The main aim of this study was to assess what range of downstream low flow changes is caused by dam construction directly. An investigation was based on the assumption that the difference in change ...ratio of flow between gauging cross-sections located downstream and upstream position of dammed reservoir identifies the scope of changes determined by dam construction. Three dammed reservoirs located on Polish rivers were selected for analysis. They were different in size, hydrological regime and water management purposes. For each reservoir pair of water, gauges were selected. The input data were daily discharge series collected by the Polish Institute of Meteorology and Water Management. For each time series 20-year period before and after dam construction was established. Comparison of annual minimum flow ratios for these peri-ods as well as analysis of low flow dynamics and inertia allowed to identify range and direction of changes caused by investigated reservoirs.
In the present study, we have assessed low-flow discharge deficits, and the characteristics of the low flows at a constant and variable (monthly) low-flow threshold. The low-flow truncation level was ...identified based on the 70th percentile from the flow duration curve (Q70%). Q95% was assumed to be the threshold for the deep low-flow discharge. Thirteen catchments in the Vistula basin, varying in size, river regime, and physico-geographical conditions, were selected for the study. The input data was a series of daily discharge data sets from the period 1951–2016, made available by IMGW-PIB (Polish Institute of Meteorology and Water Management – National Research Institute). Analyses were conducted of drought flow discharge deficit volume in absolute and relative values, and low-flow duration and deficits contributing to severe low-flows were calculated for temporal scales of months and years. Comparison of the obtained results led us to the determination of the basic factors affecting the formation of low-flow deficits, and the indication of restrictions when applying fixed and variable criteria for identifying river low-flows.
In the study, hydrological drought was identified assuming that the occurrence of river low-flow is a symptom of drought, and is also a good estimator of its progress. The research was conducted in ...the upper Dunajec river catchment, for which a series of daily discharges from 20 gauging stations during the period 1989–2018 were available. The low-flow periods were identified on the basis of the Threshold Level Method, which corresponds to the seventieth percentile of the flow duration curve. On the basis of a developed algorithm, 41 drought events were identified. Analysis included spatial parameters referring to range, severity, concentration, continuation, and the development pace of hydrological drought. Finally, on the basis of cluster analysis, five dynamic types of hydrological drought were identified.
The main aim of this study is to make an assessment of the impact of Lake Gopło on a river low-flow regime. Two water gauges were selected, located in an upstream and downstream position to the lake ...on the River Noteć. On the basis of the daily discharge series from the period 1965–1990, a group of low-flow regime estimators was computed. Analyses involved various aspects of minimum flows and drought streamflow deficits. Comparison of the data between both gauging stations showed the extent of the influence of water management on Lake Gopło on low-flow regime transformation in the River Noteć.
In river-lake systems, reservoirs significantly affect the formation of water resources in the catchment by reducing the maximum flows and floods as well as increasing the low flows. In lake ...catchments, the pace of hydrological drought progression is usually slow. However, this phenomenon can be very extreme and destructive for water balance structure as a result of the very slow renewal rate of catchment resources. An estimation of hydrological drought development was conducted in the Biebrza river catchment (6,900 km
) on the basis of a daily discharge series for 18 water-gauge stations in the period 1982–2014. The number and location of the gauges allowed reliable results of the spatial pattern of drought to be obtained. The main objective of the research was the construction and assessment of the applicability of indicators which are estimators of drought spatial progression. Comparative analysis of four proposed indices led to two of them being recommended. These characteristics estimate the direction of drought development according to the stream network hierarchy, location of sub-catchments and the direction of river basin area increase. As a result, determinants of the spatial development of hydrological drought as well as its importance in the hydrographical structure were identified. Furthermore, the intensity of drought was evaluated and all investigated indices were applied to a time series analysis.
