Modeling variations in salt composition components of river water

The balance of a component contained in river water is considered taking into account its input with lateral inflow and decay in the aquatic environment. Random changes in lateral inflow causes fluctuations in the parameters of component input and decay. A stochastic equation of component balance is derived and used as the basis for the construction of an equation for the probability density of component concentration. The solution of this equation shows that the probability density follows lognormal law. This theoretical result is applicable to the analysis of time series of water salt composition components, including pH, alkalinity, chlorides, ammonia, iron, and aluminum. The applicability of the lognormal law is proved and distribution parameters are evaluated. The distributions of three components (pH, alkalinity, and chlorides) are found to split into two lognormal branches, describing high and low component concentrations. In the case of pH and alkalinity, this splitting is due to seasonal effects, while in the case of chlorides, it is caused by the difference between concentrations in the surface runoff at the early and final stages of snow melting and rainfalls. The application of the statistical distributions for probabilistic forecasting of extreme component concentrations is considered. The exceedance probability of standard limits of the components is considered. The use of exceedance probability in hydrochemical standardization is demonstrated.     

Modeling the Mozhaisk Reservoir Genetic Structure

A box model of water mass composition is used to determine the genetic structure of the main water mass (MWM) of the Mozhaisk Reservoir in the high-water 1986–1987 and for four constructed scenarios. The greatest difference between the genetic compositions of the spring, summer, and autumn modifications of MWM manifested itself in that the winter reservoir water of the previous water management year predominates in a low-water year. Elevated proportions of snowmelt flood water were recorded in the spring and summer of a medium-water year (with high snowmelt flood and low rain floods) and in the winter of a low-water year. Possible variations (up to 27%) in the salinity and color index of MWM in years with different genetic composition are demonstrated and shown to be attributable to different water abundance in these years. The genetic structure of the reservoir water is supposed to affect possible variations in the phosphorus content of the reservoir MWM.     

Regional analysis of low flow using L-moments for Dongjiang basin,South China

Abstract

Dongjiang water has been the key source of water supplies for Hong Kong and its neighbouring cities in the Pearl River Delta in South China since the mid-1960s. Rapid economic development and population growth in this region have caused serious concerns over the adequacy of the quantity and quality of water withdrawn from the Dongjiang River in the future. Information on the magnitude and frequency of low flows in the basin is needed for planning of water resources at present and in the near future. The L-moment method is used to analyse the regional frequency of low flows, since recent studies have shown that it is superior to other methods that have been used previously, and is now being adopted by many organizations worldwide. In this study, basin-wide analysis of low flows is conducted for Dongjiang basin using five distributions: generalized logistic, generalized extreme value, lognormal, Pearson type III and generalized Pareto. Each of these has three parameters estimated by the L-moment method. The discordancy index and homogeneity testing show that 14 out of the 16 study sites belong to a homogenous region; these are used for further analysis. Based on the L-moment ratios diagram, the Hosking and Wallis goodness-of-fit statistical criterion and the L-kurtosis criterion, the three-parameter lognormal distribution is identified as the most appropriate distribution for the homogeneous study region. The regional low-flow estimates for each return period are obtained using the index flood procedure. Examination of the observed and simulated low flows by regional frequency analysis shows a good agreement in general, and the results may satisfy practical application. Furthermore, the regional low-flow relationship between mean annual 7-day low flows and basin area is developed using linear regression, providing a simple and effective method for estimation of low flows of desired return periods for ungauged catchments.     

Model of fluctuations in bacteriological indices of water quality

The bacteriological indices of water quality, including coliforms, sulfite-reducing clostridia, total microbial count, coliphages, and fecal streptococci were analyzed. A model describing fluctuations in microorganism population in the aquatic environment is proposed. A stochastic differential equation was obtained and used to derive a lognormal distribution of organism population. The model was applied to describe time series of bacteriological indices of the Moskva River Water Source. Satisfactory agreement was obtained between theoretical distributions and empirical data in a wide range of index values embracing one to three orders of variations in microorganism population. A forecast procedure was developed and applied to calculate the exceedance probabilities of different levels of bacterial pollution of the water source. Time periods with higher bacterial pollution were identified.     

