The Experts below are selected from a list of 24141 Experts worldwide ranked by ideXlab platform

Jeroen Nachtergaele - One of the best experts on this subject based on the ideXlab platform.

  • characteristics controlling factors and importance of deep gullies under cropland on loess derived soils
    Geomorphology, 2005
    Co-Authors: Tom Vanwalleghem, Jeroen Nachtergaele, Jean Poesen, Gert Verstraeten
    Abstract:

    Abstract Several studies describe the formation and importance of shallow Ephemeral gullies under cropland (depth Comparison of a dataset with 28 deep gullies, formed in the period 1985–2003 and 123 shallow Ephemeral gullies formed in the period 1994–1999 in central Belgium indicates that the deep gullies have clearly different morphological characteristics compared to shallow Ephemeral gullies. Several factors were analyzed to understand the formation of deep gullies. Plotting runoff contributing area versus slope of the soil surface at the gully head indicates that the topographical threshold for deep gully formation is significantly larger compared to Ephemeral gully formation. Deep gullies form on short, steep valley sides and their position is strongly affected by the presence of linear landscape elements. All deep gullies incised on landscape positions with a very erodible soil horizon at shallow depth. Analysis of causative rainfall showed no significant differences in incision thresholds between rills and shallow Ephemeral gullies on the one hand and deep gullies on the other hand. The relation between area-specific sediment yield in central Belgium and drainage area, indicates that the development of deep gullies contributes significantly to the sediment output of small rural catchments and causes peaks in the mean area-specific sediment yield that are up to a factor of three higher compared with catchments where shallow Ephemeral gullying occurs.

  • the value of a physically based model versus an empirical approach in the prediction of Ephemeral gully erosion for loess derived soils
    Geomorphology, 2001
    Co-Authors: Jeroen Nachtergaele, Jean Poesen, An Steegen, I Takken, L Beuselinck, L Vandekerckhove, Gerard Govers
    Abstract:

    Abstract A data set on soil losses and controlling factors for 58 Ephemeral gullies has been collected in the Belgian loess belt from March 1997 to March 1999. Of the observed Ephemeral gullies, 32 developed at the end of winter or in early spring (winter gullies) and 26 Ephemeral gullies developed during summer (summer gullies). The assessed data have been used to test the physically based Ephemeral Gully Erosion Model (EGEM) and to compare its performance with the value of simple topographical and morphological indices in the prediction of Ephemeral gully erosion. Analysis shows that EGEM is not capable of predicting Ephemeral gully cross-sections well. Although conditions for input parameter assessment were ideal, some parameters such as channel erodibility, critical flow shear stress and local rainfall depth showed great uncertainty. Rather than revealing EGEM's inability of predicting Ephemeral gully erosion, this analysis stresses the problematic nature of physically based models, since they often require input parameters that are not available or can hardly be obtained. With respect to the value of simple topographical and morphological indices in predicting Ephemeral gully erosion, this study shows that for winter gullies and summer gullies, respectively, over 80% and about 75% of the variation in Ephemeral gully volume can be explained when Ephemeral gully length is known. Moreover, when previously collected data for Ephemeral gullies in two Mediterranean study areas and the data for summer gullies formed in the Belgian loess belt are pooled, it appears that one single length ( L )–volume ( V ) relation exists ( V =0.048 L 1.29 ; R 2 =0.91). These findings imply that predicting Ephemeral gully length is a valuable alternative for the prediction of Ephemeral gully volume. A simple procedure to predict Ephemeral gully length based on topographical thresholds is presented here. Secondly, the empirical length–volume relation can also be used to convert Ephemeral gully length data extracted from aerial photos into Ephemeral gully volumes.

  • testing the Ephemeral gully erosion model egem for two mediterranean environments
    Earth Surface Processes and Landforms, 2001
    Co-Authors: Jeroen Nachtergaele, Liesbeth Vandekerckhove, Oostwoud D Wijdenes, Mariana Roxo
    Abstract:

