Minimum Water Discharge Research Articles

A 7000-year record of extreme flood events reconstructed from a threshold lake in southern Norway

Recent decades have witnessed a shift in the seasonality and frequency of river floods in Norway, primarily attributed to contemporary global warming. Such changes necessitate a more comprehensive understanding of climate-flood dynamics across river systems. A significant challenge in flood risk assessment is that instrumental data records cover only the last few decades and do not capture low-frequency, high-magnitude extremes. Another challenge is the non-stationarity of the leading atmospheric pattern over Scandinavia, the North Atlantic Oscillation (NAO), which requires a spatial understanding of extreme events through time. To address this issue, we use lacustrine sediments from southernmost Norway, aiming to extend flood records beyond the scope of instrumental and historical data by exploring a threshold lake that accumulates flood deposits only when river discharge exceeds a critical level. A multi-proxy approach, which includes X-ray fluorescence (XRF), computed tomography (CT), and magnetic susceptibility (MS), was applied to fingerprint the sediments. We detected thin layers of minerogenic sediments, which we interpreted as slackwater deposits accumulated in a lake environment during extreme flood events. These fine-grained minerogenic bands were quantified using XRF and CT data to reconstruct the frequency of major floods over the past ∼7000 years. The minimum water discharge necessary for transporting sediments into the lake was assessed with the HEC-RAS hydraulic simulation software. Our record shows a high frequency of extreme floods from 7000 to 5000 cal yr BP before a significant decrease from 5000 to 2300 cal yr BP. The frequency has been high since 2300 cal yr BP, with a peak frequency after 1600 CE, coinciding with the Little Ice Age. There is a strong co-variability between a positive NAO index, winter precipitation, and major flood events over the past 120 years. A comparison between our flood record and other palaeorecords suggests that this relationship also holds on multi-millennial time scales.

Steady flow at a breached levee

The present study uses a laboratory scale experimental model and an analytical model to study the steady flow at a breached levee. Flow past a zero height side weir is considered for the purpose. Water surface elevation and the three-dimensional velocity field are measured by a point gauge and an Acoustic Doppler Velocimeter (Vectrino), respectively. Experimental results include the velocity field, free surface elevation, turbulent kinetic energy and bed shear stress. Empirical relations to predict the minimum water depth and discharge at the breach are obtained. An analytical model to predict the approximate flow field at the breach is also developed. The model parameters are calibrated using the experimental results. The approximate flow conditions predicted by the analytical model can be used for field conditions. The 17th Street Canal breach is employed as a case study to demonstrate the performance of the analytical model.

КЛИМАТИЧЕСКИЕ ИЗМЕНЕНИЯ ГИДРОЛОГИЧЕСКИХ ХАРАКТЕРИСТИК НА РЕКАХ РЕСПУБЛИКИ САХА (ЯКУТИЯ)

The paper deals with long-term series of different hydrological characteristics (average annual water discharges, maximum discharges throughout the year, maximum discharges during spring floods and rain floods, spring flood runoff layers, minimum summer and winter water discharges) on the rivers of the Republic of Sakha (Yakutia) and their approximation by models of the non-stationary average (the linear trend and the stepwise change model). It has been found that there are practically no effective non-stationary models for the maximum water discharges, but there are such models for flood layers and for average annual and minimum water discharges, which increased mainly in the late 20th and early 21st centuries due to the possible additional inflow of water from the thawed permafrost. The number of effective non-stationary average models increases from 30% of all cases for flood layers to 50–60% for average annual and minimum summer water discharges, and almost to 100% for minimum winter water discharges. Estimation of the stationarity of the mean values and variances by statistical criteria when dividing the series of stepwise changes by year confirmed the nonstationarity of the mean values for all a priori established nonstationary models and, in some cases, the nonstationarity of the variances. The largest increase in average values up to 100% takes place in the minimum winter water discharges, up to 70–80% – in the minimum summer water discharges, and up to 40–50% – in the average annual water discharges; a change in average values up to 20% cannot be considered statistically significant and reliably determined. Relative to natural variability, the excess is up to 1.5–1.6 standard deviation, but no more. Spatial distributions of the increase in river runoff characteristics in % relative to the previous stationary period and to natural variability are constructed. The greatest increase in the minimum winter water discharge takes place in the northern part of Yakutia. In recent years, water discharges have been observed even on freezing rivers. For the minimum summer and average annual water discharges, the largest increase occurs in the northeast and east.

