Spatial and temporal variations in bank erosion on sand‐bed streams in the seasonally wet tropics of northern Australia

Bank erosion rates and processes across a range of spatial scales are poorly understood in most environments, especially in the seasonally wet tropics of northern Australia where sediment yields are among global minima. A total of 177 erosion pins was installed at 45 sites on four sand‐bed streams (Tributaries North and Central, East Tributary and Ngarradj) in the Ngarradj catchment in the Alligator Rivers Region. Bank erosion was measured for up to 3·5 years (start of 1998/99 wet season to end of 2001/02 wet season) at three spatial scales, namely a discontinuous gully (0·6 km²) that was initiated by erosion of a grass swale between 1975 and 1981, a small continuous channel (2·5 km²) on an alluvial fan that was formed by incision of a formerly discontinuous channel between 1964 and 1978, and three medium‐sized, continuous channels (8·5–43·6 km²) with riparian vegetation. The bank erosion measurements during a period of average to above‐average rainfall established that substantial bank erosion occurred during the wet season on the two smaller channels by rapid lateral migration (Tributary Central) and by erosion of gully sidewalls due to a combination of within‐gully flows and overland flow plunging over the sidewalls (Tributary North). Minor bank erosion also occurred during the dry season by faunal activity, by desiccation and loss of cohesion of the sandy bank sediments and by dry flow processes. The larger channels with riparian vegetation (East Tributary and Ngarradj) did not generate significant amounts of sediment by bank erosion. Deposition (i.e. negative pin values) was locally significant at all scales. Bank profile form and channel planform exert a strong control on erosion rates during the wet season but not during the dry season. Copyright © 2006 Commonwealth Government of Australia.     

弹性填料处理河道污水实验研究

采用弹性填料曝气生物膜法对污染的河道水体进行处理的实验研究,结果表明,在2m/h的流速、水温为16℃~18℃、气水比为1∶1的条件下,采用弹性填料的生物膜处理系统运转正常,不易发生堵塞或系统短流,系统此时的水力停留时间为3.5h左右,污水中的COD和NH3-N去除率稳定,其均值分别为49.4%和19.1%。     

Short and long memory unobserved components in hydrological time series

In this paper a semiparametric approach is introduced to decompose an ARFIMA model in the long memory and short memory unobserved components. The procedure is based on the DECOMEL method which produces a statistical decomposition by minimizing the Euclidean distance between the spectrum of the aggregated series and the sum of the parametric spectra of the components. The extension to long memory stationary models is achieved defining an approximate model where the fractional operator is replaced by the ratio of two polynomials of order one. The feasibility and performance of the proposed procedure are discussed through a case study.     

Mantle process beneath Philippine Sea back-arc spreading ridges: A synthesis of peridotite petrology and tectonics

Abstract In order to obtain a general view of the mantle process beneath a back‐arc basin spreading ridge, the diversity of peridotite petrology and tectonic occurrences in two back‐arc basin spreading ridges from the Philippine Sea were examined: the Parece Vela Rift and the Mariana Trough. The Parece Vela Basin spreading ridge (Parece Vela Rift) was a physically fast/intermediate‐spreading ridge, although many tectono‐magmatic features resemble those of slow‐ to ultraslow‐spreading ridges. Two unusual features of the Parece Vela Rift further demonstrate the uniqueness of the ridge: full‐axial development of oceanic core complexes and exposure of mantle peridotite at segment midpoints. The Parece Vela Rift yields a lithological assemblage of residual but still fertile lherzolite/harzburgite, plagioclase‐bearing harzburgite and dunite; similar assemblages are reported from the equatorial Mid‐Atlantic Ridge at the Romanche Fracture Zone and the ultraslow‐spreading ridges from the Indian and Arctic Oceans. The tectono‐magmatic characteristics of the Parece Vela Rift suggest that diffuse porous melt flow and pervasive melt–mantle interaction were the important mantle processes there. Globally, this ‘porous melt flow‐type’ mantle process is likely to occur beneath a segment midpoint of the ridge having a thick lithosphere, typically an ultraslow‐spreading ridge. In contrast, the Mariana Trough is a typical slow‐spreading ridge, exposing mantle peridotite at segment ends. The Mariana Trough yields a lithological assemblage of residual harzburgite and veined harzburgite, a common assemblage among the global abyssal peridotite suite. The tectono‐magmatic characteristics of the Mariana Trough suggest that channeled melt/fluid flow and limited melt–mantle interaction are the important mantle processes there, because of the colder wall‐rock peridotite in the segment end. This ‘channeled melt flow‐type’ mantle process is likely to occur in the shallow lithospheric mantle at the segment ends of any spreading ridges.     

