Investigations on the Runoff Generation at the Profile and Plot Scales, Swiss Emmental. Badoux, A.; Witzig, J.; Germann, P. F.; Kienholz, H.; Lüscher, P.; Weingartner, R.; and Hegg, C. 20(2):377–394.
Investigations on the Runoff Generation at the Profile and Plot Scales, Swiss Emmental [link]Paper  doi  abstract   bibtex   
This article describes an investigation on runoff generation at different scales in the forested catchment of the Sperbelgraben in the Emmental region (Swiss Prealps) where studies in the field of forest hydrology have a history of 100 years. It focuses on the analysis of soil profiles and the subsequent sprinkling experiments above them (1 m2), as well as on surface runoff measurements on larger plots (50 to 110 m2). In the Sperbelgraben investigation area, two very distinct runoff reactions could be observed. On the one hand, very high production of saturation overland flow was registered on wet areas of gleyic soils, with runoff coefficients between 0.39 and 0.94 for profile irrigation. On the other hand, almost no surface runoff was measured on Cambisols, with the exception at some sites of a hydrophobic reaction detected at the beginning of storms after dry periods (coefficients for profile irrigation: 0.01-0.16). This pattern was observed during 1 m2 soil plot irrigation and on surface runoff plots. Apart from a less distinctive signal of the water-repellent litter layer on the larger surface runoff plots, the dominant hydrological processes at the two scales are the same. The determined runoff reaction at the two scales corresponds well with information from a forest site type map describing soil and vegetation characteristics and used as a substitute for a soil map in this study. Theoretical considerations describing forest influence on flood discharge are discussed and evaluated to be in good agreement with observations. These findings are a sound foundation for application in hydrological catchment modelling. [Excerpt: Discussion and conclusions] Many irrigation experiments have been carried out all around the world. Even though some of these studies were conducted in forested catchments (e.g. Hornberger et al., 1991), most focused on grassland or f armland. Recent investigations in central Europe have been published by Scherrer and Naef (2003), Weiler and Naef (2003) and Markart and Kohl (1995). [\n] The investigations within two subcatchments of the Sperbelgraben at the profile scale show different runoff behaviours of forest soils depending on their soil type and forest site type. Artificial high-intensity precipitation on 1 m2 plots leads to a high proportion of surface runoff (coefficients from 0.39 to 0.94) on humid to wet Gleysols. Such high surface runoff coefficients are rather unexpected for forest soils, which often do not generate any surface runoff at all (e.g. Schwarz, 1986; Kohl et al., 1997; Markart et al. 1997). In contrast, the sprinkling experiments on dry to humid Cambisols result in no or only little surface runoff. For those experiments the coefficients (0.01-0.16) were found to be considerably higher after dry antecedent c onditions than after wet antecedent conditions. This strongly suggests the influence of water repellence. Looking at the corresponding soil profiles, the magnitude of the hydrophobic reaction seems to increase with increasing thickness of the organic horizon (also reported, for example, by Crockford et al. ( 1991) and Scott and Van Wyk (1990)). In the Sperbelgraben, thick organic litter layers are most probable to occur on forest site type 19 (Table II). [\n] On steep slopes, the investigation area features a very high infiltration capacity, a s has already been stated by Engler (1919) a long time ago. An exception is only made where temporary Hortonian overland flow occurs due to hydrophobic conditions. The effect of hydrophobicity is clearly visible at the profile scale, but only to a smaller degree at the plot scale, due to the fact that the thickness and the composition of the litter layer observed on the soil profiles is spatially variable. As reported by Doerr et al. (2003), for example, the influence of hydrophobic topsoils is most distinct at the small scale and decreases with increasing size of the area investigated. We conclude that, because of these spatial limitations and the temporal limitation to the beginning of a rainfall event, temporary Hortonian overland fl ow does not contribute significantly to flood generation. Therefore, it can be ignored in the concept described in the Theory section. These theoretical considerations on the forest influence on floods, though, do not contradict the findings made in the Sperbelgraben at the profile and plot scales. The temporal and spatial variability of the influence of the water storage capacity of a forest soil on runoff generation can thus be explained. [\n] The comparability of responses at the plot and profile scales is limited due to the different approach of the investigations. Whereas at the profile scale the artificial rainfall intensity is identical for all experiments, natural precipitation events are considered at plot scale, and these vary in duration and intensity. Owing to the non-linearity of hydrological processes, it is hardly possible to compare different rainfall events of profile and plot investigations. In addition, boundary effects increase with decreasing size of the areas tested. Their impact at the plot scale is considerably smaller than at the profile scale. Nevertheless, identical hydrological key processes were identified at the two different scales, and surface runoff coefficients are found to be of a similar order of magnitude for experiments on the same forest site types. Thus, we conclude that it is possible to derive qualitative statements on the main hydrological processes occurring in a specific soil type from small-scale irrigation experiments and to transfer them to larger areas under the conditions found in the Sperbelgraben. [\n] The results of the irrigation experiments and surface runoff plots show that the map of forest site types (Burger et al., 1996) is a good tool for the determination of areas with similar hydrological reactions. Its potential even goes beyond a standard soil map, as it also allows one to identify the predisposition of a site for hydrophobic behaviour. Therefore, the inclusion of vegetation information into mapping procedures for hydrological purposes, as is the case with the Swiss forest site type map, seems promising. Since such maps are widely used in Swiss forestry, they represent a potential to improve hydrological catchment modelling.
@article{badouxInvestigationsRunoffGeneration2006,
  title = {Investigations on the Runoff Generation at the Profile and Plot Scales, {{Swiss Emmental}}},
  author = {Badoux, Alexandre and Witzig, Jonas and Germann, Peter F. and Kienholz, Hans and Lüscher, Peter and Weingartner, Rolf and Hegg, Christoph},
  date = {2006-02},
  journaltitle = {Hydrological Processes},
  volume = {20},
  pages = {377--394},
  issn = {0885-6087},
  doi = {10.1002/hyp.6056},
  url = {https://doi.org/10.1002/hyp.6056},
  abstract = {This article describes an investigation on runoff generation at different scales in the forested catchment of the Sperbelgraben in the Emmental region (Swiss Prealps) where studies in the field of forest hydrology have a history of 100 years. It focuses on the analysis of soil profiles and the subsequent sprinkling experiments above them (1 m2), as well as on surface runoff measurements on larger plots (50 to 110 m2). In the Sperbelgraben investigation area, two very distinct runoff reactions could be observed. On the one hand, very high production of saturation overland flow was registered on wet areas of gleyic soils, with runoff coefficients between 0.39 and 0.94 for profile irrigation. On the other hand, almost no surface runoff was measured on Cambisols, with the exception at some sites of a hydrophobic reaction detected at the beginning of storms after dry periods (coefficients for profile irrigation: 0.01-0.16). This pattern was observed during 1 m2 soil plot irrigation and on surface runoff plots. Apart from a less distinctive signal of the water-repellent litter layer on the larger surface runoff plots, the dominant hydrological processes at the two scales are the same. The determined runoff reaction at the two scales corresponds well with information from a forest site type map describing soil and vegetation characteristics and used as a substitute for a soil map in this study. Theoretical considerations describing forest influence on flood discharge are discussed and evaluated to be in good agreement with observations. These findings are a sound foundation for application in hydrological catchment modelling.

