Preliminary study of the flushing operations of the Langmann reservoir, Austria

Preliminary study of the flushing operations of the Langmann reservoir, Austria

Den Boer, V.J.E.

De Vriend, H.J. (mentor)
Mosselman, E. (mentor)
Sloff, C.J. (mentor)
Crosato, A. (mentor)
Blom, A. (mentor)
Marence, M. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2011-06-23

The Langmann reservoir is part of the hydropower system in the river Teigitsch and in the reservoir loss of storage volume occurs. The reservoir was therefore flushed, but recently no permission is granted. The reason is the high sediment concentrations that have negative effects on the downstream region. An optimization of the flushing operations that reduces the negative effects and recovers most of the storage volume is required. Hence, insight in the flushing operations and identification of the key processes that determine the flushing efficiency are required. The reservoir is flushed by creating a riverine flow. The key processes that occur during flushing are classified as progressive erosion, retrogressive erosion and bank erosion. The flushing operations are in the maintenance phase; a channel is already formed and only recently deposited sediments are flushed out of the channel. A large peak in the sediment concentration at the transition of drawdown to riverine flow occurs. The Delft3D software is able to simulate the processes except for bank erosion. Bank erosion can be added to the model through an application that is under development. The model is very sensitive to the grid cell size, due to the small dimensions of the flushing channel. It is advised to decrease the grid cell size and to confine the grid to the flushing channel and the near surroundings as most erosion occurs within this area. The model also experiences problems in the water balance. The problems are caused by the rapid changes in water level, discharge and bottom level, but can be solved by adding and subtracting water to the model. The amount of sediment removed from the reservoir is underestimated. Data for calibration and verification are missing and therefore only the sensitivity to parameters that might increase the erosion is investigated. A measurement plan is set up in order to obtain the required data. The peak concentration is not shown in the model and so the model can not be used properly yet, to simulate different strategies that are implemented to minimize the sediment concentrations. Even though the model does not fully simulate the observed hydrological and morphological changes, it is felt that an important first step is taken in simulating the flushing operations. For the optimisation of the flushing operations a tube system combined with auxiliary channels that drain laterally is recommended. It is desirable to optimize the sediment management of the whole hydropower system in the river Teigitsch and make separate models of the three reservoirs. Pages 35-38 and Appendices B,C,D and E are removed due to secrecy.

reservoir
flushing
Delft3D
erosion
morphology

http://resolver.tudelft.nl/uuid:4f0318de-e6de-444d-b638-3fa849cd023d

2012-07-12

Student theses

master thesis

(c) 2011 Den Boer, V.J.E.