    Few models can predict Ephemeral gully erosion rates (e.g. CREAMS, EGEM). The Ephemeral Gully Erosion Model (EGEM) was specifically developed to predict soil loss by Ephemeral gully erosion. Although EGEM claims to have a great potential in predicting soil losses by Ephemeral gully erosion, it has never been thoroughly tested. The objective of this study was to evaluate the suitability of EGEM for predicting Ephemeral gully erosion rates in Mediterranean environments. An EGEM-input data set for 86 Ephemeral gullies was collected: detailed measurements of 46 Ephemeral gullies were made in intensively cultivated land in southeast Spain (Guadalentin study area) and another 40 Ephemeral gullies were measured in both intensively cultivated land and abandoned land in southeast Portugal (Alentejo study area). Together with the assessment of all EGEM-input parameters, the actual eroded volume for each Ephemeral gully was also determined in the field. A very good relationship between predicted and measured Ephemeral gully volumes was found (R2 = 0·88). But as Ephemeral gully length is an EGEM input parameter, both predicted and measured Ephemeral gully volumes have to be divided by this Ephemeral gully length in order to test the predictive capability of EGEM. The resulting relationship between predicted and measured Ephemeral gully cross-sections is rather weak (R2 = 0·27). Therefore it can be concluded that EGEM is not capable of predicting Ephemeral gully erosion for the given Mediterranean areas. A second conclusion is that Ephemeral gully length is a key parameter in determining the Ephemeral gully volume. Regression analysis shows that a very significant relation between Ephemeral gully length and Ephemeral gully volume exists (R2 = 0·91). Accurate prediction of Ephemeral gully length is therefore crucial for assessing Ephemeral gully erosion rates. Copyright © 2001 John Wiley & Sons, Ltd.

  • assessment of soil losses by Ephemeral gully erosion using high altitude stereo aerial photographs
    Earth Surface Processes and Landforms, 1999
    Co-Authors: Jeroen Nachtergaele, Jean Poesen
    Abstract:

    The objective of this study is to explore in a critical way the potential of high-altitude (stereo) aerial photographs for the assessment of Ephemeral gully erosion rates. On 28 May 1995, an intensive rainfall event (30 mm h−1 during 30 min, return period = 3 years) occurred in central Belgium. Ephemeral gullies formed within an area of 218 ha (study area 1) were mapped and measured both in the field and by high-altitude aerial photos taken at the same time. Comparison of these two methods shows that if only one of the two surveying techniques had been used, only 75 per cent of the total Ephemeral gully length would have been detected, so that the combination of aerial and field data leads, in fact, to the best possible determination of total gully length within the selected area. A correction factor (C) is proposed, so that the results of an Ephemeral gully erosion survey based on high-altitude (stereo) aerial photos can be adjusted for the undetected gullies. Next, a sequential series of high-altitude stereo aerial photographs, taken in six different years, was analysed in order to determine Ephemeral gully erosion rates in three selected study areas (study areas 2, 3 and 4). Selection criteria were chosen so that these three areas were similar to study area 1 and representative for the cultivated areas in central Belgium where intense soil erosion regularly occurs. Ephemeral gullies were mapped and their total length was measured from the aerial photos. Using a mean gully cross-section of 0·2635 m2 (determined in study area 1), the average eroded volume is 1·89 m3 ha−1 in six months for study area 1, 0·86 m3 ha−1 in six months for area 2, 1·44 m3 ha−1 in six months for area 3, and 2·37 m3 ha−1 in six months for area 4. According to the correction factor (C), these mean Ephemeral gully erosion volumes have to be increased by 44 per cent. The Ephemeral gully erosion rates based on high-altitude stereo aerial photos, correspond well with the results of other surveys carried out in the Belgian loess belt. Copyright © 1999 John Wiley & Sons, Ltd.

Mariana Roxo - One of the best experts on this subject based on the ideXlab platform.

  • testing the Ephemeral gully erosion model egem for two mediterranean environments
    Earth Surface Processes and Landforms, 2001
    Co-Authors: Jeroen Nachtergaele, Liesbeth Vandekerckhove, Oostwoud D Wijdenes, Mariana Roxo
    Abstract:

