Greece Reservoir Transparency

For the COVERED subset (~10 reservoirs: 4 EYDAP Athens reservoirs + 6 ADMIE hydropower reservoirs), data publication is daily for all covered. EYDAP publishes daily volumes for Mornos, Evinos, Yliki and Marathon via the OpenWaterAPI. ADMIE publishes daily Excel files with fill percentages for Kremasta, Kastraki, Ladon, Polyphyto, Stratos and Ilarionas. Daily granularity for the typical covered reservoir places this in the 60-79 band (the 80-99 band requires daily for >50% which is achieved, but the public-facing EYDAP portal applies a six-month publication lag, dragging the typical user experience back toward weekly/monthly for the EYDAP subset).

For the COVERED subset, EYDAP provides a genuine REST API (OpenWaterAPI, pilot status) returning JSON, with no registration required and a CC BY 4.0 license — covering 4 of the 10 covered reservoirs. ADMIE provides a file-listing API (getOperationMarketFile) that returns URLs pointing to daily XLS spreadsheets for the 6 hydropower reservoirs — functional but requires two-step download and Excel parsing. The dominant access mechanism across the covered subset is therefore a mix of documented REST API (EYDAP, 4 reservoirs) and structured downloads via XLS (ADMIE, 6 reservoirs), placing this comfortably in the 60-79 band.

Methodology v1.3.0 (capacity-weighted), conservative denominator. Reported Greek national reservoir storage capacity is approximately 11,770 hm³ dominated by Kremasta (~4,750 hm³), Mornos (~780 hm³), Yliki (~590 hm³), Marathon (~41 hm³), Evinos (~330 hm³), plus Kastraki, Ladon, Polyphyto, Stratos, Ilarionas hydropower reservoirs and numerous smaller irrigation/water-supply dams in the EEMF inventory of 135-138 large dams. Applying a +15% conservative uplift to account for the long tail of EYDATAP/local water authority irrigation reservoirs in the Peloponnese, Thessaly and Macedonia, smaller PPC/private hydropower compensation reservoirs not in the ADMIE daily Excel set, and Aegean island potable-water reservoirs that sit above the 10 hm³ threshold but never enter EYDAP's Athens-focused publication, the realistic denominator is approximately 13,600 hm³. COVERED capacity ≈ 7,500 hm³ via EYDAP OpenWaterAPI (Mornos, Evinos, Yliki, Marathon ~1,741 hm³ combined, daily volumes back to 1985) + ADMIE daily Excel publications for the 6 major hydropower reservoirs (Kremasta, Kastraki, Ladon, Polyphyto, Stratos, Ilarionas ~5,700 hm³ combined). coverage = round(100 × 7,500 / 13,600) = 55. The residual gap is the entire long tail of smaller irrigation reservoirs in the Peloponnese and Aegean, plus secondary PPC hydropower facilities not in the ADMIE daily set.

Median historical depth across the 10 covered reservoirs is approximately 14-25 years and falls firmly in the 10-20 year band (80-99). The 4 EYDAP reservoirs have daily volumes back to 1 January 1985 for three of them (Evinos from December 2001), giving 25-40 years per reservoir. The 6 ADMIE hydropower reservoirs have daily fill rates back to approximately 2011, giving ~14 years each. The median across the 10 covered reservoirs is therefore ~14 years (the ADMIE 6 dominate by count). This is an exceptionally long median.

For the COVERED subset, ADMIE publishes daily Excel files for the 6 hydropower reservoirs typically by 01:00 UTC the following day. The EYDAP OpenWaterAPI reports raw daily data, but the public-facing opendata.eydap.gr website applies a roughly six-month publication lag and updates monthly — meaning the EYDAP 4 reservoirs are nominally daily but practically delayed for general users. Researchers and journalists access EYDAP daily data through the API directly. The result is daily cadence for 6/10 covered (ADMIE), with the EYDAP 4 effectively weekly-to-monthly on the public portal. Lands at the boundary of weekly (60-79) and daily (80-99) bands.

No formal published methodology document has been found for either the EYDAP or ADMIE reservoir measurement systems. EYDAP's OpenWaterAPI documentation does not describe how volumes are measured (sensor types, bathymetric curves, uncertainty ranges). ADMIE's XLS files report only percentage fill with no methodological note. Greece's National Monitoring Water Network (YPEKA/IMBRIW) covers 26 reservoir lake bodies but publishes ecological and water-quality results, not storage volumes. The Greek Committee on Large Dams (EEMF) publishes dam capacity metadata but not operational measurement methodology.

EYDAP's opendata.eydap.gr portal offers an explicit English/Greek language toggle and publishes content in both languages. The OpenWaterAPI endpoint is language-neutral (numeric JSON data). ADMIE/IPTO operates a full English-language version of its website (admie.gr/en) including the reservoir filling-rate data section. The ENTSO-E Transparency Platform is fully English. Hydroscope.gr interfaces are primarily in Greek, though the hydroscoper R package translates variable names to English. Methodology and data dictionaries are not published in English.