How fast do gully headcuts retreat?

© 2016 Elsevier B.V. Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these led to important site-specific and regional insights, the overall importance of this erosion process or the factors that control it at a global scale remain poorly understood. This study aims to bridge this gap by reviewing research on GHR and conducting a meta-analysis of measured GHR rates worldwide. Through an extensive literature review, GHR rates for 933 individual and actively retreating gullies have been compiled from more than 70 study areas worldwide (comprising a total measuring period of >19 600 years). Each GHR rate was measured through repeated field surveys and/or analyses of aerial photographs over a period of at least one year (maximum: 97 years, median: 17 years). The data show a very large variability, both in terms of gully dimensions (cross-sectional areas ranging between 0.11 and 816 m2 with a median of 4 m2) and volumetric GHR rates (ranging between 0.002 and 47 430 m3 year- 1 with a median of 2.2 m3 year- 1). Linear GHR rates vary between 0.01 and 135 m year- 1 (median: 0.89 m year- 1), while areal GHR rates vary between 0.01 and 3628 m2 year- 1 (median: 3.12 m2 year- 1). An empirical relationship allows estimating volumetric retreat rates from areal retreat rates with acceptable uncertainties. By means of statistical analyses for a subset of 724 gullies with a known contributing area, we explored the factors most relevant in explaining the observed 7 orders of magnitudes of variation in volumetric GHR rates. Results show that measured GHR rates are significantly correlated to the runoff contributing area of the gully (r2 = 0.15) and the rainy day normal (RDN; i.e. the long-term average annual rainfall depth divided by the average number of rainy days; r2 = 0.47). Other factors (e.g. land use or soil type) showed no significant correlation with the observed GHR rates. This may be attributed to the uncertainties associated with accurately quantifying these factors. In addition, available time series data demonstrate that GHR rates are subject to very large year-to-year variations. As a result, average GHR rates measured over short (100%) uncertainties. We integrated our findings into a weighted regression model that simulates the volumetric retreat rate of a gully headcut as a function of upstream drainage area and RDN. When weighing each GHR observation proportional to its measuring period, this model explains 68% of the observed variance in GHR rates at a global scale. For 76% of the monitored gullies, the simulated GHR values deviate less than one order of magnitude from their corresponding observed value. Our model clearly indicates that GHR rates are very sensitive to rainfall intensity. Since these intensities are expected to increase in most areas as a result of climate change, our results suggest that gully erosion worldwide will become more intense and widespread in the following decades. Finally, we discuss research topics that will help to address these challenges

Contemporary gully erosion trend in the northern part of the forest-steppe zone of the Russian Plain: A case study from the Republic of Tatarstan, European Russia

© Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. This article presents results for gully head cut retreat rates (GHRR) in the Pre-Kama region (Republic of Tatarstan, Russia) based on monitoring (1984–1994 and 2015–2018) and the interpretation of high-resolution satellite images (2004–2014). The results suggested that the mean linear GHRR have reduced by about five times, from 1.6 m per year (1983–1994) to 0.4 m per year (2015–2018). The main reason for the significant decrease in gully erosion was the increase in winter-spring air temperatures, which resulted in a reduction in the depth of soil freezing and surface runoff. The impact of land use, as well as erosion control measures, which were implemented in the study area during the late 1980s and early 1990s, was found to be less important

Contemporary gully erosion trend in the northern part of the forest-steppe zone of the Russian Plain: A case study from the Republic of Tatarstan, European Russia

© Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. This article presents results for gully head cut retreat rates (GHRR) in the Pre-Kama region (Republic of Tatarstan, Russia) based on monitoring (1984–1994 and 2015–2018) and the interpretation of high-resolution satellite images (2004–2014). The results suggested that the mean linear GHRR have reduced by about five times, from 1.6 m per year (1983–1994) to 0.4 m per year (2015–2018). The main reason for the significant decrease in gully erosion was the increase in winter-spring air temperatures, which resulted in a reduction in the depth of soil freezing and surface runoff. The impact of land use, as well as erosion control measures, which were implemented in the study area during the late 1980s and early 1990s, was found to be less important

The Influence of Scavenging on Cidnp Field Dependences in Biradicals during the Photolysis of Large-Ring Cycloalkanones