СЕЗОННЫЕ ИЗМЕНЕНИЯ СОДЕРЖАНИЯ ЗАГРЯЗНЯЮЩИХ ВЕЩЕСТВ В НАНОСАХ ОВРАЖНО-БАЛОЧНЫХ КОМПЛЕКСОВ НА ТЕРРИТОРИИ САРАТОВА

The observation results of pollutant (heavy metals, oil products) concentrations in the bed load of perennial stream outlets of ravine and gully complexes in the city of Saratov are presented. A multiple exceeding of the background content for the analyzed indicators, primarily in the watercourses of industrial zones, is found. The bed load of the maximum water and solid runoff in spring is more polluted than for the minimum water discharge of the watercourses in summer. It can be concluded that it is necessary to create a surface flow treatment system on the territory of Saratov, since solid and water runoff from ravine and gully complexes enters the Volgograd Reservoir, which is a source of drinking water supply and a recreational and fishery object.

Impact of land use-land cover change on spatio-temporal trends in seasonal stream flow and suspended sediment load of Godavari basin from 1969 to 2019

Abstract Assessment of long-term trends in stream flow and sediment load is important for adopting soil and water conservation measures and for predicting morphological changes in rivers. In the present study, detailed quantification of the nature of the trend in stream flow and suspended sediment load of Godavari basin, India is reported for the period of 1969 to 2019. The Mann–Kendall test is used to check the trend of stream flow and sediment load for different seasons, namely, spring, monsoon, post-monsoon and winter. The land use-land cover of the whole basin is prepared for four decades (1980–2020). The maximum and minimum water and sediment discharge is detected in monsoon and winter season, respectively. The stream flow is found to be significantly decreased during monsoon and post-monsoon season. The sediment load is significantly decreased for monsoon and spring season. The nature of trend in sediment load is attributed to the land use and land cover change of the basin. The significant reduction of suspended sediment load is mainly due to increase in water bodies and planned agricultural area. The findings of the research would help to manage water resources as well as sustainable development in the Godavari basin.

ANALISA KETERSEDIAAN DEBIT AIR SUNGAI CIBUNI MENGGUNAKAN METODE F.J MOCK DAN NRECA

In a hydropower planning plan, an important factor that must be known is: the amount of monthly discharge and flagship discharge, as well as the river canfography. To calculate the amount of water availability in Cibuni watershed for the needs of the PLTMH, the discharge analysis of the F.J MCOK method and the NRECA method and the magnitude of the potential evapotranspiration use the Penman method. Hujang bulk data used is rainfall data obtained from 5 rain stations in the form of monthly rainfall for 16 years from 1996-2011. From the calculation of the F.J Mock method for the availability of water in Cibuni Das, a maximum discharge of 28.46 m3 / dt and minimum water discharge of 0.11 m3 / dt. As for the NRECA method is a maximum water discharge of 26.50 m3 / dt and minimum water discharge of 2.77 m3 / dt. Based on the calculation results, for the F.J Mock method is more suitable for use in Cibuni watershed compared to Nreca.

