应用CE-QUAL-W2模型模拟输水明渠冰盖的研究

以宁夏吴忠地区金积供水工程输水明渠为例,应用CE-QUAL-W2模型(二维纵向垂向平均水动力学和水质模型)进行了输水明渠冰期冰盖生消模拟的可行性研究。在此基础上,计算了南水北调中线京石段典型气温过程中不同入流量和水深条件下的冰盖发展过程,同时对模型参数进行了敏感性分析,研究结果表明:气温、入流量、水深、光遮蔽系数和风剪切系数对冰情有不同程度的影响。     

南水北调中线工程冬季输水冰情的数值模拟

南水北调中线工程总干渠是由明渠和各种过水建筑物组成的树状系统,特点是线路长、过水建筑物类型多、冰水动力学响应过程复杂。本文将冰情发展模型与树状明渠系统复杂内边界条件下的渠道非恒定流模型进行集成耦合,开发了大型长距离调水工程冬季输水冰情数值模拟平台,提出了树状明渠系统复杂内边界条件的等效变换方法和计算冰盖前缘动态发展的虚拟流动法。根据实测的沿线气象资料和设计资料,利用该平台系统模拟了在寒冷气温条件下总干渠初冰、冰盖形成、发展和消融过程。分析了冬季输水的冰情特性及冰期输水能力,提出了冰期安全运行的水力控制条件,通过对典型年总干渠敞流期、冰盖形成期、稳封期、调度期以及开河全过程的模拟,给出了安全运行输水调度方案及建议。     

CE-QUAL-W2在输水明渠冰盖计算上的应用

以宁夏吴忠地区金积供水工程输水明渠为例,验证了垂向二维模型CE-QUAL-W2模拟输水明渠冰盖生消的可行性。在此基础上,构建了南水北调京石段输水明渠冰盖模型,模拟了典型气温过程中冰盖在不同输水流量及入流温度条件下的发展过程,模拟结果表明以上因素对冰情的发展有不同程度的影响。     

冰情模型中不确定参数的影响特性分析

数学模型中参数的不确定性直接影响到模拟结果的不确定性。以南水北调中线工程冬季输水为例,根据实测和设计资料,采用自主开发的大型长距离调水工程冬季输水冰情数值模拟平台,重点分析了冰情数学模型中单一参数（冰期冰盖糙率、大气与冰盖的热交换系数）的不确定性对冰期冰盖形成、发展、消融和水位、流量等要素的影响,并计算给出了一般规律。研究表明,初始冰盖糙率的不确定性对典型年冰期水力学要素的变化过程影响较大,主要反映在沿程各计算断面的水位、流量波动以及结冰期冰盖前缘动态发展模式上,而对冰情范围及与冰相关的变量变化过程无影响。大气与冰盖的热交换系数的不确定性直接影响到最大冰盖厚度的模拟结果,而对冰盖的发展规律影响不大。建议及早准备开展中线工程冰期输水原型观测工作,对上述不确定参数进行率定。     

河冰水力学研究进展

近几十年来,随着经济的发展,河流冰情灾害引起的损失越来越大,因此很多专家、学者投入到河冰问题的研究,使得河冰水力学得到了很大的发展。分别从天然河道、水库、人工输水渠道等原型观测研究,新型冰情观测仪器的研发和使用,冰塞演变机理、冰盖下的流速分布和泥沙输移等实验研究,冬季河道冰情发展演变过程、冰塞的形成、冰塞溃决时的洪水波等河冰动力学数值模拟研究,以及基于神经网络技术的冰情预报等方面,综述了国内外学者在冰情研究中最新的研究进展,重点介绍了其中一些具有代表性的成果,并对目前河冰工程研究中仍未解决的问题和以后需要进行的工作进行了尝试性地分析。     