The bivariate lognormal distribution to model a multivariate flood episode

Complex hydrological events such as floods always appear to be multivariate events that are characterized by a few correlated variables. A complete understanding of these events needs to investigate joint probabilistic behaviours of these correlated variables. The lognormal distribution is one of frequently selected candidates for flood‐frequency analysis. The multivariate lognormal distribution will serve as an important tool for analysing a multivariate flood episode. This article presents a procedure for using the bivariate lognormal distribution to describe the joint distributions of correlated flood peaks and volumes, and correlated flood volumes and durations. Joint distributions, conditional distributions, and the associated return periods of these random variables can be readily derived from their marginal distributions. The approach is verified using observed streamflow data from the Nord river basin, located in the Province of Quebec, Canada. The theoretical distributions show a good fit to observed ones. Copyright © 2000 John Wiley & Sons, Ltd.     

Statistical distributions of phytoplankton concentration in river water

Daily time series of phytoplankton concentration are theoretically analyzed with the use of population dynamics equation with fluctuations in the growth factor and environmental carrying capacity taken into account. The statistical distributions of phytoplankton cell concentration are shown to obey different laws, depending on the season of the year: lognormal in the winter and logarithmic in the vegetation period. The probability of extremely high concentration numbers is described by the normal law. The verification of the obtained relationships against a body of empirical data confirmed the theoretical forecasts. The obtained results make it possible to predict the probabilities of various phytoplankton concentration values within a wide range, including the domain of large values, which are of greatest hazard in terms of water quality, water treatment processes, and aquatic ecosystem well-being.     

Statistical analysis of flash flood events for designing water harvesting systems in an extremely arid environment

A water harvesting system for research purposes has been established in the Lisan Peninsula of the Dead Sea in the middle of the Jordan Rift Valley, where no authorized guideline is available for designing water harvesting systems. Rainfall and runoff, which occurred as flash floods, were observed at the downstream end of a gorge with a 1.12 km² barren catchment area from October 2014 through July 2019. Due to the extremely arid environment, runoff from the catchment is ephemeral, and the flash flood events can be clearly distinguishable from each other. Thirteen flash flood events with a total runoff volume of more than 100 m³ were successfully recorded during the five rainy seasons. Pearson and Spearman correlations between duration, total rainfall depths at two points, total runoff volume, maximum runoff discharge, bulk runoff coefficient, total variation in runoff discharge and maximum variation in runoff discharge of each flash flood event were examined, revealing no straightforward relationship between rainfall and runoff. The performance of the conventional SCS runoff curve number method was also deficient in reproducing any rainfall–runoff relationship. Therefore, probability distribution fitting was performed for each random variable, focusing on the lognormal distribution with three parameters and the generalized extreme value distribution. The maximum goodness-of-fit estimation turns out to be a more rational and efficient method in obtaining the parameter values of those probability distributions rather than the standard maximum likelihood estimation, which has known disadvantages. Results support the design of the water harvesting system and provide quantitative information for designing and operating similar systems in the future.     

长江流域历史水旱灾害分析

长江流域有丰富和长期的水旱灾害史料,最早的水灾和旱灾记载有2000余年的历史,经过系统整理和分析的历史水旱灾害资料有1000余年的旱涝型年表和500余年的旱涝分布图集.在以上资料基础上,对长江流域历史水旱灾害的地域分布特性和时间变化规律进行了初步分析:500余年历史水旱灾害的地域分布显示,流域水旱灾害总体特征是水灾重于旱灾,各级水旱灾害频率的地域分布极不均匀,存在着显著的灾害多发和少发地带,它们与自然地理环境、水系特征、气候条件和社会经济条件等因素有关;1000余年旱涝型年表分析表明,长江流域洪涝和干旱频次在时间上的非均匀分布并非完全随机,表现出多种时间尺度的年际变化特征,其中主要表现为约100a上下的大干湿气候期变化及40a左右的小旱涝期振动.     

