the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 May 2023
Assessment of plot scale sediment transport on young moraines in the Swiss Alps using a fluorescent sand tracer
Florian Lustenberger
Ilja van Meerveld
Abstract. Glacial retreat uncovers large bodies of unconsolidated sediment that are prone to erosion. However, our knowledge of over-land flow (OF) generation and sediment transport on moraines that have recently become ice-free is still limited. To investi-gate how surface characteristics affect OF and sediment transport on young moraines, we installed five bounded runoff plots on two moraines of different ages in a proglacial area of the Swiss Alps. On each plot we conducted three sprinkling experiments to determine OF characteristics (i.e., total OF, peak OF flow rate) and measured sediment transport (peak tur-bidity, sediment concentrations, and total sediment yield). To determine sediment transport distances and to visualize where sediment transport takes place, we used a fluorescent sand tracer with an afterglow, together with UV and LED lamps and a high-resolution camera. The results highlight the ability of this field setup to detect sand movement, even for individual fluorescent sand particles (300–500 µm grain size), and to distinguish between the two main mechanisms of sediment transport: OF-driven erosion and splash erosion. The higher rock cover on the younger moraine with higher surface connec-tivity resulted in longer sediment transport distances and a higher sediment yield. In contrast, the higher vegetation cover on the older moraine promoted infiltration and reduced the length of the sediment transport pathways. The study, thus, demonstrates the potential of the use of fluorescent sand with an afterglow to determine sediment transport pathways, and that these observations can help to improve our understanding of OF and sediment transport processes on complex natural hillslopes.
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Fabian Maier et al.
Status: closed
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RC1: 'Comment on egusphere-2023-899', Anonymous Referee #1, 26 Jun 2023
This is an original manuscript that is partially based on an earlier version. The authors have set up sprinkling experiments on a number of plots that are located on moraine hillslope sections of different ages since deglaciation. As a tracer for sediment movement, they use lines of fluorescent sand photographed by night before and after the sprinkling experiments (that had different magnitudes); additionally, coloured water was used as a tracer of overland flow. The resulting photos are semiautomatically oriented and resampled, and then analysed to identify and quantify changes in sand cover along with transport distances across the plots. The results regarding overland flow and sediment movement and yield are correlated with surface characteristics in order to identify factors with a predictive capacity with regard to water and sediment dynamics. Compared to the previous version, the DSMs generated from the photos via Sf Mare are no longer used for flow routing, which is fine because even small vegetation is contained in the DSM.
The paper is well written and structured. Most of the methodological framework is described in a well reproducible manner, and I found no flaw in the analyses. However, I have made several comments and would be interested in the response. There’s one major concern with respect to the content. The paper has a very strong methodological focus, but considerable effort was made to conduct the experiments on a remote and steep place (moraine hillslopes). This is more than just a natural laboratory that offers a range of different surface characteristics – it is a system that changes with time passing since deglaciation. Both the analyses of different surface characteristics and the findings regarding overland flow and surface dynamics should be interpreted more in light of the processes that effect changes on moraines after deglacation. I would suggest that this be written in an additional discussion section.
In all, the paper is of potentially high interest for the community in geomorphology and soil (erosion) science. The strengths and weaknesses of the method are discussed at breadth and depth, and further developments are suggested to counter the weaknesses. If the scientific part regarding the proglacial characteristics and dynamics is strenghened a bit further, the paper can be accepted in my opinion. Please also see the comments I made in the PDF of the manuscript.
- AC1: 'Reply on RC1', Fabian Maier, 29 Jul 2023
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RC2: 'Comment on egusphere-2023-899', Anonymous Referee #2, 02 Jul 2023
In this paper, the authors use a fluorescent sand tracer method and sprinkling experiments on moraines in the Swiss Alps. This method proved to have several advantages over other techniques. In particular, the measurement of local overland flow and sediment redistribution (not required to reach lower plot), cost effectiveness, and not needing to measure photos or videos during the experiment. The overland flow and sand movement/yield results were correlated with surface characteristics in order to identify which characteristics can be used to predict water and sediment dynamics.
