The layout of water resources and the complex and rational use of them have an important role in the socioeconomic activities of an urban settlement. Transversal hydrotechnical constructions such as weirs reduce the longitudinal connectivity of rivers and streams, affecting river biodiversity as well as water quality. This paper presents an alternative method that will help restore connectivity. In order to choose the best solution, topographical measurements were taken with a total topographical station, and a professional drone was used to obtain an updated orthophoto plan. After processing the data obtained in the field, engineering software capable of simulating flow, sediment transport, and water quality in rivers was used. With the help of the software, two hypotheses were realized: hypothesis A, the case with only one weir in place, and hypothesis B, when we have the proposed case with the lowering of the height of the weir’s crest and the construction of three new control weirs downstream of it. In conclusion, the lowering of the current weir’s crest and the construction downstream of it of three new weirs of low height would have a favorable effect from an ecological and a morphological point of view, without very big consequences on the disturbance of the flow from a hydraulic point of view.
The impact of dams and reservoirs on the aquatic ecosystem of rivers is a very important topic for water resource management. These hydrotechnical facilities change the natural hydromorphological regime of the rivers. This paper analyzed the hydrodynamic characteristics of an undeveloped riverbed section downstream of the Colibița reservoir, from the Bistrita Ardeleana River hydrographic basin. After processing the data obtained on the field, two hydraulic models were made using the MIKE 11 program, which aimed to identify the hydraulic parameters such as the wet section, the depth, and the water velocity. The first modeling was used for the flow rate of Q = 54.5 m3/s: the water depth was between 1.952 m and 2.559 m; and the water velocity varied between 1.148 m/s and 1.849 m/s. The second modeling was used for a flow rate of Q = 178 m3/s and showed that the water depth had values between 3.701 m and 4.427 m; and the water velocity varied between 1.316 m/s and 2.223 m/s. Following the granulometric analysis, the average diameter of the particle in the thalweg was D50 = 25.18 mm. The conclusion reached as a result of hydraulic modeling and granulometric analyses indicated that hydromorphological processes take place along the length of the analyzed sector, which have negative effects on water quality as well as on the instability of the riverbed. To make the riverbed safe along the entire studied length, we managed to identify some alternative solutions that have the role of stabilizing the banks, respectively, to stop the deepening of the thalweg. The alternative hydrotechnical constructions will increase the roughness of the riverbed, essentially reducing the water speed and increasing the favorable conditions for the retention of alluvium.
The design of hydrotechnical constructions requires knowing certain hydrological quantities necessary for their dimensioning. The annual average turbidity is one of these quantities. The issue is that, in some river sections direct observations and measurements do not exist regarding this hydrological quantity, so that different empirical relationships developed by various authors based on long observations and measurements are applied, such as that developed by Poliakov. Turbidity depends on basin characteristics for the section considered. All coefficients that occurs in Poliakov's formula and which depend on the river section characteristics can be extracted with high precision using GIS maps and plans. The use of GIS involves the determination, in more accurate manner of the coefficients included in Poliakov's formula. The values obtained from turbidity computation on these lines must be balanced with some measurements made by competent authorities for the targeted sections to see if the values obtained empirically fall within the values obtained by direct measurements. In this paper, calibration and verification of data obtained by this method was made on Jijia River in computing section Victoria.
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