Bulgaria Reservoir Transparency

For the COVERED subset (~25 reservoirs from the MOEW 'complex and significant' list that are individually reported, supplemented by NEK hydropower reservoirs), MOEW publishes a daily water status bulletin reporting current storage volume in Mm³ and fill percentage. Daily granularity for the typical covered reservoir places this in the 80-99 band. NIMH additionally publishes daily runoff for 63 hydrometric stations via info.meteo.bg/openData. The MOEW bulletin is HTML/narrative rather than a structured per-reservoir feed, which keeps it from the top band.

For the COVERED subset the dominant access mechanism is the MOEW daily reservoir bulletin published as HTML web pages with no structured download or API endpoint; scraping is technically feasible but undocumented. ENTSO-E Transparency Platform (via ESO Bulgaria) publishes weekly aggregate hydro reservoir filling data (16.1.D) accessible through a documented REST API requiring free registration — but this is aggregate, not per-reservoir. NIMH's info.meteo.bg/openData delivers daily station-level river runoff in CSV/JSON/XML — but for stations, not reservoir volumes. The dominant per-reservoir channel is therefore scrapable HTML, placing this in the 40-59 band.

Conservative capacity-weighted estimate applied 2026-05-29. Numerator/denominator: n_covered ≈ 3,000 / n_total ≈ 6,800 hm³ across ~80 large dams >10 hm³ per ICOLD and the national dam register. Strategic reservoirs (Iskar, Koprinka, Kardzhali, Studen Kladenets, Ivaylovgrad, Belmeken, Dospat, Batak) are individually identified in the MOEW daily bulletin and NEK hydropower publications. Applying conservative downward adjustment (~-6 points) to recognise that MOEW + NEK coverage is strategic-only: many of the ~80 large dams are not in the MOEW daily bulletin individually, and ENTSO-E 16.1.D is aggregate-only without per-reservoir disaggregation. The previous estimate of ~25 individually identified reservoirs sits at the optimistic end; the conservative read recognises that ~20 reservoirs receive consistent daily individual identification. coverage = round(100 × 3,000 / 6,800) = 45.

Median historical depth across covered reservoirs is approximately 3-5 years online. The MOEW daily bulletin online archive appears to cover recent years (at least 2024-2026 visible) and individual reservoir time-series are not directly downloadable beyond the visible web archive. NIMH long-term archives (decades) exist for hydrometric stations and contribute to international networks (DanubeHIS, SeaDataNet, GRDC) but reservoir-specific storage time-series are not in the same machine-readable form. ENTSO-E reservoir filling (16.1.D) provides ~8-10 years of weekly AGGREGATE data, not per-reservoir, so does not lift the per-reservoir median. Sits in the 2-5 years band (40-59).

MOEW publishes the daily water bulletin every working day for the COVERED subset. Multiple dated bulletins were confirmed for March-April 2026, demonstrating consistent daily publication. NIMH open data updates runoff stations daily. The ENTSO-E 16.1.D dataset updates weekly. Daily cadence for >50% of covered places this in the 80-99 band; not 100 because publication is working days only and the data is one day behind.

Bulgaria's water management framework derives from the EU Water Framework Directive, which mandates River Basin Management Plans with documented methodologies. MOEW has published WFD reports describing monitoring network design and data collection standards. Reservoir capacity figures are officially registered; monthly water-use graphs for complex reservoirs are published by MOEW. The specific methodology for calculating fill percentages in the daily bulletin is not explicitly published alongside the data. ENTSO-E's Manual of Procedures documents the 16.1.D methodology for hydro generation aggregates.

The MOEW daily water bulletin is published exclusively in Bulgarian (Cyrillic script). The MOEW website has an English section but reservoir-specific data pages are not translated. English-language summaries appear only via BTA (Bulgarian state news agency) press releases. NIMH's hydro.bg portal has English navigation but operational data pages revert to Bulgarian. The ENTSO-E platform (16.1.D) is fully in English but covers only aggregate hydro filling.