Summary:

The paper summarizes the results of the work done in orders to evaluate the possibility of changing the function and utilization of rubble dosing dam on the Wieprzówka I mountain stream in order to create an artificial lake and ensure that the water level in the reservoir remains the same. The artificial lake will be valuable from the point of view of tourism and what is more it will improve the water retention of the valley. A rubble dosing dam protects the river bed by reducing the bed slope and water velocity and what is more by controlling the bedload transport so that accumulation takes place up the dam. The dam does not stop bedload transport because there are openings which dose the fine material. The fine material can be transported even if the rubble dosing dam is filled up, so the hydrodynamic equilibrium and the connection between upstream and downstream sections of the river is maintained. Hydraulic seal of the rubble dosing dam and the exploitation of accumulated bed material will break the hydrodynamic continuity of the river channel and cause erosion below the dam – a process against which the dam should protect. Field measurements carried out on the distance of 0,74 km up and down the rubble dosing dam on the Wieprzówka I, included longitudinal profile of the research reach, granulometric composition of the bed material and inspection of hydraulic structures. Simulations of changes in the water surface level for annual discharge, t-year discharges with probability between p = 50% and 1% were carried out on the basis of these measurements. A procedure TRANS based on Mayer – Peter and Muller equation has been applied to the functioning of rubble dosing dam in natural conditions – case 1 and exploitation of accumulated bed material as far as backwater reach of rubble dosing dam – case 2. It has been discovered that the flow of water is sufficient let discharges up to Q_1% pass safely. The exploitation of accumulated bed material performed to create an artificial lake does not cause the water level to drop during the flood but significantly reduce bedload transport. At cross-section km 0+874, which is upstream the backwater reach of rubble dosing dam bedload transport was evaluated as G = 70687 kN for discharge Q_1%. Under natural conditions at crosssection km 0+593, located in the vicinity of the dam, bedload transport is reduced to G = 17116 kN and bigger fractions d_i>0,08 m are not entrain to the transport. For case 2 bedload transport reduces almost to zero and stops. As a consequence, the erosion of the river bed may occur downstream the dam which can threaten the stability of the dam and valley infrastructure. Taking into account the limitations resulting from the age of the rubble dosing dam and the necessity to preserve the hydrodynamic equilibrium of river channel, the only way to create the artificial lake is to locate it outside the main channel stream.