ДОСЛІДЖЕННЯ ДЕФІЦИТІВ ВОДНОСТІ ТА ІНДЕКСІВ ПОСУХИ ДЛЯ ЗОНИ НЕДОСТАТНЬОЇ ВОДНОСТІ УКРАЇНИ

The study of the formation of water deficits on rivers in the zone of the insufficient water content of Ukraine is presented in the article. To determine the deficits, the “threshold” method was used, which involves comparing the daily water discharges in the low water period with the values of the minimum runoff of a given probability of exceeding. Long-term data of average daily and average monthly minimum water discharges during the winter and summer-autumn period on rivers located in different areas of river basins and significantly differing in the catchment area, namely the Southern Bug River – Oleksandrivka (A = 46200 km2), Kinska River – Pologi (A = 353 km2), Obitichna River – Primorsk (A = 1300 km2) for the observation period from 1953 to 2018 inclusive was used. In cases where runoff values ​​were less than Q90% or Q97%, they were considered deficient (90%) or extremely deficient (97%). The dynamics of deficits in time are analyzed, and the number of such events by decades, frequency, average volume, duration, and intensity are determined. The chronological course of runoff volumes and deficits (90%) is graphically presented. Analyzing the obtained diagrams, it can be noted that naturally, the largest water deficit was observed in low-water years (below normal), and accordingly, the lack of deficit is characteristic of multi-water periods (above normal). Additionally, extreme deficits were also estimated (97%) for the Southern Bug River – Oleksandrivka township. The study also presents the results of the calculation of various drought indices. For the rivers of the study area, using the DrinC drought calculator were calculated – the river runoff drought index (SDI), standardized precipitation index (SPI), agricultural standardized precipitation index (aSPI), drought research index (RDI), effective drought research index (eRDI) , and its relationship with water discharges during the summer-autumn period was analyzed. Long-term data of average monthly water discharges at 6 hydrological gauge (Kodyma river – Katerynka river, Ingul river – Novogorozhene river, Ingul river – Sednivka village, Kinska river – Polohy town, Kilchen river- Oleksandrivka Persha village, Kalchyk river – Kremenivka village) were used as initial information and as also average monthly air temperature and monthly precipitation at 6 meteorological stations (Odessa, Kherson, Kropyvnytskyi, Zaporizhia, Dnipro, and Mariupol). Analyzing the obtained results, it can be noted that drought indices provide an opportunity to study climatic and hydrological trends, characterize drought, assess the severity of drought, and promote early assessment of the effects of drought. In particular, the SDI index correlates well with water discharges, which opens up opportunities for forecasting runoff in the dry period.

Research of individual components of hydrological and hydrochemical regimes of the Danube River within the Ukrainian interval from Reni to Izmail

Introduction. This investigation aims at studying the individual components of the hydrological and hydrochemical regimes of the Danube River (within Ukraine) in connection with the widespread use of the river's water for water supply and irrigation in the southern region, as well as to ensure more effective regulation of water-salt regime of the Danube lakes using the Danube River as a main source for their water renewal. One of important aspects includes the study of the regime of the Danube River's suspended sediments brought to its delta due to their impact on the formation of the delta at the river's mouth of as well as due to the impact on siltation of deltaic and pre-delta lakes and canals connecting the lakes with the Danube River.
 Purpose. The purpose of the work is to study long-term and current trends related to changes in hydrological (water levels and discharges, suspended sediments runoff) and hydrochemical (mineralization) regimes of the Danube River within the Ukrainian interval from Reni to Izmail, internal annual distribution of water runoff, as well as suspended sediments runoff and mineralization during the years of varying water content.
 Results. The statistical analysis of long-term series of observations over the Danube River within the interval from Reni to Izmail resulted in discovering that time trends of average, maximum and minimum water levels (1921-2015) and discharges (1840-2015) indicate the presence of a weak increase in their growth over time, with a more pronounced increase in maximum water levels or discharges. The annual distribution shows the general synchronicity of fluctuations in runoff characteristics, and the maximum monthly values of water discharge differ have more pronounced seasonal fluctuations.
 The study shows the presence of a pronounced trend to reduction of suspended sediments runoff of the Danube River at Reni (for the period of 1840-2015), with their most intensive decrease over the period of 1990-2015. Annual distribution of average monthly suspended sediments runoff of the Danube River for the years with typical water content (for the period of 1978-2015) showed that they have seasonal fluctuations. At the same time, there is a decrease in the suspended sediments runoff along the length of the river from Reni to Izmail.
 The long-term course of average annual mineralization values of the Danube River at Izmail (1981-2015) is characterized by their decrease against the background of a small increase in average annual discharges. As per the annual distribution of mineralization values associated with all water content groups there are the periods related to the phases of the river's yearly water regime during and the economic use of water.
 Conclusion. Thus, the increase in the long-term period of the Danube River runoff within the interval from Reni to Izmail will contribute to the development of the region's economy and water supply, irrigated farming, regulation of the Danube Lakes filling with weakly mineralized river water. At the same time, the reduction of the suspended sediments runoff will restrain the siltation of the inlet canals connecting the lakes with the Danube River, which will improve the water renewal of the lakes with the river's fresh waters.

