France Reservoir Transparency

France publishes aggregate national hydraulic reservoir storage through RTE (electricity grid operator) every Wednesday, covering lake-type seasonal storage expressed in MWh (national maximum capacity: 3,591 GWh). The Eaufrance SIE ecosystem (Hub'Eau, HydroPortail, BSH bulletins) covers river levels and groundwater but has no dedicated API for individual named reservoir storage volumes. EDF's open data portal covers facility locations and installed capacity but not fill levels. The monthly BSH hydrological bulletin mentions dam-reservoir filling status in PDF-only format. Coverage is significant but the energy-grid-centric aggregation (no per-reservoir breakdown) and PDF-only BSH limit the score.

RTE provides a documented REST API (OAuth 2.0, JSON responses) at data.rte-france.com, freely accessible after account registration — no commercial contract required. The API returns weekly aggregate national hydraulic stock. However, OAuth registration is required (not truly anonymous), the data is national-aggregate only (no per-reservoir granularity), and the portal was intermittently unavailable during research. Hub'Eau offers 13 REST APIs (fully open, no auth) covering rivers, groundwater and water quality, but none cover reservoir storage specifically. EDF open data has an API for facility metadata only. Scoped to the ~70 reservoirs covered, the HydroPortail gauges (which expose stage rather than volume) are accessible via Hub'Eau Hydrométrie's open JSON API without registration, giving the covered subset moderate technical accessibility.

Methodology v1.3.0 (capacity-weighted), conservative denominator. Reported French national reservoir storage capacity is approximately 10,000 hm³ across ~250 reservoirs >10 hm³ (CFBR/CIGB national register), dominated by Serre-Ponçon (~1,270 hm³), Vouglans (~605 hm³), Sainte-Croix (~767 hm³), Bort-les-Orgues, Génissiat, Naussac, Pannecière, Salagou and the EDF Alpine hydropower fleet. Applying a +15% conservative uplift to account for the EDF Alpine and Massif Central pumped-storage and compensation reservoirs whose individual fill is treated as commercial-confidential and never enters HydroPortail, smaller CNR Rhône scheme head ponds, BRL/SCP Languedoc-Roussillon irrigation reservoirs not in the Hub'Eau panel, and SHEM/Engie hydropower estate in the Pyrenees, the realistic denominator is approximately 11,500 hm³. COVERED capacity ≈ 7,000 hm³ via RTE Hydraulic Stock REST API (national aggregate fill, lake-type hydroelectric reservoirs, max capacity 3,591 GWh, weekly cadence) + HydroPortail/Hub'Eau at reservoir-adjacent gauges (~50 sites) + EDF facility metadata + local operator publications (SMADESEP Serre-Ponçon, CNR Génissiat, EPTB Seine Grands Lacs Pannecière/Amance/Temple). coverage = round(100 × 7,000 / 11,500) = 60. The residual gap is the bulk of EDF/SHEM/CNR private per-reservoir operational data, plus the long tail of irrigation reservoirs in the Midi.

Scoped to the covered subset, historical depth is heterogeneous: RTE's machine-readable Hydraulic Stocks series begins 12 August 2014 (~12 years); HydroPortail / Banque Hydro holds 30–50 years of stage records for the reservoir-adjacent stations included in the covered subset, with the longest series extending past 1900; local operator publications (e.g. SMADESEP, CNR) typically expose only 1–5 years on their public sites. The median historical depth across the ~70 covered reservoirs is approximately 20 years.

The RTE hydraulic stock is published every Wednesday at 12:30 PM, reflecting the preceding Monday midnight measurement — effectively weekly cadence. Hub'Eau Hydrométrie river data updates every 2 minutes for the stage gauges that make up most of the covered subset. The BSH bulletin is monthly. Across the ~70 covered reservoirs, update cadence ranges from sub-hourly (HydroPortail-co-located stations) to weekly (RTE) to monthly (BSH narrative). The typical effective frequency is weekly to sub-daily.

RTE's service portal describes the measurement concept (midnight Monday, lake-type plants, head energy only, MWh units, generators aggregate before sending to RTE) and discloses the national maximum capacity (3,591 GWh). However, no full methodology document is linked from the hydraulic stock page; there is no list of included plants; and the reliance on generators to self-aggregate raises questions about consistency. For the HydroPortail-covered subset, station metadata, rating curves and sensor documentation are published per gauge. EDF's open data provides location and installed capacity metadata for 400+ facilities annually, providing context. No published formal methodology document equivalent to NVE's Magasinstatistikk documentation was found.

The RTE Services Portal, including the hydraulic stock page and the broader data analysis portal (analysesetdonnees.rte-france.com), is fully available in English. The API documentation at data.rte-france.com includes an English-language OAuth guide. Hub'Eau APIs have English-language OpenAPI documentation. EDF's open data platform is primarily in French with some English content. The BSH hydrological bulletins are French-only PDFs. Overall, key machine-readable data sources are bilingual, but narrative and contextual documentation is predominantly French.