黄土丘陵沟壑区大空间尺度林草植被减沙计算方法研究

依靠20世纪后期遥感影像数据、过去近60a的实测水文和气象数据、黄河水沙变化现有研究成果等,引入产沙系数和基于遥感影像的林草植被覆盖率概念,提出基于遥感数据、可支持大空间尺度计算的黄土丘陵区林草植被减沙量评价模型,并给出模型应用中几个关键问题的处理方法。分析认为,在林草植被覆盖率小于35%~40%的范围内,改善林草的减沙效果非常明显;林草植被覆盖率达60%以后减沙效果趋于稳定,雨强对产沙的影响权重亦不再明显。     

黄河主要产沙区近百年产沙环境变化

以来沙量占入黄总沙量90%的黄河主要产沙区为重点研究对象,通过文献检索、实测降雨和水沙数据分析、遥感调查、统计数据采集和实地调查等,分析了过去近百年产沙环境变化情况。研究认为,产沙环境在20世纪70年代以前持续恶化、70年代以后逐渐好转、1998年以后显著改善。目前,包括林草、梯田和坝地在内的综合覆盖率已经由70年代的20.6%提高到50.9%,其中黄河中游地区达到54.1%,综合覆盖率不足30%的面积占比由70年代的81.0%减少至3.5%。林草植被改善和梯田建设是研究区产沙环境改变的主要驱动力。     

黄土高原淤地坝的减沙作用及其时效性

在黄河近年来沙锐减的背景下,需要深入探究黄土高原淤地坝的减沙作用。本文基于实测数据分析了淤地坝拦沙与入黄泥沙减少量的关系、拦沙作用的时效性以及坝地的减蚀作用。研究结果表明,淤地坝拦沙量一般大于或等于相应的入黄泥沙减少量;流域的林草梯田覆盖率越大、地表土壤粒径越粗,淤地坝因拦沙所致的减沙量占其拦沙量的比例越小。淤地坝拦沙作用的时效性非常突出,拦沙库容淤满即基本失去拦沙能力。失去拦沙能力后,淤地坝仍可依靠拦沙所形成的坝地发挥减沙作用;如果流域的林草梯田覆盖状况较差,坝地减沙作用的"空间影响范围"可达自身面积的4倍。不过,随着流域的林草梯田覆盖率增大,单位面积坝地的实际减沙量会逐渐降低。     

黄河上游黄土高原入黄沙量变化分析

早在20世纪70年代黄河上游实测输沙量就开始大幅减少，其中黄河下河沿站1970—1999年和2000—2022年年均输沙量分别较天然时期减少50%、76%,但迄今有关该区沙量锐减的研究极少。以黄河李家峡大坝至青铜峡区间的黄土高原为重点，分析了该区水沙和有效降雨变化情况、水库和淤地坝在不同时期的拦沙作用，还原了1960年以来流域实际产沙量，研究了梯田和植被变化情况，计算了现状下垫面在设计降雨情景下的产沙量。研究结果表明：20世纪后期水库拦沙是研究区输沙量大幅减少的主要原因，2000年以来梯田建设和植被改善逐渐成为主要减沙因素、水库拦沙次之；基于2021年下垫面推算的下河沿以上产沙能力为5 800万～6 600万t/a、较天然时期降低约62%,清水河流域产沙能力为1 920万～2 743万t/a、较天然时期降低约53%;未来植被改善潜力很小，新建梯田仅可弥补老旧梯田田埂损毁的负面影响，因此产沙能力进一步降低的潜力极小。     

