Annual Water Discharge Research Articles

Unveiling the effects of environmental factors and Yellow River inputs on the ichthyoplankton community structure in typical bays

To unravel the effects of environmental factors on fishery resources in the bay, we conducted six biological and environmental surveys in the Laizhou Bay between 2013 and 2020. The findings of our study illuminated several key aspects: (1) The annual discharge of water and sediment from the Yellow River to Laizhou Bay exhibited notable variations, while concurrently, environmental factors including temperature, salinity, and suspended particle matter underwent fluctuations, yet remained within a relatively stable range overall. (2) A total of 8318 eggs and larvae belonging to 10 orders, 16 families, and 19 genera were collected. Significant interannual fluctuations had been documented in the species composition, abundance, and biodiversity of ichthyoplankton. Notably, both Shannon-Wiener diversity index and Pielou evenness index were significantly negatively correlated with suspended particle matter concentration. (3) The water and sediment discharge significantly positively correlated with the number of cold-temperature species. However, the sediment input negatively correlated with the number of continental shelf benthopelagic fish. (4) Redundancy and correlation analyses confirmed the strong link between spatial and temporal distribution of fish communities and environmental factors, with salinity and dissolved oxygen key for ichthyoplankton abundance. Our research offers a scientific foundation for targeted fishery protection and management, which is crucial for preserving the ecological functions of spawning grounds in the bay.

Nutrient concentration, loads and retention in a semiarid micro-estuary: The relative contribution of baseflow and flood events

Estuaries are a significant source of nutrients to the marine environment. The magnitude of this source is a function of nutrients load reaching the estuary and removal (attenuation) within estuaries. Most estuarine research is conducted in large estuaries, which do not reflect the processes in small estuaries in urban and semi-arid regions where flood water is a substantial portion of the annual discharge and the estuarine baseflow is often low and dominated by wastewater. To improve the understanding of nutrient attenuation and load into the Mediterranean, we conducted high-resolution nutrient sampling in the eutrophic Alexander micro-estuary as a test case. We sampled once per month during baseflows (years 2014–2019) and hourly during floods (years 2016–2018). The concentrations of inorganic nutrients (phosphorous (P) and nitrogen (N)) were extremely high during baseflows. Dissolved ammonium and particulate P were the only nutrients that were in the estuary (by 55 % and 30 %, respectively). Floods were rare, occurring ~4 % of the time, but contributed 62 % of the annual water discharge of the Alexander micro-estuary (14.7 ± 3.8 106 m3 y−1). The concentration of all dissolved nutrients decreased during floods but was higher than expected (DIN 584 ± 50 μmol L−1, phosphate 21 ± 2 μmol L−1), accounting for 42 % and 55 % of the overall annual DIN (123.5 ± 44.9-ton yr−1) and P (6.7 ± 1.9 ton yr−1) loads to sea, respectively. The N:P ratios were 16 and 34 during baseflow and flood events, respectively. Previously, nutrient loads were calculated by multiplying baseflow-measured concentrations by the total water volume of baseflow and floods. Our calculations, based on high-resolution sampling, revealed lower annual loads of P and N to the sea that were 56 % and 89 % of previous estimates, which is a considerable difference in an oligotrophic system such as the eastern Mediterranean.

Delta initiation under low sediment discharge: Insights from Holocene incised valley fills north of Tokyo Bay, central Japan

Modern delta formation initiated as a result of the deceleration in the rate of sea-level rise during the middle Holocene. In Asia, many deltas initiated at the mouths of rivers with large sediment discharge at 8 ka, early in the middle Holocene, when the volume of sediment supply exceeded that of the accommodation space created by sea-level rise. However, in the Japanese Islands, even some deltas formed by rivers with quite small sediment discharges initiated at 8 ka. In the area north of Tokyo Bay, a narrow, 70-km-long bay was formed during the last deglacial sea-level rise. The Tone and Watarase rivers flowed into this bay from the west and east, respectively. We carried out facies analysis and radiocarbon dating of two sediment cores obtained in the vicinity of the Watarase River mouth. The delta that formed at the tide-dominated Watarase River mouth was characterized by bay mud sediments with a narrow sand body along the axis. This deltaic sand body, which is 5–15 m thick and coarsens upward, filled a tidal channel that was 1–3 km wide and 30 km long. At the mouth of the sediment-starved Watarase River, the delta initiated at the onset of the sea-level stillstand at 7 ka. In contrast, at the mouth of the sediment-rich Tone River, a delta initiated at 8 ka, when the rate of sea-level rise decreased from 14 to 7 m/kyr. By reviewing delta initiations in the area north of Tokyo Bay and in 17 coastal lowlands of the Japanese Islands, we demonstrate that the sediment discharge threshold governing whether delta initiation occurred at 8 or 7 ka was equivalent to a mean annual water discharge of 100 m3/s.

