Seasonal and interannual variations of flow discharge from Pearl River into sea

Flow discharge from the river basin into the sea has severe impacts on the immediate vicinity of river channels, estuaries, and coastal areas. This paper analyzes the features and temporal trends of flow discharge at Pearl River’s three main gauge stations: the Wuzhou, Shijiao, and Boluo gauge stations on the West River, North River, and East River, respectively. The results show no significant trend in annual mean discharge into the sea at the three gauge stations. Changes of monthly mean discharge at the Boluo Gauge Station are evident, and a majority of monthly discharge in the dry season displays significant increasing trends. Furthermore, changes of the extreme discharge are quite evident, with a significant decreasing trend in the annual maximum discharge and a significant increasing trend in the minimum one. The significantly decreasing ratio of the flood discharge to annual discharge at the Boluo Gauge Station indicates that the flow discharge from the East River has increased in the dry season and decreased in the flood season since the construction of dams and reservoirs. At the other two gauge stations, the Wuzhou and Shijiao gauge stations, the seasonal discharge generally does not change perceptibly. Human impacts, especially those pertaining to reservoir and dam construction, appear to be responsible for the seasonal variation of flow discharge. The results indicate that the construction and operation of dams and reservoirs in the East River have a greater influence on flow discharge, which can well explain why the seasonal variation of flow discharge from the East River is more evident.     

A regional frequency study of extremal rainfall and runoff processes

The annual maximum daily rainfall and annual maximum flood discharges in Lesotho were subjected to regional analysis. The mean of both time series was found to be a satisfactory parameter for regional study. The nondimensional series generated by using the mean as the divisor rendered the sequences homogeneous in the statistical sense throughout the whole country. The processes in question obey a lognormal probability law and are random in their sequential evolution. The annual maximum daily rainfall does not produce the annual maximum peak discharge in the rivers of Lesotho.     

伊春河流域径流特征分析

以实例数据为依据,从探讨流域降雨和径流的年内、年际变化规律入手,利用样本数据的均值、极值、Cv值和出现频率等统计参数,对伊春河流域径流的成因及变化规律进行了分析研究。分析结果得出了流域径流年内分配主要集中在夏季,全年各季径流相差悬殊,流域径流年际分配相差较小,径流量年际补给较充足的结论,针对分析结果对提高流域水资源利用效率提出了建议。     

A Stream Water Availability Model of Upper Indus Basin Based on a Topologic Model and Global Climatic Datasets

Integrated water resources management at river basin scales and evaluation of effects of climate change on regional water resources require quantitative estimates of space-time variability of monthly discharges within a river network. This study demonstrates that such estimates, which can be called stream water availability, for regional river basins with meager or nonexistent gauge data, can be obtained by combining continuity models of hydrological processes, flow routing, and topology of the river basin. The hydrologic processes can be adequately modeled using high quality databases of hydrologic significance. A stream water availability model is presented for Upper Indus Basin (UIB) utilizing the most up-to-date datasets for topography, temperature, precipitation, net radiation, land cover, soil type, and digital atlas. Multiple datasets have been evaluated and the ones with best accuracy and temporal coverage have been selected for the final model. Upper Indus River and its major tributaries are highly significant in regional water resources management and geopolitics. However, UIB is a poorly studied and largely ungauged river basin with an area of 265,598 km² and extremely rugged topography. Several factors, the chief ones being the challenging terrain and the trans-boundary nature of the basin, have contributed to this knowledge gap. Hydro-climatologically it is a complex basin with a significant cryospheric component. The spatial and temporal variation of the principal climatic variables, namely precipitation, net radiation, and temperature has been thoroughly accounted for in the development of a stream water availability model based on a process model coupled with a topologic model and a linear reservoir model of river flow routing. Model calculations indicate that there are essentially two hydrologic regimes in UIB. The regime that is truly significant in contributing stream flows, originates from the UIB cryosphere containing outstanding glaciers and snowfields. The other regime, generated from wet precipitation and melt water from seasonal snow covers is insignificant due to high rates of infiltration and evaporation in the semi-desert environment prevailing at elevations below perennial snow and ice covers. In general, the modeled stream flow characteristics match with the sparse discharge measurements that are available. Flow in the Indus considerably increases at its confluence with Shyok River and further downstream where other tributaries form the north join the main stem. At or near the outlet of the basin stream flow can vary from less than 800 m³ s^− 1 in the winter and spring to nearly 8,000 m³ s^− 1 in the peak summer and can persist to over 1,500 m³ s^− 1 in the autumn. The importance of snow and glacial melt in Indus River discharge is apparent and any global or regional climate change affecting the equilibrium line elevation of the snow fields in the Karakoram will have a profound influence on the water availability in the Indus. Estimates are made for per capita water availability in Ladakh and Gilgit-Baltistan territories, controlled by India and Pakistan respectively. Geopolitical significance and climate change effects are discussed briefly.     