Analysis of variations in the regime of rivers and lakes in the Upper Volga and Upper Zapadnaya Dvina based on archaeological-geomorphological data

The geomorphological and altitudinal positions of occupational layers corresponding to 1224 colonization epochs at 870 archaeological sites in river valleys and lake depressions in southwestern Tver province. A series of alternating low-water (low levels of seasonal peaks, many-year periods without inundation of floodplains) and high-water (high spring floods, regular inundation of floodplains) intervals of various hierarchical rank was identified. In low-water epoch, an increase was recorded in the share of settlements on low elevations, including river and lake floodplains now subject to inundation. The archaeological epochs 2–3 Ky in length were found to form the following series from high-water to low-water: Mesolithic (11.8–8.0 Ky ago)-Iron age (2.8–0.3)-Neolithic (8.0–5.0)-Bronze epoch (5.0–2.8). The first half of the Iron age (2.8–1.8 Ky ago) was extremely water-abundant, while its second half (middle ages) was dry (relative to the present time). A correlation between the hydrological and temperature regimes was identified: low-water epochs closely correlate with warm epochs, while high-water ones correlate with cold epochs. This can be associated with the specific features of the present-day type of water regime with dominating spring flood; this regime is supposed to have existed during the most part of the Holocene: the runoff and the levels of floods decline during warming epochs and increase during cooling epochs.     

The information content theory for the estimation of the topographic index distribution used in TOPMODEL

This paper analyses the significance of the entropy concept in the topography parameterization within the model TOPMODEL proposed by Beven and Kirkby (1979), by means of the hydrological behaviour of an experimental basin in southern Italy. For a significant number of flood events recorded at the basin outlet, the performance of TOPMODEL for different spatial distributions of the topographic index, ln(a/tan β), has been observed. Performance is related to the information content estimated as an entropy measure, corresponding to each of the spatial distributions of the topographic index, with the aim of identifying the procedures most suitable to represent the hydrological process of rainfall–runoff. The results obtained have shown that for flood events corresponding to brief, heavy precipitation, some procedures provide better performances than others. Moreover, these improvements are justified by greater information content in the corresponding spatial distributions of the topographic index. Finally, TOPMODEL performances for some procedures have been analysed, varying the resolution scale of the topographic index. For analogous hydrological performances, scale change produced variations in some of the subsurface hydraulic parameters. These variations were proportional to a spatial variability measure of the topographic index distribution, derived from the corresponding information content. © 1997 John Wiley & Sons, Ltd.     

Concentration dynamics of biogenic elements and phytoplankton at Selenga R. Mouth and in Selenga shallows (Lake Baikal)

The seasonal and year-to-year dynamics of the concentrations of biogenic elements and organic matter, as well as quantitative composition of phytoplankton in water of Selenga delta branches is studied. The distribution of those components from the mouth of the Kharauz branch (the main branch) to the water area of the Selenga shallows in different hydrological seasons is shown. The concentrations of nitrate nitrogen and phosphate phosphorus in the zone of mixing of river and lake waters have been found to drop by 30 and 50%, respectively, because of the consumption of those substances by phytoplankton.     

Relation between variations in the characteristics of the high-latitude atmosphere and solar cosmic factors

Daily temperatures at high latitudes of the Northern and Southern hemispheres and the corresponding levels of currents of solar protons and the PC, Ap, and Dst magnetic indices are considered. The character of variations in the surface temperature depending on these indices in different seasons during strong magnetic storms, when the Dst amplitude was smaller than ?50, has been indicated. The relationship of the indices in southern and northern atmospheric oscillations (SOI and NAO) to the Ap indices has been revealed. The monthly average Ap amplitude increases before the El Nino warm period, when the SOI index decreases from 0 to ?1.5 and the NAO index increases from ?0.5 to 0.9. The La Nina cold period, when SOI increases from ?0.1 to 1.3 and NAO decreases from 0.7 to ?0.45, begins after a decrease in the Ap index.     

