DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 13/2005 str. 17 <-- 17 --> PDF |
/ . Vicha: FIFTY YEARS OF THE FORESTRY HVDRO-PEDOLOGICAL RESEARCH WITHIN THE FOREST ... Šumarski list SUPLEMENT (2005). 7-16 RESULTS OF LONG-TERM RESEARCH IN BESKYDY MTS. During the whole period of investigation within the CE basin, the average year precipitation was 1122.4 mm, run-off 646.2 mm, average year flow was 20.5 1 x s"´ x km2. In MR basin the average year precipitation was 1238.4 mm, run-off 912.0 mm, average year flow 28.9 1 x s"1 x km2. In the graphs there are average monthly precipitation and run-off in the period of 1954 to 2003. In Beskydy snow is melting in March to May, the highest precipitation is during the summer months. Water balance in the forest stands, hydrologic ally analysed in detail, is very complicated natural process. It starts in measuring of individual rain, number of days in between them, interception, evapotranspiration, soaking of water in soil, run-off under different climatic conditions, season, and natural conditions. In a strong rain, part of water is soaked by the forest soils, smaller part runs-off, mainly in plots of compacted and stabilised soil surface. Volume of water soaked by forest soils is limited. That is why aerial surface run-off can be observed, when water is concentrated in trenches and water runs. This type of water run-off represents about 15-20 % of the total amount in maximum, ant it is limited to very short time. Higher percentage is represented by fast surface run-off in flooding waves; its development depends on saturation of the basin, volume and length of rain, permeability and depth of the soils, slope inclination, and the tendency to concentrate run-off water. Retention capacity of the soil is confirmed also by the data measured in Beskydy research: Rain intensity over the whole period had hardly exceeded 2 mm per minute, it means 33 nr of water per square km per second, however. The highest specific run-off was measured in MR q= 3,144 m3 x s~´ x km2. This data confirm fast water retention by the forest soil. Some really heavy, sudden rains in Beskydy have resulted in fladdings. Also water culminations exceeding 1000 1 x s"´ x km", are of danger. During the investigation such events were observed 9 times in MR, and 7 times in CE. In MR the highest culmination recorded was after the storm-rain in July 25, 1966, it was already mentioned value of 3,144 1 x s"´ x km2. In CE the highest was culmination of August 1, 1971 - 1,576.,2 1 x s"1 x km2. It was found that for the culmination the level and intensity of given precipitation is decisive. After the regeneration of the mature stands increased number of culmination flow was not proved statistically. In heavy fladdings also branches, parts of the trees etc. are flowing down with water stream. Than sluices, bridges, and whole river and stream beds are filled with that material, water gets out of the banks and the land around can be damaged. To evaluate the small and minimal water runs during the dry period of the year is also useful. Measuring has proved, that such periods are repeated during a year more frequently then fladdings, irregularly, depending on air temperature. They arc lasting mostly several days, as usual; the time is longer in winter, even two months. During the 50 years of measuring the minimal run-off was reaching up to qm}n< 0,5 1 x s ´ x km2, endangering not only the water bio-system, but also water reservoirs in the villages in lower part of the mountains. As mentioned above, in the basin of CE investigation of the run-off water was done within the two pair basins. The research was focused on the problem, whether the different ways of management, and connected different age structure of the stands in the two basins, can be reflected by run-off regime. Evaluating the results of long-term investigation, it can be stated that provable change of the run-off conditions was not observed. Forest regeneration was not connected with the reduction of run-off water, and the older stands left, of higher timber supply, did not show higher run-off. However, it is to be stressed, that in spite of the fact that not significant changes in run-off regime were observed in the stand managed by intensive way of clear- cutting, more sensitive, nature close ways of forest management bring also other advantages, also in water regime. Forest soil is not eroded due to damage by heavy logging mechanisation, soil infiltration capacity is not disturbed, so under-surface water run-off is supported. Also area of bare land, and connected soil erosion after heavy rains, is not that big. This is mainly problem of poor sites, of insufficient vegetation cover, where soil is not covered by grass and weed. The two plots in Beskydy are moderately rich sites, and after felling the soil is covered by grass during several weeks, and thus protected against water erosion. In spite of the fact that negative impact of clear cutting, within the extent given by the law, on water run-off was not proved, other advantages of the nature close management have to be stressed. It is mainly bio-diversity preservation, higher stability of the ecosystem, preservation of genetically valuable material of autochthonous stands, and also higher esthetical and recreation value of forests. More important changes in run-off conditions were observed in the MR basin, where the main tree species beech was replaced by spruce in the regeneration process. During the years of low precipitation, water runoff was higher there. It means that in the warm period of the year water run-off is higher, in the cold period runoff is higher in the years of higher precipitation. Mainly melting snow causes higher run-off in the cold period, richer in precipitation- after stand regeneration more water of it runs-off. It can be said that change of spruce |