The paper is generally well structured and will likely be of interest to those interested in soil erosion, deglaciation of alpine environments, and sediment transport. However, as mentioned by another reviewer, the paper would benefit from a more in-depth discussion of these experiments in context of landscape change following deglaciation.
The only other substantial comment that I have is that the methods for calculating sand movement need to be described more clearly. Additionally, these methods seem to be limited by their sensitivity to the “loss” of grains – resulting in negative values that obscure whatever real transport there was. I would recommend either more clearly explaining this in the manuscript and why it is a better method for calculating transport than other metrics, or using a different metric altogether.
In my opinion, the paper is novel and very interesting, and should be accepted given the two comments above can be addressed. I have also attached a pdf with more detailed and minor comments.
- AC2: 'Reply on RC2', Fabian Maier, 29 Jul 2023
Status: closed
-
RC1: 'Comment on egusphere-2023-899', Anonymous Referee #1, 26 Jun 2023
This is an original manuscript that is partially based on an earlier version. The authors have set up sprinkling experiments on a number of plots that are located on moraine hillslope sections of different ages since deglaciation. As a tracer for sediment movement, they use lines of fluorescent sand photographed by night before and after the sprinkling experiments (that had different magnitudes); additionally, coloured water was used as a tracer of overland flow. The resulting photos are semiautomatically oriented and resampled, and then analysed to identify and quantify changes in sand cover along with transport distances across the plots. The results regarding overland flow and sediment movement and yield are correlated with surface characteristics in order to identify factors with a predictive capacity with regard to water and sediment dynamics. Compared to the previous version, the DSMs generated from the photos via Sf Mare are no longer used for flow routing, which is fine because even small vegetation is contained in the DSM.
The paper is well written and structured. Most of the methodological framework is described in a well reproducible manner, and I found no flaw in the analyses. However, I have made several comments and would be interested in the response. There’s one major concern with respect to the content. The paper has a very strong methodological focus, but considerable effort was made to conduct the experiments on a remote and steep place (moraine hillslopes). This is more than just a natural laboratory that offers a range of different surface characteristics – it is a system that changes with time passing since deglaciation. Both the analyses of different surface characteristics and the findings regarding overland flow and surface dynamics should be interpreted more in light of the processes that effect changes on moraines after deglacation. I would suggest that this be written in an additional discussion section.
In all, the paper is of potentially high interest for the community in geomorphology and soil (erosion) science. The strengths and weaknesses of the method are discussed at breadth and depth, and further developments are suggested to counter the weaknesses. If the scientific part regarding the proglacial characteristics and dynamics is strenghened a bit further, the paper can be accepted in my opinion. Please also see the comments I made in the PDF of the manuscript.
- AC1: 'Reply on RC1', Fabian Maier, 29 Jul 2023
-
RC2: 'Comment on egusphere-2023-899', Anonymous Referee #2, 02 Jul 2023
In this paper, the authors use a fluorescent sand tracer method and sprinkling experiments on moraines in the Swiss Alps. This method proved to have several advantages over other techniques. In particular, the measurement of local overland flow and sediment redistribution (not required to reach lower plot), cost effectiveness, and not needing to measure photos or videos during the experiment. The overland flow and sand movement/yield results were correlated with surface characteristics in order to identify which characteristics can be used to predict water and sediment dynamics.
The paper is generally well structured and will likely be of interest to those interested in soil erosion, deglaciation of alpine environments, and sediment transport. However, as mentioned by another reviewer, the paper would benefit from a more in-depth discussion of these experiments in context of landscape change following deglaciation.
The only other substantial comment that I have is that the methods for calculating sand movement need to be described more clearly. Additionally, these methods seem to be limited by their sensitivity to the “loss” of grains – resulting in negative values that obscure whatever real transport there was. I would recommend either more clearly explaining this in the manuscript and why it is a better method for calculating transport than other metrics, or using a different metric altogether.
In my opinion, the paper is novel and very interesting, and should be accepted given the two comments above can be addressed. I have also attached a pdf with more detailed and minor comments.
- AC2: 'Reply on RC2', Fabian Maier, 29 Jul 2023
Fabian Maier et al.
Fabian Maier et al.
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