THE DEGREE OF SILTING AND THE IMPACT ON ALLUVIAL DEPOSITS IN THE RIVER BEDS OF BISTRIŢA RIVER BASIN

Since 1960 the Bistriţa River basin came under the profound influence of anthropic incidence. This river basin represents a pattern of use for hydropower potential: reservoirs (9); channels (61 km); water dams; transfers of flows; protection structures works for banks and slopes; relocation of human settlements (13 villages); gravel pits; galleries; viaducts; communication paths, etc. Bistriţa River development has led to significant changes in the structure of the hydrological regime, through the regularization of water flows and by creating significant discontinuities in the transit of silt. Lately there has been an increase in water turbidity in the highlands. Solid flows on the lower course register a continuous decrease because of the existence of reservoir. During the execution of the hydraulic structures turbidity and sediment yield increased. When brought into service intense processes of silting occurred. Analysis covers the sediment yield in Bistriţa River basin and the evolution in time of the degree of silting of reservoir. Average production of silt varies between 1.5-2 t/ha/year. Annual rate of silting in reservoirs is between 0.6% (Izvorul Muntelui) and > 2% (Pângăraţi, Racova). Racova Reservoir was decommissioned in 2011

DETERMINATION OF THE GROUND-WATER LEVEL BY MODERN NON-DISTRUCTIVE METHODS (GPR TECHNOLOGY)

Determination of the ground-water level by modern non-dis¬tructive methods (ground-penetrating radar technology). Ground Penetrating Radar (GPR) is now a well-accepted geophysical technique, which unfortunately in our country its less used. Historically, the development of GPR comes from the use of radio echosounding to determine ice thickness and it was only a short step to enlarge the domain of research such as permafrost, geological investigation (bedrock, sedimentology), environmental assessment and hydrogeophysical studies (under-ground water location, soil water content). The GPR method measures the travel time of electromagnetic impulses in subsurface materials. An impulse radar system radiates repetitive electromagnetic impulses into the soil. A bandwidth antenna is usually placed in close proximity and electromagnetic coupled to the ground surface. It detects and measures the depth of reflecting discontinuities in subsurface soils and other earth materials to within a few centimeters depending of antenna frequency. For over 30 years, GPR has been used extensively for hydropedological investigations. Our research aims to determine the groundwater to estimate the degree of evolution of hydro-geomorphological processes

FLOODS AND DROUGHT - HYDROCLIMATIC RISKS IN SUHA RIVER BASIN

Suha is a right tributary of Moldova River, and presents a typical discharge for the geographical unit of Obcinele Bucovinei. Data used in the paper have been taken from Siret Basin Water Administration, Bacău, and represent a time sequence of 40 years. The most significant floods occurred in 1975, 1981, 1984, 1991, 2005, 2006, 2007 and 2008. The most obvious droughts occurred in 1969, 1974, 1978, 1983, 1987 and 2001. It was observed that the evolution of hydrological risk phenomena is closely linked to climatic changes. Increasing population and the need to extend the building design must take into account the extreme values of river flow over time, water resources also being important. Because extreme events occur more often, considering preventive plans against floods is needed. For this reason are analyzed the temperatures, rainfalls and discharge rates

THE ROLE OF THE HYDRO-CLIMATIC CONDITIONS IN CAUSING HIGH FLOODS IN THE SUCEVIȚA RIVER CATCHMENT

Located in the north-eastern part of Romania, the Suceviţa catchment has been affected in the last decade, by the most serious known high floods in the modern period of hydrological observations. The significant amounts of rainfall (260 mm in five days in 2008 and 150 mm in four days in 2010) have led to the formation of high floods that have affected large areas of land near the river course. These torrential rainfall led to the recording of maximum flows showing an increased tendency from 214 m3/s in 2007 to 467 m3/s in 2010 (reconstituted value exceeding the probability of occurrence of 0.1%). Even if the afforestation degree, at the level of the catchment and its tributaries, in the mountainous area, is over 80%, the morphometric conditions given by the average high values of the slopes (37-55‰) and also by the circularity ratio (0,60 – 0,73) generate a fast drainage of the precipitation water to the riverbeds. At the same time, the human activity increases the impact of flooding because of the activities carried out near watercourses. Flooding associated with these high floods have highlighted the vulnerability of the communities manifested by weak capacity to absorb the effects of the phenomenon and to recover after such events. Therefore, the high floods of 2008 and 2010 have caused extensive damage to the localities situated in the Sucevița river catchment

THE USE OF HEC-RAS MODELLING IN FLOOD RISK ANALYSIS

The fact that, in the Ozana drainage basin, most of the people have built their homes in the river valley, determines that a study focused on identifying the areas exposed to hydrological risk is vital, mostly in the development decisions for villages and in the creation of management plans for emergency situations. This study analyses the mapping methodology of the flood prone areas in the middle and lower sector of the Pluton river, which is a tributary of Ozana river, in its upper sector. In order to correctly draw the flood risk maps, the HEC-RAS method has been used, together with the HEC-GeoRAS extension, in ArcGIS. The results that have been obtained, correlate with the field situation in a very high proportion: for a 1% occurance flood, almost 123 households have been damaged, and according to the simulation, a number of 147 buildings have been damaged, therefore other probabilities (that overcome the 1% situation) can be used for similar simulations

DROUGHT ANALYSIS IN OZANA DRAINAGE BASIN

Ozana drainage basin is located at the contact between large landscape units (the Carpathian mountains, the Subcarpathian area, and the plateau region). This placement determines the existence of a complex climate in the region. Despite being small in size, and its extension on an W-E direction, differences can be observed, especially of the way extreme phenomena take place. In the case of droughts, it had different intensities in the mountains, compared to the plateau region. In order to emphasize the different distribution on the territory, several climatic indexes have been calculated, regarding dryness (De Martonne Index, Hellman criterion). The analysis of these indexes at the same monitoring stations (Pluton, Leghin and Dumbrava) emphasizes the growth of the drought periods in the plateau region and the fact that they shorten in the mountain area. In the mountainous area, where the land is very well forested, the values of the De Martonne index can reach 45.4, and in the plateau regions, where the forest associations are sparse, the values dropped to 30.6. According to the Hellman criterion, several differences can be emphasized, at basin level. In the mountainous region, there is only one month that, at a multi-annual level, has stood up among the rest, as being excessively droughty, while in the median /central region of the basin, three months have been identified, that have such potential, as well as five months, at Dumbrava