the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Characteristics of debris flows recorded in the Shenmu area of central Taiwan between 2004 and 2021
Abstract. The data of debris-flow events between 2004 and 2001 in the Shebmu area Taiwan were presented and discussed in this paper. Total of 20 debris flows were observed in this time interval. The monitored data include rainfall, flow velocity, soil moisture, and ground surface vibrations. Debris flows in the Shenmu area usually occurred in the Aiyuzi Stream during the rainy season, May to September, and about once per year after 2009. The measured rainfalls from separate monitoring stations were compared and the rainfall thresholds of the Shenmu area were analysed using the rainfall intensity (I), the accumulated rainfall (R), and durations (D). The dataset and the rainfall thresholds of the Shenmu area permits the comparison with other monitored catchments.
Yi-Min Huang
Status: final response (author comments only)
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RC1: 'Comment on nhess-2022-270', Anonymous Referee #1, 22 Jan 2023
The author presented a valuable manuscript for a debris flow monitoring site. However, there are some issues needed to complete the manuscript.
- The abstract should provide a general idea of this study, which includes the importance, the design, the process, and most important the finding from the data. The author should consider rewriting the abstract.
- The introduction should provide a basic idea of the literature and methods, which is lacking in the present form.
- Some names are different in Figure 1 and Figure 2.
- The author presents the debris period to 2021 but the data shown in tables and figures stopped in 2017.
- In line 66, the author mentions that the Aiyuzi stream is the focus of this study but the manuscript keeps mentioning the other two streams.
- In lines 115 to 116, the rainfall event with 1550 mm is missing in Table 2.
- The landslide increment seems incorrect when comparing Table 1 and Table 3.
- In line 205, “Different trends” seems the same trend in Fig. 11.
- In line 216, the velocity before 2009 has only one data and is not the same as 14.4 m/sec in Table 6.
- The soil moisture sensor can be withdrawn from the manuscript since there is no good or enough data to analyze.
- The findings from the geophone should have more descriptions and discussions with such valuable data.
- The first paragraph of the conclusions says the effective rainfall changed from 250mm to 300mm but the result is not shown in the previous part of this manuscript.
- The 3rd paragraph of the conclusions says that the frequency of debris flow is different with 1.83 and 0.75 times but cannot be seen in the previous part of this manuscript.
Citation: https://doi.org/10.5194/nhess-2022-270-RC1 -
AC1: 'Reply on RC1', Yi-Min Huang, 31 Jan 2023
Dear Anonymous Reviewer,
Thank you for helping me to submit a revised draft of my manuscript titled Characteristics of debris flows recorded in the Shenmu area of central Taiwan between 2004 and 2021 to Natural Hazards and Earth System Sciences. I appreciate the time and effort that you have dedicated to providing your valuable feedback on my manuscript. I am grateful to the reviewer’s insightful comments on my paper. I have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. I have highlighted the changes within the manuscript. After the revision, I believe that this study and its outcomes fulfil the scope of journal.
Here is a point-by-point response to the reviewers’ comments and concerns.
Comments from Reviewer RC1
The author presented a valuable manuscript for a debris flow monitoring site. However, there are some issues needed to complete the manuscript.
- Comment 1: The abstract should provide a general idea of this study, which includes the importance, the design, the process, and most important the finding from the data. The author should consider rewriting the abstract.
Response: Thank you for your suggestion. This study mainly focuses on the findings of rainfall factors, intensity (I), duration (D) and rainfall thresholds, that could contribute to the global debris-flow database. Another contribution of this study is to provide an overview of debris-flow monitoring system, available options for debris-flow early warning, and important characteristics about the debris flows in the Shenmu area Taiwan. The abstract of this study is revised in the updated manuscript (p. 1).
- Comment 2: The introduction should provide a basic idea of the literature and methods, which is lacking in the present form.
Response: Thank you for your suggestion. This study mainly focuses on the findings of rainfall factors, intensity (I) and duration (D), that could contribute to the global debris-flow database. Another contribution of this study is to provide an overview of debris-flow monitoring system, available options for debris-flow early warning, and important characteristics about the debris flows in the Shenmu area, Taiwan. Therefore, the author reviewed researches about the study area, and provided description and important references regarding the debris-flow monitoring system, types of collected data, and recent study results about the debris flows in the Shenmu area. The section of Introduction is rearranged and revised in the updated manuscript (p. 1).