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.

Transformation of the water runoff of the Volga River after the creation of the Zhiguli hydroelectric complex

For the Volga River, studies of interannual changes in water discharges in the period 1958-2021 were carried out. Systematic hydrological observations were carried out at the Zhiguli hydroelectric complex on the border of the Middle and Lower Volga. 97% of the water runoff of the entire Volga is regulated in this section in the seasonal, weekly and daily range. It was found that the average water flow was 7704 m3/s. The amplitude of interannual fluctuations was 5270-10431 m3/s. Temporal changes in the average annual water discharges were characterized by cyclicity, including the change of low-water and high-water phases. From 1958-1975 a low-water phase was observed, from 1976-1996 - high-water and since 1997-2021 - again shallow. A comparison of the historical (1877-1955) and modern (1958-2021) periods showed that over 144 years, the average water flow of the Volga River has not changed much. However, as a result of the regulation of water flow in the period 1958-2021 the value of water discharges in high-water years decreased, while in low-water years it increased.

Assessment of runoff characteristics changes of small and medium-sized rivers in Central Yakutia under the climate change influence

The response of river catchments located on the territory of Russia to climate change in recent decades has been expressed in the emergence of multidirectional trends in the series of annual runoff, maximum water discharges and the value of winter runoff. However, the response of small and medium-sized rivers to the ongoing climate warming has been poorly studied, in contrast to large rivers. In this paper, a comprehensive analysis of the climatic and hydrological characteristics of small and medium-sized rivers of Central Yakutia as well as an assessment of the climate change impact on the river runoff characteristics in various conditions of the region were carried out. It has been established that the revealed positive trends in temperature correspond to the trends typical for the rest of the Russian Federation. The response of the runoff of small and medium-sized rivers to climate change is most significant in the winter-spring months of the year: there is an increase in runoff in the spring and winter periods and for the year as a whole. A feature of the response of the river catchments of the study area in comparison with the European part of Russia and southern Siberia is the presence of statistically significant trends in the series of annual water discharges for most of the studied water gauges. The most noticeable changes (as a percentage of the base period) occurred in the annual runoff of small rivers, because small rivers respond most quickly to external influences. Its expressiveness is determined not only by the degree of changes in climatic characteristics, but also by the features of runoff formation in the watersheds of the study area, in particular, the presence of permafrost.

СЕРЕДНІЙ РІЧНИЙ СТІК ВОДИ РІЧОК УКРАЇНСЬКИХ КАРПАТ У БАГАТОВОДНІ ТА МАЛОВОДНІ ФАЗИ ВОДНОСТІ

he assessment of the average annual runoff of the rivers of the Ukrainian Carpathians in the high-water and low-water phases of water was carried out on the basis of a stochastic analysis and the identification of characteristic patterns of alternation of such periods within the boundaries of the Tisza, Dniester, Prut and Siret river systems. The study was carried out using a methodological base based on statistical means of generalization, data systematization, methods for estimating temporal random sequences, methods for analyzing the long-term variability of time series of water runoff characteristics and identifying their structure. As a result of the study, the variability in the structure of the time series of the average annual water discharge of the rivers of the Ukrainian Carpathians is clearly revealed. Such variability is similar for rivers within the studied river systems and is characterized by common patterns of stochastic relationships and cyclic fluctuations. The high reliability of cycles with periods of 29 ± 2 years indicates a stable recurrence of periods of high and low water content. The graphs of the relationships between the average annual water discharges during the periods of high and low water content and their average long-term values for the rivers of the Tisza, Prut and Siret river systems on the right bank of the Dniester showed that the qualitative characteristics of such relationships are assessed as very high. The estimates of water discharge in the water phase for the rivers of the Tisza, Prut, Siret and the right bank of the Dniester basins were checked using regression equations in comparison with empirical data and their high reliability (the probability of not exceeding probable deviations in dry periods was 77%, in high-water periods – 95%), which made it possible to generalize the probable expected average water discharges in the high-water and low-water phases of the cycle, depending on the average long-term values for the rivers of the studied basins of the Ukrainian Carpathians. Such generalizations can be used for prognostic estimates of possible values of water discharge in high-water and low-water phases for any river of the Ukrainian Carpathians. At the same time, it is necessary to take into account in which system of rivers it is located, to know the average long-term water discharge and the time frame and the chronology of the water phases.

