Role of Local Flow Conditions in River Biofilm Colonization and Early Growth

Direct numerical simulations of a turbulent boundary layer flow over a bed of hemispheres of height h are performed using an immersed boundary method for comparison with river biofilm growth experiments performed in a hydraulic flume. Flow statistics above the substrates are shown to be in agreement with measurements performed by laser Doppler velocimetry and particle image velocimetry in the experiments. Numerical simulations give access to flow components inside the roughness sublayer, and biofilm colonization patterns found in the experiments are shown to be associated with low shear stress regions on the hemisphere surface. Two bed configurations, namely staggered and aligned configurations, lead to different colonization patterns because of differences in the local flow topology. Dependence with the Reynolds number of the biofilm distribution and accrual 7 days after inoculum is shown to be associated to local flow topology change and shear stress intensity. In particular, the shear stress τ on the surface of the hemispheres is found to scale as , where Re_t = u^*h/ν, with u^* as the log law friction velocity and ν as the fluid kinematic viscosity. This scaling is due to the development of boundary layers along the hemisphere surface. Associated with a critical shear stress for colonization and early growth, it explains the increasing delay in biomass accrual for increasing flow velocities in the experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrological and sediment transport dynamics of flushing flows: implications for management in large Mediterranean Rivers

Flushing flows have been implemented in the lower Ebro River since 2003, with the principle objective of removing excess macrophytes. This paper describes the hydrology and sediment transport of these flushing flows in comparison with natural floods and discusses their effects in terms of riverbed adjustments. During flushing flows suspended sediment, concentration is more constant and double that of natural floods, although discharge is lower. Flashiness, measured as the rate of discharge increase per unit time, is an order of magnitude higher during flushing flows than during natural events. Consequently, flushing flows exhibit higher transport capacity than their natural counterparts despite their considerably lower magnitude and duration. Flushing flows remove up to 95% of macrophytes close to the dam, but their effectiveness reduces with distance downstream. Despite several constraints, flushing flows have significant potential to entrain and transport sediment and careful management of these releases may, therefore, play an important role in enhancing physical habitat in the river and supply sediment to the delta. The River Ebro case study shows that flushing flows are not incompatible with HEP production, and may actually result in a positive trade‐off due to reduced clogging of water intakes. Nevertheless, it remains important to reassess their effectiveness regularly and monitor adverse geomorphic effects such as riverbed degradation. In summary, flushing flows are an important instrument of river management, but one which must be employed as part of a spectrum of approaches to enhance physical habitat conditions. Copyright © 2008 John Wiley & Sons, Ltd.     

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.     

Macroinvertebrate Community Responses to Annual Flow Variation from River Regulation: An 11‐Year Study

The majority of the world's large river systems is affected by dams. The influences of unnatural regimes induced by flow management are wide‐ranging from both biotic and abiotic standpoints. However, many of these effects are not evident over short (1–2 years) periods (e.g. impacts of annual flow variation). This study examines the long‐term effects of annual flow variation on the macroinvertebrate community in the Chattahoochee River (GA) in the reaches below Buford Dam, the major water control structure on the river. Quarterly, macroinvertebrate samples were taken from 2001 to 2011 using Surber and Hester–Dendy plate samplers at six locations spread across 65 km below the dam. Data were analysed via analysis of similarities to determine differences in community composition between high‐flow (mean discharge = 58.27 m³/s) and low‐flow (mean discharge = 26.53 m³/s) years. Taxa that contributed most to community differences were determined via similarity percentages analyses and subsequent t‐tests. Several insect taxa (e.g. Cheumatopsyche and Ceratopsyche caddisfly larvae, Maccaffertium mayfly nymphs and Taeniopteryx stonefly nymphs) were more prevalent under the high‐flow regime. Non‐insect macroinvertebrates (e.g. Crangonyx amphipods, Tricladida flatworms and Caecidotea isopods) were more abundant under low‐flow conditions. In terms of taxon richness, no significant effects of flow regime were detected. Implications of macroinvertebrate patterns for the fishery and ecological health of the river are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrologically Based Environmental Flow Methods Applied to Rivers in the Maritime Provinces (Canada)

