Stefan Wirtz Vom Fachbereich VI (Geographie/Geowissenschaften ...

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Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen much degraded, that the most erodible material is removed and the rill's bottoms still reached the Flysch-plates . But it is a fact, that even in the slump material rills are developed. But for developing or increasing much higher water quantities and runoff intensities are needed. Considering the influence of initial soil moisture, one experiment consists of two runs. The influence of initial soil moisture was accounted by GOVERS et al. (1990) and GOVERS (1991). In their experiments under dry conditions the sediment concentrations almost reached the runoff's transport capacity, under higher initial soil moistures, the sediment concentrations were lower. In the rill experiments in the Arnás-catchment, the transport capacity was not reached because of the lack of transportable material and the low water amount. The influence of the initial soil moisture was clearly to notice, in the second run under saturated conditions the flow velocities and the runoff values were higher than in the first run with a soil moisture of about field capacity caused by snow melt . The starting moistures of the rainfall simulations were between 22 and 24 grav. %. But some experiments also show higher sediment concentrations under the higher initial soil moisture conditions in the second run (almost saturated). Under wet conditions, the flow velocities are higher and the cohesion forces are weaker, but there is less loose material in the rill. Under dry conditions, (in this case: less wet) the sediment concentrations are higher if there is a high quantity of lose material in the rill, if all this material is removed in the first run and if the higher flow velocities in the second run cannot cause an incision into the rill’s bed. 5 Conclusion Three rill experiments according the described method were executed in the Arnás-catchment in the Pyrenees. In these experiments, as well naturally developed rill, anthropogenically induced rills like rills developed from motorcycle trails as real lanes were tested. The used 72 liters of water, that were disposed with an intensity of 9 l min -1 into the rill, caused material loss in the rill, but the dimensions were really different. There were samples without detectable sediment, the highest sediment concentrations reached values of 6.31 g l -1 . These results indicate that in the Arnás catchment, the rills have developed and are still active today under higher runoff intensities than the ones used in the experiments. From the induced 72 l of water, between about 8 and 49 l reached the end of the test length, what means a rate between 11 and 68 %. Is the passed flow length accounted, r-l-factors of between 2.1 and 17.1 were calculated. This factor is necessary, because in the third 91
Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen experiment, the flow length was reduced from 25 m to 15 m for accounting the given conditions. It is clearly to detect, that the different rills have a different efficiency for runoff and sediment budget. By recording the flow velocities, slope, sediment concentrations and runoff values, the behaviour of the three tested rills in the Arnás catchment could be comprehended. But the results can only be applied to this three tested rills, it is not possible to give a statement about the behaviour of rills in a catchment. Despite similar experiment conditions, the factors slope, different development state of the rill (depth and width) and position of the rill in the landscape determine the behaviour of the rills. The furthermost developed rill shows the lowest r-l-factor, the water can’t reach the measuring point after 15 m in the first run. So, it must be assumed, that this rill has formed under much higher rainfall-runoff situations as simulated in the experiments. It is necessary to go on testing rills with a standardised method like the rill experiments to collect more information about a rill's behaviour concerning runoff and sediment transport, and maybe to give universal statements. This rill experiments offer qualitative or semi-quantitative analysis of single rills. References - BRUNO, C., DI STEFANO, C. & FERRO, V. (2008): Field investigation on rilling in the experimental Sparacia area, South Italy. - Earth Surface Processes and Landforms 33: 263-279. - BUTZEN, V., SEEGER, M. & CASPER, M. (2009 submitted): Spatial pattern and temporal variability of runoff processes in Mediterranean Mountain environments - coupling experimental measurement and GIS-analysis. - Zeitschrift für Geomorphologie; submitted. - CALVO -CASES, A., GISBERT, J.M., PALAU, E. & ROMERO, M. (1988): Un simulador de lluvia portátil de fácil construcción. - In: Sala, M. & Gallart, F. (eds.): Métodos y técnicas para la medición en el campo de processo geomorfológicos: 6-15. - CASALI, J., LOIZU, J., CAMPO, M.A., DE SANTISTEBAN, L.M. & ÁLVAREZ- MOZOZ, J. (2006): Accuracy of methods for field assessment of rill and ephemeral gully erosion. - Catena 67: 128-138. - CERDÁ, A. & GARCÍA-FAYOS, P. (1994-95): Relaciones entre las pérdidas de agua y semillas en zonas acarcavadas. Influencia de la pendiente. - Cuadernos I Geográfica 20-21: 47-63. 92
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Stefan Wirtz Vom Fachbereich VI (Ge
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Danksagung Danksagung Die vorliegen
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Dipl. Geogr. Stefan Wirtz; Physisch
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Stefan Wirtz Vom Fachbereich VI (Geographie/Geowissenschaften ...

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