Regional Differentiations of the Suspended Sediment Transport in Thuringia and Their Relation to Soil Erosion
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REGIONAL DIFFERENTIATIONS OF THE SUSPENDED SEDIMENT TRANSPORT IN THURINGIA AND THEIR RELATION TO SOIL EROSION L. BAUER and W. TILLE Germany D.D.R. ABSTRACT During the hydrologie years 1961 and 1962,13 sampling stations within thewatershed of the river Unstrut carried out systematic measurements of the suspended sediment charge. Statistical analysis of the data showed partially significant differences between the mean values of different cross sections (a = 5%) within the area which covers only about 5,000 km2. The functions for estimating suspended sediment discharge, which state the average increase of the suspended sediment discharge in g/s with the water discharge in m3/s, were calculated for 11 cross sections after the simplified method of Remy-Berzen- covich (1960). The parameters 1g b and m of this empirical function of the form Ig Qs = Igb + mlgQ were studied more closely. The parameter Ig b shows a close negative correlation with the long time mean water discharge (r, = —0.836). This is a hint al its strong dependence on the hydrologie conditions of the catchment basins of the sampling stations. The river basins with a high part of triassic limestone (Muschelkalk) and a little catchment basin at the edge of the hercynian mountains with predominantly paleozoical rocks have the highest values for m. The average value of the parameter m for these cross sections is 2,63 as against 1.78 for the remaining cross sections. After the U—test of MANN and WHITNEY the difference is significant (a = 5%). The different values of the parameter m can be explained by the specific mechanism of erosion of the different soils of Thuringia which was studied closely by Werner (1966). In the evaluation of the erodibility of these soils there exists vast agreement between the results of the plot tests made by Werner (1966) and the results of the measurement of suspended sediment described here. Hitherto existing knowledge allows to develop from the functions for estimating suspended sediment discharge, so-called functions for the estimating of washout of the form lg.4 = ]gfr+(»i—1) Ig F^—m(3—Igg). They determine the mean value of washout A in g/s.kms for every value of the runoff per square kilometer q in 1/s.km3. More detailed investigations in the catchment basin of the river Roda (243 km2), about which will be reported later, serve for the further elucidation of the connection between soil erosion and suspended sediment transport. RÉSUMÉ La différenciation régionale du transport des matières solides en suspension par rapport à l'érosion du sol en Thurlnge Pendant les années hydrologiques 1961 et 1962 des mesurages systématiques des teneurs en suspension furent exécutés à l'aide de 13 stations de prélèvement d'échan tillons du bassin versant de la rivière d'Unstrut. L'analyse statistique des observations fournissait en partie des différences notables chez les valeurs moyennes des sections différentes (a = 5%) au dedans du territoire, ayant seulement à peu près 5.000 km2. Avec la méthode simplifiée de Remy-Berzencovich (1960) les« fonctions de matières en suspension » pour 11 stations de la section transversale furent calculées, indiquant l'augmentation moyenne des débits solides en suspension en g/s avec !e débit d'eau en m3/s. Les paramètres 1g b et m de cette fonction empirique de formule lgCs = Igb+mlgQ furent étudiés de plus près. Le paramètre lg b fait voir une étroite corrélation négative avec l'annuel débit moyen (rs = —0,836). C'est une indiquation de la forte dépendance 367 de la situation hydro logique des bassins versants des stations de prélèvement d'échan tillons. Le paramètre m montre une certaine dépendance de la situation pétrographique et pédologique des bassins versants des stations. Les plus grandes valeurs pour m ont donc les bassins versants avec une grandepart de pierre calcaire triassique (Muschelkalk) et un petit bassin versant au bord des montagnes hercyniennes, où des roches palëozoiques sont prédominants. La valeur moyenne du paramètre m pour ces stations est de 2,63 en face de 1,78 pour les autres stations. La différence est suivant le « f-test» de Mann et Whitney significant (et — 5%). Les valeurs différentes du paramètre m peuvent être expliquées parle mécanisme spécifique d'érosion des sols différents en Thuringe qui a été exacte ment exploré par Werner (1966). Au point de vue de l'érodibilité de ces terrains existe aussi un accord profond des résultats des observations par Werner 11966) et les résultats des mesurages des matières solides en suspension présentés ici. Les résultats obtenus jusqu'à présent permettent de trouver en partant de l'estima tion des matières solides en suspension, les fonctions pour l'estimation delà denudation par la formule \gA = lgA + (m-l)lgFN-m(3-l6?) Elle détermine la valeur moyenne de la denudation A en g/s km3 pour chaque valeur de l'écoulement par km2 en 1/s km2. L'étude entre l'érosion du sol et le transport des matières solides en suspension fut poursuivi avec des investigations en détail au bassin versant de la rivière de Roda {243 km2) sur lesquelles un rapport également est donné. 