Stream response to precipitation variability: a spectral view based on analysis and modelling of hydrological cycle components

Hydrological processes commonly exhibit long‐term persistence, also known as the ‘Hurst phenomenon’. Here, we examine long‐term precipitation and streamflow time series from the Elbe River Basin to quantify differences in the spectral properties and in the Hurst parameter estimates () of the individual hydrological cycle components. Precipitation‐runoff modelling is performed for the Elbe River sub‐catchment Striegis using the Soil and Water Assessment Tool (SWAT). For 38 daily 50 years long streamflow time series from the Elbe River Basin, baseflow separation and spectral analysis is performed. The results show a spectral shift towards low‐frequency scales (>2 years) from precipitation to baseflow, with a parallel increase of from 0.52 (precipitation) to 0.65 (baseflow). The SWAT model is able to reproduce both, the main low‐frequency mode (≈7 yr.) and the (0.62) of the observed Striegis River flow time series. The baseflow appears to be the main component which shapes the low‐frequency response and of streamflow in the Elbe River Basin to the input precipitation. This conclusion is further confirmed through PMWIN‐MODFLOW groundwater modelling of a hypothetic phreatic stream‐connected aquifer system that consists of various soils (sand, loamy sand and silt). A power shift towards lower frequencies and an increase of for the hydraulic heads is obtained, as the aquifer's lateral dimensions increase and its hydraulic conductivity decreases. The average of the groundwater heads is 0.80, 0.90 and 1.0 for sand, loamy sand and silt aquifers, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

沈阳金融中心超高层写字楼项目不同阻尼比长周期地震动参数的确定

介绍了沈阳金融中心超高层写字楼项目如何确定不同阻尼比的长周期设计地震动反应谱,从而避免在周期10s前出现反超现象。反应谱参数确定的原则是新设计反应谱外包或略高于原规范形式的设计反应谱。以“GB50011—2010《建筑抗震设计规范》”为基础,从两方面入手调整不同阻尼比的反应谱参数。一是修改反应谱下降段的形状,去掉直角坐标系下的直线下降段,将曲线下降段延长到原直线下降部分;二是修改下降段衰减指数。这样确定的反应谱在长周期部分不会过于保守,且调整参数的难度和工作量都大大降低。对于高于阻尼比5%和低于阻尼比5%的反应谱,在参数确定上也有不同考虑。     

大口径三维曲线顶管顶力估算及实测分析

顶管顶进阻力由顶管机的迎面阻力和管节与土体间的摩阻力两部分组成,现有的顶力估算公式都具有一定的适用条件,虽然物理意义明确,但参数取值范围较大,往往估算顶力与实际工程顶力的匹配程度较低,尤其是在三维曲线顶管工程中受曲线段的影响,准确估算顶力的难度更大。以长413.0 m,外径为3.8 m,最小曲率半径为313.7 m的三维曲线顶管工程为研究对象,基于现有的顶力公式估算所需顶力大小并布设中继间,在该工程实测数据的基础上分析顶力组成及其与顶程、顶进曲率半径等影响因素之间的关系和顶管在平面曲线和垂直剖面曲线以不同曲率半径顶进的摩阻力变化规律。分析结果显示,曲线顶管摩阻力附加系数是真实存在的,且工程实测值与经验值有所偏差,但顶管在淤泥或黏土层中顶进时的摩阻力按规程推荐取值能够满足工程实践需求。最后提出了顶力估算及中继间的布置建议,为类似工程提供依据。     

海洋石油平台超长桩拒锤分析及工程实例

桩基础是海洋石油平台常用的基础形式,受海上环境的限制通常分段制造、运输和锤击贯入,各桩段通过焊接连为整体,若接桩等造成停锤时间较长,后继打桩可能产生拒锤现象。打桩过程中桩周土体会积累很大的超静孔隙水压力,使桩周一定范围内土体发生水力劈裂现象,导致桩周土体排水固结及强度恢复速度加快,停锤时间越长,土体强度恢复程度越大,造成后继打桩困难甚至拒锤。提出了一种通过疲劳因子? 考虑停锤期间土体强度的恢复,利用GRLWEAP软件计算后继打桩贯入所需锤击数并判断拒锤风险的分析方法。将工程实例和实测结果进行了对比,文中方法计算得到后继打桩贯入锤击数和实测值接近,表明其可行且应用性较强,可为工程设计和施工提供指导。     

Repeat photography as a tool for detecting and monitoring historical changes in South African coastal habitats

Repeat photography was used to illustrate long-term changes occurring in coastal habitats in the Western Cape, South Africa. Historic images were sourced from books and theses, the public and subject specialists, and repeat photographs were then taken from the same perspectives. Visible changes could be categorised into four types: (1) changes in species’ ranges; (2) biological invasions; (3) sea level changes; and (4) direct engineering impacts. In terms of range changes, the images depict a progressive easterly spread of the cold-water kelp Ecklonia maxima and parallel easterly contraction of the warmer-water mussel Perna perna, both evidence for declining water temperatures along the South-West Coast. Since c. 1980 most shores have also become conspicuously invaded by the alien Mediterranean mussel Mytilus galloprovincialis, while those on the West Coast have also been visibly invaded by the more-recently introduced Pacific barnacle Balanus glandula. No changes in vertical zonation due to changing sea levels could be detected, despite suitable images being available. Construction along the shore has radically altered the appearance of the shoreline in urban areas. Repeat photography thus proved a useful tool for both detecting and dramatically illustrating historic changes over the past century. These changes have altered substantially both the appearance and ecological attributes of many rocky shores in this region.     