Macro‐invertebrate Community Response to Multi‐annual Hydrological Indicators

Flow is widely considered one of the primary drivers of instream ecological response. Increasingly, hydroecological models form the basis of integrated and sustainable approaches to river management, linking flow to ecological response. In doing so, the most ecologically relevant hydrological variables should be selected. Some studies have observed a delayed macro‐invertebrate (ecological) response to these variables (i.e. a cumulative inter‐annual effect, referred to as multi‐annual) in groundwater‐fed rivers. To date, only limited research has been performed investigating this phenomenon. This paper examines the ecological response to multi‐annual flow indicators for a groundwater‐fed river. Relationships between instream ecology and flow were investigated by means of a novel methodological framework developed by integrating statistical data analysis and modelling techniques, such as principal component analysis and multistep regression approaches. Results demonstrated a strong multi‐annual multi‐seasonal effect. Inclusion of additional antecedent flows indicators appears to enhance overall model performance (in some cases, goodness of fit statistics such as the adjusted R‐squared value exceeded 0.6). These results strongly suggest that, in order to understand potential changes to instream ecology arising from changing flow regimes, multi‐annual and multi‐seasonal relationships should be considered in hydroecological modelling. © 2017 The Authors River Research and Applications Published by John Wiley & Sons Ltd.     

Regional flood frequency analysis in the central‐western river basins of Argentina

Knowing the probability of occurrence of a flood event is an important issue for water resources planning. At‐site probability models require a long extension of hydrological data for robust estimation of low‐frequency events. As the mean record length of 25 gauge stations in western river basins of Argentina is 49 years (until 2010), regional models are an interesting tool to determine mountain rivers system dynamics. This study aims to estimate low‐frequency quantiles of annual maximum flow in Argentinean western river basins (28°S–37°S) applying regional frequency analysis based on the L‐moments method. Besides, mean annual maximum flow of 75 gauge stations (22°S–52°S) was analysed. First, an exploratory data analysis was performed; normality, independence, and randomness were accepted in the 27%, 87%, and 91% of cases, respectively. Increasing trends in annual maximum flows in the north‐western and central‐western rivers of Argentina were detected, whereas decreasing trends in annual maximum flow in the Patagonian Andes were identified. Base on at‐site characteristics and at‐site statistics, a homogeneous region of 12 stations with a record period of 568 years was formed. General extreme value was the most appropriate distribution for this homogeneous study region. Estimation accuracy using Monte Carlo simulations was performed. The error bounds were set at 90%, the mean square error was 9.23%, and the relative bias was 1.6%. The regional method performed better than the at‐site estimation.     

Short‐term effects in a reduced flow stretch: The case of the Antas River in South Brazil

The building of adduction channels (penstocks) that conduct water from reservoirs to turbines, which are located kilometres from the dam, is becoming common, optimizing the electricity generation in small dams. This design creates a river stretch with reduced discharge between the dam and the powerhouse. This study evaluates the short‐term impacts of the below‐dam decrease in river flow on fish assemblages. Samples were collected in the reduced flow stretch of the Castro Alves Hydropower Plant (Antas River, Rio Grande do Sul, Brazil) before the reservoir started operating (January 2008; mean discharge of 103.7 m³/s) and immediately after operation began (March 2008; mean discharge of 12.4 m³/s). Sampling was conducted in distinct habitats of the reduced flow stretch (slow waters—gillnets, sand beaches—seining nets, structured littoral—electrofishing, and fast waters—cast nets) with a strongly standardized effort. The attributes of the fish assemblages were not negatively affected by the flow reduction in any habitat sampled. However, distinct changes in the spatial structure were observed considering the different types of habitat predominantly used by the species, which represents an entire reorganization of the fish assemblages in the short term. It is fundamental that these short‐term aspects be considered in the licensing of hydropower plants in addition to the long‐term changes.     