南水北调中线工程输水冰情的初步分析

本文结合南水北调中线工程初步设计方案及在冬季输水运行的防凌要求，根据南水北调工程中线沿线各地区的多年气候、邻近河道冰情实测资料的统计，分析并得出了沿线各渠段地区的气候、邻近河流冰情的变化与特征。应用一维热平衡方程对三个不同气温典型年即冷年、平均年、暖年，以出库水温和邻近渠道表面温度为初始条件和边界条件，模拟干渠郑州至北京段沿程的水流温度变化，预测冰花起始时间、冰流量、冰盖形成及冰盖厚度。估算出沿程各河段主要断面过冰能力、预测各渠段的冰塞发生位置，冰盖形成及稳定性和冰下过流能力，阐明了在寒冷地区冬季输水防凌的必要条件和可行性。研究并提出了冬季输水的防凌害初步运行方案及防凌措施。     

长距离明渠系统反向输水冰情模拟

针对长距离明渠-闸门-泵站系统冬季反向输水可能出现的冰问题,以南水北调来水调入密云水库调蓄工程为研究对象,升级开发了调水工程冬季输水冰情数值模拟平台。根据实测气象资料和设计资料,对冰情数学模型中的相关参数进行了率定和检验。在此基础上,研究了冰期明渠反向安全输水的水力约束条件,通过模拟调蓄工程典型气温年工况下畅流期、冰盖形成期、稳封期、消融期等冰情演变过程,分析了反向输水的输水能力和冰情特性,并与正向冰期输水能力进行了对比。计算表明,通过控制抽水流量使各渠段泵吸水口拦冰(拦污)设施、倒虹吸或闸门位置处断面佛汝德数满足快速成冰的约束条件,可以保证反向输水;典型年气温下沿程冰厚略小于正向输水工况,且形成冰盖时最大水位波动为0.35 m;从冰封起始的12月中旬提前1~2周启动冬季输水运行工况较为适宜。研究成果可供决策管理部门在冰期制定北京多水源联合调度方案时参考。     

黄河内蒙古河段典型凌情过程模拟

近十几年受人类活动和气候变化等影响,黄河内蒙古河段冰情出现新的特征,突发凌情频繁出现,原有的内蒙古河段冰模拟方法已不能满足当前凌情防治的需要,亟待建立能反映凌情物理特性变化规律的河段冰情动态发展数学模型.在实测资料基础上,研究了黄河内蒙古河段冰情时空变化规律,以及河道资料不完整、支流流量资料缺乏及冰桥位置的确定等问题....     

南水北调中线总干渠冰情预测模型参数敏感性分析及率定

南水北调中线工程黄河以北总干渠冬季由于受气温的影响,将有不同程度的冰情产生,总干渠将处于无冰、流冰、冰盖下输水等多种复杂运行状态,运行不当则可能发生冰塞、冰坝危害。为了更准确地预测冰情,文章利用详细热量交换法对不同条件下渠道内一维冰盖生消进行数值模拟,根据2012年冬季的冰清观测结果以均方根差最小的原则率定模型参数。随后通过改变反射系数α、云量C、虚拟冰盖厚度Δh、风速Va、折减系数Cc及Ce、初始水温等分析冰盖厚度对于模型参数的敏感性。仿真结果显示,模型参数中反射系数α、虚拟冰盖厚度Δh这两个参数对冰盖厚度影响较大,气温数据中云量C对冰厚结果影响较大,且在高云量区域敏感性为极敏感,这些规律可以为寒区渠道系统冰情预测模型的开发及率定提供参考。     

北方河流冰期水流阻力分析

本文通过由流速分布推求冰期河道冰盖糙率系数,提出了由流速分布推算冰盖及河床糙率的计算方法,同时考虑冰盖影响区与河床的流速分布,确定最大流速位置,阐述了冰盖对水流的阻力是研究河道冰情演变及其运动规律的依据.并对河道冰期形成冰盖,其阻力使河道水位升高、过流能力降低、水位流量关系改变.流速分布推算冰盖及河床糙率的计算方法进行了分析.为北方地区基层测站的冰期测验工作提供参考.     

