Author(s): Preseren Tanja; Steinman Franci; Klasinc Roman; Gosar Leon
Linked Author(s): Roman Klasinc, Franc Steinman
Keywords: Hydraulic modelling; Sediment transport; Two-dimensional numerical model; Model similarity laws; Free surface flow; Hydropower plant
Abstract: The construction of hydropower plants triggers a multitude of phenomena as well as impacts which cannot always be fully envisaged despite the experience gained. The construction and operation of a plant frequently destroy the balance in the natural processes of sediment transport. Any changed conditions in the riverbed, such as increased erosion and uneven deposition of materials in the channel and along the banks, are unfavourable both in terms of the river morphology and the water ecosystem and concerning the exploitation of water energy. Extraordinary amounts of gravel may be deposited in manmade storage reservoirs behind dams, decreasing the useful volume, which weakens (or completely disables) the functions of the dam. In run-of-the river power plants, with no storage reservoir, the problems are somewhat different. A relatively typical example is the St. Veit Hydropower Plant on the Salzach river, Austria, where there has been an enlarged gravel deposition downstream of the dam in the recent years of its operation. It is primarily critical during high water, when engine room operators are forced to stop the turbine drive and the water only runs off downstream over the overflow spillways. Mechanical removal of materials has become indispensable for a normal operation of the St. Veit Hydropower Plant, which increased its costs. To answer the questions concerning river hydraulics, the hydraulic laboratory of the Institute for Hydraulic Engineering and Water Resources Management at Graz (IWW, TUG) started experimenting on a physical model. The goal of the research was to determine the measures to be used to reduce the volume of gravel deposition, so as to avoid uneconomical maintenance. Subsequently, the Chair of Fluid Mechanics (KMTe, UL) also produced a two-dimensional numerical model of a section of the Salzach river by means of the SMS interface and the FESWMS application for hydraulic modelling, with a special challenge lying in the modelling of the operating conditions of the hydropower facility. A mathematical model was used to examine the hydraulic conditions in different hydrological and operating situations. The model was also expected to study sediment transport, however, due to deficiencies in the software, these calculations have not yet been made. This is a case where the unfavourable impact on the water flow was not sufficiently examined during the designing of the hydropower facility. Hydraulic modelling as a tool for analysing the impact of the hydropower facility on the runoff regime is an aid in the optimisation of the construction of the building, thus providing technically, ecologically and economically better solutions on the long run.
Year: 2007