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.

Large dams, as well as conventional hydrotechnical constructions with the role of breaking the drainage slope (waterfalls or bottom sills), flood mitigation or with the role of protection against floods (shore defences) have a profound impact on the environment. Due to these constructions, the ecosystems on the Bistrița Ardeleană river have undergone changes or even established new ones. This paper wants to highlight the morphological changes of the Bistriţa riverbed by analysing the transversal profiles made between 1972 and 2015. The profiles were made in the flow measurement section at two hydrometric stations, one being located in the upstream part of the river basin and the other before the Bistrița river flows into the Șieu river. By comparing the results obtained from the profiles made before the Colibița hydrotechnical system was started or completed with the data obtained from the profiles after the commissioning of the Colibița hydropower plant, we managed to highlight that the Bistrița Ardeleană riverbed registered several negative effects in terms of morphologically both vertically and horizontally. We also found that the riverbed downstream of the dam there is a phenomenon called hydraulic paving.

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.