Occasional Floods On The Rivers Of Russian Plain In The 20<sup>Th</sup> –21<sup>St</sup> Centuries

The article focuses on the study of flood flow changes on the rivers of the European Territory of Russia (ETR) in the last thirty years. This is an extremely important problem, as with floods, whose contribution to the structure of the annual flow of European rivers in recent decades has been increasing, the most destructive floods are associated. On the example of 55 representative hydrological gauge stations located on the ETR in regions with different conditions of runoff formation, the features of both summer and winter floods formation are considered. It has been established that over the past thirty years on the most rivers there has been an intensive reduction in the ratio of volumes and maximum flood discharges in relation to the similar characteristics of the basic runoff. Increased groundwater supply is observed, and the absence of significant freezing of the soil leads to an increase in infiltration. The volumes of flood runoff and the basic runoff become comparable or the proportion of the latter begins to prevail. The main reason for the increase in minimum water discharge is associated with an increase in flood flow under the influence of more intense and prolonged thaws. A distinctive feature of the water regime of recent decades has been the flood peaks in almost any season of the hydrological year. In the middle and southern part of the ETR – in the basins of the Volga, Oka, Vyatka, Don Rivers – there is an increase in low-water flow and in the quota of flood in annual flow. On some rivers of the ETR, the spring flood runoff currently accounts for less than 50% of the annual runoff.

Calculation of winter average ten-day minimum flows of rivers of the Lake Sevan Basin and analysis of its time variability

Studying decadal minimum costs, especially in the context of expected climate change, is relevant and urgent. Both on the rivers of the study area and the whole republic, minimum water discharge is observed during periods of summer- autumn and winter low water. In both cases, the power of the rivers is mostly underground. However, summer-autumn rains can often disrupt the river’s feeding patterns and cause flooding. The paper calculated the winter average ten-day minimum costs for posts that have a long series of observations on rivers flowing into Lake Sevan. In a number of longterm observations, the dynamics of changes in the winter average ten-day minimum costs of rivers flowing into the basin and the patterns of their spatial distribution have been estimated. As a source material daily data from actual observations at 12 hydrological posts in the study area of the Service of the Hydrometeorology and Active Influence on Atmospheric Phenomena, Ministry of Emergency Situations of the Republic of Armenia, are used. All observed hydrological posts have a number of observations 40 years or more. The methods used in the work are: mathematical-statistical, extrapolation, interpolation, analysis, analogue and correlation. It turned out that most rivers in the Lake Sevan Basin have a tendency to increase in winter average ten-day minimum costs.

Temporal variation of water discharges in the lower course of the Danube River across the area from Reni to Izmail under the influence of natural and anthropogenic factors

