Abstract
Abstract. Based on an inventory of 69 dams formed by rock slope failures in southwestern Norway and published inventories from other parts of the world, we developed semi-empirical relationships linking the maximum dam height (HD.max in metres) to dam volume (VD in 106 m3) and other relevant parameters such as valley width (WV in metres) or dam area (AD in square kilometres). Power laws are obtained for HD.max=f(VD) and HD.max=f(VD, WV), while a linear relationship links HD.max to the ratio VD∕AD. For dams in southwestern Norway, the linear relationship HD.max=1.75×VD/AD has the least uncertainties and provides the best results when comparing predicted dam heights with a validation dataset composed of existing dams in northern Norway and numerically modelled dams for possible rock slope failures. To assess the stability of future dams, we use the predicted dam heights in the dimensionless blockage index (DBI) and relating this index to the probability of dam failure derived from our dataset and other published databases on landslide dams. This study underlines the potential of semi-empirical relationships for assessing dam height and stability that needs to be included in preliminary hazard and risk assessment for unstable rock slopes, because damming of a river is an important secondary effect of landslides due to upstream flooding and possible outburst floods in the case of dam failure.
Highlights
Landslides, and more large rockslides and rock avalanches, have formed natural dams in many mountainous regions (Korup, 2002; Casagli et al, 2003; Evans et al, 2011; Hermanns et al, 2011a; Weidinger, 2011; Dufresne et al, 2018)
Many historic events of landslide dam failures are reported to have occurred within a few days to years after a landslide event, causing catastrophic outburst floods in the valley downstream of the dam (Groeber, 1916; Hewitt, 1982; Costa and Schuster, 1988; Evans, 2006) and leading to major destruction and loss of life (Evans et al, 2011)
Systematic mapping of rock slope failures (RSFs) dams in southwestern Norway was carried out by Jakobsen (2015) using the online orthophoto map service “Norge i bilder” (Norwegian Mapping Authority, 2020b) and its associated web map service (WMS) in a geographical information system (GIS) (Fig. 1b)
Summary
Landslides, and more large rockslides and rock avalanches, have formed natural dams in many mountainous regions (Korup, 2002; Casagli et al, 2003; Evans et al, 2011; Hermanns et al, 2011a; Weidinger, 2011; Dufresne et al, 2018). Many historic events of landslide dam failures are reported to have occurred within a few days to years after a landslide event, causing catastrophic outburst floods in the valley downstream of the dam (Groeber, 1916; Hewitt, 1982; Costa and Schuster, 1988; Evans, 2006) and leading to major destruction and loss of life (Evans et al, 2011). Most of them were earth and debris slides (153) and only 22 events were rockslides or rock avalanches Many of those events created only minor damming of rivers without significant consequences. There were several major events with significant consequences in terms of loss of life or long-lasting landscape changes: the worst natural disaster in Norway’s history occurred on 21 September 1345 when the Gaula River was dammed by a massive debris slide that created a 14 km long lake. In 1823, a rock avalanche dammed the Frondøla River and formed the Lintuvatnet Lake
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