黄土丘陵沟壑区典型流域产沙的降雨阈值变化

2000年以来,随着黄土高原林草植被大幅改善和大规模梯田建成,加之坝库拦截,黄土高原入黄沙量锐减,从而使黄土高原现状产沙情势的认知成为近年关注的热点。目前,增大林草和梯田覆盖状况可减少或遏制侵蚀产沙的观点已被广泛认可,但其在流域层面上的减沙机制仍有待深入认识。本文以黄土丘陵沟壑区30条面积较小的流域作为样本,以场次降雨为分析对象,以场次降雨的面雨量、最大1 h降雨量和降雨侵蚀力为降雨指标,以场次降雨的产沙强度≥500 t/km2为流域产沙的判断标准,探讨了林草梯田覆盖程度变化与可致流域产沙的降雨阈值之间的响应关系。研究表明,无论地貌类型如何,随着流域林草梯田覆盖程度的增大,流域产沙的降雨阈值均明显增加,其中黄土丘陵第1—3副区的降雨阈值与林草梯田有效覆盖率之间呈正向的指数函数关系。在相同下垫面下,黄土丘陵第1—3副区的降雨阈值差别很小;或因植被主要分布在梁茆,或因河道产沙占比较大,因此,砒砂岩区、黄土残塬区和黄土丘陵第5副区更易产沙,其降雨阈值明显小于第1—3副区。本成果不仅为诠释林草梯田减沙的机制提供了科学支撑,而且也可为黄河水沙情势的评价和入黄沙量预报提供重要参考。     

黄土丘陵沟壑区林草变化对流域产沙影响的规律及阈值

围绕植被变化与土壤侵蚀的关系,已有海量研究成果,但提出的植被盖度～土壤侵蚀量响应规律多是基于坡面小区上的观测成果,反映的是植被变化在"本地"的水沙响应,不能反映植被变化对小区下游的坡面、沟谷和河道的"异地"效应。在近20年黄河来沙锐减的背景下,如何在较大的流域尺度上,评价林草植被变化对流域产沙量的影响,已经成为亟待解决的重大科学问题。本文在对黄土丘陵区地貌和产沙特点分析的基础上,引入了易侵蚀区、林草有效覆盖率(V_e)和产沙指数(S_i)等新概念,利用黄土丘陵区流域实测的林草、降雨和水沙数据,分析了林草植被变化与流域产沙能力之间的响应规律及其机制,提出了可基本遏制流域产沙的林草阈值。研究结果表明,流域的产沙指数均随林草有效覆盖率V_e的增大而减小,二者呈指数关系;当V_e≤40%～45%时,产沙指数随V_e增大而迅速降低,不过在V_e20%时改善植被的减沙作用不太稳定;V_e40%～45%后,改善植被导致的产沙指数递减速率越来越小。流域的林草植被覆盖程度越差,产沙强度对雨强越敏感;当V_e50%～60%后,决定流域产沙量的首要因素是有效雨量,雨强次之。林草植被改善是通过对流域产洪量和含沙量的共同减少、以及地表径流输移阻力的增大,实现对流域产沙量的削减;削减洪水和增大阻力均将导致黄丘区地表的水蚀动力降低,含沙量降低则是地表物质补给困难的直接反映。对于黄土丘陵区的第1～4副区,要实现流域产沙模数≤1000 t/(km~2·a)的目标,林草有效覆盖率应达55%～65%以上,该阈值自东向西递增。对于黄土丘陵区的第5副区,当林草有效覆盖率V_e45%～50%后,流域产沙量也趋于稳定,但因产沙机制特殊,即使林草梯田有效覆盖率达到60%以上,仍难以基本遏制流域的产沙;而且,河(沟)床产沙占比越高,依靠林草植被改善而削减产沙的难度越大。该成果可为认识近20年黄土高原植被改善与黄河泥沙锐减的关系,提供理论依据。     

黄土高原现状产沙情势评价

在黄河来沙锐减背景下，厘清现状黄土高原在不同降雨情景的年均产沙量，对客观认识黄河未来水沙情势具有十分重要的意义。本文分析了过去60年黄土高原汛期径流及含沙量变化特点，认为该区2010年以来的下垫面可作为现状产沙情势评价的代表下垫面。采用理论推算和实际产沙能力分析等两种方法，计算了黄土高原现状下垫面在4种降雨情景下的年均产沙量。结果表明，如果汛期降雨较1956—2019年均值偏丰0～17.3%,2010—2019年下垫面的年均产沙量为3.9亿t/a～5亿t/a;若基于2018年以来的下垫面，其年均产沙量为3.6亿t/a～4.5亿t/a;受坝库工程拦截影响，可输送至潼关断面的沙量更少。分析了黄土高原植被和梯田的发展趋势，并考虑流域产沙指数与植被梯田覆盖状况的响应规律，认为该区产沙能力进一步降低的潜力很小。事实上，由于年降雨量450 mm以下地区的新生植被抵御恶劣气候和人类干扰的能力较低，黄土高原产沙量存在反弹至5亿t/a～8亿t/a的风险。     