The Danube River mouth is a main source for fresh water used for water supply and irrigation purposes in the arid southern part of Ukraine. In addition, the water of the mouth is used for filling the Danube Lakes. Climate change and numerous social and economic factors reduce the area and the water level of the Danube Lakes and increase their salinity. Under these circumstances the water exchange between the Danube River and the lakes is a very important process which allows maintenance of the water–salt balance of the latter. Such water exchange massively depends on the Danube River regime. The paper presents research of temporal variation of typical water discharges in the lower course of the Danube River associated with assessment of natural and anthropogenic factors affecting river runoff fluctuations. Time series of annual average water discharge at the water gauging stations of such cities as Reni and Izmail were considered uniform for the selected periods. They cover the period of conventionally natural river runoff regime (1840–1920), the period of the least altered river runoff regime (1921–1960) and the most altered river runoff regime under a heavy anthropogenic influence (1961–1989). The analysis of the impact of climate changes on the river runoff allowed introduction of a new, modern period of the Danube River hydrological regime (1990–2015). It is established that the series of maximum and minimum water discharges are characterized by the lack of their uniformity from the beginning of the period of initial influence of hydraulic engineering structures on the hydrological regime (since 1961). The analysis of the aggregate multi-year series (1840–2015) of average annual, maximum and minimum water discharges of the Danube River across its length from Reni to Izmail showed the presence of positive trends. At the same time the period of climatic changes (after 1989) is characterized by a less intensive growth of maximum water discharges. The research resulted in establishing the periodicity and synchronism of water discharge fluctuations in the lower course of the Danube River from Reni to Izmail within the territory of Ukraine. In particular, the study showed for the first time that from the 2000s onwards the redistribution of river runoff between the Danube River branches led to unsynchronization of minimum river runoff in different parts of the Danube Delta. The research shows that comprehensive analysis of the Danube River hydrological regime under modern climatic conditions is required to ensure efficient engineering regulation of the Danube Lakes filling pattern. Such regulation, in its turn, will ensure that the water supply and irrigation purposes are achieved.

Efficiency of a siphon drainage system under conditions in a low gradient area

The drainage system designs and their function principles at the experimental production plot for the siphon- and vacuum-assisted drainage in the Mugan-Salyan massif characterized by the nongradient area have been described. The surveys are carried out in the natural environments during the vegetation period for the irrigation of cotton occupying the entire area of the experimental plot. A high efficiency of the siphonand vacuum-assisted drainage system has been calculated. In addition, the drain discharge and the discharge module are closely connected to the existing water pressure value in the interdrain. In the vegetation period, the maximum and minimum water discharges comprised 11.1 L/sec and 2.8 L/sec, respectively. The drainage module value varied from 0.14 to 0.55 L/sec hectare. It has been ascertained that the drainage system operation provides the opportunity to lower the depth of the groundwater table within the interdrain up to 250–280 cm (the initial depth is 120–150 cm). The possibilities of significant increases in the flushing intensity and the reduction of the terms of the regulated ameliorative activities within the certain hydrogeological regime have been proven.

Chronological trends in maximum and minimum water flows of the Teesta River, Bangladesh, and its implications

Bangladesh shares a common border with India in the west, north and east and with Myanmar in the southeast. These borders cut across 57 rivers that discharge through Bangladesh into the Bay of Bengal in the south. The upstream courses of these rivers traverse India, China, Nepal and Bhutan. Transboundary flows are the important sources of water resources in Bangladesh. Among the 57 transboundary rivers, the Teesta is the fourth major river in Bangladesh after the Ganges, the Brahmaputra and the Meghna and Bangladesh occupies about 2071 km2. The Teesta River floodplain in Bangladesh accounts for 14% of the total cropped area and 9.15 million people of the country. The objective of this study was to investigate trends in both maximum and minimum water flow at Kaunia and Dalia stations for the Teesta River and the coping strategies developed by the communities to adjust with uncertain flood situations. The flow characteristics of the Teesta were analysed by calculating monthly maximum and minimum water levels and discharges from 1985 to 2006. Discharge of the Teesta over the last 22 years has been decreasing. Extreme low-flow conditions were likely to occur more frequently after the implementation of the Gozoldoba Barrage by India. However, a very sharp decrease in peak flows was also observed albeit unexpected high discharge in 1988, 1989, 1991, 1997, 1999 and 2004 with some in between April and October. Onrush of water causes frequent flash floods, whereas decreasing flow leaves the areas dependent on the Teesta vulnerable to droughts. Both these extreme situations had a negative impact on the lives and livelihoods of people dependent on the Teesta. Over the years, people have developed several risk mitigation strategies to adjust with both natural and anthropogenic flood situations. This article proposed the concept of ‘MAXIN (maximum and minimum) flows’ for river water justice for riparian land.

