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

More documents

Recommendations

Info

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen Due to difficulties to measure certain parameters, models have to be calibrated. During this process, the phenomenon of equifinality can appear: different parameter sets show the same result. Another point of criticism in model developing methods is that parameters for rill hydraulics are often adapted from equations made for describing flow behaviour in rivers. Govers and his colleagues [13, 44] showed that these equations are not suitable for rill erosion processes. Therefore, there is often a mismatch between model results and observed or measured “reality” [43]. Additionally, models only project the concepts of the designer, not necessarily the reality. Herein, there is a reproducibility of the modelling results, contrasting with the measurements, which often have a high inconsistency and can be modelled by a flexible set of input variables. In laboratory experiments, the initial and boundary conditions are well controlled. Soil parameters are well known and rill forms and slope can be adapted to the specific question. Thus, physical laws can be tested/ controlled in a well defined environment. However, Giménez and Govers [5] showed that parameters determined under laboratory conditions are not easily transformable to natural environments. One disadvantage of former laboratory experiments or field observations is that in most cases only total runoff and sediment output are measured while the relative contribution of the individual processes is not considered [45]. Field data is as close as possible to reality. Nevertheless, observations as well as experiments show certain disadvantages: (I) Measurement techniques may disturb the observed processes, (II) time scale of human observations is shorter than that of the process under study, (III) some processes cannot be measured directly or indirectly and (IV) some processes are chaotic and the spatial and temporal variations are difficult to specify [43]. The linear or two-part-linear relationship between soil detachment and hydraulic parameters used in soil erosion models is in most cases deduced from laboratory experiments. The question to be answered is: Are these relationships suitable for erosion processes in natural rills? Thus, the experiments have been accomplished in the field and not in artificial laboratory rills. The setup used enables to measure the input parameters for calculating hydraulic parameters. Therefore, it is no need to build on estimations as it is done in the small number of published field experiments. The advantages of laboratory experiments are combined with the advantage of testing natural rills. That means in all experiments, the same experimental setup was used (similar inflow intensity, same water quantity, same sampling scheme, same measurement of hydraulic parameters) and these experiments have been accomplished under field conditions (no artificial laboratory rills in bulk substrates but 181
Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen naturally developed rills in naturally developed soils). The purpose of the field experiments was to quantify in a detailed temporal and spatial resolution the soil erosion dynamics in natural rills under concentrated flow and to compare the measured sediment dynamics with those calculated by means of the most common detachment and transport equations. The aims of this paper are 1) to elucidate the relationship between hydraulic parameters such as shear stress, unit length shear force, unit stream power, stream power, effective stream power and the Reynolds number and soil detachment in natural rills. 2) An additional aim is to explain the reasons for the obvious problems of the physically based soil erosion models in reflecting the processes in rills. 3) Finally a basic consideration is employed: Are the currently used model approaches able to describe rill erosion with all involved processes in general? The overall aim of this paper is to have a critical view on concepts for modeling rill erosion based on experiments performed in naturally developed rills. 2 Material and Methods Ethics Statement: No specific permits were required for the described field studies. The mayors of the towns next to the study sites or the owners of the fields were informed about the intended activities and were asked for permission. The test sites Freila, Negratin and Salada are abandoned fields which are sporadically used as pasture for goats or sheep and in Belerda the experiment was accomplished on an almond field. The locations Freila, Negratin end Salada are not privatelyowned and permission was granted from the owner of the study site Belerda. None of the study sites are protected in any way and the field studies did not involve endangered or protected species. Study areas: The four study areas in Andalusia are located at Negratin, Freila, Salada and Belerda. UTM coordinates of the tested rills are given in Table 1. 182
Page 1 and 2:
Stefan Wirtz Vom Fachbereich VI (Ge
Page 3 and 4:
Danksagung Danksagung Die vorliegen
Page 5 and 6:
Inhaltsverzeichnis Inhaltsverzeichn
Page 7 and 8:
Inhaltsverzeichnis Abbildungsverzei
Page 9 and 10:
Experimentelle Rinnenerosionsforsch
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138: Experimentelle Rinnenerosionsforsch
Page 187: Experimentelle Rinnenerosionsforsch
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Dipl. Geogr. Stefan Wirtz; Physisch
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?