1. INTRODUCTION Studies of the suspended sediment transport of running waters have been carried out in the German Democratic Republic only to a little extent in comparison with various other countries. The important tasks of water management, however, which have to be solved now and in near future, call for more intensive scientific investigations into this hydrologie phenomenon. The systematic establishment of an official obser vation network for suspended sediment discharge measurements has been taken into the Programme of the German Democratic Republic for the International Hydro- logical Decade 1965-75. Recently results of possible importance for our future work have been gained by studies on the suspended sediment transport of some water courses in Thuringia which were carried out independently of the IHD. These studies were limited in time. Measurements of the silt charge have been carried out in Thuringia since I960. Their aim is, in addition to the usual quantitative recording of the suspended sediment transport of the water courses that have not yet been recorded in that respect, to clear up the factors which decisively influence the suspended sediment transport of the rivers in this area. The answer to this questions makes necessary positions of the observation stations which offer the same possibilities for comparison of water courses whose drainage areas show different characteristic features. The geological constitution and in close connection with that the soil conditions are such an important feature in Thuringia. The central part of Thuringia, the Thuringian basin, is geologically clearly divided in consequence of the alveolate occurrence of the 3 epochs of the German Trias (Buntsandstein, Muschelkalk, Keuperl and is bounded in the North and in the South by the paleozoic rocks of the Hercynian and Thuringian mountains. Generally, the soil conditions follow the distribution of the rocks, but they are in detail far more complicated, because often covers of pleistocenic hillside wastes, which are located above the bed rock (Schilling and Wiefel, 1962, Siegel, 1963, Werner, 1964a) and loess covers, especially in the central area, are of importance as being the original substratum for pedogenesis, and not the bed rock itself. The relations between the pleistocenic hillside wastes and the bed rock are close enough, however, to reflect the geological macrostructure in the kinds of soil. Generally sandy to loamy soils correspond 368 to the lower Trias (B un tsand stein), limy-clayey soils to the upper Trias (Keiiper), The loess deposits reach their largest extent in the Keuper area. Therefore, silly soils are very extensive in this area. Under these circumstances the geological macrostructure of the Thuringian basin had to be taken into consideration when ihe observation network for suspended sediment measurements was established, in order to study the possible influence of the rocks and soils. 2. CHARACTERIZATION OF THE SUSPENDED SEDIMENT TRANSPORT IN THE THURINGIAN BASIN The main part of the Thuringian basin is drained by the river Unstrut (6,388 km2). 13 sampling stations were established within this area and one out of it. Altogether they control 5,319 km2. The area of the catchment basins of the stations and their distribution over the most important rock series is shown in table 1. TABLE 1 Area and distribution of the catchment basins of the stations over the most important rock series Area of the Predominant rocks Watercourse Samplingstation catchment basin (km3) Paleozoical rocks (schists, Krebsbach I berg 14 conglomerates, porphy- rites) Lower triassic sandstones Roda Zollnitz 254 (Bun tsand stein) Wîpper KannawuiT 639 Helme Bennungen 897 Middle triassic limestones Linderbach Linderbach 42 and argillaceous rocks Helbe Bliederstedt 260 Unstrut Merxleben 650 Unstrut Nâgelstedt 725 Upper triassic plasterstones Gramme Wer ningshausen 291 and clays incl. larger Lossa Leubingen 392 loess deposits Very different rocks Apfelstâdt Ingersleben I 369 (paleozoic and Trias) Gera Ingersleben II 443 Gera Ingersleben III 812 Unstrut Oldisleben 4,168 When the sampling stations were established the existing gauge network and water management needs (storage reservoir) were also of importance. Therefore, in addition to the most important rocks mentioned above others also occur in ibe drainage basin, 369 though to a lesser degree. Only the catchment basin of the station Roda/Zôllnitz has an ideal structure (only Buntsandstein). The measurements of the silt charge were carried out according to the filter method following the procedure of the Bayerische Landesstelle fur Gewàsserkunde, MOnchen (1952|. The sampling was carried out in all observation stations nearly at the same time, mostly during the two hydrologie years 1961 and 1962. In Thuringia these two years differ clearly from each other in their hydrologie character.