The Danube River and its Basin Physical Characteristics, Water Regime and Water Balance

Abstract

The Danube Monograph (RZD 1986, Die Donau und ihr Einzugsgebiet. Eine hydrologische Monographie. Band I, II, III (The Danube Monograph, German version). Bayerisches Landesamt für Wasserwirtschaft, München) was the first published work derived from the results of the hydrological co-operation of the Danube countries. The Danube Monograph included three chapters:

(1) Physical, geographical and water management characteristics of the river basin.

(2) Water regime of the River Danube and its most important tributaries for the period 1931–1970.

(3) Hydrological balance for the period 1931–1970.

Since the publication of the Monograph several follow-up volumes (please see Chapter 1 of this book, Table 1.3) have been published. These follow-up volumes provide additional studies, more detailed information and studies with an updated database. Thus, some sections of the 1986 Monograph chapters are out of date or to a greater or lesser extent have been improved upon:

• Chapter 1: Additional studies have been carried out (e.g. palaeogeography of the catchments in addition to geography and geology; river training and hydraulic structures), but they do not change the original content. With regard to the number of countries within the catchment’s area it has increased for political reasons.

• Chapter 2 was based on data for the period 1931–1970. However, since its publication new data over a longer period has been collected (with data capture continuing in the future). This led to the publication of an updated study based on the period 1931–1990 in 2004 (RCDC 2004a). However, in spite of a slightly modified methodology some of the former results are still interesting. They will be offered in this chapter together with some results of a few special studies (e.g. flood regime).

• Chapter 3 (Water balance) is not influenced by the updated hydrological database: Between the mean annual discharges of the period 1931–1970 and those of the period 1931–1990 there are only small or minute differences – please see Table 2.1.

An abridged and partly improved version of Chapter 3 of the Danube Monograph (1986) is offered herein (subchapter 2.4). The simplest type of multi-annual water balance, expressing the equilibrium of precipitation P versus evapotranspiration E plus runoff R, has been compiled for the period 1931–1970, first for 47 subcatchments and then for 12 partial national areas, as balance units. For each of these units the regional average values of the three balance components, expressed in mm year^–1, have been determined by transforming the hydrological isoline maps (scale: 1:2,000,000), printed in 1984 in Budapest, into planimetric maps. The errors of balance do not exceed, with a few exceptions, the yearly favourable limit of ±5%.

As hydrologic characteristics, the runoff coefficients were calculated for each balance unit both individually and as a longitudinal function of the whole Danube. The latter also includes the (cumulative) regional average values of precipitation and runoff for the catchments belonging to any arbitrary Danube section. With the help of this longitudinal profile, it was possible to compare the discharges derived from the runoff isoline map with the corresponding values calculated from observed data series of Danube gauges. The result of this comparison was satisfactory, too.

As water management characteristics for each of the 12 national catchments areas, the following indices have been determined: “own” surface water resources; relative contribution to the total water resources of the Danube Basin; and the ratio of “own” to “transit” water resources, the lowest value of the latter characterising the national area of Hungary.

On the basis of the results obtained, it can be stated that the isoline maps, printed beforehand in 1984 as annexes to the Danube Monograph (1986), reflect the regional distribution of long-term average values of the water balance elements in compliance with reality and in comprehensible interrelation. Both the maps and the data in the balance tables derived from the former may be recommended as internationally co-ordinated basic information, reflecting our present level of knowledge. This information may be useful for all further work aiming at water resources development in the Danube Basin.