- Comment 3: Some names are different in Figure 1 and Figure 2.
Response: Thank you for your suggestion. The name of Shenmu Sta. is corrected in Figure 1, and the name of Chusuei Stream is corrected in Figure 2.
- Comment 4: The author presents the debris period to 2021 but the data shown in tables and figures stopped in 2017.
Response: Thank you for your comment. The period of study is from 2004 to 2021, and there were no debris flows occurred after 2017. Therefore, the data in tables and figures obtained for debris-flow cases stopped in 2017. Additional description about the captured debris-flow events is added in the manuscript (see Line xxx to xxx).
- Comment 5: In line 66, the author mentions that the Aiyuzi stream is the focus of this study but the manuscript keeps mentioning the other two streams.
Response: Thank you for your comment. There are three potential debris-flow torrents in the Shenmu area. To help readers better understand the local environment and the case history, the author included the description of all three streams in a few paragraphs, as addressed in the Section 2. Other than that, Aiyuzi Stream is the main focus of this study.
- Comment 6: In lines 115 to 116, the rainfall event with 1550 mm is missing in Table 2.
Response: Thank you for your comment. The event of Typhoon of Morakot was included in Table 2, and the author tried to emphasize the extreme impacts of Typhoon Morakat by pointing out the three-day (Aug. 7 to Aug. 9) accumulated rainfall of this event. The value of 1,550 mm is corrected to 1,872 mm in the manuscript after revision (see Line xxx to xxx). Table 2 shows the average of hourly rainfall based on the durations.
- Comment 7: The landslide increment seems incorrect when comparing Table 1 and Table 3.
Response: Thank you for your comment. Table 1 describes the total landslide areas after Typhoon Morakot in 2009, not the landslide increment. Table 3 shows the annual increment landslide areas, which area the difference between two consecutive years. The unit in Table 1 and Table are changed to m2, to avoid confusion and for comparison.
- Comment 8: In line 205, “Different trends” seems the same trend in Fig. 11.
Response: Thank you for your suggestion. The trend line of data from CWB (before 2009) is added to Fig. 11, to be used for comparison between the trends from the data before and after 2009 in the figure.
- Comment 9: In line 216, the velocity before 2009 has only one data and is not the same as 14.4 m/sec in Table 6.
Response: Thank you for your suggestion. The average velocity is estimated before and after 2010, not 2009. The manuscript content has been correctee in the Section 3.4.
- Comment 10: The soil moisture sensor can be withdrawn from the manuscript since there is no good or enough data to analyze.
Response: Thank you for your suggestion. Considering the monitoring system in the study area, the use of soil moisture should be addressed to provide a complete debris-flow warning approach in the study area. Although the soil moisture data may not be useful for debris-flow warning at present, it still can be a part of monitoring system and we continue to collect data for further analysis.
- Comment 11: The findings from the geophone should have more descriptions and discussions with such valuable data.
Response: Thank you for your suggestion. Vibrational signals from geophones are promising for debris-warning based on the research. More detail can be found from the references, and recent study results from the author is added in the Section 3.5.
- Comment 12: The first paragraph of the conclusions says the effective rainfall changed from 250 mm to 300 mm but the result is not shown in the previous part of this manuscript.
Response: Thank you for your suggestion. The description of rainfall thresholds is in the content of Section 3.1, more detail is added, and the paragraph is revised (see Line xxx to xxx).
- Comment 13: The 3rd paragraph of the conclusions says that the frequency of debris flow is different with 1.83 and 0.75 times but cannot be seen in the previous part of this manuscript.
Response: Thank you for your suggestion. The analysis and results are added in the manuscript and the content of Section 2 is revised (see Line xxx to xxx).
Additional clarifications
In addition to the above comments, all spelling and grammatical errors pointed out by the author and the editing supervisor have been corrected.
I look forward to hearing from you in due time regarding the submission and to respond to any further questions and comments you may have.
