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Hydrology

Volume XIX |

Flood Mapping and Estimation of Flood Water-Level Using Fuzzy Method and Remote Sensing Imagery (Case Study: Golestan Province, Iran)

Abstract: Recently, the heavy precipitation occurred across the north of Iran caused an unprecedented flood. Due to the topographic conditions of the study area, not paying attention to the regular dredging of the river has caused a lot of problems for the local people. On the other hand, due to the frequent rainfall, the occurrence of flooding for a long time was another major problem. The combination of Remote Sensing and GIS can make a substantial contribution to flood assessment and management. In the present study, a fuzzy method is developed to show the hidden potential of Landsat satellite images for flood mapping. This paper presents the process of rapid access to water level information, which can provide valuable data for decision makers. The overall accuracy obtained for the flooded and damaged area is 87.23% and 46% respectively, and Root Mean Square Error (RMSE) of 27.68 cm is obtained for water-level based in the proposed algorithm.

Volume XIX |

The Buzău river alluvial fan – a groundwater modeling approach to sustainable exploitation

Abstract: Knowledge of groundwater resources is a key challenge for hydrogeologists, especially due to a continuous increase in demand for drinking water. This paper aims to investigate the consequences of overexploitation of the phreatic aquifer from the Buzău River alluvial fan and to assess alternatives operating programs related to achieving a sustainable groundwater exploitation. The study was achieved using data (groundwater level and general information from 97 hydrogeological boreholes) from the National Institute of Hydrology and Water Management, Romania, and collected in the field between July 18-19, 2017 (river stages for Buzău and Călmățui). The aquifer data was statistically analyzed and the obtained results allowed the design of a conceptual model for the hydrostructure and a mathematical model for the groundwater flow, using the FREEWAT software. Continuous exploitation of the phreatic aquifer through the catchment fronts that supply the city of Buzău (Crâng, Zahăr I, and Sud fronts) was simulated using the hydrodynamic model, in a transient regime. The maximum allowable flows were defined for each hydrogeological borehole that exploits the phreatic aquifer, using the mathematical model (values between 4.0 and 19.0 l/s). The exploitation of these flows was performed for 10 years, with time steps that allowed an analysis of the depression cone extension and drawdown value after 90 days, 180 days, one year, and five years of continuous pumping. After ten years, the resulting depression cone reached a diameter of 9.8 km and the groundwater level decreased with a maximum of 8.26 m, in a hydrogeological borehole. For stationary simulation (which is not influenced by the time parameter), it was observed that pumping with the maximum allowable flows resulted in a drawdown that exceeds one-third of the water column, which indicates overexploitation.

Volume XIX |

The occurrence of the armored mud balls during the flash flood phases of the streams from the Meledic Plateau – the Curvature Subcarpathians, Romania

Abstract: Armored mud balls that form in fluvial environments were observed on the river bed of two small streams from South-East Subcarpathians Bend, in the area of Miocene deposits with salt dia-pirs. Pieces of well-rounded clay mate-rial but with coarse surface were found on the gravel banks as well as partially submerged into stream channel and embedded in soft sediments of stream banks. The surfaces of mud balls, nearly spherical and ranging from 5 cm to 17 cm in diameter, were studded with sand grains and gravel that collected during flash floods as a result of bedload transport. The main source material of the armored mud balls consists of dark clay material detached from the cap rock of the salt massif that is crossed by the two streams. The newly formed armored mud balls, which were found among the gravels on the stream bed following the summer flash flood event from June 2019, supports the fact that these particular sedimentary features form during exceptional floods when pieces of clay material are rolled by the high-energy water flow, which results in acquiring of their spherical shape and the pebble shell. This paper represents the first report on the occurrence of modern armored mud balls formed in a fluvial environment, located in the Curvature Subcarpathians, Romania.

Volume XIX |

On the linear trends of a water discharge data under temporal variation. Case study: the upper sector of the Buzău river (Romania)

Abstract: The aim of this paper is to provide a statistic overview of the hydrological impact of the Siriu Dam on the Buzau River (Romania), taking into account the temporal variations. Our case study uses the daily mean discharges of the Buzau River (1st of January 1955 to 31st of December 2010), registered at Nehoiu hydrometric station. The building of the Siriu Dam in 1984 required the division of the study interval into two sub-periods, each being analyzed annually and seasonally, on the series themselves or on the pre-whitened ones when prior required. The existence of a linear trend on different periods and sub-periods has been studied by using the Mann-Kendall and Seasonal Mann-Kendall tests. In the case of the existence of a linear trend, the slopes have been calculated with Sen’s Slope Estimator. The stationarity has been studied by using the Dickey-Fuller and Kwiatkowski–Phillips–Schmidt–Shin tests. According to our preliminary results, the stationarity in trend after the dam’s construction, respectively increasing linear trends for almost all the data series and subseries was observed. The trend and stationarity outcomes proved that the Siriu Reservoir has a good impact on the homogeneity of the Buzau River’s discharge and the increasing trends are related to human activity impact coupled with climate change/variability.

Volume XVIII |

Hydro-ecological investigation of the Lazeshchyna River in Transcarpathian region of Ukraine

Abstract: This paper focuses on the hydro-biological and hydro-chemical analysis of the Lazeshchyna River, one of the tributaries of the Tisza River from the cross-border territory within Rakhiv area of Ukraine’s Transcarpathian region. For this purpose, we used the results of route survey, hydro-biological and hydro-chemical analysis of the Lazeshchyna River surface water samples, which were collected forhydrochemical studies in 2017-2018. On the basis of water sampling we thoroughly analyzed the hydro-chemical water quality indicators of Lazeshchyna River according to the following groups of indicators: physic and chemical features, organic matter, water mineralization, major ions, nutrients, trace elements and specific pollutants. Hydrobiological studies were conducted in 2015-2016. Based on them, the water quality was assessed according to the Trent Biotic Index bioindication. The ratio of actual and maximum permissible concentration (MPC) hydro-chemical parameters are investigated, moreover we pointed out the seasonality in the ratio of water consumption and concentration of individual indicators. The study underlines the role of natural and anthropogenic factors for the Lazeshchyna River water quality.