Derivation of basic hydrological data (M-day discharges) for the reference period 1991–2020 in the Czech Republic

According to the standard CSN 75 1400 "Hydrological data of surface waters", M-day discharges are among the basic hydrological data. The Czech Hydrometeorological Institute is responsible for deriving and providing these basic hydrological data.

The objective of the research was to derive basic hydrological data of low flows for description of the hydrological regime, to propose new methodological procedures for deriving basic hydrological data, which include the long-term average discharge Qa and M-day discharges. These data are, among other things, the basis for decision-making of water authorities. Updated information of the hydrological regime will serve to improve planning in the water sector and will contribute to maintain and improve water management as a key commodity for preserving and increasing the quality of life.

The paper presents methodical approaches used to derive basic hydrological data of low flows in the network of water gauging stations in the Czech Republic. Statistical processing used a five-parameter log-normal distribution (LN5), which is essential for accurate representation of extreme values ​​in hydrology. Furthermore, the paper shows the input data that went into the derivation and presents the resulting database of basic hydrological data for unobserved catchments.