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Abstract: Characteristics of rainfall events (RE) play a determinant role in the hydrologic process in a small catchment (e.g., runoff formation, flood elements), water balance and water resource management. The goal was to investigate temporal rainfall properties at events scale. The study was based on long-term properties of rainfall events (e.g., depths, intensities), recorded in the warm semester (the period between 1 April and 30 September; 1980-2010) at Voinești Experimental Basin (VEB), Romania. Rainfall events values were recorded by a pluviograph, production of the former USSR. The rain gauge is situated at the central place of the VEB (altitude 500 m a.s.l.), in Curvature Subcarpathians. A valuable database with 1852 rainfall events characteristics was created. The depths (mm) and durations (min) of each RE were recorded and rainfall maximum and average intensities (mm/min) were calculated. Rainfall events were characterized by small depth (up to 15.7 mm; up to 90th percentile) ~ 93% and they were concentrated (34.4%) in May. Almost half of RE (48.2%), had short duration (up to one hour) and the smallest depth (95% confidence interval, 3.85–4.56 mm), while those with durations longer than 5 hours (10.5%) were specific the September (22.5%). Regarding maximum intensities of rainfall events, just 16 events exceeding 1 mm/min (0.86%), which denote insignificant occurrence – encountered phenomenon in all months, especially in August – and mild torrential character. Insignificant rainfall events correlations between rainfall parameters were observed. Just “time – depth” correlation has been notable (Pearson’s r: 0.631). Absolute frequency of rainfall events parameters in most cases shows a strong density of smallest interval. These results may have important implications for next runoff plot study.
Abstract: The study aims to analyse floods from May 1970, June 1974 and May 2015, which occured in the Bârsău catchment area, one of the right tributaries of the Someș River. The junction between these two rivers is downstream of Satulung locality in Maramureș County. Bârsău catchment area is located between the Someș and Lăpuș catchment areas and has a surface of 152 km2. The floods of the Bârsău River are fast and have a very short propagation time. They are caused both by rainfalls and snow melting. This is the case of the flood from May 1970, which had a duration of two days, whereas the floods from June 1974 and May 2015 occured just because of heavy rainfalls. From the three analyzed floods, the May 2015 flood, with a pluvial origin, reached the maximum level of 220 cm (DL+20 cm) at Buciumi gauging station and its effects strongly affected local people. Thus, the damages in the villages located inside the basin were recorded first, then quantified. After that, there were made the integrating maps of the flood prone areas as well as the hydrological and associated risks in order to identify areas with different degrees of vulnerability.
Abstract: This study refers to the spatio-temporal dynamics of human pressure in Preajba basin, located in the southeastern part of Craiova municipality. The statistic and cartographic analysis is based on the determination of a variety of environmental indices: index of human pressure by demographic dynamics, index of human stress through agricultural land use, naturality index, artificialization index and environmental change index. Choosing a grid of 1.5 sqkm for calculating and comparing the artificialization index of the landscape allows a concise analysis on the environmental transformation in the above-mentioned area. Complementary, temporal dynamics of the environmental indices values is highlighted by the choice of some benchmark years, i.e. 1992, 2002, 2012, 2014 to which data and recent cartographic materials from 2009 and 2014 are added. Results, materialized in the obtained values present the state of the environment and the human pressure implications on the Preajba lacustrine ecosystem (maximum values obtained at period level): physiological or agrarian density – 52 inhabitants/ha in 1992 (Craiova); human pressure index through arable – 1.4 ha/inhabitants in 1992 and 2002 (Malu Mare); naturality index of the landscape – 9.43 in 1992 (Malu Mare); environmental change index – 3.69 in 2012 (Coşoveni). Field campaigns conducted in 2015 and 2016 confirm the research results and visually support human pressure on the environment. The proposed measures, in order to stabilize and maintain the good environmental quality in the Preajba basin targets the lacustrine ecosystem by involving local authorities in order to protect the avi-faunistic natural area status of “Preajba-Făcăi Lacustrine Complex”.
Abstract: Based on the data series of average daily streamflow and suspended sediment load recorded between 2000 and 2014 at four gauging stations (Lunca de Sus, Goioasa, Târgu Ocna and Vrânceni), the temporal variation of the suspended sediment transport was investigated according to the prevalence of source areas. Thus, a significant temporal variability (monthly, seasonal, annual) was determined, in close relation with the amount of precipitation and the streamflow. The following equation was determined between the mean monthly suspended sediment load (Ṝ) and the mean discharge (Ǭ) at Vrânceni section: R= 0,0035Q2,2895, r=0,899. We believe this relation has a high degree of confidence for the indirect determination of solid load and it is comparable with other equations of this type. Along the entire length of the river, July was the month during which the highest suspended sediment load was recorded, with an average percentage of 37% of the total amount. At the opposite end, December is the month with the lowest documented suspended sediment load, with just 0.5% of the total amount transported annually by the Trotuş. As regards the seasonal variability of the suspended sediment load, the following values were determined along the entire length of river Trotuş: during the winter season the volume of sediment carried by the river amounts to approx. 2.1% of the total annual transported suspended sediment, the spring season accounts for 33.7% of the annual volume, the summer season accounts for ca. 55.5%, and the fall for 8.7%. In order to plot the R-Q correlation, the wettest, as well as driest years were selected for every gauging station. On the resulting plots, there were identified the thresholds based on which the two sources were separated depending on the area of origin: dominant from the catchment or dominant from the river bed. Overall, during the investigated period on the Trotuş river, the river beds contributed with about 21% of the total volume of transported suspended sediment. Depending on the type of the year (wet, dry or normal), the average input of the beds to the annual volume of suspended alluvium was as follows: 4% in wet years; 43% in dry years; 15% in normal years. The total volume of suspended sediment transported through the four sections on the Trotuş river between 2000 and 2014 amounted to approx. 39×106 t, thus the average annual volume was 2,598,000 t. A large share of this suspended sediment yield was produced during major floods. For example, at Vrânceni ca. 61% of the total sediment yield for the 15 year-period under investigation resulted from just 3 flood events (2005, 2010 and 2012).
Abstract: The seasonality of stream flow variability indicates special feature of local cycle of precipitations, evaporation and the timing of snow melt. This study presents seasonal occurrence of maximal and minimal annual flows and spatial variability of seasonal index (Is) in the Middle and Lower Danube basin. The analysis is based on 47 time series of monthly runoff (12 for the Danube and 35 for its tributaries), which are collected from public database. The results show that the maximum annual stream flow appears during all months, but with highest frequency in April for 68% from watersheds. It varies between one and 60% (Danube – Baziaz). The monthly flow is concentrated in summer–autumn hydrological season, except for the Jalomita, Siret and Prut river basins, where it is in the winter. The highest frequency of minimum monthly runoff for the Danube and the Tisza is in October and November and for the Sava and Velika Morava – in August and September. The lowest and highest monthly discharge of the given month in the entire period were recorded in different years. Seasonal index (Is) is between 0.98 and 3.18. It is about 1.00 for the Danube and more than 2.00 for the Tisza, Ialomita, Siret and Prut watersheds. Is is stability – coefficient of variation is up to 0.30 with the exception of several river basins. Stream flow variability of the Middle and Lower Danube can provide valuable information for scientific studies and integrated management of water resources.
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