National Hydrogeological Network in Bulgaria

The National Hydrogeological Network (NHGN) in Bulgaria was found in 1958-1961. Nowadays the National Institute of Meteorology and Hydrology is responsible for data collection, processing, maintenance of stations and archives, supplying the state institutions and consumers with data from NHGN, and dissemination of information. Data received from NHGN includes time series for groundwater levels in observational wells and discharge for springs (Orehova & Roussev 2004).

The frequency of discharge measurements using a current meter is mainly once per month. For selected karstic springs, daily data are obtained using rating curves. At some springs the water level is recorded by limnigraph (water-level recorder), at other stations, water level is measured every day by observers. For the majority of the springs the measurements of discharge are made once or twice a month without daily observations of water level.

Water level in observational wells is measured usually once a month. Water level analogous recorders are available only for limited parts of the stations.

Many karstic basins in different parts of Bulgaria give rich material for analyses. Various karstic springs are characterized by a specific regime that represents the dynamics of the recharge and particular structure of the basin. Observational wells in kettles and into alluvial deposits along the rivers are subject to investigations of groundwater regime.

The groundwater quality is determined four times per year for selected springs and pumping stations. Basic chemical components and nitrates are defined.

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