[Excerpt: Discussion and conclusions] Many irrigation experiments have been carried out all around the world. Even though some of these studies were conducted in forested catchments (e.g. Hornberger et al., 1991), most focused on grassland or f armland. Recent investigations in central Europe have been published by Scherrer and Naef (2003), Weiler and Naef (2003) and Markart and Kohl (1995).

[\textbackslash n] The investigations within two subcatchments of the Sperbelgraben at the profile scale show different runoff behaviours of forest soils depending on their soil type and forest site type. Artificial high-intensity precipitation on 1 m2 plots leads to a high proportion of surface runoff (coefficients from 0.39 to 0.94) on humid to wet Gleysols. Such high surface runoff coefficients are rather unexpected for forest soils, which often do not generate any surface runoff at all (e.g. Schwarz, 1986; Kohl et al., 1997; Markart et al. 1997). In contrast, the sprinkling experiments on dry to humid Cambisols result in no or only little surface runoff. For those experiments the coefficients (0.01-0.16) were found to be considerably higher after dry antecedent c onditions than after wet antecedent conditions. This strongly suggests the influence of water repellence. Looking at the corresponding soil profiles, the magnitude of the hydrophobic reaction seems to increase with increasing thickness of the organic horizon (also reported, for example, by Crockford et al. ( 1991) and Scott and Van Wyk (1990)). In the Sperbelgraben, thick organic litter layers are most probable to occur on forest site type 19 (Table II).

[\textbackslash n] On steep slopes, the investigation area features a very high infiltration capacity, a s has already been stated by Engler (1919) a long time ago. An exception is only made where temporary Hortonian overland flow occurs due to hydrophobic conditions. The effect of hydrophobicity is clearly visible at the profile scale, but only to a smaller degree at the plot scale, due to the fact that the thickness and the composition of the litter layer observed on the soil profiles is spatially variable. As reported by Doerr et al. (2003), for example, the influence of hydrophobic topsoils is most distinct at the small scale and decreases with increasing size of the area investigated. We conclude that, because of these spatial limitations and the temporal limitation to the beginning of a rainfall event, temporary Hortonian overland fl ow does not contribute significantly to flood generation. Therefore, it can be ignored in the concept described in the Theory section. These theoretical considerations on the forest influence on floods, though, do not contradict the findings made in the Sperbelgraben at the profile and plot scales. The temporal and spatial variability of the influence of the water storage capacity of a forest soil on runoff generation can thus be explained.

[\textbackslash n] The comparability of responses at the plot and profile scales is limited due to the different approach of the investigations. Whereas at the profile scale the artificial rainfall intensity is identical for all experiments, natural precipitation events are considered at plot scale, and these vary in duration and intensity. Owing to the non-linearity of hydrological processes, it is hardly possible to compare different rainfall events of profile and plot investigations. In addition, boundary effects increase with decreasing size of the areas tested. Their impact at the plot scale is considerably smaller than at the profile scale. Nevertheless, identical hydrological key processes were identified at the two different scales, and surface runoff coefficients are found to be of a similar order of magnitude for experiments on the same forest site types. Thus, we conclude that it is possible to derive qualitative statements on the main hydrological processes occurring in a specific soil type from small-scale irrigation experiments and to transfer them to larger areas under the conditions found in the Sperbelgraben.

[\textbackslash n] The results of the irrigation experiments and surface runoff plots show that the map of forest site types (Burger et al., 1996) is a good tool for the determination of areas with similar hydrological reactions. Its potential even goes beyond a standard soil map, as it also allows one to identify the predisposition of a site for hydrophobic behaviour. Therefore, the inclusion of vegetation information into mapping procedures for hydrological purposes, as is the case with the Swiss forest site type map, seems promising. Since such maps are widely used in Swiss forestry, they represent a potential to improve hydrological catchment modelling.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-13681046,~to-add-doi-URL,forest-resources,runoff,sediment-transport,soil-erosion,soil-hydrophobicity,soil-resources,switzerland},
  number = {2}
}
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