Application of wavelet analysis for monitoring the hydrologic effects of dam operation: Glen Canyon Dam and the Colorado River at Lees Ferry,Arizona

Wavelet analysis is a powerful tool with which to analyse the hydrologic effects of dam construction and operation on river systems. Using continuous records of instantaneous discharge from the Lees Ferry gauging station and records of daily mean discharge from upstream tributaries, we conducted wavelet analyses of the hydrologic structure of the Colorado River in Grand Canyon. The wavelet power spectrum (WPS) of daily mean discharge provided a highly compressed and integrative picture of the post‐dam elimination of pronounced annual and sub‐annual flow features. The WPS of the continuous record showed the influence of diurnal and weekly power generation cycles, shifts in discharge management, and the 1996 experimental flood in the post‐dam period. Normalization of the WPS by local wavelet spectra revealed the fine structure of modulation in discharge scale and amplitude and provides an extremely efficient tool with which to assess the relationships among hydrologic cycles and ecological and geomorphic systems. We extended our analysis to sections of the Snake River and showed how wavelet analysis can be used as a data mining technique. The wavelet approach is an especially promising tool with which to assess dam operation in less well‐studied regions and to evaluate management attempts to reconstruct desired flow characteristics. Copyright © 2005 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.     

Impacts of Projected Climate Changes on Streamflow and Sediment Transport for Three Snowmelt‐Dominated Rivers in the Interior Pacific Northwest

Anthropogenic climate change is likely to have significant impacts on river systems, particularly on rivers dominated by seasonal snowmelt. In addition to altering the timing and magnitude of streamflow, climate change can affect the energy available to transport sediment, as well as the availability of sediment to be transported. These hydrologic changes are sensitive to local climate, which is largely controlled by topography, but climate models cannot resolve processes at these scales. Here, I investigate impacts of climate change on streamflow and suspended‐sediment transport for three snowmelt‐dominated rivers in the interior Pacific Northwest – the Tucannon River in Washington and the South Fork Coeur d'Alene and Red rivers in Idaho – using downscaled climate simulations from regional climate models (a range of three models plus an ensemble average) to drive a basin‐scale hydrologic model. The results indicate that climate change is likely to amplify the annual cycle of river discharge, producing higher winter discharge (increases in ensemble mean January discharge ranging from 4.1% to 34.4% for the three rivers), an earlier spring snowmelt peak (by approximately one month), and lower summer discharge (decreases in ensemble mean July discharge ranging from 5.2% to 47.2%), relative to a late 20th‐century baseline. The magnitude of the largest simulated flood under the ensemble‐average climate change scenario increases by 0.6–41.6% across the three rivers. Simulated changes in suspended‐sediment transport generally follow the changes in streamflow. These changes in discharge and sediment transport will likely produce significant impacts on the study rivers, including changes in flooding, physical habitat, and river morphology. Copyright © 2014 John Wiley & Sons, Ltd.     

The Impact of Low Flow on Riverine Food Webs in South‐Central Newfoundland

Low‐flow events can reduce food availability and decrease the feeding niche of consumers within rivers. Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope and stomach content analyses were employed to evaluate resource use and overlap between fish species in a natural and regulated river in normal and low‐flow years, with the use of multiple methodological approaches providing the best means of understanding short‐term and long‐term observations on fish feeding and resource overlap under changing flow conditions. Diet analyses generally indicated significant inter‐specific differences in the diets of key fish species within rivers and similarities in resource use between rivers. In comparison with fish from the natural river, fish from the regulated river had lower and less inter‐annually variable δ¹³C values. In the natural river, there was a significant reduction and increase, respectively, in δ¹³C and δ¹⁵N variation in the low‐flow year. Intra‐annual or inter‐annual differences in trophic niche area were not apparent in the regulated river, whereas within the natural river, intra‐annual and inter‐annual differences in trophic niche were found. Resource overlap between key fish species was also higher in the low‐flow year and lower in the spring and higher in the summer as a result of differences in flow. Resource overlap was also higher between rivers in the low‐flow year. High resource overlap between rivers during decreased summer flow indicates a strong effect of flow on river organisms, where both fish and their invertebrate prey resources are concerned. Copyright © 2014 John Wiley & Sons, Ltd.     

渭河流域陕西片降雨径流及水环境特性分析

对渭河流域陕西片的降雨径流特性进行了分析,结果表明:研究区降水量逐年减少;高强度降雨最易产生地表径流,对河道流量的贡献最大,但这种降雨在年内的出现概率仅为3.7%,导致流域内的产、汇流有限且分布不均匀,不足以稀释入河污染负荷。提出了改善渭河水质的两项措施:①削减入河污染负荷,同时保证河道基流量;②加大宝鸡峡水库向下游河道的放水量。     

