# Distribution characteristics of gullies with slope gradient in Northeast China

- College of Water Conservancy, Shenyang Agricultural University, Shenyang, China (fanhaoming@163.com)

Twenty selected watersheds were divided into five small watershed sets according to location in Liaoning Province (LN), China. Watersheds and slopes were extracted from a 1:50,000 DEM, and gully data for each watershed were obtained by remote sensing interpretation. The gullies and associated slopes within the small watersheds were identified, and the distributions of gully density, proportion of dissected land, and gully length-width ratio in each small LN watershed and in the five small watershed sets were obtained. The correlations between the small watershed sets and the gully distributions throughout LN demonstrate regional distribution differences, and the watershed area has a great influence on both the area and length of gullies. Regional differences are present in the gully density and the proportion of dissected land in the small watersheds. The distribution of gullies with respect to slope depends on both the gully parameters and the proportion of terrain in the different slope grade ranges. The distribution results for the five small watershed sets are similar to those from a census of the Liaoning-Around Bohai mountainous and hilly sub-region. The gully density and proportion of dissected land in LN showed a single-peak curve with respect to slope, with slope thresholds of 8° and 5°, respectively. The constructed distribution equation has a high degree of fit. The comprehensive distributions of gully density, proportion of dissected land, and length-width ratio with slope indicate that gully erosion in LN is serious within the slope range of 3~8°.

**How to cite:**
Fan, H. M. and Wang, D. C.: Distribution characteristics of gullies with slope gradient in Northeast China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2875, https://doi.org/10.5194/egusphere-egu2020-2875, 2020

## Comments on the display

AC: Author Comment |CC: Community Comment | Report abusedisplays version 1– uploaded on 03 May 2020AC1: Distribution characteristics of gullies with slope gradient in Northeast China, Hao Ming Fan, 06 May 20201.Introduction

1.1 Serious gully erosion:

Gully destroy farmland.

After several years of farming, we can find gullies in most of the slope farmland, and these gullies destroy the land year by year.

Gully cut off country road.

The country road cut off by the gully, and farm machine can’t across the road; Farmers are worried that their crops will not get out of their fields.

Gully destroy woodland and grassland.

Trees fell into the developing gully.

1.2 The combined use of RS, GIS, and GPS is gradually emerging in the field of soil erosion . Although the precision of a remote sensing interpretation is relatively poor compared with that of an interpretation using GPS data and drone imagery , remote sensing platforms are suitable for the acquisition of data over large spatial scales.

GPS measurements are used in the study of the distribution of erosion channels in small watersheds and are combined with other watershed data for analysis. Large-scale distribution studies are based on remote sensing interpretation. There is a lack of transition between small watershed studies and large regional studies

Therefore, by selecting 20 small watersheds, erosion gullies are identified via remote sensing interpretation, and the differences in the distribution of erosion gullies between different watersheds are studied. Consequently, this work built the relationship of small-scale and large-scale studies

2. Materials and methods

2.1 Study area: Liaoning Province, China.

The center is the Liao River plain.Theland area proportions of mountainous terrain, plains, and water bodies are 58%, 33% and 9%, respectively. Mountainous hills are roughly distributed along the eastern and western sides.

2.2 Location of the small watersheds

Tab. 1 Table of parameters of the small watersheds and gullies

2.3 Data acquisition

The data on the small watersheds and gullies in this study were based on the soil erosion census data of LN collected in 2015. The extraction threshold for small watersheds was iteratively established based on a 1:50,000 digital elevation model (DEM) and 845 river basins in LN with an area of more than 50 km2, and the threshold was then compared with that of a typical small watershed. Finally, the threshold was set to 10000

A general investigation of gullies was carried out based on remote sensing images with a resolution of 2 m and a 1:50,000 DEM. Interactive GIS techniques were used to extract information on the length, area, type, longitudinal gradient, and location of the gullies. The steps in these interactive GIS techniques include (1) transforming the projection, (2) correcting the RS images to eliminate band and spot errors, (3) joining and splitting the images, and (4) loading the images into a database. The RS data are then checked through interpretation and field surveys to avoid missing data and errors, and an attribute table and spatial data for each gully can then be successfully created. The gully survey object is a channel with a length of 100~5000 m, which can be clearly identified in a remote sensing

image.