ГИДРОЛОГИЧЕСКИЙ ПРОФИЛЬ ВОДОСБОРА БАССЕЙНА ТРАНСГРАНИЧНОЙ РЕКИ ШУ

An analysis of changes in the hydrological indicators of the catchment area of the transboundary Shu River basin in the spatio-temporal aspect, based on information and analytical materials from the hy-drological posts of Kochkarka, Orto-Tokai, Milyanfan, Tashotkol, the Furmanovs hydroelectric com-plex and Ulanbel in a long period of observations covering 1931…2020, shows the presence of their constant fluctuations over the years under the influence of natural and anthropogenic factors. The hy-drological regime of the catchment area of the transboundary Shu River basin on a spatio-temporal scale with a positive or negative trend in the average annual water discharge is determined by the gen-eral nature of natural factors and changes due to increased anthropogenic activity on river systems. The results obtained indicate that the influence of natural and anthropogenic factors are less pronounced in the mountainous and foothill geographic zones than in the foothill-plain and desert zones of the catch-ment area of the transboundary river Shu.

Declining water resources in response to global warming and changes in atmospheric circulation patterns over southern Mediterranean France

Abstract. Warming trends are responsible for an observed decrease of water discharge in southern France (northwestern Mediterranean). Ongoing climate change and the likely increase of water demand threaten the availability of water resources over the coming decades. Drought indices like the Reconnaissance Drought Index (RDI) are increasingly used in climate characterization studies, but little is known about the relationships between these indices, water resources, and the overall atmospheric circulation patterns. In this study, we investigate the relationships between the RDI, water discharge, and four atmospheric teleconnection patterns (TPs) for six coastal river basins in southern France, both for the historical period of the last 60 years and for a worst-case climatic scenario (RCP8.5) reaching the year 2100. We combine global and regional climate model (CGM and RCM, respectively) outputs with a set of observed climatic and hydrological data in order to investigate the past relationships between the RDI, water discharge, and TPs and to project their potential evolution in space and time. Results indicate that annual water discharge can be reduced by −49 % to −88 % by the end of the century under the extreme climate scenario conditions. Due to unequal links with TPs, the hydroclimatic evolution is unevenly distributed within the study area. Indeed a clustering analysis performed with the RDI time series detects two major climate clusters, separating the eastern and western part of the study region. The former indicates stronger relationships with the Atlantic TPs (e.g. the North Atlantic Oscillation (NAO) and the Scandinavian Oscillation (Scand) patterns), whereas the latter is more closely related to the Mediterranean TPs (Mediterranean Oscillation (MO) and Western Mediterranean Oscillation (WeMO)). The future climate simulations predict an antagonistic evolution in both clusters which are likely driven by decreasing trends of Scand and WeMO. The former provokes a general tendency of lower P in both clusters during spring, summer, and autumn, whereas the latter might partly compensate for this evolution by enhanced precipitation in the eastern cluster during autumn and winter. However, compared to observations, representation of the Mediterranean TPs WeMO and MO in the considered climate models is less satisfactory compared to the Atlantic TPs NAO and Scand, and further improvement of the model simulations therefore requires better representations of the Mediterranean TPs.