The demand for water withdrawal continues to increase worldwide. These water withdrawals from rivers can affect fish habitat and aquatic life. As such, environmental flow assessment methods are used in order to protect rivers against excessive water withdrawals. The concept of environmental flow relates to the quantity of water required in rivers to sustain an acceptable level of living conditions for aquatic biota at various phases of their development. For many agencies, environmental flow methods are essential in environmental impact assessments and in the protection of important fisheries resources. The present study deals with the evaluation of hydrologically based environmental flow methods within the Maritime Province of Canada. In total, six hydrologically based environmental flow methods were compared using data from 52 hydrometric stations across the region. Some methods provided adequate environmental flow protection (e.g. 25% mean annual flow and Q₅₀ flow duration method); however, other methods did not provide adequate flow protection (e.g. Q₉₀ flow duration method and 7Q10 and 7Q2 low‐flow frequency). The 70% Q₅₀ method provided adequate flow protection only under good baseflow conditions and should be applied with extreme caution. The present study shows the importance of the hydrologic flow regime, particularly as it pertains to the baseflow component, as a significant determinant in the level of instream flow protection. © 2014 Her Majesty the Queen in Right of Canada. River Research and Applications © 2014 John Wiley & Sons, Ltd.     

几种陂路结合结构在山区中小河流治理中的应用

该文主要根据山区河流两岸村庄日常交通和灌溉等需求,介绍一些常用的陂路结合形式,分别就其结构样式、使用材料、适用范围等对进行论述,并进行比较分析,为山区中小河流治理中类似结构提供借鉴。     

坡面汇流法计算小河流域暴雨洪水(第二部分)

系统地介绍了一维水动力学(运动波)与水文学方法相结合的数学模型的算法原理。利用已知任意雨型的净雨时程分配,可以随之求出洪水流量过程线。文中将一场洪水计算分为坡面流计算及河槽洪水演算两部分,用57次野外实测洪水进行了验证。结果说明:一个概化的一维模式一旦与水文学方法相结合,可以得到与实测过程线相当接近的成果。模型参数比较稳定;有利于工程的安全和经济;可以电算,也可以手算;便于编程接入各地水情信息自动化系统,服务于防灾、减灾。本篇属论述第二部分。     

坡面汇流法计算小河流域暴雨洪水(第一部分)

系统地介绍了一维水动力学（运动波）与水文学方法相结合的数学模型的算法原理。利用已知任意雨型的净雨时程分配,可以随之求出洪水流量过程线。文中将一场洪水计算分为坡面流计算及河槽洪水演算两部分,用57次野外实测洪水进行了验证。结果说明：一个概化的一维模式一旦与水文学方法相结合,可以得到与实测过程线相当接近的成果。模型参数比较稳定;有利于工程的安全和经济;可以电算,也可以手算;便于编程接入各地水情信息自动化系统,服务于防灾、减灾。本篇属论述第一部分。     

Assessing Juvenile Native Fish Demographic Responses to a Steady Flow Experiment in a Large Regulated River

The Colorado River below Glen Canyon Dam, Arizona, is part of an adaptive management programme which optimizes dam operations to improve various resources in the downstream ecosystem within Grand Canyon. Understanding how populations of federally endangered humpback chub Gila cypha respond to these dam operations is a high priority. Here, we test hypotheses concerning temporal variation in juvenile humpback chub apparent survival rates and abundance by comparing estimates between hydropeaking and steady discharge regimes over a 3‐year period (July 2009–July 2012). The most supported model ignored flow type (steady vs hydropeaking) and estimated a declining trend in daily apparent survival rate across years (99.90%, 99.79% and 99.67% for 2009, 2010 and 2011, respectively). Corresponding abundance of juvenile humpback chub increased temporally; open population model estimates ranged from 615 to 2802 individuals/km, and closed model estimates ranged from 94 to 1515 individuals/km. These changes in apparent survival and abundance may reflect broader trends, or simply represent inter‐annual variation. Important findings include (i) juvenile humpback chub are currently surviving and recruiting in the mainstem Colorado River with increasing abundance; (ii) apparent survival does not benefit from steady fall discharges from Glen Canyon Dam; and (iii) direct assessment of demographic parameters for juvenile endangered fish are possible and can rapidly inform management actions in regulated rivers. Copyright © 2015 John Wiley & Sons, Ltd.     