ANALISIS DEBIT AIR DAN AIRTANAH DANGKAL DAERAH ALIRAN SUNGAI (DAS) PRUMPUNG, KABUPATEN TUBAN

The water demand increases in line with the growths of population, industry and business, but the water availability is ascertained to satisfy those needs continuously. Therefore, it is necessary to analyze water availability in a specified watershed integrated with various aspects in hydrology. The objective of this study were (1) to identify of landuse at Prumpung watershed,(2) to determine water availability in Prumpung watershed by analyzing the relationship of rainfall and river discharge using the Soil and Water Assessment Tool (SWAT) and (3) to influence government policies relation with urban planning of Tuban Regency. The watershed is located in Tuban Regency and based on urban planning of Tuban Regency 2012-2032 which is covering 22,319.14 ha. Input data were Digital Elevation Models, land use, and soil map. The procedures were including collection and process of climate data, trend analysis of water availability, discharge measurements, discharge analyze and calibration using SWAT. The results of existing landuse showed that the minimum water discharge was 0.338 m3/s to the maximum 5,945 m3/s with groundwater availability was maximum until 3,070 mm on July to September 2014. SWAT has generated 27 HRUs that described the spatial condition of the whole watershed. Calculated discharges with SWAT compared to the measured discharges having The NashSutcliffe Efficiency (NSE) of 0.77 and correlation coefficient of 0.79. Conservation scenario has been conducted at several landuses for water availability and based on conservation area. The results showed that the minimum water discharge was 0.334m3/s to the maximum 4.842 m3/s with groundwater availability was maximum until 3,140 mm. There were no significant change of groundwater based on urban planning and scenario at Prumpung watershed, Tuban Regency.Identification of Prumpung watershed produced relatively small water discharge compared than water demand based urban planning of Tuban Regency. A plan of water management for exploiting of high rain fall in rainy season will contribute in consideration of the appropriate water supply/demand balance in dry season.

Statistical Characterization of Extreme Hydrologic Parameters for the Peripheral River System of Dhaka City

Selection of appropriate probability distribution function is one of the most important steps of frequency analysis. Due to the existence of large number of distributions, hydrologists follow different methods to select the best one. In this paper, annual maximum, minimum water level and discharge of five peripheral rivers, namely Buriganga, Turag, Tongi, Balu and Lakhya around Dhaka city have been analyzed to compute the basic statistics and fit them with sixty two probability density functions (PDF). Three goodness-of-fit (GoF) statistics, namely Chi-square, Kolmogorov–Smirnov and Anderson Darling were used to rank each of the distribution. Furthermore, ranks obtained from three GoF were used to compute overall rank of all distributions for each hydrologic parameter. The study reveals that, four different distributions were found best fit for four extreme cases. Dagum (4P) and Chi-square (2P) fit best for annual maximum and minimum water level respectively, whereas Cauchy and Johnson SB were found for annual maximum and minimum discharge respectively. Moreover, ranks of frequently used distributions, namely General Extreme Value (GEV), Log-Pearson III (LP3), Log-normal (LN) and Gumbels were compared with the best fit distributions and did not give satisfactory results. The method used in this study would be helpful for flood frequency analysis of other rivers of Bangladesh. This may also be used for evaluation of best fit distribution of river system for other countries as well.

Probabilistic characterization of hydrological droughts

It is proposed to use the joint distribution of probabilities of minimum water discharges and the river runoff depth to characterize the severity and danger of durable low-flow periods. The copula theory is used to construct this distribution that enables to take account of differences in the types of one-dimensional probability distributions of initial variables and of the correlation between them. The studies were carried out for the vegetation periods using the data of the runoff depth measurements in Georghiu-Dej on the Don River in 1895–1980 and in Kirov on the Vyatka River in 1878–1980. The selection of copulas was based on comparing empirical and theoretical joint distributions of low-flow characteristics. It is demonstrated that the best results for the approximation of the joint probability distribution of low-flow characteristics are obtained from the Frank copula. Plotted are the dependences of low-flow frequency on the specified values of corresponding minimum water discharges and the river runoff depth during vegetation periods. Estimated are the probability and frequency of some most severe lowflow periods observed on the Don and Vyatka rivers.