Dam Impacts on Seasonality of Water and Sediment Transport in Intensively Managed River Basins: A Case Study of the Yangtze River

AbstractExtensive studies have been performed on water and sediment transport of the Yangtze River in recent decades, but very few studies were focused on seasonal and daily variations. After the construction of Three Gorges Dam (TGD) in 2003, several key cascade dams were built on the Yangtze upstream. Annual, monthly, and daily data were used to study the seasonality change on water level, water discharge, and sediment load in response to multiple reservoir impoundments. TGD impacted the water level inside the reservoir greatly by shifting the peak water level from summer to winter and made the hydrograph more asymmetrical. In contrast, minor changes in water levels (<2 m) occurred at stations downstream of the TGD mainly due to channel incision. Downstream of TGD at Yichang station, annual hydrograph was flattened slightly: water discharge in the dry season increased 49% whereas that of flood season decreased 14% from 1956–2002 to 2013–2017. Mean annual water discharge downstream of the TGD was slightly impacted because the impounded water was <5% of annual inflow of the reservoir. Comparing with the Yangtze, the annual hydrographs of other intensively managed rivers like the Yellow, Missouri, and Colorado have been flattened more effectively by reservoir impoundments. The sediment rating curves at Yichang and Hankou changed from an oval‐like shape before 2013 to two overlapping and flattened lines in 2013–2017. This shift indicates that the rising and falling limbs of the hydrograph experienced similar sediment concentrations in 2013–2017 and suggests a less obvious hysteresis effect. Over 50% of the sediment load observed at the seaward‐most Datong station was contributed by the large tributaries in the upper reach, like Jinsha and Jialing rivers, before 2003. The channel scour downstream of TGD contributed 49%–64% of the Datong sediment load after 2003.

Trend of snow cover under the influence of climate change using Google Earth Engine platform: A case study of Astore (Western Himalayas) and Shigar (Karakoram region)

Freshwater resources present in the Upper Indus Basin (UIB) supply water to Pakistan’s irrigation. Half of the annual water discharge in the UIB is contributed from the glacier and snow-fed basins in the Hindu Kush, Karakoram, and Himalaya (HKH) region, and it is currently under the threat of climate change. Therefore, it is very necessary to study and monitor the spatiotemporal changes in the snow cover area (SCA) and its response to climate variables to efficiently manage water reservoirs. Thus, keeping this problem in mind, we conducted this study using the Google Earth Engine Application Programming Interface (GEE API) for Astore and Shigar. We used mean annual Landsat data between 1991 and 2021 to derive the SCA using the normalized difference snow index (NDSI). ASTER GDEM data was used to extract the elevation and analyze the distribution of SCA on different elevation zones. Eventually, we used the climate research unit (CRU) data (rainfall and temperature) to analyze them with SCA. The results revealed that SCA in Astore and Shigar has an increasing trend with a rate of 11.16 km2/year and 4.27 km2/year, respectively. Mean annual precipitation and temperature also confirmed the increasing trend of SCA because mean annual precipitation is increasing and temperature is decreasing in both regions. SCA and elevation analysis revealed that SCA is decreasing on foothills while increasing at the valley top. This is because temperature is increasing and precipitation is decreasing from zone 1 to zone 3 and vice versa for zone 4. It is found that Astore and Shigar in UIB have an increasing trend of SCA and are not affected by global warming. Therefore, it is necessary to conduct studies on large scale to efficiently evaluate the impact of climate change on SCA.

ДИНАМИКА ИЗМЕНЕНИЯ РЕСУРСОВ РЕЧНОГО СТОКА ТОБЫЛ -ТОРГАЙСКОГО ВОДОХОЗЯЙСТВЕННОГО БАССЕЙНА

The study presents results of assessing the resources of the river flow of the Tobyl - Torgai water management basin. The purpose of the work is to update the previously developed methodology for assessing the annual runoff resources of individual rivers and river runoff resources of the considered water management basin of the Republic of Kazakhstan. The calculations used the average monthly and average annual water discharge of the main rivers. Methods have been developed for determining and restoring the observed and natural runoff, long-term statistical characteristics and its values of probability of exceeding. The equations for determining the water resources of local runoff and water resources coming from other regions are obtained. As a result of the work done on the preliminary calculation, the total surface water resources for the Tobyl – Torgai water management basin, formed in Kazakhstan and coming from the territory of the Russian Federation for a long-term period from 1931 to 2019, on average amount to 1,67 km3, of which: resources formed within Kazakhstan - 1,33 km3, inflow – 0,34 km3. The runoff formed in the territory of the basin, for the disturbed period, relative to the conditionally natural period, decreased by 8%, the runoff coming from the Russian Federation decreased by 12%, and the total water resources by 9%

