Germany Reservoir Transparency

Re-verification shows the network of public German reservoir portals is denser than previously credited. Sachsen LTV's Talsperrensteuerzentrale lists 48 facilities (dams, retention basins, reservoirs) with water level, storage volume and inflow/outflow — not the handful documented before. NLWKN Niedersachsen pegelonline has integrated the six Harz reservoirs (Oker, Grane, Innerste and others) with explicit Beckeninhalt (Mio. m³) and Füllgrad (%) on dedicated Speicher pages. Talsperrenbetrieb Sachsen-Anhalt covers 36 dams including Rappbode. Talsperrenleitzentrale Ruhr (9 reservoirs, sub-hourly), Wupperverband Hochwasserportal (14 reservoirs with % and hm³), WVER Eifel-Rur server.wver.de/pegeldaten (6 reservoirs incl. Rurtalsperre Schwammenauel ~203 hm³, ~2h updates), Aggerverband GIS (Wiehl, Genkel, Agger fill levels), Thüringen HNZ (11 reservoirs), Rheinland-Pfalz Wasserportal (water-level/discharge for hundreds of gauges incl. reservoir outlet stations), and LUBW HVZ Baden-Württemberg (~250 state gauges) round out a roughly 10-portal landscape. All major named reservoirs (Edersee, Rappbode, Bleiloch, Hohenwarte, Möhne, Bigge, Sorpe, Rurtalsperre, Sylvenstein, Schluchsee, Forggensee) have at least one public fill-level source. Still no national aggregation: DTK's Kartenanwendung shows static dam locations, not operational data; BfG WasserBLIcK is a reporting platform, not a fill-level feed; LAWA coordinates but does not publish operational storage.

Still the weakest dimension but slightly better than the 2025 assessment. No documented REST API publishes reservoir storage data anywhere — federal or state. PEGELONLINE (pegelonline.wsv.de) remains the only mature national hydrological REST API; the March 2026 ITZBund release added official water-level forecasts and an MQTT subscription channel, but coverage is still federal waterway gauges (~640 stations) only, not reservoirs. The LHP cross-state flood API (hochwasserzentralen.de/developers) returns GeoJSON/JSON/XML for ~1,200 gauges but explicitly excludes water-level and discharge values — only flood classifications, no storage. NLWKN pegelonline has a documented webservice (PDF user-guide) but the reservoir Speicher pages display data without a documented JSON endpoint. Rheinland-Pfalz Wasserportal offers a download-assistant covering thousands of time series in standard formats — no registration required, but UI-driven not programmatic. GKD Bayern allows CSV download per station. A community Go proxy (marians/lanuv-nrw-water-level-api on GitHub) exists for LANUV NRW but is unofficial. All operational reservoir portals (LTV Sachsen, Talsperrenleitzentrale Ruhr, Wupperverband, WVER, Aggerverband GIS, TSB Sachsen-Anhalt, Thüringen HNZ) are browser-rendered tables with no documented machine-readable endpoints.

Conservative capacity-weighted estimate applied 2026-05-29. Numerator/denominator: n_covered ≈ 130 / n_total ≈ 200 reservoirs >10 hm³ per GRanD cross-reference and the ESSD 2021 GFZ inventory filtered for permanent reservoirs above threshold (concentrated in Sachsen, NRW, Niedersachsen/Harz, Sachsen-Anhalt, Bayern and Thüringen). Länder portals (Sachsen LTV, NRW Ruhrverband/WVER/Wupperverband/Aggerverband, NLWKN Harz, Talsperrenbetrieb Sachsen-Anhalt, Thüringen HNZ, GKD Bayern, LUBW Baden-Württemberg, Hessen Edersee) collectively cover the strategic reservoir estate. Applying conservative downward adjustment (~-10 points) to recognise structural gaps: (1) many Bavarian small reservoirs not in GKD's main portal, (2) private hydropower operators (E.ON/Uniper/VERBUND/Vattenfall) publish no operational fill data for their dispatch-relevant reservoirs, (3) Hochwasserrückhaltebecken just above the 10 hm³ threshold are inconsistently reported. coverage = round(100 × 130 / 200) = 65. Germany still ranks high in absolute terms but the federalism-driven gaps in private hydropower and small Länder structures are real.

Where historical data exists, depth remains substantial — and Rheinland-Pfalz's Download-Assistent is a stronger asset than previously credited, exposing thousands of time series for water level and discharge across decades, accessible without registration. GKD Bayern's per-station total-period downloads (e.g. Walchensee from 1975) still exist; NLWKN pegelonline Speicher pages now expose 24h/7d/30d diagrams plus extreme values reaching back to the 1950s for Harz reservoirs. Harzwasserwerke TALIS still shows statistical summaries from 1958. Bulk multi-reservoir historical download remains absent at most portals — Sachsen LTV, Wupperverband, WVER and Talsperrenleitzentrale Ruhr expose only current snapshots or short rolling windows for storage volume. The ESSD 2021 GFZ inventory provides static metadata (height, volume, construction year) for 530 dams as a downloadable dataset. No portal yet offers a one-click multi-decade storage time series across multiple reservoirs in machine-readable form.

Update frequency remains a clear strength and the re-verification strengthens the picture. Talsperrenleitzentrale Ruhr and Harzwasserwerke TALIS publish at 15-minute cadence; NLWKN pegelonline's Harz Speicher pages refresh at the gauge's 15-min rhythm. Sachsen LTV's Talsperrensteuerzentrale page declares hourly website refresh ('Letzte Aktualisierung der Webseite ... Uhr (MESZ)'). Wupperverband Hochwasserportal shows timestamps within the last hour for all 14 reservoirs. WVER pegeldaten updates every ~2 hours. Thüringen HNZ delivers 'ungeprüfte Rohwerte automatically captured and transmitted.' Talsperrenbetrieb Sachsen-Anhalt updates daily. PEGELONLINE federal waterways API delivers minute-cadence raw values plus official forecasts since March 2026. These are genuine operational feeds, not monthly bulletins. Weakness: cadence varies operator-by-operator and several portals do not document the refresh interval explicitly.

Largely unchanged. Capacity figures are published alongside fill levels by all major operators, making percentage calculations verifiable. NLWKN's Speicher pages explicitly list maximum storage capacity, catchment area and operator (Harzwasserwerke GmbH) per station. Sachsen LTV publishes capacity per facility. Wupperverband shows '91% / 21,52 hm³' style dual-format values. The ESSD 2021 scientific inventory (530 dams) remains the strongest single methodological transparency asset, freely downloadable from GFZ Data Services with a citable DOI. Stage-storage curves and exact measurement methodology are not published online by most operators. The standard disclaimer 'ungeprüfte Rohwerte, alle Angaben ohne Gewähr' appears on most state portals — honest, but signals limited QA documentation. DTK's Talsperren-Wiki provides editorial/engineering background but not operational methodology per dam.

Unchanged. The vast majority of operational reservoir portals are German-only. Talsperrenleitzentrale Ruhr, Harzwasserwerke TALIS, NLWKN pegelonline, Sachsen LTV TSZ, Talsperrenbetrieb Sachsen-Anhalt, Thüringen HNZ, Wupperverband Hochwasserportal, WVER pegeldaten and Aggerverband GIS are all German-only. GKD Bayern remains the clearest exception with an English interface (gkd.bayern.de/en/). Ruhrverband and Schluchseewerk AG publish English overview pages but their operational data portals stay German. BfG and LUBW publish partial English front matter. A non-German speaker can read what Germany has but cannot reasonably navigate the data layer.