Responses of Chironomid larvae (insecta,Diptera) to ecological quality in Mediterranean river mesohabitats (South Italy)

Chironomid larvae and pupae were studied in selected Mediterranean rivers with the aim of identifying pool and riffle taxa assemblages and of analysing their response to ecological quality gradients. Macroinvertebrate samples were collected in six Italian rivers along a pool‐riffle sequence in three seasons following a multihabitat sampling technique. Chironomids were identified as genus/species, other macroinvertebrates as family/genus. The main physico‐chemical, hydromorphological and geographical data were collected. Samples were ascribed to five quality classes according to the STAR_ICM index. Based on Chironomid taxa, principal component analysis (PCA) axis 1 represented an organic pollution gradient, axis 2 represented seasonality. Pool and riffle samples were significantly different according to taxa assemblages. Similar results were obtained with PCA based on the whole macrobenthic community. Indicator value (IndVal) analysis facilitated the detection of the Chironomid indicators of high/good quality pools (e.g. Conchapelopia pallidula, Rheopelopia ornata, Epoicocladius ephemerae) and riffles (Tvetenia calvescens, Eukiefferiella gracei). The Berger–Parker dominance index based on Chironomid assemblages in pools was correlated to PCA axis 1 and performed well in discriminating between quality classes. In riffles, no correlations to PCA axes were detected and a wide overlap between quality classes was present. Thus, assessment in the analysed river type may focus on pool mesohabitat as this seems to represent best the ecological gradient of sites. Copyright © 2009 John Wiley & Sons, Ltd.     

2000—2014年云南省陆地生态系统水分利用效率的时空变化

基于MODIS卫星遥感数据,计算了云南省2000—2014年陆地生态系统水分利用效率(WUE),结合国家气象站点的观测数据,采用趋势分析、EOF分析和相关性分析等方法,获取了云南省陆地生态系统WUE时空变化规律和主要驱动因子。结果表明:云南省陆地生态系统WUE空间分布差异明显,呈现南北低、中间高的格局,WUE在大部分地区呈现了明显的季节变化,而在低值区变化不显著;WUE年际变化趋势存在明显的南北差异,北方主要呈增加的趋势,南方主要呈减少的趋势,蒸散发是其变化的主导因素;WUE空间模态呈现南北反向分布模式,北方增加,南方减少,反之亦然;WUE驱动因子自北向南依次为相对湿度、最高温度和日照时数,相关关系呈现南北差异。     

The Mann-Kendall Test Modified by Effective Sample Size to Detect Trend in Serially Correlated Hydrological Series

The non-parametric Mann-Kendall (MK) statistical test has been popularly used to assess the significance of trend in hydrological time series. The test requires sample data to be serially independent. When sample data are serially correlated, the presence of serial correlation in time series will affect the ability of the test to correctly assess the significance of trend. To eliminate the effect of serial correlation on the MK test, effective sample size (ESS) has been proposed to modify the MK statistic. This study investigates the ability of ESS to eliminate the influence of serial correlation on the MK test by Monte Carlo simulation. Simulation demonstrates that when no trend exists within time series, ESS can effectively limit the effect of serial correlation on the MK test. When trend exists within time series, the existence of trend will contaminate the estimate of the magnitude of sample serial correlation, and ESS computed from the contaminated serial correlation cannot properly eliminate the effect of serial correlation on the MK test. However, if ESS is computed from the sample serial correlation that is estimated from the detrended series, ESS can still effectively reduce the influence of serial correlation on the MK test.     

