About the Climate
Operational hydro-meteorological data
observation stations are of two types, with respect to the data transmission:
- Operational stations transmitting data at real or near real time.
The most important 12 river level gauging stations are transmitting daily data
to the NIMH regional branches and headquarters. The rest 32 the operational stations
are transmitting daily data at weekly intervals. On Wednesday each week NIMH receives
daily data for the previous 7 days. Similarly the groundwater observation stations transmit
daily or weekly data at weekly or monthly intervals from 160 wells and 25 springs.
200 operational rain gauges are transmitting daily precipitation totals every day, when it is raining.
The location of the stations is given on the schemes below.
- Regime stations are not transmitting data. Different paper forms are prepared by the observers
and posted to the NIMH branches at monthly intervals.
Some of the hydrometeorological parameters regularly observed over the
Bulgarian territory are relevant for the analysis of the variability of the groundwater recharge.
Those are: precipitation, thickness of the snow pack, river and spring discharge, and groundwater tables.
General information on the monitoring practices and data pre-processing for those parameters is given below
Discharges are received via rating curve through the observations of the water
levels. The levels are generally observed manually with footgauge by observer at 8 o'clock a.m.
local time. Because of the high variability of the levels in the small basins, mechanical level
recorders are working at approximately half of the stations, using weekly papertapes. Observers
of small amount of stations at larger basins are transmitting daily levels via telegram/telephone,
while their reporting tables are collected monthly by post. Discharges are measured 8-12 times per
year by current meters, or floats in case of dangerous floods. Small springs are measured via
volume method. Most of the stations are equipped with measurement bridges. Cross-section profiles
are measured one or twice per year, which generally do not include the floodplanes. The frequency
of those observations depends on the stability of river bed at the measuring section. Provisional
rating curves are maintained for the cross-sections with daily data transmission, while for all
stations rating curves and daily mean discharges are validated annually. Certain amount of small
river basins having an area of 50-100 km2 are observed above the hydrotechnical structures (dams,
derivation channels), while the others with measuring sections located at the lowlands have an area
of 200-400 to 1000-5000 km2. Reservoir cascades regulate more than 50% of the surface waters.
In most cases groundwater tables are observed using suitable wells constructed
for some other purposes, but not used at present (water supply, exploration, etc.). In a few cases
shallow waters are observed using dug wells in the villages. The NIMH permanent technical staff via
portable instruments once or two times per month measures the levels. In a few cases wells with higher
variability of the levels are observed with mechanical level recorders with monthly papertapes.
Relevant number of stations are transmitting levels monthly for operational purposes, while the
rest of the data are collected annually. Generally all porous and plain karst aquifers are covered
by water level observations.