Types of probability distributions in the evaluation of extreme floods

The development of an optimal scheme for evaluation of maximal water discharges is discussed, including adequate probability distribution laws, an effective procedure for their approximation based on observational data, and reliable goodness-of-fit tests for analytical and empirical distributions. One-dimensional probability distribution laws are systematized. Promising distributions were identified, including generalized distribution of extreme values, lognormal distribution, Pearson type V power distribution, and GPD, for evaluating maximal discharges. The available methods for approximating analytical curves, including the up-to-date method of L-moments are considered. Parameter estimation algorithm based on L-moment method for Pearson type III distribution is considered. Pearson type III distribution, lognormal distribution, GEV, and GPD are compared in the approximation of maximal water discharges in rivers of Austria, Siberia, Far East, and the Hawaiian Islands.     

Hydrochemical Characteristics of the Upper Volga Reservoirs in the Low-Water Season of 1997

The results of studies of the Ivankovo, Uglich, Rybinsk, and Gorkii reservoirs are analyzed. The studies involved a wide range of hydrochemical (salt composition, biogenic elements, organic matter, oil products, and heavy metals) and hydrophysical characteristics in the summer low-water period. The concentrations of organic matter and major biogenic elements are shown to decrease downstream along the chain of reservoirs with a respective general decrease in the trophic status. Large built-up areas located downstream of the Rybinsk Hydroelectric Plant are shown to adversely affect the river water quality.     

Spatio-temporal analysis of daily,seasonal and annual precipitation concentration in Jharkhand state,India

Nowadays, climate change and global warming have led to changes in the distribution of precipitation, which affect on the availability of water resources. Therefore, investigating the temporal and spatial variations of precipitation in the previous period is highly important in the future planning for flood control and local management of water resources. Considering the importance of this issue, in the present study, the precipitation concentration indices have been used for analysing precipitation changes at daily, seasonal, and annual time scales in the period of 1971 to 2011 over the Jharkhand state, India. Also, Modified Mann–Kendall test has used to study the trend of precipitation concentration indices in annual and seasonal time scales. The result shows a highly irregular and non-uniform distribution in the annual scale. For the seasonal scale an irregular and non-uniform distribution has been also observed, although the summer had a better situation than other seasons. For daily scale, none of the stations had a regular concentration and in the northeast and southern parts of the study area, there have been more irregularities. Furthermore, the results of investigating annual precipitation trend showed a combination of increasing and decreasing trend over the study area. The results of this study can be applied to manage water supplies, drainage projects, construct collection structures of urban flood, develop plans to prevent soil erosion, and designing appropriate plans to cope with drought conditions.     

Field survey and modelling of irrigation water quality indices in a Mediterranean island catchment: a comparison between spatial interpolation methods

ABSTRACT

A biannual survey of physico-chemical quality indices of 104 irrigation-water wells located in a cultivated plain of a Mediterranean island catchment was conducted using a multi-parameter probe. The campaign was planned so as to differentiate between the dry and wet seasons. The acquired data constituted the test bed for evaluating the results and the features of four spatial interpolation methods, i.e. ordinary kriging, universal kriging, inverse distance weighted and nearest neighbours, against those of the recently introduced bilinear surface smoothing (BSS). In several cases, BSS outperformed the other interpolation methods, especially during the two-fold cross-validation procedure. The study emphasizes the fact that both in situ measurements and good mathematical techniques for studying the spatial distribution of water quality indices are pivotal to agricultural practice management. In the specific case studied, the spatio-temporal variability of water quality parameters and the need for monitoring were evident, as low irrigation water quality was encountered throughout the study area.     