大庆水库冰表面温度特征及其在冰工程实践应用方法探讨

根据冰面热平衡方程并以大庆红旗泡水库冰面观测的气温、太阳辐射、风速、相对湿度、冰厚数据以及水库附近安达气象站记录的云量、湿度和海平面气压数据,求解了2009/2010年度冬季的冰表面温度,并分析了冰表面温度特征及其同太阳辐射之间的关系、同气温、风速之间的响应关系。在此基础上,就传统考虑的抗冰工程设计所需的设计冰表面温度进行了评估;就日益增加的安全用冰工程设计所需冰表面温度取值也给予定量讨论;对气候变化下的冰内和冰下水体生态适应问题所需的冰面温度日内变化速率和开河期冰凌爆破所需冰表面温度的取值也进行探索。尽管受国际气象资料观测规定的限制,历史资料的应用存在利用接近观测时刻资料的事实,但仍然期望这些分析和讨论能够推动科学地、更广阔地应用冰表面温度。     

用气温和冰厚修正黄河冰内雷达波速的物理机理和参数化

黄河平封冰和立封冰中冰晶体间以水膜形式存在有未冻结的自由水和非自由水,其含量随冰温变化。理论上冰内雷达波速取决于冰体自身的晶体结构和组分,但冰内未冻水含量可对其产生明显的影响;冰内未冻水含量取决于冰温,冰温又受控于气温、辐射和冰厚。分析了黄河什四份子2020—2021年冬季气温和雷达探测冰厚数据,发现气温主导的未冻水含量变化是影响雷达准确探测平封冰厚度的首要因子。通过确定黄河冰-水界面热通量,并引入含有气温、辐射、风速、云量的一维冰热力学模型,结合13个钻孔实测冰厚,计算了与雷达探测冰厚时刻一致的1251个热力学模拟冰厚。在此基础上,分别获得了气温升高过程和降低过程中粒状冰、柱状冰内雷达波速受气温影响以及受气温和冰厚联合影响的统计关系。最终确定将气温和冰厚对雷达波速联合影响的统计关系作为平封冰雷达波速动态修正的参数化方案,依此将固定式雷达冰内雷达波速由常数更换为函数,从而提高了平封冰雷达冰厚探测的精度。根据黄河存在非冻结冰花和堆积碎冰块,建议开展不同类型冰厚探测研究。     

Understanding the Thermal Regime of Rivers Influenced by Small and Medium Size Dams in Eastern Canada

Although small and medium‐size dams are prevalent in North America, few studies have described their year‐round impacts on the thermal regime of rivers. The objective of this study was to quantify the impacts of two types of dams (run‐of‐river, storage with shallow reservoirs) on the thermal regime of rivers in eastern Canada. Thermal impacts of dams were assessed (i) for the open water period by evaluating their influence on the annual cycle in daily mean water temperature and residual variability and (ii) for the ice‐covered winter period by evaluating their influence on water temperature duration curves. Overall, results showed that the run‐of‐river dam (with limited storage capacity) did not have a significant effect on the thermal regime of the regulated river. At the two rivers regulated by storage dams with shallow reservoirs (mean depth < 6 m), the annual cycle in daily mean water temperature was significantly modified which led to warmer water temperatures in summer and autumn. From August to October, the monthly mean water temperature at rivers regulated by storage dams was 1.4 to 3.9°C warmer than at their respective reference sites. During the open water period, the two storage dams also reduced water temperature variability at a daily timescale while increased variability was observed in regulated rivers during the winter. Storage dams also had a warming effect during the winter and the winter median water temperature ranged between 1.0 and 2.1°C downstream of the two storage dams whereas water temperature remained stable and close to 0°C in unregulated rivers. The biological implications of the altered thermal regimes at rivers regulated by storage dams are discussed, in particular for salmonids. Copyright © 2016 John Wiley & Sons, Ltd.     

