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The Solis dam was built in 1986 by the Electric Power Company of Zurich (ewz). Ever since the construction, large amounts of sediments accumulated in the reservoir and led to severe sediment aggradation. As a consequence, the storage volume was reduced by about 50% till 2012 causing loss of energy production. Additionally, in the near future sediments may have caused severe damage at the dam due to blockage of the bottom outlets. Therefore, in 2011 and 2012 a sediment bypass tunnel was realized in order to redirect the incoming sediments into the tailwater to inhibit sediment aggradation. Since its inauguration, the tunnel was operated four times including a 100-year flood event in August 2014. First operational experiences are described herein.
This paper describes the design of the new tunnel invert lining of the 9-foot tunnel at Mud Mountain Dam, Washington, USA. The tunnel diverts all bed load sediments into the tailwater. Major invert abrasion has been observed in the existing steel lining. The new invert design consists of 0.59 m2 and 0.79 m2 granite blocks that are 0.25 m thick and placed tightly together along the tunnel. Stability analysis showed factors of safety ranging from 1.2 to 2.6 against uplift. This will be achieved with strip drains placed in the bedding material along the tunnel. A service-design-life analysis was performed using abrasion prediction modelling.
This model was based on abrasion measurement data acquired from granite field tests at Pfaffensprung sediment bypass tunnel, Switzerland. The estimated annual abrasion depths for the granite were approximately 0.50 mm/year for average sediment transport conditions.
For long term use of dams, it is required to develop methods of sediment management in reservoirs.
As one method, Sediment BypassTunnels (SBT) are operated in Japan and Switzerland to prevent reservoir sedimentation. SBT reduces sedimentation in reservoirs by routing the incoming sediments around the dam. SBT, however, is prone to severe invert abrasion caused by high sediment flux. Therefore, it is necessary to establish a measurement system of sediment transport rates in the SBT. A geophone was experimentally investigated in a laboratory flume at ETH Zurich. The sediment transport rate is calculated based on the plate vibration caused by hitting of gravels. In this paper, in order to alleviate disadvantages of a geophone, two newly developed sensor systems, a plate microphone and plate vibration sensor, are suggested and the results of their calibration experiments are shown. Finally, they are compared with the existing methods.
This paper deals with an experimental investigation of the mean and turbulence characteristics of supercritical quasi-uniform and gradually varied open-channel flows over a transitional rough bed. These conditions are typical for sediment bypass tunnels. The results show that the log-law holds well in the inner region across the channel. The roughness shifts the velocity profiles downward by an amount of ΔU+. The velocity-dip phenomenon and strong secondary currents exist in the channel for narrow open-channel flow. These currents cause the Reynolds shear stress distributions to deviate from the linear distribution and an undulation on the transversal distribution of the bed shear stress, which matches with the bed abrasion pattern. The streamwise turbulence intensity profiles deviate from the semi-empirical universal function whereas the vertical turbulence intensity profiles fit well with it only at the centerline of the channel. A strong wall effect exists on the turbulence intensities in the outer region.
Sedimentumleitstollen leiten die sedimentreichen Hochwasserspitzen um die Tal-sperre herum in den Unterlauf des Flusses und verhindern so eine fortschreitende Verlandung des Stauraums. Aufgrund der hohen Fließgeschwindigkeiten und gro-ßen Sedimentfrachten in Umleitstollen weisen diese starke Verschleißerscheinun-gen auf, die zu hohen Unterhaltskosten führen. Es gibt verschiedene Konzepte um diesem Problem entgegen zu wirken. Einerseits kann der Umleitstollen hydrau-lisch optimiert werden, um die Belastung auf die Sohle zu minimieren. Auf der anderen Seite kann der Widerstand der Stollensohle verbessert werden. An der Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie (VAW) der ETH Zü-rich werden zur Zeit zwei Forschungsarbeiten durchgeführt, die sich diesen zwei Aspekten widmen. In großskaligen Laborversuchen erfolgt eine systematische Untersuchung und Optimierung der maßgebenden Parameter wie Fortbewegungs-art des Sediments und Abrasionstiefe der Stollensohle. Anhand von Prototypver-suchen im neu errichteten Sedimentumleitstollen Solis in Graubünden (Schweiz) werden die Zusammenhänge zwischen Beanspruchung, Materialeigenschaften und Abrasion im Prototyp ermittelt. Darauf basierend können Empfehlungen be-züglich Materialwahl, konstruktiver Durchbildung und Dimensionierung abgege-ben und so zu einer nachhaltigen und wirtschaftlichen Wasserbewirtschaftung in Stauseen beigetragen werden.
