Wood dynamics in upland streams under different disturbance regimes     

Leonora King  Marwan A. Hassan  Xiaohua Wei  Leif Burge  Xiaoyong Chen 《地球表面变化过程与地形》2013,38(11):1197-1209

This paper presents reach scale large wood (LW) budgets of 12 upland streams in the Okanagan Basin of British Columbia. The study included 100 m long reaches at three wildfire sites and three undisturbed sites in the Interior Douglas‐fir (IDF) biogeoclimatic zone, and three recent Mountain Pine Beetle (MPB) infestation sites and three undisturbed sites in the Montane Spruce (MS) zone. Detailed information on wood recruitment, output and storage were obtained from repeated annual surveys. Recruitment from the riparian zone was found to dominate wood inputs, with fluvial import of secondary importance. In undisturbed streams, wood exhumation was found to be of tertiary importance, but was not observed in disturbed streams. Relative wood length was found to be a strong predictor of wood stability, with wood length to channel width and wood diameter to channel depth ratios of 1:1 forming an approximate maximum threshold of wood mobility. Volumetric decomposition was, on average, a third of the value of fluvial export, and the average residence time of wood in the channels was 20 years. In undisturbed reaches, wood storage indicated a slow depletion of wood from the channels. In the disturbed reaches, wildfire was found to significantly increase annual wood recruitment by more than an order of magnitude over undisturbed or control streams. MPB had not significantly increased LW recruitment, but is expected to increase over the coming decades. Storage rates at the disturbed streams indicated a net accumulation of wood over the study period. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A component approach for the hysteretic behaviour of connections in cross‐laminated wooden structures     

Giovanni Rinaldin  Claudio Amadio  Massimo Fragiacomo 《地震工程与结构动力学》2013,42(13):2023-2042

In this paper, a numerical model to estimate the dissipative capacity and describe the cyclic response of cross‐laminated (X‐lam) timber buildings is presented. The connections between panels and to the foundation (metal hold‐downs and angle brackets, and screwed connectors) are modelled with nonlinear hysteretic multispring elements taking into account the strength interaction between different degrees of freedom according to a predefined domain. The timber components (solid X‐lam floors and wall panels) are modelled using elastic shell elements. By calibration on experimental cyclic tests carried out on each degree of freedom, important features of timber connection behaviour such as post‐peak strength, pinching and stiffness degradation can all be considered. In addition, the effect of friction at the interface between panels and with foundation can be taken into account. These springs have been implemented as external subroutines in a widespread software package such as Abaqus. By comparison with the experimental results of cyclic tests carried out on single X‐lam walls, coupled X‐lam walls and a single‐storey X‐lam building, the accuracy of the proposed model is demonstrated. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Organic carbon export in the form of wood during an extreme tropical storm,Upper Rio Chagres,Panama     

Ellen Wohl  Fred L. Ogden 《地球表面变化过程与地形》2013,38(12):1407-1416

Widespread, intense rainfall over the Upper Rio Chagres watershed (414 km²) in central Panama during December 2010 triggered numerous landslides that introduced large numbers of trees to the river network. We flew by helicopter along the mainstem Upper Chagres and the adjacent margins of Lake Alhajuela, into which the Upper Chagres flows, in February and June 2011. We used low‐elevation video photography from these flights to tally the number of wood pieces stored along the lake margin and within the channel, and the number of landslides reaching the mainstem. We used these tallies with ground‐verified estimates of average wood piece size and landslide surface area, and assumptions about wood density, carbon content, and aboveground biomass, to develop a first‐order estimate of carbon export in the form of wood from the Upper Chagres following the 2010 storms. Based on the wood tally, we estimate 9 · 6 to 16 Mg C/km² export, and from the landslide tally we estimate 24 Mg C/km². We believe the landslide tally provides a more accurate minimum estimate of carbon export from the Upper Chagres during the December 2010 storms. These values are an order of magnitude higher than limited data for average or background rates of wood‐based carbon export from other catchments, but two orders of magnitude lower than wood‐based carbon export during extreme storms in Taiwan. The findings suggest that duration of flood flow above a threshold for mobilizing wood within the channel network exerts a more important control on wood export from the Upper Chagres than magnitude of flood peak. Copyright © 2013 John Wiley & Sons, Ltd.  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   

Uniform hazard versus uniform risk bases for performance‐based earthquake engineering of light‐frame wood construction     

Yue Li  Yuejun Yin  Bruce R. Ellingwood  William M. Bulleit 《地震工程与结构动力学》2010,39(11):1199-1217

This paper investigates the implications of designing for uniform hazard versus uniform risk for light‐frame wood residential construction subjected to earthquakes in the United States. Using simple structural models of one‐story residences with typical lateral force‐resisting systems (shear walls) found in buildings in western, eastern and central regions of the United States as illustrations, the seismic demands are determined using nonlinear dynamic time‐history analyses, whereas the collapse capacities are determined using incremental dynamic analyses. The probabilities of collapse, conditioned on the occurrence of the maximum considered earthquakes and design earthquakes stipulated in ASCE Standard 7‐05, and the collapse margins of these typical residential structures are compared for typical construction practices in different regions in the United States. The calculated collapse inter‐story drifts are compared with the limits stipulated in FEMA 356/ASCE Standard 41‐06 and observed in the recent experimental testing. The results of this study provide insights into residential building risk assessment and the relation between building seismic performance implied by the current earthquake‐resistant design and construction practices and performance levels in performance‐based engineering of light‐frame wood construction being considered by the SEI/ASCE committee on reliability‐based design of wood structures. Further code developments are necessary to achieve the goal of uniform risk in earthquake‐resistant residential construction. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The effects of river restoration on catchment scale flood risk and flood hydrology   总被引：1，自引：0，他引：1       下载免费PDF全文

