Vízügyi Közlemények, 2004 (86. évfolyam)

1-2. füzet - Konecsny Károly: A 2003. évi nyári aszály kialakulásának időjárási és hidrológiai okai és vízjárási következményei a Felső-Tisza vidékén

A 2003. évi nyári aszály kialakulásának időjárási és hidrológiai okai és 195 In the year 2003 no significant floods were generated under the weather conditions discussed. Larger than average fullness of the channel was observed only in January (Figure 9). The precipitation-free cold weather resulted, as early as in March, in low water conditions. The minimum water stage at station Tivadar of the River Tisza was -255 cm, while the water level stayed below 200 cm in the period 21 February - 04 March (Figure 10). Lower than the observed minimum water levels (H

mj

n) occurred in August at several stations (Table 2). The duration of low water was also significant. At Station Tivadar this lasted for 156 days between May and October. The water level was lower here than the so far observed minimum of-293 cm (in 1942) for 37 days (Figure 10). At station Záhony this lasted for 49 days. New sand bars and isles arose from the water in the rivers Tisza and Szamos in the low water period, piers of old abandoned bridges could also be observed (Figure 11). The low water profile measured on the 28

t

h of August, 2003, indicates varying slopes of the water level with several break-points (Figure 12). Fortnightly flow measurements were also carried out in the low water period (Table 3). In the drought period the discharge was also low but did not fall below the ever-measured minimum Q

mi

n (Table 4). The 100 year annual low flow water level time series show a decreasing linear trend. This is related not only to the decrease of flow but also to the deepening of the channel. At Station Tivadar the decrease of annual minimum water level reached 1.5 m. This decrease is not linear but can be approximated by polynomial regression (Figure 14). For the river Szamos the decrease was also 1.5 m, but here the best fit is achieved by logarithmic trend (Figure 15). In some of the tributaries (rivers Túr and Kraszna) opposite trends can be observed, e.g. the low water levels are rising. In the River Kraszna at station Agerdőmajor the low water level was increased by about 1.0 metre in the period 1948-2003 (Figure 16). Results of the statistical analysis of the low flows of Tivadar station are shown in Figures 17 and 18. A polynomial curve gives the best fit to the series of annual low flows for both the Tisza and its tributaries (Figures 19 and 20). The low flow time series of Agerdőmajor shows a rising trend similarly to that of the water levels (Figure 21). As it was already discussed before (Konecsny 1999, 2000) the increase of the annual low flows at the station Ágerdőmajor is due to human influence in the form of inflow discharges. The probability of the low flows of the River Tisza, measured in August 2003, varied in the range of 69% and 96% (Figure 22). Multi-annual changes of the ground water levels are shown in Figure 23 for the period 1955-2003. In the growing season the moisture content of the upper layer of the soil decreased drastically. This is also indicated by the moisture content of the samples taken in the summer-fall period of 2003 (Figure 24). The drastic summer water shortage was observed also in the water levels of the reservoirs. For example the storage volume of the reservoir Rétköz was decreased to the one-fourth in the period January-August (Figure 25).