黄土高塬沟壑区产沙驱动力及减沙潜力分析

20世纪70年代以来,黄河上中游绝大部分支流来沙明显减少,但泾河流域黄土高塬沟壑区的核心地区无明显减沙趋势。以地处董志塬核心区的南小河沟和砚瓦川流域为例,分析了水土流失治理前后的降雨—产沙关系,以及塬面、坡面和沟谷的产水产沙量,结果表明:塬面径流集中下沟是流域产沙的主要驱动力,尤以庄院和道路径流集中下沟为甚;在塬面面积占流域面积60%以上的完整高塬区,梯田和林草措施的减沙潜力很难超过10%;尽可能减少集中下沟的塬面径流量是遏制该区侵蚀产沙的关键。     

黄河主要产沙区近年降雨及下垫面变化对入黄沙量的影响

近几年,黄河来沙量锐减原因成为人们普遍关注的热点问题。本文以天然产沙量约占流域入黄沙量90%的黄河潼关以上主要产沙区为研究范围,优选了降雨因子和模型的函数型式,改进或构建了各支流在天然时期的降雨~产沙相关模型,进而分析了该区近35年不同时段的降雨和下垫面因素的减沙作用。研究表明,若以各支流1956—1975年前后的降雨-产沙响应关系为基准,1980年以来下垫面减沙作用越来越大,近十多年最为突出。近10年研究区降雨总体偏丰、其中近5年明显偏丰,因此降雨变化不是黄河该时段来沙锐减的原因;2005—2014年和2010—2014年,下垫面因素的实际总减沙量分别为13.87~15.45亿t/a和15.70~18.70亿t/a。     

黄河中游水土保持措施减沙量宏观分析

对黄河中游水土保持措施减沙量进行了宏观分析，研究结果分为黄河中游水土保持措施减沙量、水利措施减沙昔、水利水土保持措施减沙量、“水保法”计算的水土保持综合减沙超和黄土高原水土保持措施减沙量等5个层次：结果表明，1970～1996年：①黄河中游水土保持措施年均减沙3．2亿t，黄河中游水利水土保持措施年均减沙4．5亿t，“水保法”计算的黄河中游水土保持年均综合减沙量为4．2亿t，黄土高原水土保持措施年均减沙3．5亿t，黄土高原水利水土保持措施年均减沙4．8亿t；②若扣除1970年以前的减沙量，则黄河中游水土保持措施年均新增减沙量2．1亿t，黄河中游水利水土保持措施年均新增减沙量2．6亿t，黄土高原水土保持措施年均新增减沙量1．7亿t，黄土高原水利水土保持措施年均新增减沙量2．2亿t.     

Call for Papers

正As the eldest and most distributed professional journal of water industry,Water Wastewater Engineering(W WE)gained very wide acceptance from the colleagues working in this field in this country since start publication in 1964.Now it is administrated by the Ministry of Construction of the People’s Republic of China and sponsored by the China Civil Engineering Society etc.     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Automated system for removal and pneumatic transport of fly ash from electric precipitator hoppers

A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system, configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants of dry ash utilization and the advantages of producing of size-separated particles are considered. __________ Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008).     

The flood pulse advantage and the restoration of river-floodplain systems

The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed.     

基于BP神经网络-马尔科夫链模型的隧道围岩位移预测

在隧道工程施工中,围岩位移预测起着很重要的作用。将BP神经网络-马尔科夫链模型引入到隧道围岩位移预测中来,通过对训练样本的学习,利用BP神经网络实现了对位移时间序列的滚动预测,同时得到了实测值与预测值的相对误差;在此基础上利用马尔科夫链对相对误差进行修正,有效地提高了预测结果的精度。并将该模型应用于某公路隧道拱顶下沉位移时序预测中,结果表明该模型具有精度高、科学可靠的特点,为隧道围岩变形的预测提供了新的途径。     

Short communication. Pipelines as a refuge for freshwater snails

In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.