Simon J. Dixon  David A. Sear  Nicholas A. Odoni  Tim Sykes  Stuart N. Lane 《地球表面变化过程与地形》2016,41(7):997-1008

A rising exposure to flood risk is a predicted consequence of increased development in vulnerable areas and an increase in the frequency of extreme weather events due to climate change. In the face of this challenge, a continued reliance on engineered at‐a‐point flood defences is seen as both unrealistic and undesirable. The contribution of ‘soft engineering’ solutions (e.g. riparian forests, wood in rivers) to integrated, catchment scale flood risk management has been demonstrated at small scales but not larger ones. In this study we use reduced complexity hydrological modelling to analyse the effects of land use and channel changes resulting from river restoration upon flood flows at the catchment scale. Results show short sections of river‐floodplain restoration using engineered logjams, typical of many current restoration schemes, have highly variable impacts on catchment‐scale flood peak magnitude and so need to be used with caution as a flood management solution. Forested floodplains have a more general impact upon flood hydrology, with areas in the middle and upper catchment tending to show reductions in peak magnitude at the catchment outflow. The most promising restoration scenarios for flood risk management are for riparian forest restoration at the sub‐catchment scale, representing 20–40% of the total catchment area, where reductions in peak magnitude of up to 19% are observed through de‐synchronization of the timings of sub‐catchment flood waves. Sub‐catchment floodplain forest restoration over 10–15% of total catchment area can lead to reductions in peak magnitude of 6% at 25 years post‐restoration. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

新疆奇台硅化木的结构及成分分析          下载免费PDF全文

徐均强  卢宝玉  杜韦 《山东国土资源》2013,29(1):18-20

新疆奇台是我国硅化木的重要产地,学者研究和资料表明奇台硅化木是亿万年前树木被SiO2交代的产物。SiO2结合的方式是多种多样的,能形成不同的矿物。根据奇台硅化木的不同颜色,利用偏光显微镜和红外光谱仪对同一块硅化木的3种代表颜色进行测试分析。经研究分析认为:奇台硅化木的结构是木质纤维结构,颜色不同SiO2交代的程度不同。奇台硅化木样品颜色不同物质成分也不同,绿色部分主要的物质成分是玛瑙,黑色部分主要的物质成分是蛋白石,灰色部分主要的物质成分是玉髓。  相似文献   

木质锚杆加固土遗址边坡的稳定性分析          下载免费PDF全文

石玉成  秋仁东 《地震工程学报》2015,37(3):809-815

基于有限元强度折减法,以新疆吐鲁番交河故城的典型工程加固剖面为实例,计算分析木质锚杆加固土遗址坡体在静力、地震作用下的安全系数,同时分析木质锚杆长度、锚固角度等因素对其安全系数的影响,评价木质锚杆加固土遗址坡体的可行性,并在此基础上探讨其相关机理及设计中应注意的问题。研究成果可为木质锚杆加固土遗址坡体的相关工程实践提供参考。  相似文献   

Progress in refining the global radiocarbon calibration curve using New Zealand kauri (Agathis australis) tree-ring series from Oxygen Isotope Stage 3     

《Quaternary Geochronology》2015

Ancient kauri (Agathis australis) buried in bogs across Northland, New Zealand, provide potential for a continuous high-precision radiocarbon calibration curve that extends to the full chronologic range of the dating method. Here we report four new tree-ring series which in addition to previous work represent some 5312 years across Oxygen Isotope Stage 3, a period during which human evolution, migration and extinction took place against a backdrop of extreme and abrupt global climate and environmental change. We compare our radiocarbon-dated series against three different calibration datasets and find considerable differences in the wiggle-matched solutions, demonstrating the difficulty in undertaking high-precision correlation between ice, marine and terrestrial sequences. One way around the apparent impasse is the use of ¹⁰Be in the Greenland and Antarctic ice cores to precisely link to kauri ¹⁴C from which a decadally/bidecadally-resolved floating ‘calibration’ dataset can be generated.  相似文献   

Firewood consumption amongst poor inhabitants in a semiarid tropical forest: A case study from Piura,northern Peru     

《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(1):28-41

Semiarid forests are disappearing on a large scale and are considered to be the most endangered ecosystems in the lowland tropics. The deforestation rate in Peru is among the highest in Latin America and the Caribbean. Poor people are often more dependent on forest resources than those who are well off. However, little is known about poor people's use of forest resources or the effect of logging in semiarid forests. The article deals with household energy use and the source of firewood (bought or collected, either locally or over some distance) in two semiarid forests in Piura, northern Peru. The most used tree species and the vulnerability of the species are also examined in order to understand deforestation. Peru has introduced regulations on the use of forest resources and the article focuses on how these regulations are locally understood. The methodology includes questionnaires, recording local household practices, and in-depth interviews with local informants and both governmental and non-governmental organizations. The daily wood consumption rates per person were measured. The findings reveal that household economy is not the only factor affecting daily firewood consumption rate, but also climate, ecology, access to firewood, and traditions are contributing factors.  相似文献