    Few models can predict Ephemeral gully erosion rates (e.g. CREAMS, EGEM). The Ephemeral Gully Erosion Model (EGEM) was specifically developed to predict soil loss by Ephemeral gully erosion. Although EGEM claims to have a great potential in predicting soil losses by Ephemeral gully erosion, it has never been thoroughly tested. The objective of this study was to evaluate the suitability of EGEM for predicting Ephemeral gully erosion rates in Mediterranean environments. An EGEM-input data set for 86 Ephemeral gullies was collected: detailed measurements of 46 Ephemeral gullies were made in intensively cultivated land in southeast Spain (Guadalentin study area) and another 40 Ephemeral gullies were measured in both intensively cultivated land and abandoned land in southeast Portugal (Alentejo study area). Together with the assessment of all EGEM-input parameters, the actual eroded volume for each Ephemeral gully was also determined in the field. A very good relationship between predicted and measured Ephemeral gully volumes was found (R2 = 0·88). But as Ephemeral gully length is an EGEM input parameter, both predicted and measured Ephemeral gully volumes have to be divided by this Ephemeral gully length in order to test the predictive capability of EGEM. The resulting relationship between predicted and measured Ephemeral gully cross-sections is rather weak (R2 = 0·27). Therefore it can be concluded that EGEM is not capable of predicting Ephemeral gully erosion for the given Mediterranean areas. A second conclusion is that Ephemeral gully length is a key parameter in determining the Ephemeral gully volume. Regression analysis shows that a very significant relation between Ephemeral gully length and Ephemeral gully volume exists (R2 = 0·91). Accurate prediction of Ephemeral gully length is therefore crucial for assessing Ephemeral gully erosion rates. Copyright © 2001 John Wiley & Sons, Ltd.

Fairfield University Art Museum - One of the best experts on this subject based on the ideXlab platform.

Jean Poesen - One of the best experts on this subject based on the ideXlab platform.

  • characteristics controlling factors and importance of deep gullies under cropland on loess derived soils
    Geomorphology, 2005
    Co-Authors: Tom Vanwalleghem, Jeroen Nachtergaele, Jean Poesen, Gert Verstraeten
    Abstract:

    Abstract Several studies describe the formation and importance of shallow Ephemeral gullies under cropland (depth Comparison of a dataset with 28 deep gullies, formed in the period 1985–2003 and 123 shallow Ephemeral gullies formed in the period 1994–1999 in central Belgium indicates that the deep gullies have clearly different morphological characteristics compared to shallow Ephemeral gullies. Several factors were analyzed to understand the formation of deep gullies. Plotting runoff contributing area versus slope of the soil surface at the gully head indicates that the topographical threshold for deep gully formation is significantly larger compared to Ephemeral gully formation. Deep gullies form on short, steep valley sides and their position is strongly affected by the presence of linear landscape elements. All deep gullies incised on landscape positions with a very erodible soil horizon at shallow depth. Analysis of causative rainfall showed no significant differences in incision thresholds between rills and shallow Ephemeral gullies on the one hand and deep gullies on the other hand. The relation between area-specific sediment yield in central Belgium and drainage area, indicates that the development of deep gullies contributes significantly to the sediment output of small rural catchments and causes peaks in the mean area-specific sediment yield that are up to a factor of three higher compared with catchments where shallow Ephemeral gullying occurs.

  • the value of a physically based model versus an empirical approach in the prediction of Ephemeral gully erosion for loess derived soils
    Geomorphology, 2001
    Co-Authors: Jeroen Nachtergaele, Jean Poesen, An Steegen, I Takken, L Beuselinck, L Vandekerckhove, Gerard Govers
    Abstract:

    Abstract A data set on soil losses and controlling factors for 58 Ephemeral gullies has been collected in the Belgian loess belt from March 1997 to March 1999. Of the observed Ephemeral gullies, 32 developed at the end of winter or in early spring (winter gullies) and 26 Ephemeral gullies developed during summer (summer gullies). The assessed data have been used to test the physically based Ephemeral Gully Erosion Model (EGEM) and to compare its performance with the value of simple topographical and morphological indices in the prediction of Ephemeral gully erosion. Analysis shows that EGEM is not capable of predicting Ephemeral gully cross-sections well. Although conditions for input parameter assessment were ideal, some parameters such as channel erodibility, critical flow shear stress and local rainfall depth showed great uncertainty. Rather than revealing EGEM's inability of predicting Ephemeral gully erosion, this analysis stresses the problematic nature of physically based models, since they often require input parameters that are not available or can hardly be obtained. With respect to the value of simple topographical and morphological indices in predicting Ephemeral gully erosion, this study shows that for winter gullies and summer gullies, respectively, over 80% and about 75% of the variation in Ephemeral gully volume can be explained when Ephemeral gully length is known. Moreover, when previously collected data for Ephemeral gullies in two Mediterranean study areas and the data for summer gullies formed in the Belgian loess belt are pooled, it appears that one single length ( L )–volume ( V ) relation exists ( V =0.048 L 1.29 ; R 2 =0.91). These findings imply that predicting Ephemeral gully length is a valuable alternative for the prediction of Ephemeral gully volume. A simple procedure to predict Ephemeral gully length based on topographical thresholds is presented here. Secondly, the empirical length–volume relation can also be used to convert Ephemeral gully length data extracted from aerial photos into Ephemeral gully volumes.

