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Hydrology

Volume XIII |

Extreme low flow of the Topolovets and Voinishka Rivers (Danube tributaries, Bulgaria)

Abstract: The minimal stream flow is the most sensitive characteristic of stream flow. The aim of the paper is the assessment of the duration and the frequency of low flow through threshold method on daily discharges. The daily data of the two Danube tributaries (the Topolovets and Voinishka) have been used. The results present the following: low flow typically appears in the summer and episodically in the spring and winter; the duration varies between some days to month; the spatial distribution of extreme minimum flow is discrete and depends on climatic and anthropogenic activities. The method of quantiles gives good threshold level for defining extremely low stream flow, but have to apply in keeping with concrete conditions and purposes.

Volume XIII |

The analysis of the susceptibility of the flash-floodsʼ genesis in the area of the hydrographical basin of Bâsca Chiojdului river

Abstract: The present article aims to identify the areas with high susceptibility in the acceleration of the surface flowing of the water and thus, in the delivery of the flash-floods from the hydrographical basin of the Bâsca Chiojdului river, which is situated in one of the most vulnerable areas in Romania (bend area) at the hydrological phenomena of risk. The analysis of the susceptibility was possible by taking into consideration ten main factors that we considered to play an essential role in the genesis of the flash-floods. There resulted a map of the flankʼs surfaces with high susceptibility in the flash-floods’ delivery and their triggering at the layer level of the hydrographical network in the basin. The proposed index, FFSI (Flash Floods Susceptibility Index), resulted from the summation of the analyzed factors, presents mainly the highest values within the area of Drajna Depression, where most of the settlements from the basin are located. The high genesis susceptibility of the flash-floods in this area is due to the association of the most numerous risk factors that we analysed, namely lithology favourable to the pronounced flowing, slopes with high values, high degree of deforestation etc. The areas identified as being critical from the point of view of the potential of flash-floods formation present a high risk for the genesis and triggering other related phenomena such as floods and landslides.

Volume XIII |

Statistical assessing of hydrological alteration of Buzău River induced by Siriu Dam (Romania)

Abstract: In this paper we evaluate the hydrological impact produced on the river mean daily discharge (water) of Buzău River by Siriu Dam. The study data was the daily mean discharge registered from the 1st of January 1955 to the 31st of December 2010, at the Nehoiu hydrometric station on the Buzău River. The flow of this river is controlled in its upper reach by Siriu Dam, from 1984. The main method used for the evaluation of the hydrologic alteration at temporal scale was based on the tests provided by the Indicators of Hydrologic Alteration (IHA) software. The statistical analysis proved that the built of Siriu Dam had a moderate influence on the mean daily discharge regime of Buzău River at large time intervals, significant changes appearing at small time scales.

Volume XII |

New Techniques for the Analysis of the Limno-morpho-bathymetric Parameters in the Lacustrine Basins. Case Study: Red Lake in the Hăşmaş Mountains (Romania)

Abstract: Red Lake in the Hăşmaş (Curmăturii) Mountains was formed by the natural barrage of the Bicaz brook in 1837. The north-western slope of the Ghilcoş Mountain, covered with gravel, slide as a result of the alteration layer water saturation following the abundant rains in that period. The lake has an „L” shape, or the shape of a leg with the foot oriented towards north. Red Lake is supplied by several brooks with permanent character: Oii, Ghilcoş, Vereşcheu, Suhard. As a result of the measurements we made in the summer of 2009, using Leica Total Station and sonar, the following data were obtained: area 12.01 hectares; perimeter 2905.79 m; maximum length 1361.72 m; maximum width 160.24 m; maximum altitude upstream in the south 965.199 m; maximum altitude upstream in the north 966.041 m; maximum depth 10.50 m etc. The greatest depths, of 10.5 m, are recorded in the central sector, close to the outlet of the two arteries. In a transversal profile, the western bank is steeper and hard (lithologically), and the eastern bank is mild and crumbly (landslide diluvium). In the same way the submerse slopes are maintained as well. New techniques of analysing the hydro-morphological parameters for a lacustrine basin have been used. Methods specific to land geomorphology (slope inclination, slope orientation etc) have also been used. The cartographic representation, as a new thing in the field, is suggestive, and helps in elaborating an interdisciplinary interpretation, of a limno-ecological nature.

Volume XI |

The sediment transport of the Siret River during the floods from 2010

Abstract: Beginning with 2004 in the Siret River Catchment there occurred exceptional flash floods that exceeded the maximum historical values recorded, on the main river and on its tributaries (2004, the Trotuş River; 2005, the Siret River, the Trotuş River, the Bistriţa River, the Putna River; 2006 – the Clit River from the Suceava River Catchment; 2008, the Siret River, the Suceava River). The 2010 summer flood from the Siret River also falls in this category. This paper uses hydrological data (water discharge, suspended sediment discharge) between the 20th of June and 10th of July 2010 from 5 gauging stations located on the Siret River: Siret, Hutani, Lespezi, Dragesti, Lungoci, and also meteorological data (rainfall) measured at different gauging stations from the Siret River Catchment. The rainfall recorded in this time of the year in the catchment was very high, with values up to 210 l/m2 in approximately 10 days. The hydrographs of the flash flood indicate the fact that the transit of the water trough the reservoirs system from the Siret River (Rogojeşti – Bucecea and Răcăciuni – Bereşti –Călimăneşti – Movileni) reduced the maximum water discharge with values between 7-27%. The values of the maximum sediment discharge also recorded a reduction while transiting this reservoirs system with approximately 60%. The evolution of the Siret river bed channel during this flood (aggradations with values between 15-100 cm and degradations starting from 65 cm until 200 cm, in different moments of the flood) is influenced by the high values of the water and sediment discharge and by anthropogenic interventions on the river bed (pit-ballast, regularization of the river bed, reservoirs). Processing the hydrological and meteorological data recorded during the flood (20th of June – 10th of July 2010) indicates two important features of this event: the climatic variability – exemplified by the big values of precipitations from the catchment and the anthropogenic impact revealed by the transit of the flood wave and the evolution of the river bed.