Analysis of seasonal flow and minimum water discharge of Veliki Rzav for the purposes of regional water supply system "Rzav"

Minimum water discharge and seasonal flow calculations of Veliki Rzav at Arilje have been conducted for the purposes of regional water supply system "Rzav". For the first time for this hydrological station minimum water discharges have been calculated by frequency curves, parameters of which have been determined by method of moments. Also for the first time in Serbia seasonal flow was calculated using "composing method". Analysis presented in this paper can be used for exploitation and planning of upcoming water management activities in the regional water supply system "Rzav.

Hybrid Enhanced Lagrangian Relaxation and Quadratic Programming for Hydrothermal Scheduling

This article proposes a hybrid enhanced Lagrangian relaxation and quadratic programming (hybrid LRQP) for hydrothermal scheduling. Hybrid LRQP minimizes the total production cost subject to power balance, spinning reserve, generation limit, minimum up and down time, generation ramp limit, on/off line minimum level, transmission line, limited fuel, environmental, water discharge and water balance constraints. The proposed solution method solves hydrothermal scheduling problem using two coordination procedures. In the first procedure, enhanced Lagrangian relaxation (ELR) is used to find the base feasible schedule of all thermal generation system excluding hydro power plants and relaxing transmission line constraints. ELR is enhanced by new initialization and adaptive Lagrangian multipliers to speedup the convergence. In the second procedure, economic dispatch by quadratic programming, thermal unit decommitment and hydro unit commitment are carried out. The proposed 24-hour economic dispatch could easily consider generation ramp rate limit, and time coupling constraints such as limited fuel supply, environmental, water discharge, and water balance constraints. Hybrid LRQP is tested on hydrothermal system with 17 thermal, 2 hydro and 2 pumped storage hydro plants, and IEEE 24 bus reliability test system. Test results indicate that hybrid LRQP could obtain better solutions than those obtained from augmented hopfield network and augmented Lagrangian relaxation.

Low flow — the river's ecosystem limiting factor

The main objectives of this study were to: (1) find out the minimum water discharge needed to maintain good biological and chemical quality for surface water; (2) achieve categories of biological indicators for water quality; and (3) compare these biological categories with physical–chemical parameters. The study has been carried out on the River Strouma using two approaches: — in time: by determination of the relationship between the biotic indices and the water discharge as a result of the processes that have been realised at the moment of their registration — in space (along the river): by discrete study of specific river stretches dominated by one or more specific anthropogenic impacts on the natural flow regime and/or on the water quality. In a 3-year period, parallel field measurements and hydrobiological samplings have been carried out, supplementing the heretofore existing scarce information.

Migratory behaviour of adult fast‐growing brown trout ( Salmo trutta, L.) In relation to water flow in a regulated Norwegian river

The migration pattern of spawners of brown trout (Salmo trutta) in relation to water flow was analysed by radio-tracking in the regulated River Gudbrandsdalslagen, Norway. During the upstream spawning migration in the high flow period, trout (2–12 kg) were caught, tagged and released 15 km downstream of a fish ladder at the Hunderfossen waterfall. The released fish displayed a systematic and directional upstream movement to the outlet of the tunnel from the hydroelectricity plant. In autumn and winter there is a minimum water discharge of 20–2 m3/s on p.s. in the river between the dam and the outlet of the tunnel, which has a discharge of 200–300 m3/s. When the water flowing over the Hunderfossen dam decreased to 20 m3/s, the ascent of brown trout up the river stopped and fish periodically entered the power plant tunnel. To determine the flow necessary to attract fish into the spawning reach above the tunnel outlet, two experiments were undertaken using 12 and 17 radio-tagged trout. In the first experiment, 60 m3/s of water released for 24 h resulted in the migration of 50% of the trout up the river. The second experiment, releasing 60 m3/s for 24 h, followed by 30 m3/s for 24 h two days later, resulted in the migration of 60% of the trout. Only one fish ascended the river at a flow of 30 m3/s. It is recommended that a repeated release of water at 60 m3/s is made in periods of minimum water discharge to save the spawning migration. The results demonstrate the advantage of using radio-tracking in experiments dealing with fish migration in relation to water-flow management.