Investigation of the CIDNP field dependences of acyl-alkyl biradicals formed by Norrish type-I reaction during the photolysis of cycloundecanone and cyclododecanone in the presence of the scavenger CBrCl3 has been performed at low (up to 0.08 T) magnetic fields. In addition to the emissive polarization with the main maxima caused by the S-T mechanism we observed an absorptive polarization with maxima at low fields (< 0.01 T) for alpha-CH2 protons of initial ketones. A quantitative analysis of CIDNP amplitude dependences on scavenger concentration allows the estimation of the kinetics of biradical geminate recombination near the emissive maxima. It is demonstrated that the biradical scavenging rate constant can be determined using the kinetic data for high magnetic fields. The scavenging rate constant of CBrCl3 estimated by this method is (2.3 +/- 0.4) X 10(9) M(-1) s(-1). Two competitive channels of singlet-triplet conversion have been revealed and the qualitative picture of their contribution to the kinetics of the low-field CIDNP is presented

How fast do gully headcuts retreat?

© 2016 Elsevier B.V. Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these led to important site-specific and regional insights, the overall importance of this erosion process or the factors that control it at a global scale remain poorly understood. This study aims to bridge this gap by reviewing research on GHR and conducting a meta-analysis of measured GHR rates worldwide. Through an extensive literature review, GHR rates for 933 individual and actively retreating gullies have been compiled from more than 70 study areas worldwide (comprising a total measuring period of >19 600 years). Each GHR rate was measured through repeated field surveys and/or analyses of aerial photographs over a period of at least one year (maximum: 97 years, median: 17 years). The data show a very large variability, both in terms of gully dimensions (cross-sectional areas ranging between 0.11 and 816 m2 with a median of 4 m2) and volumetric GHR rates (ranging between 0.002 and 47 430 m3 year- 1 with a median of 2.2 m3 year- 1). Linear GHR rates vary between 0.01 and 135 m year- 1 (median: 0.89 m year- 1), while areal GHR rates vary between 0.01 and 3628 m2 year- 1 (median: 3.12 m2 year- 1). An empirical relationship allows estimating volumetric retreat rates from areal retreat rates with acceptable uncertainties. By means of statistical analyses for a subset of 724 gullies with a known contributing area, we explored the factors most relevant in explaining the observed 7 orders of magnitudes of variation in volumetric GHR rates. Results show that measured GHR rates are significantly correlated to the runoff contributing area of the gully (r2 = 0.15) and the rainy day normal (RDN; i.e. the long-term average annual rainfall depth divided by the average number of rainy days; r2 = 0.47). Other factors (e.g. land use or soil type) showed no significant correlation with the observed GHR rates. This may be attributed to the uncertainties associated with accurately quantifying these factors. In addition, available time series data demonstrate that GHR rates are subject to very large year-to-year variations. As a result, average GHR rates measured over short (100%) uncertainties. We integrated our findings into a weighted regression model that simulates the volumetric retreat rate of a gully headcut as a function of upstream drainage area and RDN. When weighing each GHR observation proportional to its measuring period, this model explains 68% of the observed variance in GHR rates at a global scale. For 76% of the monitored gullies, the simulated GHR values deviate less than one order of magnitude from their corresponding observed value. Our model clearly indicates that GHR rates are very sensitive to rainfall intensity. Since these intensities are expected to increase in most areas as a result of climate change, our results suggest that gully erosion worldwide will become more intense and widespread in the following decades. Finally, we discuss research topics that will help to address these challenges

How fast do gully headcuts retreat?

