Multidecadal Sediment Balance Modelling of a Cascade of Alpine Reservoirs and Perspectives Based on Climate Warming

Sebastián Guillén-Ludeña,Pedro Manso,Anton Schleiss

doi:10.3390/w10121759

Sebastián Guillén-Ludeña, Pedro Manso + Show 1 more

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https://doi.org/10.3390/w10121759

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Abstract

This paper presents a comprehensive methodology to model and determine the annual sediment balance of a complex system of interconnected reservoirs, based on the detailed interpretation of a multi-decadal data series of reservoir management and modelling of sediment fluxes. This methodology is applied to the reservoirs of Oberaar, Grimsel, Räterichsboden, and Trift, which are located in the Swiss Alps. Additionally, the effects of climate warming on the annual sediment yield are investigated. Modelling results show that at present, the hydropower cascade formed by Oberaar, Grimsel, and Räterichsboden retains about 92% of the annual sediment yield, of which only the finest fraction leaves the system and enters the river network. Very fine sediments (d < 10 μm) account for 28% of the total sedimentation rate and in the case of Oberaar, it can reach up to 46% of the total sedimentation rate. Under a climate warming scenario, both sediment yield and runoff are expected to increase in terms of the annual average throughout the XXIst century, which will likely lead to greater annual inputs of sediments to the reservoirs. This, in turn, will lead to a higher sedimentation rate and suspended sediment concentration in the reservoirs, unless active management of the sediment fluxes is implemented.

Highlights

Reservoir sedimentation is at present a major concern in the operational management of dams, as the volume of sediments deposited annually in water reservoirs reduces their storage capacity and may even threaten the operability of dams and their sustainability [1]
The results obtained for these catchments by other methods, such as the Universal Soil Loss Equation (USLE) [20] and that proposed by Gavrilovic
The results show that the annual balance of sediments exchanged between Oberaar and Grimsel through Grimsel 2 is nearly nil (Figure 6b) as the sediment volumes transferred from Oberaar to Grimsel in turbine mode are equivalent to those sediment volumes transferred from Grimsel to Oberaar in pumping mode (Figure 6b)

Summary

Introduction

Reservoir sedimentation is at present a major concern in the operational management of dams, as the volume of sediments deposited annually in water reservoirs reduces their storage capacity and may even threaten the operability of dams and their sustainability [1]. In Alpine rivers where the catchments are partially covered by glaciers, the sediment load supplied by small creeks to the rivers is characterized by a high concentration of suspended sediments [7,10,11,12,13], mainly in the spring and summer time. When these fine sediments enter a reservoir, they plunge beneath the clear water surface owing to their higher density, thereby forming a turbidity current that progresses downstream to the dam [1,14,15]. The presence of fine sediments in the vicinity of the dam may result in partial or total blockages of the water release structures, and in turbine

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