The slopes were divided into nine classes, which were derived from the Standard of Water and Soil Conservation in the Black Soil Region (SL-2009)

The DEM of the slope was converted into polygons and stored as shape files to enable the distributions to be extracted. The small watershed data and gully data were superimposed to ensure that no erosion gullies within the small watershed were statistically lost; subsequently, related parameters, such as the erosion gully length and area, were calculated. These parameters were then superimposed with the slope layer to obtain the gully slope distribution features

3. Results and discussion

3.1 Distribution characteristics of gullies in the small

Tab. 2 Correlation coefficients between the areas of small watersheds and gully parameters

Tab. 3 Correlation coefficients between the small watershed area and gully parameters

3.2 Distribution characteristics of gully density along slope gradient

Fig.2 Distribution of gully densityTab. 4 Correlation between the slope and gully density in the watershed sets

Although the gully density is not related to the proportion of each slope range in the small watershed, the influence of the topography on the gully density distribution can be determined by comparing the trend of the gully density distributions among the different small watersheds and the five watershed sets.

For slopes of 0~0.25°, the gully densities are higher in the northern and middle small watershed sets than in others. This pattern is chiefly because the proportions of the slope areas in the northern and middle watershed sets are smaller than those of the gullies within this slope range. The gully density in the middle small watershed set is obviously higher than those in the other small watershed sets in the slope gradient range from 25 to 90°.

Although the proportion of the slope gradient (0.16%) and the proportion of the gully length (0.39%) are low, they are different by a factor of 2.44, which is obviously larger than the differences associated with the other slope classes in this small watershed set. Therefore, the distribution of gullies is correlated with the topography.

3.3 Distribution characteristics of the proportion of dissected land along the slope gradient

Fig. 3 Distribution of the proportion of land cut by gullies

The gully data from the five watershed sets were again integrated with the terrain data. The results show that the proportion of land cut by gullies increases with the slope gradient, forming a single-peak curve consistent with the gully density distribution curve. The proportion of dissected land first increases and then decreases with the slope gradient, and it increases when the slope gradient is greater than 5°.

3.4 Distribution characteristics of the gully length-width ratio along the slope gradient

Fig. 4 Length-width ratio distribution of gullies

As the slope increases, the gullies gradually change from short and wide to long and thin upon reaching the first slope threshold. Although only one threshold exists in the western small watershed set, two slope thresholds exist in the eastern, middle, and southern small watershed sets. The southern small watershed set displays the first gradient threshold at 1.5°, while the other three sets present their first gradient threshold (the only one in the western small watershed set) at 3°. In these small watershed sets, when the slope is 5°, the gullies transition from being short and wide to being long and thin.

4. Conclusions

Each watershed set has its own distribution characteristics in terms of the gully density, the proportion of dissected land and the gully length-width ratio. The distribution of gullies with respect to the slope depends on both the gully parameters and the proportion of terrain in the slope grade ranges.

The gully density and the proportion of land dissected by gullies in Liaoning Province showed single-peak curves with increasing slope, with slope thresholds of 8°

and 5°, respectively. The constructed distribution equations have a high degree of fit.

The length-width ratio of each small watershed set changes repeatedly with increasing slope. However, an analysis of the gully density and the proportion of dissected land revealed that the gully density and proportion of dissected land are larger in the slope range of 3~8°and that the length-width ratio is small in this slope range. Therefore, many relatively short gullies are located within this slope range and that gully erosion is serious.

Thanks for your attention

AC2: Distribution characteristics of gullies with slope gradient in Northeast China, Hao Ming Fan, 06 May 20201.Introduction

1.1 Serious gully erosion:

Gully destroy farmland.

After several years of farming, we can find gullies in most of the slope farmland, and these gullies destroy the land year by year.

Gully cut off country road.

The country road cut off by the gully, and farm machine can’t across the road; Farmers are worried that their crops will not get out of their fields.

Gully destroy woodland and grassland.

Trees fell into the developing gully.

1.2 The combined use of RS, GIS, and GPS is gradually emerging in the field of soil erosion . Although the precision of a remote sensing interpretation is relatively poor compared with that of an interpretation using GPS data and drone imagery , remote sensing platforms are suitable for the acquisition of data over large spatial scales.

GPS measurements are used in the study of the distribution of erosion channels in small watersheds and are combined with other watershed data for analysis. Large-scale distribution studies are based on remote sensing interpretation. There is a lack of transition between small watershed studies and large regional studies

Therefore, by selecting 20 small watersheds, erosion gullies are identified via remote sensing interpretation, and the differences in the distribution of erosion gullies between different watersheds are studied. Consequently, this work built the relationship of small-scale and large-scale studies

2. Materials and methods

2.1 Study area: Liaoning Province, China.

The center is the Liao River plain.Theland area proportions of mountainous terrain, plains, and water bodies are 58%, 33% and 9%, respectively. Mountainous hills are roughly distributed along the eastern and western sides.

