Flood Protection for Munich and Bad Tölz

The Syl­ven­stein­ reservoir lies on the northern foothills of the Alps, around 60 km south of Munich. The dam protects against flooding and reg­u­lates the minimum water level of the river Isar while also sup­ply­ing two power plants. Weilheim water au­thor­ity decided to revamp the dam to ensure its struc­tural sta­bil­ity for future gen­er­a­tions. CDM Smith was com­mis­sioned with the nec­es­sary en­gi­neer­ing services such as property and struc­tural planning, dam sta­bil­ity analysis and land­scape con­ser­va­tion planning as well as site su­per­vi­sion in the 24 Mio EUR project.

A soil cement-filled di­aphragm wall drilled adjacent to the existing loam seal now keeps the 180 m long and 42 m high earth-fill dam wa­ter­tight. The two-phase di­aphragm wall milled into the side rock has a depth of 70 m, an en­gi­neer­ing first in Germany. A new gallery mea­sur­ing three metres across at the base of the dam allows leakage mon­i­tor­ing; any seepage will be caught here and led off via drainage piles at 40 m depth. A vertical shaft and a gallery into the rock provide access from both sides.

The Syl­ven­stein­spe­icher dam rests on alluvial river sed­i­ments con­sist­ing of clay gravel and sand from the Isar River. We used finite element cal­cu­la­tions in planning the dam reinforcement under these ge­o­log­i­cal con­di­tions and studying the in­ter­ac­tions between the struc­ture and its foun­da­tion. Sta­bil­ity analysis has con­firmed that the approach taken by our team was the ideal solution, keeping the Syl­ven­stein reservoir dam safe and secure to protect future gen­er­a­tions from flooding.