The study applied the method of hydrological season identification in a time series of river total and base flows and in groundwater levels. The analysis covered a series of daily measurements from ...the period 2008–2017 in nine catchments located in different geographical regions of Poland. The basis of the classification of hydrological seasons, previously applied for river discharges only, was the transformation of the original variables into a series reflecting three statistical features estimated for single-name days of a year from a multiyear: average value, variation coefficient, and autocorrelation coefficient. New variables were standardized and after hierarchical clustering, every day of a year had a defined type, valorizing three features which refer to quantity, variability, and the stochastic nature of total and base river flow as well as groundwater stage. Finally, sequences of days were grouped into basic (homogenous) seasons of different types and transitional seasons including mixed types of days. Analysis indicated determinants of types, length, and frequency of identified hydrological seasons especially related to river regime, hydrogeological and hydrometeorological conditions as well as physiographical background were directly influenced by geographical location. Analysis of the co-occurrence of the same types of hydrological seasons allowed, in some catchments, periods of synchronic alimentation (groundwater and base flow, mainly in the cold half-year) and water shortages (all three components, mainly in the warm half-year) to be identified.
Finding an efficient and reliable streamflow forecasting model has always been an important challenge for managers and planners of freshwater resources. The current study, based on an adaptive ...neuro-fuzzy inference system (ANFIS) model, was designed to predict the Warta river (Poland) streamflow for 1 day, 2 days, and 3 days ahead for a data set from the period of 1993–2013. The ANFIS was additionally combined with the ant colony optimization (ACO) algorithm and employed as a meta-heuristic ANFIS-ACO model, which is a novelty in streamflow prediction studies. The investigations showed that on a daily scale, precipitation had a very weak and insignificant effect on the river’s flow variation, so it was not considered as a predictor input. The predictor inputs were selected by the autocorrelation function from among the daily streamflow time lags for all stations. The predictions were evaluated with the actual streamflow data, using such criteria as root mean square error (RMSE), normalized RMSE (NRMSE), and
R
2
. According to the NRMSE values, which ranged between 0.016–0.006, 0.030–0.013, and 0.038–0.020 for the 1-day, 2-day, and 3-day lead times, respectively, all predictions were classified as excellent in terms of accuracy (prediction quality). The best RMSE value was 1.551 m
3
/s and the highest
R
2
value was equal to 0.998, forecast for 1-day lead time. The combination of ANFIS with the ACO algorithm enabled to significantly improve streamflow prediction. The use of this coupling can averagely increase the prediction accuracies of ANFIS by 12.1%, 12.91%, and 13.66%, for 1-day, 2-day, and 3-day lead times, respectively. The current satisfactory results suggest that the employed hybrid approach could be successfully applied for daily streamflow prediction in other catchment areas.
Low-flows are an important component of the river regime. Their identification advances our knowledge about the formation of water resources in drought conditions. The analyses that we have carried ...out aimed to indicate the spatial structure of these flows. Our study area was the Warta River catchment up to the water-gauge at Sieradz. The input research material consisted of a sequence of daily discharge data for 12 gauging stations located in this catchment, in the period of 1971-2000, made available by IMGW-PIB. At the first stage, periodic flows based on flow time-duration curve and annual minimum flows were determined. Their values have been converted into specific flows, which facilitated the conduct of comparative analyses. On the basis of the obtained results, the spatial variability of low-flows in studied catchment was evaluated. The annual number of days with low-flows was identified for all gauge sections. The dynamics and distribution of low flow appearing in the multiannual period were evaluated. The analyses we have carried out made it possible to identify the factors, which determine the structure of low-flows. Research results have been illustrated with relevant maps and graphs.
In the present study, identification of hydrological drought was made, assuming that the low-flow period, which is a symptom of drought, is also a good estimator of its progression. The research was ...conducted in the upper Warta river catchment, for which the series of daily discharge for 12 gauging stations from the period 1971–2000 were available. The low-flow periods were identified on the basis of the constant threshold level, which corresponds to the 70th percentile of the flow duration curve (Q70%). For the identified low-flow episodes, parameters pertaining to its duration, streamflow deficit, and flow dynamics have been estimated. The established identification and separation criteria made it possible to assess the simple and compound hydrological droughts. Transformation of characteristics related to low-flow duration, relative drought streamflow deficit as well as low-flows’ share in the total number of gauging stations resulted in the evaluation of hydrological drought in terms of its severity and range. The characteristics, which constitute estimators of hydrological drought progression and recession rate, made it possible to define the determinants of the studied phenomenon along with its variability in time.
Various criteria used for identification of a hydrological drought are presented on the basis of the threshold level method. Genetic criteria as well as temporal variability are analysed. In ...conclusion chosen criteria for lake catchments are recommended.
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