Vízügyi Közlemények, 2003 (85. évfolyam)
2. füzet - Zellei L.-Sziebert J.: Dombvidéki vízfolyások medre és hullámtere vízszállító képességének vizsgálata
240 Zellei L.—Sziebert J. The water carrying capacity of earth channels may change substantially in function of their vegetation growth and other parameters. The value of hydraulic roughness is an important item in both the planning phase and in the determination of the flow carrying capacity of the channels. The actual flow carrying capacity depends on: the bed material, the sediment particle size, the shape and irregularities of the cross-section, the hydraulic character and the velocity of the flow, the slope of the channel side, the aquatic and river-bank vegetation their size and its density. The factors affecting the vegetation, such as soil type, supply of water, seasonal variation, nutrient content of the water and the weather, are also defining the flow carrying capacity. A given channel section is characterised by the maintenance-period and thus by the seasonal water regime. The watercourses included in the study are shown in Table I. In order to be able to compare different cross-sections the parameters are represented by their relationship to the medium depth h m. In the case of the smoothness factor the к '=f(h„) relationship has shown a wide variance, especially in the low flow domain. Thus the relationships were defined for the weighed points of water depth zones or bands (that of 0.1 m) (Figure 4.). Time series were also separated according to periods of time, as it was indicated by their periodic variations, thus deriving seasonal relationships for the various factors. In order to characterise seasonal variations spring-summer (months 04-10) and fall-winter (months 11—04) periods were separated. In processing the 10-14 years data of the 7 reaches of 6 watercourses we had to make several compromises for nearly all factors. We had to exceed the minimum reach lengths (50—200 m) specified for the distance between measured cross sections at slope domain of 5=0.5—2.0 m/km. We also had to disregard the requirement for identical flow pattern, varying slope, tributary water courses and the lack of cross-section data. The method of the data processing is shown for the creek Karasica (on the S-W slope of the Mecsek mountain) for its reach between Szederkény and Kátoly, using the data of 1989—1998. As the data of Figure 1. indicates the measurements were made mainly at identical water depth. The area-function fitted to the data allows an extrapolation also to the results of the low number of high water measurements The function k-k', shown in Figure 2, justifies the selection of the mean water depth and indicates that the values of the smoothness factor k' should be decreased by 10% when making transformation for the actual smoothness factor k. Figure 3, showing the measured data of the smoothness factor and the various hydraulic parameters, indicates that starting with 01, 01, 1994 there was a significant change in the smoothness, along with the changes of the intensity of the water regime. Figure 4 shows the reach smoothness factors in function of the mean depth. The values are splitting into two distinct groups in function of the time, thus indicating the changes of the channel, Figure 5 , showing the results made with seasonal separation of the data, does not allow the identification of any unambiguous relationship. The smoothness decreases to a small extent with the increase of the mean water depth from about 50 m ,/ 3/s to 25 m 1/ 3/s, above 0.8 m mean depth. This is indicated by Figure 6, which is a summary relationship between channel smoothness and mean water depth. The depth dependent smoothness corrected version of the flow rating curve shown in Figure 7 shows, when compared with one made by extrapolating for the high water domain on the basis of measurements made mainly low and mean flow regime, that in the high water regime the water carrying capacity increases only moderately. The relatively low number of high-flow measurement data confines the reliability of these conclusions. This is well indicated