Sincerely,
Yi-Min Huang
Jan. 29, 2023
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AC4: 'Reply on AC1', Yi-Min Huang, 26 Feb 2023
The revised Abstract and Introduction.
Abstract
The data of debris-flow events between 2004 and 2021 in the Shenmu area Taiwan were presented and discussed in this paper. Total of 20 times of debris-flow events were observed in 18 years. Debris flows in the Shenmu area usually occurred in the Aiyuzi Stream during the rainy season, May to September, and about once per year between 2009 and 2017. The rainfall thresholds from the observed data were proposed as Imax, R24, and Rt of 9, 23, and 67.8 mm, respectively. The rainfall data also implied that the trend curves of intensity-duration (I-D) were different before and after 2009, which due to the extreme rainfall event, Typhoon Morakot in 2009. The I-D curve obtained from the post-2009 data was proposed as the baseline of debris-flow I-D relationship in the study area. The extreme rainfall event also influenced the flow speed (average 14.3 m/sec before 2010 and 4.46 m/sec after 2010) and the occurrence frequency of debris flow (1.83 times per year before 2009 and 0.75 times after 2009). Recent findings indicated that the ground surface vibrational signals of debris flows were potentially useful for debris-flow early warning in terms of accumulated energy, and the characteristic frequency of debris flow in the study area was below 40 Hz. The dataset and the rainfall thresholds in this study permits the comparison with other monitored catchments and is advantageous to the global debris-flow dataset.
Introduction
The debris flows have become a common disaster in Taiwan in the past two decades (Huang et al., 2013; Huang et al., 2016; Huang et al., 2017). To understand the characteristics, especially the triggering factors, of debris flows, devices and monitoring stations had been installed and established at the areas prone to the debris flows. Given the environmental conditions at the mountain areas in Taiwan, it is more desired to deploy the monitoring instrumentation at the potentially streams, especially at the upper sections of them. But it usually encounters problems, like the power supply and communication interruption, when trying to install sensors at distant mountain areas. It is difficult for debris-flow research to obtain the full-scale experimental data that can represent the in-situ conditions. Instead, the observation data from these monitoring stations in Taiwan provides valuable information for debris-flow characteristic studies (Huang et al., 2013; Hürlimann et al, 2019).
In Taiwan, the debris flow monitoring system had been built by Taiwan government, the Soil and Water Conservation Bureau (SWCB), by designing and applying different types of monitoring stations (Wang et al., 2011; Huang et al., 2013). Permanent and automatic monitoring devices were installed on sites to collect data about debris flows. In a potential area, the debris flows usually occur in a low frequency and are considered as uncommon events when comparing to other natural hazards, e.g., the heavy rainfalls. But at some locations, the occurrence frequency of debris flow is higher than other locations (Marchi et al, 2021). The Shenmu area in Taiwan is the one where debris flows had occurred more often than other locations, and almost once every year in the past 18 years (2004 to 2021).
The studies about debris-flow characteristics started from Japan and China (Marchi et al., 2021). A review by Hürlimann et al. (2019) has addressed the collected information from nine monitoring sties and discussed the achievements and the types of monitoring systems. The monitoring site conditions, local features of Shenmu area, and debris flow events were used as an important monitoring case in many studies (Huang et al, 2013; Huang et al., 2016; Lee at al, 2017; Wei et al, 2018; Hürlimann et al., 2019). Therefore, the available data collected from the Shenmu Debris Flow Monitoring Station during the period of 2004 to 2021 were used for this work. It should be noted that there were no debris flows occurred after 2017, and the tables and figures in this study present the results of recorded debris-flow events.
This study focuses on the rainfall data obtained from recorded debris-flow events in the Shenmu area, and the potential indicators or factors that could be used for debris-flow early warning. The purpose of this research includes the discussion of rainfall characteristics, in terms of rainfall intensity (I), duration (D), and accumulated rainfall (R), and the recent findings about the impacts of extreme weathers, variation of soil moisture, and ground surface vibrational signals of debris flows. A dataset of debris flows recorded in the Shenmu area between 2004 to 2021 is presented in this study. The event data were collected from various available sources. The data prepared in this study include dates of debris flow events, time of debris flow occurrence (whenever available), the triggering rainfalls (rainfall intensity, accumulated rainfall, and duration), and a brief review of soil moisture and vibrational signal graphs (for some events).
