Detection of lineaments using airborne laser scanning technology: Laxemar-Simpevarp, Sweden

Abstract

The Swedish power industry has been generating electricity by means of nuclear power, and the company Svensk Karnbranslehantering AB (Swedish Nuclear Fuel and Waste Management Co., SKB) manages and disposes of the resulting nuclear waste. SKB’s reference method for disposal involves deposition in a repository at approximately 400–700 metres below ground level (m bgl) in crystalline bedrock. In 2002, site investigations commenced in two municipalities, with the intention of selecting a site for future waste disposal. One of these municipalities is Oskarshamn where the Laxemar-Simpevarp area is located (Fig. 1). In the crystalline bedrock of Sweden, the groundwater flow is almost exclusively restricted to the existing fractures. Hydraulic pathways occur in single fractures in the intact rock, but more extensively in regions of multiple fractures, in “deformation zones”. Many of the deformation zones in the Laxemar-Simpevarp area contain several generations of fractures and may control a major part of the groundwater flow. Light detection and ranging (LIDAR) is a scanning and ranging laser system which determines the distance to the terrain or the target from the instrument (Kraus and Pfeifer 1998; Pfeifer and Briese 2001). Using the data from LIDAR, these deformations zones are frequently manifested as linear escarpments, down to the scale of an individual fracture. However, for the investigated area this effect is occasionally masked, mainly in troughs in the bedrock, by a cover of lateand postglacial reworked deposits. The rock itself has generally only suffered from minor superficial weathering phenomena. Descriptive models are being devised for geology, groundwater flow and biosphere at each site, to assess the long-term safety of the deep repository. The descriptive model of the geology constitutes the basis for SKB’s site descriptive hydrogeological model; of primary interest are large deformation zones, which are defined in space. Some local minor deformation zones will be defined in space (increasingly so as the investigations proceeds), but most of them will be considered as stochastic distributions within the modelled volume together with single fractures (SKB 2004).