How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed?
In January 1980, during exceptional cyclonic rainfall, an atypical landslide, called <i>déboulé</i>, rapidly generated the permanent 700 m-long gully of the Ravine de l’Eglise on an inhabited plateau in Reunion Island (Indian Ocean). Retrieving the initial conditions that led to this his...
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| Format: | Article |
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MDPI AG
2022-02-01
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| Series: | Earth |
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| Online Access: | https://www.mdpi.com/2673-4834/3/1/20 |
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| author | Claire Rault Yannick Thiery Bertrand Aunay Bastien Colas Kahina Reboul Thomas J. B. Dewez |
| author_facet | Claire Rault Yannick Thiery Bertrand Aunay Bastien Colas Kahina Reboul Thomas J. B. Dewez |
| author_sort | Claire Rault |
| collection | DOAJ |
| description | In January 1980, during exceptional cyclonic rainfall, an atypical landslide, called <i>déboulé</i>, rapidly generated the permanent 700 m-long gully of the Ravine de l’Eglise on an inhabited plateau in Reunion Island (Indian Ocean). Retrieving the initial conditions that led to this historical process is both challenging and necessary for understanding the mechanism of gully incision and providing pointers for improving risk mitigation in relation to this phenomenon. In this study, we reconstruct the pre- and post-failure topographies using SFM (structure from motion) applied on archive aerial photographs. Based on the comparison of these digital elevation models, we estimate the volume of material eroded to be ca. 0.63 Mm<sup>3</sup>. Groundwater level increase, part of the triggering mechanism, is hindcast in the catchment of the gully using a lumped hydrological model. This model shows that in only a fortnight the groundwater level probably rose by 36 m, which could have caused a progressive increase in pore pressure and triggered formation of the gully by retrogressive landslides. We test this hypothesis by considering the pre-failure topography and the hindcast groundwater level in a deterministic model based on limit equilibrium equations to explore ground stability. The evolution of ground stability with a rise in the water table shows that the gully may have extended in a headward direction by retrogressive landslides. This is the first quantitative reconstruction of an exceptional historical event affecting the territory of Reunion Island. The methods used to investigate the Ravine de L’Eglise incision thus offer new complementary insights and challenges for understanding the mechanism and the temporality of gully formation. |
| first_indexed | 2024-03-09T19:54:50Z |
| format | Article |
| id | doaj.art-2a8a2542bd8d475dbe0080a940f15555 |
| institution | Directory Open Access Journal |
| issn | 2673-4834 |
| language | English |
| last_indexed | 2024-03-09T19:54:50Z |
| publishDate | 2022-02-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Earth |
| spelling | doaj.art-2a8a2542bd8d475dbe0080a940f155552023-11-24T00:58:37ZengMDPI AGEarth2673-48342022-02-013132434410.3390/earth3010020How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed?Claire Rault0Yannick Thiery1Bertrand Aunay2Bastien Colas3Kahina Reboul4Thomas J. B. Dewez5BRGM, CEDEX, F-97400 Saint-Denis, FranceBRGM, CEDEX 2, F-45060 Orléans, FranceBRGM, CEDEX, F-97400 Saint-Denis, FranceBRGM, CEDEX 2, F-45060 Orléans, FranceBRGM, CEDEX, F-97400 Saint-Denis, FranceBRGM, CEDEX 2, F-45060 Orléans, FranceIn January 1980, during exceptional cyclonic rainfall, an atypical landslide, called <i>déboulé</i>, rapidly generated the permanent 700 m-long gully of the Ravine de l’Eglise on an inhabited plateau in Reunion Island (Indian Ocean). Retrieving the initial conditions that led to this historical process is both challenging and necessary for understanding the mechanism of gully incision and providing pointers for improving risk mitigation in relation to this phenomenon. In this study, we reconstruct the pre- and post-failure topographies using SFM (structure from motion) applied on archive aerial photographs. Based on the comparison of these digital elevation models, we estimate the volume of material eroded to be ca. 0.63 Mm<sup>3</sup>. Groundwater level increase, part of the triggering mechanism, is hindcast in the catchment of the gully using a lumped hydrological model. This model shows that in only a fortnight the groundwater level probably rose by 36 m, which could have caused a progressive increase in pore pressure and triggered formation of the gully by retrogressive landslides. We test this hypothesis by considering the pre-failure topography and the hindcast groundwater level in a deterministic model based on limit equilibrium equations to explore ground stability. The evolution of ground stability with a rise in the water table shows that the gully may have extended in a headward direction by retrogressive landslides. This is the first quantitative reconstruction of an exceptional historical event affecting the territory of Reunion Island. The methods used to investigate the Ravine de L’Eglise incision thus offer new complementary insights and challenges for understanding the mechanism and the temporality of gully formation.https://www.mdpi.com/2673-4834/3/1/20gullycyclonic rainfallarchive aerial photographsstructure from motionhindcast historic groundwater levellumped hydrological model |
| spellingShingle | Claire Rault Yannick Thiery Bertrand Aunay Bastien Colas Kahina Reboul Thomas J. B. Dewez How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed? Earth gully cyclonic rainfall archive aerial photographs structure from motion hindcast historic groundwater level lumped hydrological model |
| title | How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed? |
| title_full | How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed? |
| title_fullStr | How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed? |
| title_full_unstemmed | How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed? |
| title_short | How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed? |
| title_sort | how can the morphometric characteristics and failure conditions of a historic gully caused by intense rainfall be reconstructed |
| topic | gully cyclonic rainfall archive aerial photographs structure from motion hindcast historic groundwater level lumped hydrological model |
| url | https://www.mdpi.com/2673-4834/3/1/20 |
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