HEC-RAS模型在山区中小河流水面线计算中的应用研究 ——以铁场河综合整治工程为例

山区中小河流具有坡降大、水工建筑物多、水流急的特点,在水面线推算上相比平原区河流难度较大。常规的水面线方法在急流及多水工建筑物情况下容易出现突变,需分段推求水面线,计算精度较差。该文选定铁场河综合整治工程案例,建立HEC－RAS一维模型推算铁场河干流水面线,并与常规的水面线方法结果对比,分析HEC－RAS模型在山区中小河流水面线推算中的优点。     

基于SCS模型的岩溶地区生态恢复的水文响应研究

生态恢复是目前岩溶地区生态环境保护和水土流失治理的主要手段。为寻找相关生态恢复项目的理论指导,在遥感和地理信息技术的支持下,采用SCS模型对贵州平湖流域进行不同生态恢复情景下的土地利用覆被变化的径流深水文响应进行模拟。研究结果表明：平湖流域林地和草地对水源涵养具有重要作用,且林地的涵养作用大于草地,而耕地的增加使径流深增大,加剧了水土流失,因此岩溶地区在生态恢复过程中退耕还林（草）十分必要的。     

基于SCS模型的岩溶地区生态恢复的水文响应研究

生态恢复是目前岩溶地区生态环境保护和水土流失治理的主要手段.为寻找相关生态恢复项目的理论指导,在遥感和地理信息技术的支持下,采用SCS模型对贵州平湖流域进行不同生态恢复情景下的土地利用覆被变化的径流深水文响应进行模拟.研究结果表明:平湖流域林地和草地对水源涵养具有重要作用,且林地的涵养作用大于草地,而耕地的增加使径流深...     

不同输沙流态对多沙河流水库水沙调节计算结果影响的分析研究

在利用水沙数学模型进行多沙河流水库水沙调节计算时,准确的预判相应的来水来沙条件和库型边界条件下入库含沙水流的输沙流态并确定相应的控制方程,是确保计算结果准确的关键.通过建立水库一维非饱和输沙数学模型,对相同库型条件和相同来水来沙条件时不同输沙流态时人库水流的泥沙冲於量进行计算,初步量化回答了不同输沙流态对多沙河流水库水...     

Response by fish assemblages to an environmental flow release in a temperate coastal Australian river: A paired catchment analysis

Defining appropriate environmental flow regimes and criteria for the use of environmental water allocations requires experimental data on the ecological impacts of flow regime change and responses to environmental water allocation. Fish assemblages in one regulated and one unregulated tributary paired in each of two sub‐catchments of the Hunter River, coastal New South Wales, Australia, were sampled monthly between August 2006 and June 2007. It was predicted that altered flow regime due to flow regulation would reduce species richness and abundance of native fish, and assemblage composition would differ between paired regulated and unregulated tributaries. Despite significant changes in richness, abundance and assemblage composition through time, differences between regulated and unregulated tributaries were not consistent. In February 2007, an environmental flow release (‘artificial flood’) of 1400 ML was experimentally released down the regulated tributary of one of the two catchments over 6 days. The flow release resulted in no significant changes in fish species abundances or assemblage composition when compared to nearby unregulated and regulated tributaries. Flow regulation in this region has reduced flow variability and eliminated natural low‐flow periods, although large floods occurred at similar frequencies between regulated–unregulated tributaries prior to and during 2006–2007, resulting in only moderate changes to regulated flow regimes. Barriers to dispersal within catchments also compound the effects of flow regulation, and findings from this study indicate that the location of migratory barriers potentially confounded detection of the effects of flow regime change. Further experimental comparisons of fish assemblages in regulated rivers will refine river‐specific response thresholds to flow regime change and facilitate the sustainable use of water in coastal rivers. Copyright © 2010 John Wiley & Sons, Ltd.