Rosshaupten dam rehabilitation: a project in challenging circumstances

Rosshaupten in Bavaria, Germany, is a central core earthfill dam which has been in service since the 1950s. During regular detailed inspections, the owner and operator noticed that the groundwater monitoring wells recorded a constantly increasing difference in porewater pressure, leading to serious questions over the existing sealing element and the dam foundation. Further measurements from the hydrometric monitoring network, geohydraulic numerical modelling and investigative drilling in the ground strata showed zones of increased permeability and preferred seepage pathways. As a result of these findings, the water level in the reservoir was reduced in 2018 and design work started for rehabilitation measures, grouting, and a two-phase diaphragm wall with maximum depth of 70 m for sealing the dam and foundation. After a year, and € 30 million of investment, the new sealing system was in place to enable full impoundment of Lake Forggensee for the 2019 tourist season.