基于图像处理技术的岩心裂缝图像提取

基于数字图像处理技术,利用油田大量现场岩心纵向(或平面)劈开面图像资料,可直接分离出岩心剖面上裂缝信息.最大类间方差法的二值化算法是基于类间方差达到最大为准则,采用该法获得了理想的二值化效果,较准确地从岩心剖面中提取出裂缝图像信息.     

基于改进的Elman神经网络的中长期径流预报

径流中长期预报长期以来一直都是人们关注的热点研究问题。现行的径流预报方法很多,传统的有时间序列法,多元回归分析法等,这些方法虽然简单易用,但是如果预报对象提供的样本容量偏小或者因子选择不够合理,都会造成预报精度偏差过大,难于有效的指导工程应用。鉴于此,本文提出一种改进的采用局部回归的Elman神经网络方法。并应用到凤滩水库优化调度的径流预报中。结果表明,与回归分析法、BP网络相比较,该方法不仅提高了算法的效率,而且提高了预报的精度,在径流预报中具有有效性和优越性。     

区域水资源可持续利用评价

水资源可持续利用评价是可持续发展战略研究的核心问题之一,选取合适的评价方法是正确评价水资源可持续利用的基本前提。在目前提出的评价方法中,关键性的问题是如何合理确定各个评价指标的权重,层次分析法是解决这一问题常用的有效方法。但是,层次分析法没有给出判断矩阵一致性的调整方法;而且评价结果也只能表明各个指标对水资源可持续利用的影响大小,并不能判断研究区水资源可持续利用程度。本文在层次分析法的基础上,探讨了判断矩阵一致性的修正方法,构造出判断水资源可持续利用程度的综合指数,并对云南省水资源可持续利用程度进行评价。     

贵州七星洞滴水的水文水化学特征及其意义

本文对贵州都匀七星洞9个滴水点进行厂为期1年的动态临测，结果显示滴水的物质组成直接源自于洞穴环境，即土壤和岩石。而大气降雨携带的物质成分较少。洞穴滴水的化学组成中元素含量变化主要由水运移过程中水-土、水-岩作用导致的岩石溶解-方解石沉淀过程所控制。QXD-1#、QXD-2#、QXD-6#、QXD-7#、QXD-8#由于水运移过程中经过的土壤较薄。水-岩作用对滴水化学特性的贡献略大。稀释作用发生在干旱条件下的QXD-2#滴水点，活塞作用在雨季对QXD-7#、QXD-9#滴水产生影响，在不同的季节，QXD-1#、QXD-3#、QXD-8#滴水点的滴率产生跳跃式变化。这些作用均受控于水的来源差异。所有这些过程对滴水点水化学产生影响但其效果较弱。滴水的Mg／Ca指示了大气降雨的变化，其值受控于洞穴顶板内水运移过程中水-土、水-岩作用下的水文地球化学过程即岩石的溶解、方解石沉淀过程及土壤物理、化学、生物学过程等。     

基于用户星精密轨道的TDRS卫星定轨

分析了TDRS卫星的轨道特性及传统的地基测距跟踪技术定轨精度不高的现状,研究了基于空基的用户星精密轨道的TDRS卫星定轨,解决了基于空基的一般GEO卫星定轨问题。     

华北盛夏旱涝的环流型特征及其在初夏的预兆

文中应用NCEP/NCAR 500 hPa逐日资料对影响华北盛夏旱涝的环流特征进行分析,给出了盛夏旱涝分别与“西高东低”和“东高西低”流型的对应关系。并进一步研究初夏与盛夏的环流演变特征,得知若在6月500 hPa华北出现异常增高过程时,则盛夏多出现“西高东低”流型,华北少雨;反之,6月华北出现异常低压过程时,盛夏多出现“东高西低”流型,华北多雨。6月华北高压区环流特征与盛夏的环流型相关系数达0.597,与华北中部盛夏降水相关系数为0.562,为初夏进行盛夏旱涝短期气候预测提供了依据。以此为根据建立了初夏对于天津盛夏降水短期气候预测的经验方法,在2002—2004年的业务应用中预报趋势都是正确的。