© 2016 Elsevier B.V. Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these led to important site-specific and regional insights, the overall importance of this erosion process or the factors that control it at a global scale remain poorly understood. This study aims to bridge this gap by reviewing research on GHR and conducting a meta-analysis of measured GHR rates worldwide. Through an extensive literature review, GHR rates for 933 individual and actively retreating gullies have been compiled from more than 70 study areas worldwide (comprising a total measuring period of >19 600 years). Each GHR rate was measured through repeated field surveys and/or analyses of aerial photographs over a period of at least one year (maximum: 97 years, median: 17 years). The data show a very large variability, both in terms of gully dimensions (cross-sectional areas ranging between 0.11 and 816 m2 with a median of 4 m2) and volumetric GHR rates (ranging between 0.002 and 47 430 m3 year- 1 with a median of 2.2 m3 year- 1). Linear GHR rates vary between 0.01 and 135 m year- 1 (median: 0.89 m year- 1), while areal GHR rates vary between 0.01 and 3628 m2 year- 1 (median: 3.12 m2 year- 1). An empirical relationship allows estimating volumetric retreat rates from areal retreat rates with acceptable uncertainties. By means of statistical analyses for a subset of 724 gullies with a known contributing area, we explored the factors most relevant in explaining the observed 7 orders of magnitudes of variation in volumetric GHR rates. Results show that measured GHR rates are significantly correlated to the runoff contributing area of the gully (r2 = 0.15) and the rainy day normal (RDN; i.e. the long-term average annual rainfall depth divided by the average number of rainy days; r2 = 0.47). Other factors (e.g. land use or soil type) showed no significant correlation with the observed GHR rates. This may be attributed to the uncertainties associated with accurately quantifying these factors. In addition, available time series data demonstrate that GHR rates are subject to very large year-to-year variations. As a result, average GHR rates measured over short (100%) uncertainties. We integrated our findings into a weighted regression model that simulates the volumetric retreat rate of a gully headcut as a function of upstream drainage area and RDN. When weighing each GHR observation proportional to its measuring period, this model explains 68% of the observed variance in GHR rates at a global scale. For 76% of the monitored gullies, the simulated GHR values deviate less than one order of magnitude from their corresponding observed value. Our model clearly indicates that GHR rates are very sensitive to rainfall intensity. Since these intensities are expected to increase in most areas as a result of climate change, our results suggest that gully erosion worldwide will become more intense and widespread in the following decades. Finally, we discuss research topics that will help to address these challenges

How fast do gully headcuts retreat?

© 2016 Elsevier B.V. Gully erosion has important on and off site effects. Therefore, several studies have been conducted over the past decades to quantify gully headcut retreat (GHR) in different environments. Although these led to important site-specific and regional insights, the overall importance of this erosion process or the factors that control it at a global scale remain poorly understood. This study aims to bridge this gap by reviewing research on GHR and conducting a meta-analysis of measured GHR rates worldwide. Through an extensive literature review, GHR rates for 933 individual and actively retreating gullies have been compiled from more than 70 study areas worldwide (comprising a total measuring period of >19 600 years). Each GHR rate was measured through repeated field surveys and/or analyses of aerial photographs over a period of at least one year (maximum: 97 years, median: 17 years). The data show a very large variability, both in terms of gully dimensions (cross-sectional areas ranging between 0.11 and 816 m2 with a median of 4 m2) and volumetric GHR rates (ranging between 0.002 and 47 430 m3 year- 1 with a median of 2.2 m3 year- 1). Linear GHR rates vary between 0.01 and 135 m year- 1 (median: 0.89 m year- 1), while areal GHR rates vary between 0.01 and 3628 m2 year- 1 (median: 3.12 m2 year- 1). An empirical relationship allows estimating volumetric retreat rates from areal retreat rates with acceptable uncertainties. By means of statistical analyses for a subset of 724 gullies with a known contributing area, we explored the factors most relevant in explaining the observed 7 orders of magnitudes of variation in volumetric GHR rates. Results show that measured GHR rates are significantly correlated to the runoff contributing area of the gully (r2 = 0.15) and the rainy day normal (RDN; i.e. the long-term average annual rainfall depth divided by the average number of rainy days; r2 = 0.47). Other factors (e.g. land use or soil type) showed no significant correlation with the observed GHR rates. This may be attributed to the uncertainties associated with accurately quantifying these factors. In addition, available time series data demonstrate that GHR rates are subject to very large year-to-year variations. As a result, average GHR rates measured over short (100%) uncertainties. We integrated our findings into a weighted regression model that simulates the volumetric retreat rate of a gully headcut as a function of upstream drainage area and RDN. When weighing each GHR observation proportional to its measuring period, this model explains 68% of the observed variance in GHR rates at a global scale. For 76% of the monitored gullies, the simulated GHR values deviate less than one order of magnitude from their corresponding observed value. Our model clearly indicates that GHR rates are very sensitive to rainfall intensity. Since these intensities are expected to increase in most areas as a result of climate change, our results suggest that gully erosion worldwide will become more intense and widespread in the following decades. Finally, we discuss research topics that will help to address these challenges