom friction is slightly larger than r_cr. For channel widths more comparable to the tidal excursion length, multiple stable steady states may exist for bottom friction parameter values below r_cr. Regardless of channel width, stable time-periodic equilibria seem to emerge as the bottom friction is increased.Responsible Editor: Jens Kappenberg     

Copula-based identification of the non-stationarity of the relation between runoff and sediment load

It is important to identify the non-stationarity in the relation between runoff and sediment load under the backdrop of the changing environment. This relation helps to further understand the mechanisms of runoff and sediment yield. A copula-based method was used to detect possible change points in the relation between runoff and sediment load in the Wei River Basin (WRB), China, where soil erosion is a very severe issue. The modified Mann-Kendall trend test method was applied to obtain the trends of runoff and sediment load spanning 1960–2010 at monthly and annual timescales. Finally, the causes of the identified non-stationarity of the relation between runoff and sediment load were roughly analyzed from the perspective of climate change and human activities. Results indicated that:(1) the runoff and sediment load in the Jinghe and Wei rivers were generally characterized by noticeably decreasing trends at both monthly and annual timescales;(2) both the Jinghe and Wei rivers had a common change point (2002), implying that the stationarity of the relation between runoff and sediment load in the Jinghe and Wei River was invalid; (3) human activities including increasing water consumption and growing application of soil conservation practices are dominant factors resulting in non-stationarity in the rela-tion between runoff and sediment load in the WRB. This study provides a new idea for identifying the non-stationarity of multivariate relation in the hydro-meteorological field under the background of the changing environment.     

Trend analysis of nutrient loadings in a large prairie catchment

Nutrient loadings in many river catchments continue to increase due to rapid expansion of agriculture, urban and industrial development, and population growth. Nutrient enrichment of water bodies has intensified eutrophication which degrades water quality and ecosystem health. In this study, we carried out a trend analysis of total phosphorus and total nitrogen loads in the South Saskatchewan River (SSR) catchment using a novel approach to analyse nutrient time series. Seasonal analysis of trends at each of the water quality stations was performed to determine the relationships between annual flow regimes and nutrient loads in the catchment, in particular, the influence of the high spring runoff on nutrient export. Decadal analysis was also performed to determine the long-term relationships of nutrients with anthropogenic changes in the catchment. Although it was found that seasonal and historical variability of nutrient load trends is mainly determined by streamflow regime changes, there is evidence that increases in nitrogen concentration can also be attributed to anthropogenic changes.     

移动荷载作用下Kerr地基梁稳态响应解答

研究Kerr地基上的均质Euler-Bernoulli梁在移动集中荷载作用下的稳态响应,分析有无阻尼存在时列车速度、地基压缩刚度、剪切刚度对Kerr地基梁挠度曲线的影响。计算结果表明,地基阻尼的存在能明显减少移动荷载引起的地基梁挠度,地基梁的挠度受地基压缩刚度的影响比剪切刚度更为明显。