Isar-Plan – Water management plan and restoration of the Isar river, Munich (Germany)

Munich faces changing rainfall patterns; major Alpine heavy-rain floods in 1999, 2005 and 2013 caused substantial damage in southern Germany. Bavaria's 2016 Climate Change Adaptation Strategy projects a shift of peak areal precipitation from summer to winter and a temperature rise of +0.9 to +1.7C by mid-century, with implications for the hydrologic regime and flood risk.

Improve flood control by increasing water retention capacity of the Isar river stretch in Munich, restore habitat and biodiversity along the river, and improve recreational quality in a dense urban area.

The formerly canalised, 8km riverbed was widened from about 50m to up to 90m, replacing concrete embankments with gravel banks/islands and natural sloping banks, and replacing impassable cross-river sills with fish-passable stone ramps. Dikes were raised/relocated (while maintaining existing tree populations) to keep a 1-metre safety margin above expected flood water levels. Public participation included a landscape design competition for the 1.6km city-centre stretch.

The project cost about EUR 35 million (EUR 28 million construction plus EUR 7 million for contaminated-site and wartime munitions remediation), funded 55% by the Bavarian state government and 45% by the City of Munich. Post-restoration, flood water can run off at up to 1,100 m3/s without damage. The 2005 Isar catchment flood caused comparatively limited damage in Munich versus other affected areas in southern Germany. Bathing water quality was achieved after upgrading wastewater treatment plants along the river with UV disinfection.

Strong cross-stakeholder cooperation and sustained public participation (including the design competition) were key success factors, though the process also involved controversial debate, resolved via a compromise between flood-protection- and renaturation-focused designs. The 11-year implementation phase required adaptive management, notably after the 2005 flood affected project sequencing.