the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Geospatial modelling of large wood supply to rivers: a state-of-the-art model comparison in Swiss mountain river catchments
Virginia Ruiz-Villanueva
Alexandre Badoux
Christian Rickli
Andrea Mini
Markus Stoffel
Dieter Rickenmann
Abstract. Different models have been used in science and practice to identify instream large wood (LW) sources and to estimate LW supply to rivers. This contribution reviews the existing models proposed in the last 35 years and compares two of the most recent GIS-based models by applying them to 40 catchments in Switzerland. Both models, which we call here empirical GIS approach (EGA) and Fuzzy-Logic GIS approach (FGA), consider landslides, debris flows, bank erosion, and mobilization of instream wood as recruitment processes and compute volumetric estimates of LW supply based on three different scenarios of process frequency and magnitude. Despite being developed following similar concepts and fed with similar input data, the results from the two models differ markedly. In general, estimated supply wood volumes were larger in each of the scenarios when computed with the FGA and lower with the EGA models. Landslides were the dominant process identified by the EGA, whereas bank erosion was the predominant process according to the FGA model. These differences are discussed and results compared to available observations coming from a unique database. Regardless of the limitations of these models, they proved extremely useful for hazard assessment, and the design of infrastructure and other management strategies.
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Nicolas Steeb et al.
Status: closed
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CC1: 'Comment on esurf-2022-69', Andrés Iroumé, 21 Feb 2023
I am really enjoying this manuscript.
Some general comments:
- In page 1, lines 31-33, the authors write: “Regardless of the limitations of these models, they
proved extremely useful for hazard assessment, and the design of infrastructure and other management strategies”. Is this a result from this ms, or the models had been used for hazard assessment? In addition, how accurate can they be to assess hazard in particularly because, as the authors write, they provide different outcomes both in terms of LW volumes and LW sources.
- Page 4, lines 67-68. About the data scarcity. Perhaps there are more recent publications?
- Page 4, lines 83-84. The existing approaches are the published approaches? Seems a redundance.
- Page 5, line 115, about source area. The areas can source LW to the streams if they are connected to the streams. The issue of connectivity is little addressed, here and along the text. Page 6 line 131 and page 7 line 151, the issue of connectivity is briefly presented. As an example, in page 13, lines 195-196 the authors refer to volume reduction factors. I assume that connectivity is a driving issue. Please comment.
- Page 15, line 239. The revised literature here, is from Swiss channels?
- In general, the two models identify different dominant processes as wood sources (landslides by the EGA, and bank erosion by the FGA model). So, can they really be comparable? Perhaps one is more suited to smaller headwaters, and the other to larger rivers? Please comment.
Citation: https://doi.org/10.5194/esurf-2022-69-CC1 - AC1: 'Reply on CC1', Nicolas Steeb, 18 Apr 2023
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RC1: 'Comment on esurf-2022-69', Anonymous Referee #1, 01 Mar 2023
The comment was uploaded in the form of a supplement: https://esurf.copernicus.org/preprints/esurf-2022-69/esurf-2022-69-RC1-supplement.pdf
- AC2: 'Reply on RC1', Nicolas Steeb, 18 Apr 2023
-
RC2: 'Comment on esurf-2022-69', Francesco Comiti, 28 Mar 2023
Dear Authors,
I have really enjoyed reading your ms, which I think represents a very valuable piece of work for improving the quantitative estimation - and most importantly the knowledege about related uncertanties - of wood fluxes during flood events. In my opinion the text is generally clear enough and figures/Tables quite informative. I just have a few suggestions to improve the work, as listed below:
- in the description of the FGA, I think it would be useful for reader to have the relationship between the max distance and slope steepness for the landslide "connectivity" assessment. At the moment it says just "further away if slope >40% (line 318). But how far upslope? this is an important parameter, I believe.
- for both EGA and FGA please make explicit whether for bank erosion the erodibility of the lateral channel boundaries are considered or not. In other terms, can the models exclude (or greatly limit) bank erosion inputs in case of bedrock banks? If I am not wrong this is not the case, and thus I suspect bank erosion contribution may be overestimated, especially in steep reaches by FGA as the use of the width ratio is related to channel steepness, but steep channels may be extensively bordered by stable bedrock areas. I think the authors may wish to discuss how the introduction of erodibile vs non-erodible areas for both models may improve the performance of models. Such an approach was introducted by Franceschi et al. (2019) in combination with the use of width ratios (whose values can be set by the users)
- Unfortunately Franceschi et al (2019) is not published yet, as you know. However, please not that the preprint has a longer list of authors that those reported in the references. Please check it here "https://www.researchgate.net/publication/330397920_GIS-based_approach_to_assess_large_wood_transport_in_mountain_rivers_during_floods". Also note that this model accounts for both landslides and bank erosion inputs, differently from what reported at lines 625. In addition, Franceschi et al model is capable to work with single trees and thus provide statistics about number of elements and their size (For table 1).