The Gaulwerk hydropower plant (HPP) has a design discharge of 3.5 m3/s and generates about 6.5 GWh per year. The HPP has been in operation since 1963 and uses the flow of two alpine streams. The HPP impounds a 300 m long reservoir with a 6.50 m high weir. The storage is completely filled with sediments and is classified as a valuable habitat for fauna and flora. Due to the sedimentation, the area upstream of the reservoir head inundates about two to three times per year during small flood events, leading to complaints from affected landowners and adjacent municipalities. To investigate sustainable solutions, a study of alternatives has been carried out in which three alternatives to im-prove both the sediment and flood situation are being investigated. In addition, the residual flow release will be adjusted and fish facilities realized in all alternatives. The paper will summarize the analysis of the alternatives encompassing the (1)
flood situation, (2) sediment management, (3) reha-bilitation measures of the hydraulic structures and their costs and (4) the environmental impact.
Entlandung des Stausees Solis mit Hilfe eines Geschiebeumleitstollens – hydraulische Modellversuche
(2009)
Das Reservoir der Talsperre Solis in Graubünden wurde 1986 vom Elektrizitätswerk der Stadt Zürich (ewz) in Betrieb genommen. Bei Hochwasserereignissen werden grosse Sedimentmengen in den Stausee transportiert. Über 25 % des ursprünglichen Reservoirvolumens sind bereits verlandet. Aus diesem Grund plant ewz den Bau eines Geschiebeumleitstollens, der das bei Hochwasser ankommende Sediment um die Talsperre herum in Richtung Unterwasser leitet. Die Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie (VAW) der ETH Zürich untersucht und optimiert in einem hydraulischen Modell den projektierten Umleitstollen. Bei Hochwasser wird der Stausee auf den minimalen Betriebswasserspiegel abgesenkt, der Verlandungskörper liegt grösstenteils frei, das Sediment erodiert. Mit Hilfe einer Leitkonstruktion wird die Strömung in Richtung Einlaufbauwerk des Stollens gelenkt und der Abfluss sowie das Geschiebe durch diesen geleitet. Bei Abflüssen, die die Ausbaukapazität des Stollens (HQ5) überschreiten, wird die überschüssige Strömung in den vorderen Bereich des Sees in Richtung Grundablass abgeführt. Das Geschiebe wird dennoch nahezu vollständig in den Stollen eingeleitet. Bei Hochwasser mit Schwemmholzaufkommen wird mit Hilfe einer Tauchwand sowie einer Teilablleitung des Hochwasserabflusses in den vorderen Seebereich verhindert, dass Schwemmholz in den Umleitstollen
eingezogen wird.
Without adequate measures, reservoirs are not sustainable, neither the
reservoir itself due to continuous sedimentation, nor the downstream ecosystem due to altered sediment continuity. Appropriate actions are inevitable and require a systematic sedimentation management. Sediment bypassing constitutes one effective strategy that routes sediment load around reservoirs during floods. A sediment bypass system has the advantage that only newly entrained sediment is diverted from the upstream to the downstream reach thereby re-establishing sediment connectivity. Hence, such a system contributes to a sustainable water resources management while taking the downstream environment into consideration. This paper gives a state-of-the-art overview
encompassing design, bypass efficiency, hydraulics, challenges due to abrasion, positive effects on both downstream morphology and ecology, and makes design recommendations.
In this paper typical bypass efficiencies of sediment bypass tunnels (SBTs) used to counter reservoir sedimentation are described, distinguishing between two layouts of the tunnel intake. It results that SBTs are an effective measure to reduce the sedimentation of dam reservoirs, particularly of type (A) with intake at the reservoir head. The hydroabrasive wear of tunnel inverts is significant and
has to be mitigated by using adequate invert liners. The invert abrasion can be estimated based on an abrasion model where a correct input value of the bed material resistance coefficient is paramount to limit model uncertainties. Based on abrasion measurements at prototype SBTs typical values of the material resistance coefficient are recommended for high-strength concrete, natural stones and steel liners. The field experiences gathered so far and the comparison of various invert materials suggest granite pavers as a promising lining material for severe abrasion conditions.
Sediment Bypass Tunnels are operated to divert sediment around reservoirs reducing reservoir sedimentation. A major drawback of these tunnels is severe invert abrasion due to high velocity and sediment flows. There is an urgent need to establish innovative measurement systems of sediment transport rates in SBTs. In this paper, three bedload measuring systems, namely hydrophones, geophones, and newly developed plate microphones are introduced and compared. The Koshibu SBT is planned to operate from 2016. Plate microphones combined with geophones and other planned systems are installed in the tunnel. Results of preliminary tests and installation plans of bedload
measurement are presented.
