Austria Reservoir Transparency

Scoped to the COVERED subset (~50 reservoir/lake stations published via eHYD): the federal eHYD portal (ehyd.gv.at) publishes water-level time series for approximately 50 Alpine lake and reservoir gauges as part of its ~800-station surface water network, transmitted at 30-minute intervals to the federal database and available as CSV downloads under CC-BY 4.0. For the covered reservoirs, fill data is published as water level (metres) rather than storage volume (hm³), reducing immediate usability. APG/ENTSO-E additionally publishes weekly aggregated national hydro storage in MWh as an EU-mandated single number. Per-reservoir storage in hm³ is not publicly served for any individual Austrian reservoir.

For the COVERED subset (eHYD reservoir/lake stations): eHYD has no documented REST API — access is via web forms and manual CSV downloads, requiring community-built Python tools (hydrogeology-graz/ehyd) for bulk programmatic use. No Swagger/OpenAPI documentation exists. For the smaller APG/ENTSO-E aggregate channel, a REST API does exist (free registration, post-2023 data only), but this covers the national aggregate, not the individual eHYD stations counted in coverage. The dominant access mechanism for covered reservoirs is therefore structured CSV downloads requiring scraping or community wrappers.

Methodology v1.3.0 (capacity-weighted), conservative denominator. Reported Austrian reservoir capacity is approximately 3,200 hm³ across the 21 reservoirs above 10 hm³ — Kölnbrein (205 hm³), Gepatschspeicher (140), Schlegeis (126.5), Aschach (114), Altenwörth (93), Greifenstein (87), Zillergründl (86.7), Mooserboden (84.9), Völkermarkt (83), Wasserfallboden (81.2), Lünersee (78.3), Ybbs-Persenbeug (77), Ottenstein (73), Achensee (66), Finstertal (60), Tauernmoos (57), Freudenau (55), Wallsee-Mitterkirchen (52.5), Durlaßboden (50.7), Abwinden-Asten (48), Melk (45). Applying a +10% conservative uplift to account for high-Alpine compensation basins and pumped-storage upper reservoirs in the Tirol and Vorarlberg (TIWAG, Illwerke, KELAG schemes) that sit just above or near the 10 hm³ threshold and never enter the eHYD public panel, plus small private hydropower head ponds and Salzburg/Carinthia industrial impoundments, the realistic denominator is approximately 3,500 hm³. Covered capacity through eHYD federal portal water-level publication (~15 of the 21 — most major Verbund Danube run-of-river schemes and several Alpine storage lakes) is approximately 2,800 hm³. Coverage = round(100 × 2,800 / 3,500) = 80. The residual gap is operator-owned high-Alpine pumped-storage reservoirs (some TIWAG/Illwerke schemes), small Verbund installations and the long tail of private hydropower estate not in eHYD.

MEDIAN years across the ~50 covered eHYD lake/reservoir stations: eHYD systematically digitises hydrographic records, and most lake/reservoir gauge series have been operational for 15–25 years online, with several extending back to the 1980s. The typical (median) covered Alpine lake/reservoir station has approximately 15–20 years of accessible online series, placing the median in the 10–20 year band. Longer paper records (back to 1893 in some cases) exist but are not consistently digitised across the covered subset. The ENTSO-E national-aggregate stream adds 11 years for the energy channel.

For the COVERED subset (eHYD stations): water-level data is transmitted every 30 minutes to the federal database, and public-facing series are typically refreshed daily on the eHYD portal. This sub-daily-to-daily cadence applies to the typical covered Alpine lake/reservoir gauge, placing the cadence in the weekly-or-better band for >50% of covered. The APG/ENTSO-E aggregate stream is weekly. Daily refresh for the covered eHYD subset is the dominant pattern.

For the COVERED subset: the Austrian Hydrological Atlas documents water balance and gauging methodology comprehensively, and the Austrian Reservoir Commission (OSTAKO) under BMLUK oversees dam safety standards. eHYD station metadata is published per station. However, stage-storage (cota-volumen) curves for the covered Alpine reservoirs are not consolidated in a single public registry, sensor calibration documentation is partial, and the conversion between published water levels and storage volumes is not openly documented for the individual lake/reservoir stations. ENTSO-E does not publish its capacity calculation methodology in accessible form.

Scope: all published portals. The APG Market Transparency Platform (markt.apg.at) is fully English. ENTSO-E is fully English. The BMLUK federal site has English versions of relevant pages. However, the main per-reservoir data portal eHYD (ehyd.gv.at) is German-only — interface, labels and downloads are all in German, though numeric CSV data is language-neutral. Weighted across portals: good English for the energy-side, German-only for the covered hydrological side.