Early research reveals the potential I-D curves from the global event data (Caine, 1980; Guzzetti et al., 2008). These curves can be used as a baseline, the minimum rainfall thresholds, for debris flows by considering the rainfall intensity and duration of a given area. The dataset prepared for this study was compared with the global I-D curves. The rainfall data obtained and used in this study are from the Shenmu Village rainfall station (23°31.9645’N, 120°50.62’E) maintained by the Central Weather Bureau (CWB) and from the Shenmu debris flow monitoring station (23°31.6938’N, 120°51.3927’E) maintained by the Soil and Water Conservation Bureau (SWCB). These data were collected from the instrumentation installed in the study area and were used to describe the important characteristics of debris-flow I-D curves in the Shenmu area and compare them with the global debris-flow database. Analysis of debris-flow rainfall thresholds is also discussed from different approaches. The change of rainfall thresholds used for debris flow early warnings by the local government, and the characteristics of maximum hourly rainfall, effective accumulated rainfall, and rainfall intensity-duration (I-D) of debris flow events in Shenmu are described and compared here.
Other monitoring data that could be potentially useful for the debris-flow early warning are also discussed in this study, including the soil moisture and ground surface vibrational signals. The impacts of extreme weathers, the Typhoon Morakot in 2009 in this study, are also analysed and compared using the flow speeds, estimated from the video cameras available online for several events, and the occurrence frequency of debris flow. Conclusions are made to highlight the contributions of this work at the end.
Citation: https://doi.org/10.5194/nhess-2022-270-AC4
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CC1: 'Comment on nhess-2022-270', Chihping Kuo, 12 Feb 2023
This article presents a valuable evaluating procedure of threshold values to occur debris flow for a site. Some comments were proposed here for the author to revise or add in the article.
- Line 7: the location name “Shebmu” is different from others in the article, please revise it.
- Line 8: the description “Total of 20 debris flows were observed in this time interval.” seems to be 20 times of debris flow events occurred in this time interval but not 20 amounts. It is suggested to rewrite or clarify the description.
- Line 42-45: two important rainfall data resources were proposed here. Please address them in Fig.1 or 2.
- Line 54-56: is the abbreviation DF a name or index system for Debris Flow in Taiwan or this research?
- Line 60-62: please unify the expression of slope, i.e. degree or percentage.
- The collection of data in this article is very complete. Does the author possible suggest an enough and proper period of monitoring for evaluating similar threshold values as characteristics of a site?
- The format of vertical and horizontal axis is suggested to be uniform in Fig.7 to 11
Citation: https://doi.org/10.5194/nhess-2022-270-CC1 -
AC2: 'Reply on CC1', Yi-Min Huang, 15 Feb 2023
Dear Dr. Chihping Kuo,
Thank you for helping me to submit a revised draft of my manuscript titled Characteristics of debris flows recorded in the Shenmu area of central Taiwan between 2004 and 2021 to Natural Hazards and Earth System Sciences. I appreciate the time and effort that you have dedicated to providing your valuable feedback on my manuscript. I am grateful to the reviewer’s insightful comments on my paper. I have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. I have highlighted the changes within the manuscript. After the revision, I believe that this study and its outcomes fulfil the scope of journal.
Here is a point-by-point response to the reviewers’ comments and concerns.
Comments from Reviewer CC1
This article presents a valuable evaluating procedure of threshold values to occur debris flow for a site. Some comments were proposed here for the author to revise or add in the article.
- Comment 1: Line 7: the location name “Shebmu” is different from others in the article, please revise it.
Response: Thank you for your suggestion. The name of location is corrected as “Shenmu.”
- Comment 2: Line 8: the description “Total of 20 debris flows were observed in this time interval.” seems to be 20 times of debris flow events occurred in this time interval but not 20 amounts. It is suggested to rewrite or clarify the description.
Response: Thank you for your suggestion. The content is modified as 20 times of debris-flow events, and the revised content is as follows.
