Case Study Modeling of Sediment Management for the Lavey Run-of-River HPP in Switzerland Martin Bieri 1 ; Michael Müller 2 ; Jean-Louis Boillat, D.Sc. 3 ; and Anton J. Schleiss, D.Sc. 4 Abstract: Reservoir sedimentation hinders the operation of the Lavey run-of-river hydropower plant (HPP) on the Rhone River in Switzerland. Deposits upstream of the gated weir and the lateral water intake reduce the flood release capacity and entrain sediments into the power tunnel. Past flushing operations of the relatively wide and curved reservoir have been inefficient. To improve sediment manage- ment, the enhanced scheme Lavey+ with an additional water intake and a training wall for improving flushing was set up. The performance of the enhancement project was tested on a physical model. For its calibration, sediment transport, deposition, and flushing of the present scheme were investigated and compared with prototype measurements. The enhanced scheme was then analyzed in detail to define the flushing discharge and duration, and define the gate operation to ensure maximal erosion of deposits with minimal water loss. DOI: 10.1061/(ASCE)HY.1943-7900.0000505. © 2012 American Society of Civil Engineers. CE Database subject headings: River systems; Reservoirs; Sediment; Switzerland; Hydro power; Power plants. Author keywords: Run-of-river HPP; Physical modeling; Reservoir sedimentation; Flushing. Introduction Present Scheme Construction of the Lavey run-of-river hydropower plant (HPP) on the Rhone River in Switzerland [Figs. 1 and 2(a)] was completed in 1949. The current existing water intake (subscript TE) on the right river bank supplies the underground power house with a maxi- mum discharge (Q TE ) of 220 m 3 =s. The head varies between 34 and 42 m. Three 31 MW turbine units produce approximately 400 GWh=m 3 =year. At El. 435, the weir has three 13-m wide openings equipped with drum gates. Between gates 2 and 3, a sub- merged training wall with its crest at El. 444 allows equilibrated flow patterns for operation mode and for flood events. The Rhone River at Lavey has a mean annual discharge (Q a ) of 180 m 3 =s. Approximately 50% of the water volume is associated with discharges (Q R ) between 100 and 200 m 3 =s. Flood events re- sulting from heavy rainfall, snow, and glacier melt generally occur in August. The annual flood (HQ 1 ) is approximately 500 m 3 =s. The design flood corresponds to the probable maximum flood (PMF), which authorities in 2008 increased from 1;750 m 3 =s to 1;915 m 3 =s. For technical reasons relating to trash rack blockage, turbining is stopped at discharges (Q R ) greater than 800 m 3 =s. As is often the case for run-of-river HPPs, the Lavey scheme is affected by continuous reservoir sedimentation. According to prototype observations, bed load transport starts at flows greater than 300 m 3 =s, producing 80% of total sediment transport to the reservoir of approximately 25;000 m 3 =year. During the flood event in October 2000, inundations at the dam site at Lavey were nar- rowly avoided. Measurements after the event revealed significant deposits along the entire 3-km length of backwater, which primarily originated from the bed load transport. Significant sediment depos- its up to 8 m thick were detected, especially at the inner river bend of the curve immediately upstream of the weir. In the past, regular flushing was necessary to maintain reservoir volume and to reduce the inundation risk during floods. Every 2 to 13 years, flushing was conducted when the control transversal profile upstream of the weir showed excessive deposition as in 1968, 1969, 1982, 1985, 1990, 1997, and 2005. The efficiency of these flushing operations was always quite low and even decreased over time because a concen- trated stream developed along the outer bank. Sediments were only eroded in front of the weir and near the intake, whereas substantial deposits at the inner side of the curve were not removed. Enhanced Scheme Lavey+ In 2007, the owner of the HPP investigated the enhancement project, Lavey+ [Fig. 2(b)]. In addition to improving sediment management, a parallel supply tunnel will reduce head losses in the existing power tunnel. An additional turbine increases the flexibil- ity of power production. The additional water intake (subscript TN) with a design discharge (Q TN ) of 140 m 3 =s is located 37 m up- stream of the existing intake on the right river bank. The lengthened training wall [D in Fig. 2(b)] and the rounded inner bank create a continuously constricting flushing channel toward gates 1 and 2. These constructive measures should avoid sediment entrainment toward the intakes and promote efficient flushing. To adequately supply the new water intake, the crest of the training wall at El. 444 is lowered to El. 443 for the 44-m long notch [E in Fig. 2(b)]. Behind the training wall, a 13-m wide secondary 1 Laboratory of Hydraulic Constructions, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland (corresponding author). E-mail: martin.bieri@epfl.ch 2 Laboratory of Hydraulic Constructions, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland. E-mail: michael.mueller@ epfl.ch 3 Laboratory of Hydraulic Constructions, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland. E-mail: jean-louis.boillat@ epfl.ch 4 Professor, Laboratory of Hydraulic Constructions, Ecole Polytechni- que Fédérale de Lausanne, CH-1015 Lausanne, Switzerland. E-mail: anton .schleiss@epfl.ch Note. This manuscript was submitted on April 29, 2011; approved on September 14, 2011; published online on September 19, 2011. Discussion period open until September 1, 2012; separate discussions must be sub- mitted for individual papers. This paper is part of the Journal of Hydraulic Engineering, Vol. 138, No. 4, April 1, 2012. ©ASCE, ISSN 0733-9429/ 2012/4-340–347/$25.00. 340 / JOURNAL OF HYDRAULIC ENGINEERING © ASCE / APRIL 2012