Lake Chivero (Zimbabwe) and its climatic environment

The mean temperatures and mean maximum temperatures in Lake Chivero indicate a warming trend, which is not evident in mean minimum temperatures. The mean annual precipitation also exhibits a declining trend, as does the Manyame River flow trend. The relation between run‐off, river flow and precipitation indicate a discontinuous trend at a piecewise regression breakpoint of 998 mm precipitation. Above the breakpoint, the river flow is related exponentially with precipitation, while the run‐off relationship is linear, although with a low R² value. Below the breakpoint, both the run‐off and river flow exhibit a low variance accountability. Considered within the context of the IPCC findings of a subcontinent warming faster than the rest of the southern hemisphere, along with declining precipitation, these data suggest an uncertain water supply security for the City of Harare and its satellite settlements. The detectable warming of the lake, taken together with observations in Lake Kariba, also suggests an ecological shift that could be dominated by a shift to a permanent cyanobacteria‐dominated ecosystem, which is currently dominated by Microcystis and Anabaena species.     

灞河流域气候因子对水沙变化的影响

利用灞河流域蓝田气象站和马渡王水文站1960—2012年的气象、水文实测资料,分析灞河流域气候及水沙变化规律,同时运用相关性分析、灰色关联分析、多元线性回归模型等多种方法探讨了该流域水沙变化与气候变化的关系。结果表明:灞河流域降雨量、蒸发量、径流量和输沙量皆呈显著下降趋势,而气温呈上升趋势;降雨量与水沙都有重要的相关关系,1960—1990年影响径流量的气候因子敏感度由大至小依次为降雨量、气温、蒸发量,而1991—2012年则为降雨量、蒸发量、气温,当气温和蒸发量不变时,降雨量每增加1 mm,两阶段的年径流量分别增加0.14亿m3和0.08亿m3;1960—2012年影响输沙量的气候因子敏感度由大至小依次为降雨量、气温、蒸发量,当气温和蒸发量不变时,降雨量每增加1 mm,年输沙量增加0.668万t。     

防洪减灾规划中的中小流域暴雨洪水研究

论述了日本城原川流域的防洪减灾措施及暴雨洪水特性,分析了在短历时集中降雨次数增加情况下,城原川流域短历时降雨对洪峰形成过程的影响,并利用改进的水箱模型对该流域年最大流量进行了模拟,指出对年最大流量贡献度较大的降雨历时为3～6 h,河道整治以48 h历时降雨为标准对河流流量进行推算的规划设计与实际情况背离。     

Hydrological Effects on Relationships Between δ15N of River Nitrate and Land Use in a Rural River Basin,Western Japan

This study aimed to examine how the relationship between δ¹⁵N of nitrate (δ¹⁵N_NO3) in rivers and land use within a river basin changes with varying hydrological conditions. This information would aid in identifying the dominant source contributing to increased nitrate concentrations in rural rivers. For this, δ¹⁵N_NO3 in river water was investigated monthly in the five subbasins of the Hii River basin (area: 911 km²), western Japan, for 1 year and 3 months. There were significant correlations (p < 0.05) between δ¹⁵N_NO3 and the land‐use ratio (i.e. ratios of forested, agricultural and residential areas in a subbasin) for the majority of the observation days, indicating that δ¹⁵N_NO3 reflected land use within the basin. δ¹⁵N_NO3 ranged from +1.4‰ to +8.5‰ and was lower in a subbasin with a higher forested area ratio. We found that the absolute value of the regression slope of the relationship between δ¹⁵N_NO3 and the land‐use ratio decreased with increasing river discharge. This finding demonstrates that differences in δ¹⁵N_NO3 among subbasins with different land‐use compositions became smaller under higher flow conditions. Because δ¹⁵N_NO3 decreased with increasing river discharge, the small absolute value of the regression slope under high flow conditions indicates that forested areas could be the dominant source of river nitrate during high flows in all subbasins investigated regardless of land‐use composition. The results suggest that forested areas make a large contribution to the increase in nitrate concentration in downstream rivers during high flows, because the nitrate concentration increased with increasing river discharge. Copyright © 2014 John Wiley & Sons, Ltd.     

A novel SON2‐based similarity index and its application for the rationalization of river water quality monitoring network

In this paper, a novel self‐organizing network (SON) based similarity index and its application for the optimization of sampling locations in an existing river water quality monitoring network (WQMN) is presented. A rationalization of the River Danube WQMN on its stretch through Serbia was performed using the proposed SON²‐based similarity index. A high‐dimensional dataset was used, which is composed of 18 water quality parameters that were collected during the period 2002–2010 at 17 monitoring locations. The SON‐based seasonal classification that divides 12 months into the cold, moderate, and warm seasons was employed, whereas its second application on each seasonal class yielded subclasses that were used to compare the monitoring locations. The obtained SON²‐based similarity index can be utilized for analysing seasonal variations, as well as overall similarities among neighbouring sites. Based on the calculated similarities of locations and characteristics of the River Danube basin a rationalized WQMN, which uses 30% less monitoring sites, has been proposed.     