“Abstract. The data of debris-flow events between 2004 and 2021 in the Shenmu area Taiwan were presented and discussed in this paper. Total of 20 times of debris-flow events were observed in 18 years. Debris flows in the Shenmu area usually occurred in the Aiyuzi Stream during the rainy season, May to September, and about once per year between 2009 and 2017. The rainfall thresholds from the observed data were proposed as Imax, R24, and Rt of 9, 23, and 67.8 mm, respectively. The rainfall data also implied that the trend curves of intensity-duration (I-D) were different before and after 2009, which due to the extreme rainfall event, Typhoon Morakot in 2009. The I-D curve obtained from the post-2009 data was proposed as the baseline of debris-flow I-D relationship in the study area. The extreme rainfall event also influenced the flow speed (average 14.3 m/sec before 2010 and 4.46 m/sec after 2010) and the occurrence frequency of debris flow (1.83 times per year before 2009 and 0.75 times after 2009). Recent findings indicated that the ground surface vibrational signals of debris flows were potentially useful for debris-flow early warning in terms of accumulated energy, and the characteristic frequency of debris flow in the study area was below 40 Hz. The dataset and the rainfall thresholds in this study permits the comparison with other monitored catchments and is advantageous to the global debris-flow dataset.”
- Comment 3: Line 42-45: two important rainfall data resources were proposed here. Please address them in Fig.1 or 2.
Response: Thank you for your suggestion. The rainfall stations are added and marked on Figure 1.
- Comment 4: Line 54-56: is the abbreviation DF a name or index system for Debris Flow in Taiwan or this research?
Response: Thank you for your comment. The abbreviation DF stands for Debris Flow, and the index names of the potential debris flow streams in the study area are used in Taiwan.
- Comment 5: Line 60-62: please unify the expression of slope, i.e. degree or percentage.
Response: Thank you for your suggestion. The slope in the manuscript is expressed in degree format.
- Comment 6: The collection of data in this article is very complete. Does the author possible suggest an enough and proper period of monitoring for evaluating similar threshold values as characteristics of a site?
Response: Thank you for your comment. Based on the monitoring results in the study area, the author would suggest that the initial 5-year monitoring is necessary after the monitoring system started, and additional 5 years, resulting in total of a 10-year monitoring period, is favorable for data collection and analysis, especially when encountering unusual rainfall events and varied weather patterns.
- Comment 7: The format of vertical and horizontal axis is suggested to be uniform in Fig.7 to 11.
Response: Thank you for your suggestion. The format of axes in Figure 7 and Figure 8 are changed to the same format as in Figure 9 to Figure 11.
Additional clarifications
In addition to the above comments, all spelling and grammatical errors pointed out by the author and the editing supervisor have been corrected.
I look forward to hearing from you in due time regarding the submission and to respond to any further questions and comments you may have.
Sincerely,
Yi-Min Huang
Feb. 15, 2023
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RC2: 'Comment on nhess-2022-270', Anonymous Referee #2, 24 Feb 2023
This article presents a valuable evaluating procedure of threshold values to occur debris flow for a site. Some comments were proposed here for the author to revise or add in the article.
1.Line 7: the location name “Shebmu” is different from others in the article, please revise it.
2.Line 8: the description “Total of 20 debris flows were observed in this time interval.” seems to be 20 times of debris flow events occurred in this time interval but not 20 amounts. It is suggested to rewrite or clarify the description.
3.Line 42-45: two important rainfall data resources were proposed here. Please address them in Fig.1 or 2.
4.Line 54-56: is the abbreviation DF a name or index system for Debris Flow in Taiwan or this research?
5.Line 60-62: please unify the expression of slope, i.e. degree or percentage.
6.The collection of data in this article is very complete. Does the author possible suggest an enough and proper period of monitoring for evaluating similar threshold values as characteristics of a site?
7.The format of vertical and horizontal axis is suggested to be uniform in Fig.7 to 11Citation: https://doi.org/10.5194/nhess-2022-270-RC2 -
AC3: 'Reply on RC2', Yi-Min Huang, 24 Feb 2023
Dear Anonymous Referee #2,
Thank you for helping me to submit a revised draft of my manuscript titled Characteristics of debris flows recorded in the Shenmu area of central Taiwan between 2004 and 2021 to Natural Hazards and Earth System Sciences. I appreciate the time and effort that you have dedicated to providing your valuable feedback on my manuscript. I am grateful to the reviewer’s insightful comments on my paper. I have been able to incorporate changes to reflect most of the suggestions provided by the reviewers. I have highlighted the changes within the manuscript. After the revision, I believe that this study and its outcomes fulfil the scope of journal.