Determination of four trihalomethanes in ship ballast water by gas chromatography-negative chemical ionization-mass spectrometry

我国每年的船舶压载水排放量巨大,压载水中含有浮游生物、病原体及其幼虫或孢子等,若处理不当,会对排放水域的生态环境造成严重影响。排放压载水前常使用电解法对其进行处理,电解产生的次氯酸钠溶液,能有效杀灭残余的微生物。但电解后会产生副产物三卤甲烷(THMs),其对人体有一定的健康风险,建立船舶压载水中三卤甲烷的测定方法具有重要意义。该研究建立了采用气相色谱-负化学源质谱(GC-NCI-MS)测定船舶压载水中4种三卤甲烷(包括三氯甲烷、二氯一溴甲烷、一氯二溴甲烷、三溴甲烷)的分析方法。船舶压载水样品经过顶空进样技术处理后,通过DB-5MS UI毛细管色谱柱(30 m×0.25 mm×1.0 μm)分离,气相色谱-负化学源质谱仪测定,在选择离子扫描(SIM)模式下分析,采用外标法进行定量。4种三卤甲烷在0.2~50 μg/L范围内线性关系良好,相关系数(r)≥0.995,定量限(S/N=10)为0.1~0.2 μg/L,在0.2、0.5、2.0 μg/L 3个加标水平下,4种THMs的平均回收率为90.3%~106.8%,相对标准偏差(RSD)为1.4%~6.2%。该方法准确、稳定、可靠,可用于测定船舶压载水中4种THMs的含量。使用建立的测定方法对36个船舶压载水进行测定,三溴甲烷、二溴一氯甲烷、一溴二氯甲烷与三氯甲烷的检出率分别为83.3%、69.4%、22.2%和19.4%,检出值分别为34.25~221.5 μg/L、3.52~41.87 μg/L、1.52~8.56 μg/L和0.02~5.46 μg/L。

Evolution patterns and spatial sources of water and sediment discharge over the last 70 years in the Yellow River, China: A case study in the Ningxia Reach

The hydrology and sediment processes in large rivers play important roles in maintaining aquatic and coastal ecosystems and advancing civilization and production in human systems. Therefore, quantitatively analyzing the spatiotemporal variability and dynamics of water and sediment discharge in large rivers is essential for improving watershed management and sustainable development in the areas surrounding rivers, especially the Yellow River, which is one of the most sediment-laden rivers in the world. In this study, we analyzed the evolution patterns and spatial sources of water and sediment discharge in the Yellow River from 1951 to 2020 and determined the impacts of different factors on water and sediment discharge variations. The results showed that the annual water and sediment discharge significantly decreased (p < 0.05) over the past 70 years, with an abrupt change occurring in 1986. The first dominant periodicity of water discharge was approximately 29 years, while the first dominant periodicity of sediment discharge was approximately 28 years. In terms of the water and sediment discharge sources, the dominant factor affecting variations in water discharge was water diversion from 1951 to 2020, while the dominant factor affecting variations in sediment discharge was sediment aggradation from 1951 to 1985 and changed to tributary inflow sediment from 1986 to 2020. In addition, the water and sediment discharge changes were also affected by anthropogenic activities, such as water and sediment diversions, dams and reservoirs, and water and soil conservation measures. In particular, the water and sediment interception capabilities of the established soil and water conservation measures gradually became saturated over time. Specifically, the maximum water and sediment interception capabilities of the current soil and water conservation measures were 12.2 billion m3 and 1.9 Gt, respectively. Overall, the results of the present study can help tailor water and sediment regulation countermeasures in the future.

