Characterization of the runoff regime and its stability in the Danube Catchment

Abstract

The main purposes of this investigation were to typify the runoff regime (i.e., the typical timely distribution of their flow discharges within the year) in the various regions of the Danube Catchment, and to determine the areal distribution within the Danube Catchment of various indices, each of which characterize the stability of one selected (or integrated) element of the interannual distribution of the flow discharges in the rivers. The present investigation was carried out as one of the projects of the hydrological co-operation of the 13 Danube Countries in the frame of IHP (International Hydrological Programme) UNESCO. The computations necessary for the investigations were carried out by processing the series of monthly mean discharge values of 206 gauging stations operated on the river network of the Danube Catchment. Data series covering 51 years (1950-2000) or the only slightly shorter length of 42 years could be provided for the majority (95%) of the stations. The identification of runoff regime types and stability is based on the probability of occurrence of six particular hydrological events: the first, second and third greatest monthly mean discharges of the year, symbolized with MAX1, MAX2 and MAX3, and the first, second and third lowest monthly mean discharges of the year, min1, min2 and min3. The numerical results of the runoff regime type identification process can be seen in Table 5.5 and in Annex 3. They are graphically displayed on the map of the Danube Catchment in Annex 2. Eight main runoff regime types and 17 subtypes were found in the Danube Catchment. Various indices characterizing the stability of the runoff regime, N(MAX1), N(MAX2), N(MAX3), N(min1), N(min2), N(min3), along with the synthesizing indices NMAX, Nmin and N R, as defined, after Nováky, by the formulae Eq. (5.2) and Eq. (5.6), were computed and displayed on the maps of Annexes 4-6. © 2010 Springer Science+Business Media B.V.