Integration of transfer function model and back propagation neural network for forecasting storm sewer flow in Taipei metropolis

Typhoons and storms have often brought heavy rainfalls and induced floods that have frequently caused severe damage and loss of life in Taiwan. Our ability to predict sewer discharge and forecast floods in advance during storm seasons plays an important role in flood warning and flood hazard mitigation. In this paper, we develop an integrated model (TFMBPN) for forecasting sewer discharge that combines two traditional models: a transfer function model and a back propagation neural network. We evaluated the integrated model and the two traditional models by applying them to a sewer system of Taipei metropolis during three past typhoon events (NARI, SINLAKU, and NAKR). The performances of the models were evaluated by using predictions of a total of 6 h of sewer flow stages, and six different evaluation indices of the predictions. Finally, an overall performance index was determined to assess the overall performance of each model. Based on these evaluation indices, our analysis shows that TFMBNP yields accurate results that surpass the two traditional models. Thus, TFMBNP appears to be a promising tool for flood forecasting for the Taipei metropolis sewer system. For publication in Stochastic Environmental Research and Risk Analysis.     

Seasonal deformation regime of rifts in lowland rivers

Various schemes of within-year transformations of rifts from spring flood to low-water period and autumn freshets have been considered. Such transformations have been shown to manifest themselves in the displacement of rift trough from the upper to the lower point bars, accumulation of sediments in one phase of water regime and erosion of ridges in the other phase, as well as in the advancement of ridge-type micro- and meso-forms of channel relief onto rift saddle. Differences have been revealed between the regimes of rifts composed of sand and pebble-boulder sediments; specific features were identified in the regime of rifts in rivers in permafrost zones and rifts with rock protrusions on the bed.     

The response of braided planform configuration to flow variations,bed reworking and vegetation: the case of the Tagliamento River,Italy

Morphological features of braided rivers (bars, channels and pools) experience major changes in area, shape and spatial distribution as a response to (i) the pulsation of discharge during a flood and (ii) the bed evolution induced by floods. In this work, at‐a‐station relationships between water level and planform configuration were investigated on the Tagliamento River, a large gravel‐bed braided river in northeast Italy, over a 2‐year study period comprising three bankfull events and several small‐to‐medium floods. The analysis was performed on two 1‐km‐long reaches, characterized by different riparian vegetation cover. Ground‐based images with an hourly temporal resolution were acquired using software‐controlled, digital cameras. Bars, channels, pools and vegetated patches were manually digitized on more than 100 rectified images. Sequences of constant‐level images spanning the study period were used to quantify the impact of floods on the stability of at‐a‐station relationships and on the turnover rate of water bodies. The analysis shows that wetted area increased almost linearly with water level in both reaches. The average number of branches per cross‐section peaked at intermediate flow levels, increasing from 2 at low flow up to 6–7. The number of branches displayed the largest fluctuations over time, with significant changes produced also by moderate floods. Turnover rates were high in both reaches, with more than 30% of wetted areas at low flow converting into bare gravel in less than 2 months. Vegetation colonization was found to limit the mobility of the low flow channels over time by concentrating the flow in fewer, deeper anabranches. The number of channels per cross‐section was 30–40% less in the vegetated reach and the proportion of low flow water bodies in the same position after 12 months increased from 3% to 14%. Copyright © 2012 John Wiley & Sons, Ltd.     

长江流域汛期降水集中程度和洪涝关系研究

用新定义的降水集中度和集中期分别讨论了我国长江流域不同地段汛期降水在时间和空间上的分布特征和变化规律. 结果表明在对长江流域旱涝灾害研究方面,降水集中度和集中期能够定量地表征降水量在时空场上的非均匀性,提取出最大降水重心对应的时段,因此可以比较理想地分析旱涝灾害发生的基本特征及其形成机制. 并且在长江中下游地区的降水集中度与东亚副热带季风之间存在着比较密切的联系.