Hydrological changes and river regulation in the UK

Water levels of streams and rivers in the United Kingdom have been regulated by weirs for more than one thousand years, but regulation of the flow regime by impoundments began in the latter half on the 19th Century. Organized river flow measurements were not undertaken until 1935, and today the average record length is about 20 years. Only three gauging stations have provided data suitable for pre- and post-impoundment comparisons. Other studies have relied on the comparison of regulated and naturalized discharges. In either case climate and land-use changes make evaluation of the hydrological effect of impoundments problematic. This paper reviews research on hydrological changes due to river regulation in the UK, and presents a case study of the River Severn to evaluate the influence of Clywedog Reservoir on flood magnitude and frequency. Consequent upon dam completion, on average, median flows have been reduced by about 50per cent; mean annual floods have been reduced by about 30per cent; and low flows have been maintained at about 22 per cent higher than the natural Q₉₅ discharge. However, marked differences exist between rivers. The direct effect of reservoir compensation flows and the indirect effect of inter basin transfers for supply have significantly increased minimum flows in most rivers, although in the case of the latter this involves the discharge of treated effluents. In contrast, the effects of impoundments on flood magnitude and frequency is less clear and on the River Severn, at least, changes in flood hydrology during the past two decades are shown to be more related to climate change than to river regulation.     

THE MANAGEMENT MODES OF SEASONAL FLOODS AND THEIR IMPACT ON THE RELATIONSHIP BETWEEN CLIMATE AND STREAMFLOW DOWNSTREAM FROM DAMS IN QUEBEC (CANADA)

The goal of the study was to compare the modes of management of seasonal floods for different dams and to constrain their impact on the relationship between climate variables and streamflow downstream from the dams. At the Rawdon dam, downstream from which the Ouareau River is characterized by a natural‐type regulated flow regime, a ‘type A’ flood management mode prevails, in which the same rainfall and/or snowmelt events account for seasonal floods both in the unregulated (natural) stretch of river upstream from the dam and in the river downstream from the dam. As a result, seasonal floods in the natural setting and downstream from the dam are nearly synchronous. In contrast, downstream from the Matawin dam (Matawin River), which produces an inversion‐type regulated flow regime, the prevalent flood management modes are of types B and D, whereby seasonal floods observed upstream and downstream from the dam are not caused by the same rainfall and/or snowmelt events and, as a result, are not synchronous. This difference in seasonal flood management modes affects the interannual variability of the magnitude of seasonal daily maximum flows related to the seasonal floods. Thus, the interannual variability of these flows downstream from the Matawin dam differs significantly from that of flows upstream. No correlation is observed between climate variables and streamflow downstream from the Matawin dam. This absence of correlation disappears gradually at the annual scale, at which streamflow is correlated with rainfall, as is observed upstream from the dam. Copyright © 2013 John Wiley & Sons, Ltd.     

River regulation and riparian woodlands: Cottonwood conservation with an environmental flow regime along the Waterton River,Alberta

Following water withdrawal, riparian cottonwoods have declined downstream from some dams in western North America. Analyses of aerial photographs and field observations in the 1980s suggested that the black and narrowleaf cottonwoods (Populus trichocarpa and Populus angustifolia) along the Waterton River, Alberta, were declining due to drought stress following the 1964 damming and diversion. This raised concern for the riverine ecosystems and in 1991, “functional flows” commenced with 2 changes: (a) the minimum flow was increased from 0.9 to 2.3 m³/s (mean discharge 21.9 m³/s) and (b) flow ramping provided gradual stage recession after the spring peak. This provided an environmental flow regime that was delivered for 2 decades and this study investigated the consequent river flow patterns and riparian woodlands upstream and downstream from the Waterton Dam. Analyses of aerial photographs from 1951 to 2009 assessed 4 flow management intervals: (a) the free‐flowing predam condition, (b) the initial dammed interval to the mid‐1970s, (c) a drought interval in the 1980s, and (d) with the environmental flow regime after 1991. Analyses revealed woodland reduction from 1961 to 1985 due to losses through bank erosion with major floods and apparent decline due to low flows following a regional drought and water withdrawal for irrigation. With the subsequent environmental flow regime, there was apparent woodland recovery, despite drought in 2000 and 2001. This study demonstrated that the correspondence between river flow patterns and the extent of riparian woodlands and the benefit from the environmental flow regime that probably reduced drought stress and mortality.