Effects of Alpine hydropower dams on particle transport and lacustrine sedimentation

Abstract

Abstract. The effects of high-alpine hydropower damming on lacustrine sedimentation and transport of solid particles were investigated in the glaciated Grimsel area and in downstream Lake Brienz, providing quantitative denudation rates and sediment yield on a source-sink basis. A total of 271 kt/yr of solid particles entered the Grimsel reservoirs on average in the last 71 years, mostly by turbiditic underA C H T U N G T R E N N U N G flows that focused sedimentation in depocenters upA C H T U N G T R E N N U N G stream of obstacles such as bedrock ridges, submerged moraines, or dams. This is equivalent to a sediment yield of 2430 t/(km 2 yr) in the catchment (111.5 km 2 ) or a denudation rate of 0.94 mm/yr. A total of 39 kt/yr of the fine fraction (<~4 mm) leave the reservoirs and are transported to downstream Lake Brienz, while 232 kt/ yr of mostly coarse particles are retained, reducing total sediment input of the River Aare into Lake Brienz by two thirds. Modeling the particle budgets in the Aare with and without dams indicates that the fine fraction budgets are only slightly affected by damming, but that the reservoirs cause a shift in seasonal runoff timing resulting in increasing and decreasing particle transport in winter and summer, respectively. Thus, hydrodamming alters mostly deltaic sedimentation in Lake Brienz, where the coarse fraction is deposited, whereas fine grained distal sedimentation and varve formation on lateral slopes are less affected. All varved records of the reservoirs and Lake Brienz that provide sediment rates and grain size records on an annual basis indicate that climate is the main control on these proxies, while, for instance, the onset of pump storage activity in the reservoirs did not impose any significant change in lacustrine sedimentation pattern.

Hydroclimatic control on suspended sediment dynamics of a regulated Alpine catchment: a conceptual approach

“…This is most likely related to the fact that water fluxes downstream of Alpine hydropower dams have lower concentrations of suspended sediment compared to fluxes entering the reservoirs, due to sediment trapping in the reservoirs (Loizeau and Dominik. 2000;Anselmetti et al, 2007). This 5 is in agreement with results of the sediment fingerprinting analysis recently performed in the catchment, which suggests the underrepresentation of sediments originated in the most highly regulated lithological unit .…”

“…It should also be noted that the effect of hydropower reservoirs on sediment storage is grain size dependent (e.g. Anselmetti et al, 2007) and may be substantially 10 different for coarser grains transported as bedload.…”

“…In Alpine environments, it is especially water impoundment and flow regulation due to hydropower production which may substantially influence the suspended sediment regime (e.g. Anselmetti et al, 2007). The impacts of hydropower operations on suspended sediment dynamics may vary substantially between catchments, depending on the specific features of the 25 hydropower system (e.g.…”

Human impact on the transport of terrigenous and anthropogenic elements to peri-alpine lakes (Switzerland) over the last decades

“…Fig. 1 Map of the studied area presenting the old and new courses of the Kander and Aare rivers, the location of the dams mentioned in the text (marked by black rectangles), the location of the sediment cores (indicated by red dots) retrieved from Lake Biel (BIE10-3; this study), Brienz (BR03-10; Anselmetti et al 2007) and Thun (THU07-06; Wirth et al 2011), as well as the location of the Mühleberg nuclear power plant and the gauging stations (grey dots) mentioned in the text. Upper right insert Map of Switzerland indicating mean annual precipitation (1961-1990MeteoSwiss 2012), the studied area (white dashed square) and the catchment area of Lake Biel (non-shaded area) Lake Thun Lake Thun is situated downstream of Lake Brienz along the Aare River course (Fig.…”

A Process–Based Rating Curve to model suspended sediment concentration in Alpine environments

“…(e.g. 10 Jansson, 1996;Finger et al, 2006, Anselmetti et al, 2007, De Girolamo et al, 2015, or for different precipitation intensity ranges (Guzman, 2013). A more direct way of including sediment supply is to add a supply-function to the rating curve for representing the depletion of sediment throughout the hydrological year, as proposed by Van Sickle and Beschta (1983).…”