Design and calibration of an acoustic telemetry system subject to upwelling events

The experiments described were designed to calibrate a hexagonal array of VEMCO VR2 receivers and transmitters (model V9P-6L-S256) in isothermal and stratified water columns off the south coast of South Africa. The array, configured with 500 m between receivers, was designed to study the influence of water temperature and turbidity on the spawning behaviour of chokka squid Loligo reynaudii. Range tests comprised fixing a single VR2 receiver 2 m from the seabed and placing a V9P transmitter at distances of 0 m, 75 m, 150 m, 225 m, 300 m, 375 m, 450 m and 500 m from the receiver for periods of 10 minutes at each position under isothermal conditions and in the presence of a thermocline. The data indicated a range of 300 m for the former and 75 m for the latter conditions. The field performance of the V9P transmitter in a non-stratified water column compared well with the theoretical range of 352 m calculated using software to calculate range. System saturation was investigated by repeating the range test using four, eight and 14 transmitters simultaneously. Field data indicated a significant decrease in signal detections due to signal collisions when more than eight transmitters were active simultaneously. It was demonstrated that the hexagonal configuration of VR2s is optimal during isothermal conditions but inadequate during stratified conditions when acoustic dead zones of 350 m between VR2 receivers can occur.     

Comparative salinity tolerances of four siphonariid limpets in relation to habitat restriction of the rare and endangered Siphonaria compressa

The salinity tolerances of four South African species of limpet in the genus Siphonaria were experimentally tested, in the context that one of them, S. compressa, is South Africa's most endangered marine mollusc and is restricted to two lagoonal localities that normally experience little variation in salinity. Its habitat is additionally restricted in that it occurs only on the eelgrass Zostera capensis. The other three species, S. capensis, S. concinna and S. serrata, are abundant and widespread on temperate rocky shores. We hypothesised that S. compressa would have limited tolerance to low salinities, contributing to its absence from otherwise suitable estuaries that experience regular fluctuations of salinity. The percentage survival of the limpets was recorded in salinities ranging from 2 to 35 over that period. Both salinity and species significantly affected the survival of the limpets over the 96 hours. Survival was highest in salinities close to those of normal seawater, and greatly reduced in the hypo saline waters. S. compressa had the lowest salinity tolerance of the four species, its time-to-50% mortality in hyposaline waters being significantly less than that for the other three species, which differed in a manner that could be correlated with their zonation patterns. Restriction to eelgrass, coupled with low salinity tolerance, probably explains why S. compressa is found at only two localities, both of which normally experience salinities close to that of seawater. Even there, mass mortalities of S. compressa have been recorded in association with die-backs of eelgrass after abnormal freshwater flooding or sedimentation—further emphasising the vulnerability of S. compressa to extinction.     

Lensphoto系统在3维重建中的应用及若干问题探讨

对多基线数字近景摄影测量理论在3维重建应用中的注意事项及遇到的若干问题进行了初步探讨。文章以青铜塑像为例,对3维重建中外业布设控制点时的注意事项进行了阐述,并针对后期点云处理和纹理粘贴时遇到的问题进行了探讨。事实证明,该方法在3维重建中不仅具有较高的精度,同时还能以更经济的方法迅速得到同3维激光扫描相媲美的点云数量,为保护文物的3维重建提供了有效的方法。     

利用全站仪进行大跨度网架沉降观测

大跨度钢制网架结构广泛应用于大型封闭场馆屋顶的建设中,为了解网架在施工的不同阶段和在使用运营的过程中出现的沉降变形情况,分析其安全稳定性,并及时加以维护,需要进行必要的定期沉降变形观测,但大跨度网架的搭建都比较高,与地面联系的通道一般只有梯子,水准仪及水准尺无法在其上面安放,由于其空间的特殊性,很难进行精密水准测量,本文提出一种观测方法解决该问题,即利用测角精度2"以内的全站仪通过三角高程测量的方法对网架进行沉降观测,并在实际工程中验证了该方法的可行性和可靠性,同时对精度进行了分析和论证,可以满足相关变形测量规范和网架设计方的要求。在该工程中作者运用了两个自己在平时工作中研发的软件,给数据处理带来了便捷和准确,高程基准点的二等水准测量使用了"PLS软件"记录和严密平差,沉降变形数据使用了"BXZS软件"处理,计算单次和累计沉降量及沉降速率,并自动绘制"沉降量-时间"曲线图,直观地反映出沉降量与时间的关系,是分析沉降稳定性的重要依据。     

多卫星传感器数据的Brovey融合改进方法

提出一种针对当前不同卫星传感器数据融合的新方法。该方法基于Brovey融合方法的思想,充分考虑了不同卫星传感器全色影像与多光谱影像的光谱范围差异以及光谱响应差异,通过公式推导建立了基于权重系数β和比例系数w两个因子的全色影像与多光谱影像的关系式,并根据这两个因子重新构建了Brovey融合过程中的乘积系数。改进后的方法有效地改善了传统Brovey融合方法的光谱畸变问题。将上述方法应用于北京1号、SPOT 4/5、Landsat5(TM)以及环境一号卫星数据之间的4例融合实验中,并与Brovey融合、Modified IHS融合方法进行定性和定量评价,结果表明其综合性能优于其他方法,在细节融入度高的基础上,仍能保持良好的光谱信息,而且保留了Brovey融合快速的优点,易于推广和应用。