АНАЛІЗ ПОВТОРЮВАНОСТІ ДОЩОВИХ ПАВОДКІВ НА РІЧКАХ В БАСЕЙНІ ТИСИ (В МЕЖАХ УКРАЇНИ)

Rain floods on the rivers in the Tisza basin within Ukraine are formed several times during the entire warm period. The purpose of the presented study is a detailed analysis of the frequency of such floods on the rivers of the region under study in terms of the series of annual maximum average daily water discharges and the series of maximum average daily discharges of partial probability. The first series, called the “multi-annual series”, includes only one of the highest discharges each year, in our case, one for the warm period – May-October. The second row includes all values hat exceed some limit value, which corresponds to the smallest value from the series of annual maximum annual water discharges. To carry out the work, we used observational data on the average daily water flow from the following hydrological posts on the rivers: the Uzh River – Uzhgorod, the Latoritsa River – Mukachevo, the Rika River – Mezhgorye, the Teresva River – Ust-Chernaya, the Tisza River – Rakhiv for the observation period 1946 (47 ) to 2019. To obtain the long-term series and partial probability necessary for the study, first, chronological samples of rain flood maxima were formed for both series separately, then they were ranked and the estimated return period was determined for each member of the series. The series of maximums of partial probability according to the data from the studied hydrological stations in their number on average 4-6 times exceed the number of values of the series of annual maxima. The calculated return periods are determined by the inverse formula to the Weibull formula. Graphs of the frequency of rain floods by annual maxima and maxima of partial probability for the stations under study were constructed, which made it possible to notice the following features: 1) the discharges maxima of rain floods with a frequency of less than 5-10 years differ for a number of annual maximum water discharges and a series of partial probability; 2) partial probability series better describe minor floods, especially those with a short return period. The analysis of the frequency of rain floods on the rivers in the Tisza basin within Ukraine made it possible to estimate the possible magnitudes of rain floods that can form during a warm period of time and to estimate their frequency of a certain magnitude. This is of practical interest as knowledge of potential floods can be used to assess the nature of potential floods in the future.

МАКСИМАЛЬНЫЕ ГОДОВЫЕ РАСХОДЫ ВОДЫ МАЛЫХ РЕК СЛАВСКОГО РАЙОНА КАЛИНИНГРАДСКОЙ ОБЛАСТИ

Purpose: to restore the series of maximum annual water discharges (MAWD) of small rivers in Slavsky district Kaliningrad region and determine the calculated values of MAWD with the necessary availability for designers. Materials and methods. The basic material – observational data of Roshydromet for water discharges on the Zlaya, Osa and Nemoninka (Nemonin river basin) rivers and on the Instruch river. The Instruch river was used as an analogue for the restoration of the MAWD on the Zlaya river for a few missed years of observation. The river Osa has the shortest series of observations, for its restoration, as well as for the Nemonin river, the Zlaya river served as an analogue. A hypothesis that the MAWD of the rivers of the Slavsky district obey a three-parameter gamma distribution (Kritsky-Menkel) was put forward. To solve the system of integral equations, a previously developed numerical method was used. Results. A close stochastic relationship between the MAWD of the tributaries of the Nemonin river has been determined for years of joint observations. This made it possible to obtain the restored MAWD series for 1955–2019. The probability curves of three small rivers were constructed, and the hypothesis on possibility of using the Kritsky-Menkel distribution was confirmed. According to the analytical expressions of the specified distribution, the calculated values of the MAWD of the given exceedance probabilities were found. Conclusions. The hydrological characteristics of the studied rivers of the Nemonin basin are strongly influenced by the functions of water intakes of draining reclamation systems. Due to the impossibility of dividing the peak annual discharges into the maxima of rain and melt water for each river, a single series of MAWD was restored, regardless of their origin. At the tributaries of the Nemonin river, the ratio of maximum discharges to average annual ones is noticeably lower than that of the Instruch river, which is under the similar hydrological conditions, but is not subject to such a strong anthropogenic impact. The calculated MAWD modules of the given exceedance probabilities can be used in the design of drainage systems and hydraulic structures.

