Flood Protection for Munich and Bad Tölz

Flood Protection for Munich and Bad Tölz
Water Authority Weilheim, Bavaria Lenggries, Bavaria, Germany
The Sylvenstein reservoir stormwater retention basin protects Munich and Bad Tölz from flooding from the Isar. Built in 1959, the dam underwent a revamping project that lasted from 2010 to 2015 to protect future generations.

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.

diaphragm wall depth
drainage piles
access shaft depth

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 construction measures are a technical masterpiece that will have defined new standards.
Heiko Nöll, Senior Project Manager

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.

The new dam is a life insurance policy for the Isar valley and Munich.

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