- The authors should comment about the need/benefit for hazard prediction to modiel - in addition to the wood supply presented here - the propagation of LW in channels during floods (1D or 2D, including critical sections as bridges where most LW can get trapped), I think that especially for the larger basins the lack of propagation (and thus the longitudiinal disconnectivity) may be partially responsible for the important overestimations showed in this study.
I hope you will find my comments of use. Best wishes!
Francesco Comiti
Citation: https://doi.org/10.5194/esurf-2022-69-RC2 - AC3: 'Reply on RC2', Nicolas Steeb, 18 Apr 2023
Status: closed
-
CC1: 'Comment on esurf-2022-69', Andrés Iroumé, 21 Feb 2023
I am really enjoying this manuscript.
Some general comments:
- In page 1, lines 31-33, the authors write: “Regardless of the limitations of these models, they
proved extremely useful for hazard assessment, and the design of infrastructure and other management strategies”. Is this a result from this ms, or the models had been used for hazard assessment? In addition, how accurate can they be to assess hazard in particularly because, as the authors write, they provide different outcomes both in terms of LW volumes and LW sources.
- Page 4, lines 67-68. About the data scarcity. Perhaps there are more recent publications?
- Page 4, lines 83-84. The existing approaches are the published approaches? Seems a redundance.
- Page 5, line 115, about source area. The areas can source LW to the streams if they are connected to the streams. The issue of connectivity is little addressed, here and along the text. Page 6 line 131 and page 7 line 151, the issue of connectivity is briefly presented. As an example, in page 13, lines 195-196 the authors refer to volume reduction factors. I assume that connectivity is a driving issue. Please comment.
- Page 15, line 239. The revised literature here, is from Swiss channels?
- In general, the two models identify different dominant processes as wood sources (landslides by the EGA, and bank erosion by the FGA model). So, can they really be comparable? Perhaps one is more suited to smaller headwaters, and the other to larger rivers? Please comment.
Citation: https://doi.org/10.5194/esurf-2022-69-CC1 - AC1: 'Reply on CC1', Nicolas Steeb, 18 Apr 2023
-
RC1: 'Comment on esurf-2022-69', Anonymous Referee #1, 01 Mar 2023
The comment was uploaded in the form of a supplement: https://esurf.copernicus.org/preprints/esurf-2022-69/esurf-2022-69-RC1-supplement.pdf
- AC2: 'Reply on RC1', Nicolas Steeb, 18 Apr 2023
-
RC2: 'Comment on esurf-2022-69', Francesco Comiti, 28 Mar 2023
Dear Authors,
I have really enjoyed reading your ms, which I think represents a very valuable piece of work for improving the quantitative estimation - and most importantly the knowledege about related uncertanties - of wood fluxes during flood events. In my opinion the text is generally clear enough and figures/Tables quite informative. I just have a few suggestions to improve the work, as listed below:
- in the description of the FGA, I think it would be useful for reader to have the relationship between the max distance and slope steepness for the landslide "connectivity" assessment. At the moment it says just "further away if slope >40% (line 318). But how far upslope? this is an important parameter, I believe.
- for both EGA and FGA please make explicit whether for bank erosion the erodibility of the lateral channel boundaries are considered or not. In other terms, can the models exclude (or greatly limit) bank erosion inputs in case of bedrock banks? If I am not wrong this is not the case, and thus I suspect bank erosion contribution may be overestimated, especially in steep reaches by FGA as the use of the width ratio is related to channel steepness, but steep channels may be extensively bordered by stable bedrock areas. I think the authors may wish to discuss how the introduction of erodibile vs non-erodible areas for both models may improve the performance of models. Such an approach was introducted by Franceschi et al. (2019) in combination with the use of width ratios (whose values can be set by the users)
- Unfortunately Franceschi et al (2019) is not published yet, as you know. However, please not that the preprint has a longer list of authors that those reported in the references. Please check it here "https://www.researchgate.net/publication/330397920_GIS-based_approach_to_assess_large_wood_transport_in_mountain_rivers_during_floods". Also note that this model accounts for both landslides and bank erosion inputs, differently from what reported at lines 625. In addition, Franceschi et al model is capable to work with single trees and thus provide statistics about number of elements and their size (For table 1).
- The authors should comment about the need/benefit for hazard prediction to modiel - in addition to the wood supply presented here - the propagation of LW in channels during floods (1D or 2D, including critical sections as bridges where most LW can get trapped), I think that especially for the larger basins the lack of propagation (and thus the longitudiinal disconnectivity) may be partially responsible for the important overestimations showed in this study.
I hope you will find my comments of use. Best wishes!
Francesco Comiti
Citation: https://doi.org/10.5194/esurf-2022-69-RC2 - AC3: 'Reply on RC2', Nicolas Steeb, 18 Apr 2023
Nicolas Steeb et al.
Nicolas Steeb et al.
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