THE SOLAR‐TO‐STREAM POWER RATIO: A DIMENSIONLESS NUMBER EXPLAINING DIEL FLUCTUATIONS OF TEMPERATURE IN MESOSCALE RIVERS

The diel variation of temperature in mesoscale river reaches (catchment area > 1000 km²) is analysed using concurrent measurements of water temperature and of those meteorological (incident short‐wave radiation, air temperature, relative humidity and wind speed variables) and hydraulic variables (streamflow, top width, channel slope and flow depth) controlling the thermal regime. Measurements were taken along two river reaches located in central Chile, on the Itata (11 290 km², Strahler's order 6, reach length 30 km, Q_bankfull = 400 m³ s^?1) and Vergara (4340 km², Strahler's order 5, reach length 20 km, Q_bankfull = 85 m³ s^?1) rivers. The measuring frequency was 15 min. The relevant energy fluxes at the air–water interface, that is, atmospheric long‐wave radiation, net short‐wave radiation, radiation emitted by the water body, evaporation (latent heat) and conduction heat are computed and analysed for four scenarios of 12 days duration each, representing typical conditions for the austral winter, spring, summer and autumn. We find large differences in the diel river temperature range between the two sites and across seasons (and thus, flows and meteorological conditions), as reported in previous studies, but no clear relationship with the controlling variables is overtly observed. Following a dimensional analysis, we obtain a dimensionless parameter corresponding to the ratio of solar‐to‐stream power, which adequately explains the diel variation of water temperature in mesoscale rivers. A number of our own measurements as well as literature data are used for preliminary testing of the proposed parameter. This easy‐to‐compute number is shown to predict quite well all of the cases, constituting a simple and useful criterion to estimate a priori the magnitude of temperature diel variations in a river reach, given prevailing meteorological (daily maximum solar radiation) and hydrologic–hydraulic (streamflow, mean top width) conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

考虑太阳辐射的寒区混凝土衬砌渠道冻害机理

针对太阳辐射作用下季节冻土区渠道衬砌冻害机理研究的局限性,从气象参数的角度,考虑辐射、气温、风速等实际环境因素,结合原型观测资料,通过建立非稳态相变温度场有限元模型,对靖会总干渠混凝土衬砌渠道东西走向段渠坡冻结期热状况及其与吸收的太阳辐射能之间的关系进行分析。结果表明渠基温度场的横向不对称不均匀分布是季节冻土区渠道冻害的主要原因;渠坡日平均日照时长和日平均辐射总量呈横向不对称不均匀分布;阴、阳坡渠基浅层(衬砌板下0.4 m)平均温差与坡板平均太阳辐射量差呈多项式关系;渠基最大温差与深度呈线性关系;太阳辐射吸收系数对渠基热交换影响较大,阴、阳坡板表面最大温差随着吸收系数的增大而线性增加;吸收系数由0.65增加至0.8时,阴、阳坡冻深分别减少25%和37%。     

长江源区年际冰水情变化及其影响因子分析

受限于高寒山区地形、气候和环境条件,目前关于长江源区河流的冰水情研究较少,源区降雨径流年际变化和冰盖分布等规律不明确。为了明晰长江源区水文与水资源现状和冰水情本底,本文收集整理了2006—2018年沱沱河和直门达水文站近十年的降雨、蒸发、径流、水温、气温和冰厚资料,采用统计分析、线性回归、单一因子分析和相关性分析等结合的研究方法,重点揭示了源区河流流量、冰期和冰厚现状、其年际变化特征和主要影响因子。研究表明,源区河流洪峰年际波动范围超50%,洪峰集中在7—9月,非汛期流量仅为汛期流量的1/7,非汛期流量年际波动小于汛期,且直门达站水位流量年际变化幅度小于上游沱沱河站;沱沱河站冰期持续时间7个月,而下游直门达站冰期为5个月,多年平均冰盖厚为0.15 m,造成两站冰情差异的主要原因是源区垂直地形急变引起的高程差;源区降雨量年际波动与年际径流波动一致,蒸发量年际波动仅为降雨量的一半,因此两站流量的年际波动受降雨影响较大。长江源区降雨和气温变化是冰水情变化的主要驱动因子,与源区河流的地形高程密切相关,亟需系统的科考进一步明晰长江源冰水情时空变化规律。     

Long-Term Changes in the Course of Ice Phenomena on the Oder River along the Polish–German Border