  • assessment of soil losses by Ephemeral gully erosion using high altitude stereo aerial photographs
    Earth Surface Processes and Landforms, 1999
    Co-Authors: Jeroen Nachtergaele, Jean Poesen
    Abstract:

    The objective of this study is to explore in a critical way the potential of high-altitude (stereo) aerial photographs for the assessment of Ephemeral gully erosion rates. On 28 May 1995, an intensive rainfall event (30 mm h−1 during 30 min, return period = 3 years) occurred in central Belgium. Ephemeral gullies formed within an area of 218 ha (study area 1) were mapped and measured both in the field and by high-altitude aerial photos taken at the same time. Comparison of these two methods shows that if only one of the two surveying techniques had been used, only 75 per cent of the total Ephemeral gully length would have been detected, so that the combination of aerial and field data leads, in fact, to the best possible determination of total gully length within the selected area. A correction factor (C) is proposed, so that the results of an Ephemeral gully erosion survey based on high-altitude (stereo) aerial photos can be adjusted for the undetected gullies. Next, a sequential series of high-altitude stereo aerial photographs, taken in six different years, was analysed in order to determine Ephemeral gully erosion rates in three selected study areas (study areas 2, 3 and 4). Selection criteria were chosen so that these three areas were similar to study area 1 and representative for the cultivated areas in central Belgium where intense soil erosion regularly occurs. Ephemeral gullies were mapped and their total length was measured from the aerial photos. Using a mean gully cross-section of 0·2635 m2 (determined in study area 1), the average eroded volume is 1·89 m3 ha−1 in six months for study area 1, 0·86 m3 ha−1 in six months for area 2, 1·44 m3 ha−1 in six months for area 3, and 2·37 m3 ha−1 in six months for area 4. According to the correction factor (C), these mean Ephemeral gully erosion volumes have to be increased by 44 per cent. The Ephemeral gully erosion rates based on high-altitude stereo aerial photos, correspond well with the results of other surveys carried out in the Belgian loess belt. Copyright © 1999 John Wiley & Sons, Ltd.

Fa Lee - One of the best experts on this subject based on the ideXlab platform.

  • bovine Ephemeral fever in asia recent status and research gaps
    Viruses, 2019
    Co-Authors: Fa Lee
    Abstract:

    Bovine Ephemeral fever is an arthropod-borne viral disease affecting mainly domestic cattle and water buffalo. The etiological agent of this disease is bovine Ephemeral fever virus, a member of the genus Ephemerovirus within the family Rhabdoviridae. Bovine Ephemeral fever causes economic losses by a sudden drop in milk production in dairy cattle and loss of condition in beef cattle. Although mortality resulting from this disease is usually lower than 1%, it can reach 20% or even higher. Bovine Ephemeral fever is distributed across many countries in Asia, Australia, the Middle East, and Africa. Prevention and control of the disease mainly relies on regular vaccination. The impact of bovine Ephemeral fever on the cattle industry may be underestimated, and the introduction of bovine Ephemeral fever into European countries is possible, similar to the spread of bluetongue virus and Schmallenberg virus. Research on bovine Ephemeral fever remains limited and priority of investigation should be given to defining the biological vectors of this disease and identifying virulence determinants.

  • invasion of exotic bovine Ephemeral fever virus into taiwan in 2013 2014
    Veterinary Microbiology, 2016
    Co-Authors: Luje Ting, Mingshiuh Lee, Mingchu Cheng, Fa Lee
    Abstract:

    Abstract Bovine Ephemeral fever virus is a member of the family Rhabdoviridae and bovine Ephemeral fever has frequently affected cattle population in Taiwan since 1967. During the outbreaks in 2013 and 2014, exotic bovine Ephemeral fever viruses were detected by reverse transcription polymerase chain reaction and nucleotide sequencing. Sequence comparison showed that the exotic viruses shared 99.0–99.4% nucleotide identities (99.4–100.0% amino acid identities) with Chinese viruses and, on the contrary, 96.2–97.2% nucleotide identities (97.8–98.6% amino acid identities) with indigenous Taiwanese viruses. Additionally, our phylogenetic analysis also supported that the newly invaded bovine Ephemeral fever viruses were closely related to the Chinese strains. These exotic 2013–2014 viruses have become prevalent and displaced indigenous virus strains since their appearance.