Here is a point-by-point response to the reviewers’ comments and concerns.
Comments from Reviewer RC2
This article presents a valuable evaluating procedure of threshold values to occur debris flow for a site. Some comments were proposed here for the author to revise or add in the article.
- Comment 1: Line 7: the location name “Shebmu” is different from others in the article, please revise it.
Response: Thank you for your suggestion. The name of location is corrected as “Shenmu.”
- Comment 2: Line 8: the description “Total of 20 debris flows were observed in this time interval.” seems to be 20 times of debris flow events occurred in this time interval but not 20 amounts. It is suggested to rewrite or clarify the description.
Response: Thank you for your suggestion. The content is modified as 20 times of debris-flow events, and the revised content is as follows.
“Abstract. The data of debris-flow events between 2004 and 2021 in the Shenmu area Taiwan were presented and discussed in this paper. Total of 20 times of debris-flow events were observed in 18 years. Debris flows in the Shenmu area usually occurred in the Aiyuzi Stream during the rainy season, May to September, and about once per year between 2009 and 2017. The rainfall thresholds from the observed data were proposed as Imax, R24, and Rt of 9, 23, and 67.8 mm, respectively. The rainfall data also implied that the trend curves of intensity-duration (I-D) were different before and after 2009, which due to the extreme rainfall event, Typhoon Morakot in 2009. The I-D curve obtained from the post-2009 data was proposed as the baseline of debris-flow I-D relationship in the study area. The extreme rainfall event also influenced the flow speed (average 14.3 m/sec before 2010 and 4.46 m/sec after 2010) and the occurrence frequency of debris flow (1.83 times per year before 2009 and 0.75 times after 2009). Recent findings indicated that the ground surface vibrational signals of debris flows were potentially useful for debris-flow early warning in terms of accumulated energy, and the characteristic frequency of debris flow in the study area was below 40 Hz. The dataset and the rainfall thresholds in this study permits the comparison with other monitored catchments and is advantageous to the global debris-flow dataset.”
- Comment 3: Line 42-45: two important rainfall data resources were proposed here. Please address them in Fig.1 or 2.
Response: Thank you for your suggestion. The rainfall stations are added and marked on Figure 1.
- Comment 4: Line 54-56: is the abbreviation DF a name or index system for Debris Flow in Taiwan or this research?
Response: Thank you for your comment. The abbreviation DF stands for Debris Flow, and the index names of the potential debris flow streams in the study area are used in Taiwan.
- Comment 5: Line 60-62: please unify the expression of slope, i.e. degree or percentage.
Response: Thank you for your suggestion. The slope in the manuscript is expressed in degree format.
- Comment 6: The collection of data in this article is very complete. Does the author possible suggest an enough and proper period of monitoring for evaluating similar threshold values as characteristics of a site?
Response: Thank you for your comment. Based on the monitoring results in the study area, the author would suggest that the initial 5-year monitoring is necessary after the monitoring system started, and additional 5 years, resulting in total of a 10-year monitoring period, is favorable for data collection and analysis, especially when encountering unusual rainfall events and varied weather patterns.
- Comment 7: The format of vertical and horizontal axis is suggested to be uniform in Fig.7 to 11.
Response: Thank you for your suggestion. The format of axes in Figure 7 and Figure 8 are changed to the same format as in Figure 9 to Figure 11.
Additional clarifications
In addition to the above comments, all spelling and grammatical errors pointed out by the author and the editing supervisor have been corrected.
I look forward to hearing from you in due time regarding the submission and to respond to any further questions and comments you may have.
Sincerely,
Yi-Min Huang
Feb. 24, 2023
-
AC3: 'Reply on RC2', Yi-Min Huang, 24 Feb 2023
Yi-Min Huang
Yi-Min Huang
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