Ice phenomena are a major component of the hydrological regime of east-central and northern European rivers. However, their occurrence disturbs inland water transportation, particularly affecting the major rivers of the Central European Plain that are part of Europe’s international waterways. The Oder is one of these rivers, and is located on the boundary between the much warmer and the much colder part of the temperate climatic zone. This makes the course of ice phenomena on the river difficult to predict. The main purpose of this work is to document and analyse the dynamic of changes occurring for over 60 years (1956–2015) in the ice phenomena of a river that demonstrates a transitional ice regime. It was found that the duration of all ice phenomena decreased (by up to 0.58 days·year^?1) and so did the duration of ice cover (by up to 0.46 days·year^?1). The rates and trends of the two parameters were, however, different in different parts of the lower stretch of the river. This fact is especially important in the context of climate changes whose characteristics include an increased incidence of extreme weather situations, both meteorological and hydrological. There was also found to be a strong correlation (R² from 0.69 to 0.81) between the duration of ice phenomena and the mean air temperature in winter (December to February) and a much weaker correlation between the duration of ice phenomena and the NAO index (R² from 0.42 to 0.48). Such a little correlation of ice phenomena with NAO is likely to result from the pollution of the Oder River (in particular in the second half of the twentieth century) and icebreaking operations on the river.

     

WATER TEMPERATURE PATTERNS BELOW LARGE GROUNDWATER SPRINGS: MANAGEMENT IMPLICATIONS FOR COHO SALMON IN THE SHASTA RIVER,CALIFORNIA

Elevated stream temperature is a primary factor limiting the coho salmon (Oncorhynchus kisutch) population in California's Shasta River Basin. Understanding the mechanisms driving spatial and temporal trends in water temperature throughout the Shasta River is critical to prioritising river restoration efforts aimed at protecting this threatened species. During the summer, the majority of streamflow in the Shasta River comes from large‐volume, cold‐water springs at the head of the tributary Big Springs Creek. In this study, we evaluated the initial character of this spring water, as well as the downstream fate and transport of these groundwater inflows during July and August 2008. Our results indicated that Big Springs Creek paradoxically provided both cool and warm waters to the Shasta River. During this period, cool groundwater inflows heated rapidly in the downstream direction in response to thermal loads from incoming solar radiation. During the night time, groundwater inflows did not appreciably heat in transit through Big Springs Creek. These diurnally varying water temperature conditions were inherited by the Shasta River, producing longitudinal temperature patterns that were out of phase with ambient meteorological conditions up to 23 km downstream. Findings from this study suggest that large, constant temperature spring sources and spring‐fed rivers impart unique stream temperature patterns on downstream river reaches that can determine reach‐scale habitat suitability for cold‐water fishes such as coho salmon. Recognising and quantifying the spatiotemporal patterns of water temperature downstream from large spring inflows can help identify and prioritize river restoration actions in locations where temperature patterns will allow rearing of cold‐water fishes. Copyright © 2013 John Wiley & Sons, Ltd.     

拱坝坝面太阳辐射强度计算

本文基于三维拱坝有限元模型,建立了采用ASHRAE晴空模型,利用光线追踪算法准确计算周围地形和自身遮蔽的坝面太阳辐射计算框架。该方法能够准确计算拱坝坝面太阳辐射的不均匀分布,为温度场计算提供准确的边界条件。现场实拍照片与计算瞬时坝面辐射的比较,验证了光线追踪算法的准确性。冬季和夏季日平均太阳辐射计算结果表明,坝面太阳辐射分布随季节变化明显,以某工程为例,冬季左右岸差值可达100W/m2。考虑太阳辐射以后的计算温度场与实测值符合良好,证明该方法可用于工程实际。对计算结果的分析表明,拱坝的日平均太阳辐射主要是太阳直射辐射。坝面辐射分布主要由拱坝朝向决定,辐射强度由坝址纬度和朝向共同作用。     

引水流量对引水渠道中水内冰演变影响的数值模拟

水电站引水渠道中的冰害会影响水电站的安全运行,危害当地人民的人身安全。为开展引水渠道中水内冰演变的研究,建立了三维非稳态欧拉两相流模型,动量方程考虑了相间曳力、升力、虚拟质量力,热量传递方程中考虑了冰水之间的热量传递以及太阳辐射、有效辐射、蒸发热损失、水面对流热损失等。模拟分析了不同引水流量下温度及冰体积分数的沿程分布,结果表明：冰温沿程逐渐升高;水温沿程先降低后升高、沿程出现最低点。冰体积分数沿程存在突变点,且突变点在水温最低点附近。随着引水流量减小,产冰起始位置向渠道上游移动,但最终的产冰量和冰体积分数逐渐减小。通过与黄河上游河道中水内冰演变计算结果对比,验证了模型的可靠性。