Hydrological System of the Plitvice Lakes—Trends and Changes in Water Levels, Inflows, and Losses

The Plitvice Lakes National Park is inscribed on UNESCO’s World Heritage List. The lake system is composed of 16 cascading lakes of different sizes separated by tufa barriers, which are the park’s key phenomenon. The lakes are characterized by highly diverse trends of the characteristic hydrological indicators—mean annual water levels, discharges, and tufa barrier growth. The analyses carried out in this paper identified that in the period before the early 1990s, Kozjak Lake had a trend of decreasing discharges, together with a trend of increasing water levels and growing tufa barriers. In contrast to this, in the period after 2001, a trend of increasing discharges was recorded, as well as a trend of decreasing water levels and decreasing tufa barriers. A potential cause of the barriers decreasing in size were the extremely high discharges during the last decade, which resulted in increased erosion of the tufa barriers. Losses of water due to the sinking from the lake system as well as the upper Korana course were confirmed, and it was identified that during the analyzed period the losses had not changed significantly. It was determined that the losses of water from Kozjak Lake occurred during low-water periods; however, they depended not only on the quantity of water flowing through the lakes but also on the hydrological conditions underground. The analyses carried out and the methodological procedures used in the analyzed area of the Plitvice Lakes are useful examples for the performance of analyses at similar lakes in karst formed by tufa deposition processes.

Formation of variability of flow quality in the top of the Luga river in inter-annual and short-term time. Part 1. Interannual variability

The study of the interannual variability of the flow quality of the Luga River was carried out in the section of the village of Tolmachevo 3 km downstream of the confluence of the Oredezh River according to the data of the North-West UGMS 2000–2017. Water pollution in the runoff was assessed in accordance with RD 52.24.643-2002. For 11 years out of 18, the water in the effluent was “very polluted”, 2 years – “dirty”, 3 – “polluted”, and only in 2016 and 2017 – “slightly polluted”. The use of factor analysis showed that the variation of Vzag% of the runoff of the most polluted water of classes 3 and 4 is influenced by factor 1 (33% of the total variance), which is associated with the value of the highest water discharge. Factor 2 (22%) has a positive relationship with the variation in average and lowest water discharges. Four components Mn2+, Fetot, COD and Cu2+ are distinguished, polluting most of the volume of water flow annually. Factor 1 (21%) affects Vzag% of water contaminated with single components. It has a negative relationship with Vzag% of water, the oxygen saturation of which is below normal. This, possibly, can serve as a marker of the contribution of the Oredezh River to the formation of runoff in the section of the village of Tolmachevo. Factor 2 (18%) showed an inverse relationship between the variation of Vzag% of the runoff of water contaminated with Cu2+ and the average annual water discharges

Freshwater discharge from the large and coastal peninsular rivers of India: Areassessment for sustainable water management.

This study offers an updated mean annual water discharge of 10 large and 11 coastal basins of the Indian Peninsula and looks into environmental parameters influencing the water flux and discharge trends. The mean annual discharge of large and coastal rivers is estimated to be 221 and 294 km3. Thus, despite draining 25% of the Indian Peninsula, coastal rivers deliver more than half of the annual flux, and west-flowing coastal rivers contribute 85% of it. This study demonstrates temporal changes in the water discharge of various river basins. The presence of dams regulates discharge regimes of large rivers. The construction of large dams resulted in a significant decline in the water discharge of the Krishna, Cauvery, and Narmada. Through this study, we demonstrate the role of rainfall, catchment size, water loss through evapotranspiration and infiltration, and societal use of water in determining the runoff of each basin. We recommend tapping the water resources of the west-flowing rivers for proper planning, development, and management to reduce the water stress in the peninsular region and promoting sustainable management.

Statistical Assessment of the Runoff Variability of Small Rivers in the Middle Zeravshan Basin

The article deals with the issues of statistical assessment of the variability of the runoff of small rivers in the Middle Zeravshan basin. For this purpose, the average monthly and annual water discharges were used, taken into account at 11 hydrological stations located on small rivers and water resources in the Middle Zeravshan basin. Calculations to estimate the coefficient of variability of river runoff were carried out for two periods: the first calculation period includes the base climatic period (1961-1990), and the second calculation period includes 1991-2018. Based on the analysis of the results obtained, an increase in the value of the coefficient of variation (Cv) in the second calculation period relative to the first calculation period was revealed.