Switzerland Reservoir Transparency

Scoped to the COVERED subset (~50 BAFU/FOEN lake and reservoir gauging stations). BAFU Hydrodaten publishes water-level time series for approximately 50 lake and reservoir stations as part of its broader ~250-station surface water network. These cover natural Alpine lakes used as managed reservoirs (Lake Lucerne, Lake Constance, Lake Geneva) and some smaller managed reservoirs. Storage is published as water level (m) rather than as storage volume (Mm³) for most stations, reducing immediate usability. The SFOE additionally publishes weekly aggregated hydroelectric storage in 4 regional groups (Central/Eastern/Western/Southern Alps) in MWh — useful for energy monitoring but not individual reservoir tracking. For the typical covered station, daily water-level data is published.

For the COVERED subset: BAFU Hydrodaten offers documented web services and data feeds (CSV, RSS, OGC) for its gauging stations, including the lake and reservoir subset. This is a structured API-like service for the covered subset, although not a formal REST endpoint specifically labelled for reservoirs. The CKAN open data portal (opendata.swiss) provides metadata discovery. SFOE's aggregate weekly data is Excel/PDF only. The dominant access mechanism for the covered BAFU subset is structured downloads + web services — a tier above pure scraping.

Methodology v1.3.0 (capacity-weighted), conservative denominator. Reported Swiss reservoir capacity captured by BAFU/SFOE is approximately 4,000 hm³ across the 48 reservoirs >10 hm³ (Grande Dixence ~400 hm³, Emosson ~225, Mauvoisin ~211, Sihlsee ~96, Lac des Dix, Marmorera, Göscheneralp, Lago di Lei, Mattmark, Lago di Luzzone, Limmern, Lago Bianco, Lac de l'Hongrin and 30+ other major hydroelectric reservoirs above 50 hm³). Applying a +10% conservative uplift to account for smaller operator-owned pumped-storage reservoirs (Axpo, Alpiq, BKW, Repower) only present in the SFOE 4-regional aggregate, plus small Alpine compensation basins and run-of-river head ponds below the headline census, the realistic denominator is approximately 4,400 hm³. Covered capacity through BAFU/FOEN Hydrodaten plus operator publications totals approximately 3,500 hm³ (the ~40 largest reservoirs and managed Alpine lakes — Lac des Dix, Mauvoisin, Emosson, Lac de l'Hongrin, Geneva, Constance, Lucerne, Maggiore, Neuchâtel, Brienz, Thun). Coverage = round(100 × 3,500 / 4,400) = 80. The residual gap is smaller operator-owned pumped-storage reservoirs whose data is captured only in the 4 SFOE regional aggregates, plus minor utility holdings that never enter BAFU's gauging network.

MEDIAN years across the ~50 covered BAFU lake/reservoir stations: BAFU Water Data Online contains multi-decade water-level records for the typical covered station, with many lake gauges (Geneva, Constance, Lucerne, etc.) operational since the 19th century and digitally accessible for 30+ years. Smaller reservoir stations typically have 10–20 years of online series. The typical covered station has approximately 20–30 years of accessible online history, comfortably above the 20-year threshold. SFOE regional aggregates extend back to ~2002 (~24 years) and weekly granularity since 2015.

For the COVERED subset: BAFU Hydrodaten updates water-level data for its gauging network (including covered lake/reservoir stations) at sub-daily intervals — typically every 10 minutes for telemetered stations, with public dashboard refresh every hour or better. Sub-daily/daily refresh applies to >50% of covered stations. SFOE regional aggregates are weekly. The dominant cadence for the covered subset is sub-daily.

For the COVERED subset: BAFU Hydrodaten station metadata is detailed for each gauging station, including coordinates, sensor types, operational dates, and basin characteristics. Measurement methodology for water levels is documented in the broader BAFU hydrometric standards. SFOE documents the 4 regional groupings used for aggregation and the total capacity per region. However, the relationship between individual covered station readings and storage volumes is not openly documented (stage-storage curves for the covered Alpine lakes are not published in a consolidated form), and operator-derived capacity figures for the underlying reservoirs are not consistently exposed.

Scope: all published portals. BAFU Hydrodaten is available in all four national languages (German, French, Italian, Romansh) plus comprehensive English support — the English version is operationally complete. SFOE publishes in German, French and Italian with partial English translation; the hydroelectricity statistics page has English versions of key documents but much detailed documentation and older bulletins are German-only. CKAN opendata.swiss offers English. Overall good multilingual coverage with strong English support on the primary covered-subset portal.