Vízügyi Közlemények, 2003 (85. évfolyam)
3. füzet - Rövidebb tanulmányok, közlemények, beszámolók
Magyarország belvíz-veszélyeztetettségi térképe 521 Map of excess water inundation-prone areas of Hungary by Dr. Imre PÁLFAI С. E. In order to provide a map of the excess water inundation-prone areas of Hungary one has to define first the drainage basins of the flat-land parts of the country. These areas fall mostly onto the Alföld (Great Plains) and Kisalföld (Small Plains), while there are smaller ones along the rivers Dráva, Sió-Sárvíz, Kapos and around Lake Balaton. The required specific flow-carrying capacity of the excess water drainage canals have been determined for 80 drainage basins, on the basis of data on soil, precipitation and catchmcnt geometry. On the basis of this data one may estimate the danger of inundation in an approximate manner. The construction of the map of excess-water inundation danger consisted of two steps, in the first step the number of inundation events were determined for each site on the basis of the records of 1961-1980. Dividing this number by 20 one obtains the relative frequency of occurrence of inundations. These were listed in Table I into four categories, along with a qualification text. By marking the patches of these categories in different way one obtains the "excess-water frequency" map, which may be called the first approximation to the map of excess water inundation danger. In the second step the base map of "excess-water frequency" was draped over the maps of the terrain (contour line maps), soil, ncar-surface-geology and of the shallow groundwater table. The maps of land uses, wetlands and canals were also used in the same way. After each drape-over certain corrections of the base map were made, taking the possibilities of occurrence of excess water inundation into account. A sample of the map produced in this way is shown in Figure 1. This is the "final" result, which still needs some polishing. On the basis of the map of the excess water inundation-danger of Hungary one finds that a significant part (round 60%) of the flat-land regions of the total of 45,000 km' of Hungary is substantially endangered by excess water inundation. This means that in the case of an unfavourable coincidence of meteorological and hydrological factors an enormous part of this area may be inundated. The highly endangered (Zone 4) areas are found in small patches, but mostly in the lower parts of the river valleys. Their total area is 2,300 km : or 5% of the total flat-land area The areas of medium inundation danger (Zone 3) fall around the former ones, but cover a substantially larger region, a total of 11,800 km 3 . The area moderately endangered by excess water inundation (Zone 2) covers 12,900 knv, the 29% of the total area. The excess water-free, hardly endangered area (Zone 1) covers 18,000 km J. which is 40% of the total flat-land region. On the basis of the map of excess water inundation-prone areas of Hungary one is able to define the danger of excess water inundation of a given area (a drainage basin or an administrative unit) with a single index value (termed BV). This is done in such a way that the mean of the upper and lower limit values of the relative frequencies given in Table I were weighed according to the areas involved (equation 1). The national average value of excess water inundation index BV, as obtained from Figure / and from the map, is round 8.0. In evaluating the excess water inundation danger of a given area and in making the relevant water management, drainage and land-use decisions, one should also consider, in addition to index BV, the value of the arable lands of that area. The inner parts of settlements form a special category, for which the national map of excess water inundation danger provides no sufficient information. Therefore individual evaluation of such situations is needed.