2.2 Location of the small watersheds

Tab. 1 Table of parameters of the small watersheds and gullies

2.3 Data acquisition

The data on the small watersheds and gullies in this study were based on the soil erosion census data of LN collected in 2015. The extraction threshold for small watersheds was iteratively established based on a 1:50,000 digital elevation model (DEM) and 845 river basins in LN with an area of more than 50 km2, and the threshold was then compared with that of a typical small watershed. Finally, the threshold was set to 10000

A general investigation of gullies was carried out based on remote sensing images with a resolution of 2 m and a 1:50,000 DEM. Interactive GIS techniques were used to extract information on the length, area, type, longitudinal gradient, and location of the gullies. The steps in these interactive GIS techniques include (1) transforming the projection, (2) correcting the RS images to eliminate band and spot errors, (3) joining and splitting the images, and (4) loading the images into a database. The RS data are then checked through interpretation and field surveys to avoid missing data and errors, and an attribute table and spatial data for each gully can then be successfully created. The gully survey object is a channel with a length of 100~5000 m, which can be clearly identified in a remote sensing

image.

The slopes were divided into nine classes, which were derived from the Standard of Water and Soil Conservation in the Black Soil Region (SL-2009)

The DEM of the slope was converted into polygons and stored as shape files to enable the distributions to be extracted. The small watershed data and gully data were superimposed to ensure that no erosion gullies within the small watershed were statistically lost; subsequently, related parameters, such as the erosion gully length and area, were calculated. These parameters were then superimposed with the slope layer to obtain the gully slope distribution features

3. Results and discussion

3.1 Distribution characteristics of gullies in the small

Tab. 2 Correlation coefficients between the areas of small watersheds and gully parameters

Tab. 3 Correlation coefficients between the small watershed area and gully parameters

3.2 Distribution characteristics of gully density along slope gradient

Fig.2 Distribution of gully densityTab. 4 Correlation between the slope and gully density in the watershed sets

Although the gully density is not related to the proportion of each slope range in the small watershed, the influence of the topography on the gully density distribution can be determined by comparing the trend of the gully density distributions among the different small watersheds and the five watershed sets.

For slopes of 0~0.25°, the gully densities are higher in the northern and middle small watershed sets than in others. This pattern is chiefly because the proportions of the slope areas in the northern and middle watershed sets are smaller than those of the gullies within this slope range. The gully density in the middle small watershed set is obviously higher than those in the other small watershed sets in the slope gradient range from 25 to 90°.

Although the proportion of the slope gradient (0.16%) and the proportion of the gully length (0.39%) are low, they are different by a factor of 2.44, which is obviously larger than the differences associated with the other slope classes in this small watershed set. Therefore, the distribution of gullies is correlated with the topography.

3.3 Distribution characteristics of the proportion of dissected land along the slope gradient

Fig. 3 Distribution of the proportion of land cut by gullies

The gully data from the five watershed sets were again integrated with the terrain data. The results show that the proportion of land cut by gullies increases with the slope gradient, forming a single-peak curve consistent with the gully density distribution curve. The proportion of dissected land first increases and then decreases with the slope gradient, and it increases when the slope gradient is greater than 5°.

3.4 Distribution characteristics of the gully length-width ratio along the slope gradient

Fig. 4 Length-width ratio distribution of gullies

As the slope increases, the gullies gradually change from short and wide to long and thin upon reaching the first slope threshold. Although only one threshold exists in the western small watershed set, two slope thresholds exist in the eastern, middle, and southern small watershed sets. The southern small watershed set displays the first gradient threshold at 1.5°, while the other three sets present their first gradient threshold (the only one in the western small watershed set) at 3°. In these small watershed sets, when the slope is 5°, the gullies transition from being short and wide to being long and thin.

4. Conclusions

Each watershed set has its own distribution characteristics in terms of the gully density, the proportion of dissected land and the gully length-width ratio. The distribution of gullies with respect to the slope depends on both the gully parameters and the proportion of terrain in the slope grade ranges.

The gully density and the proportion of land dissected by gullies in Liaoning Province showed single-peak curves with increasing slope, with slope thresholds of 8°

and 5°, respectively. The constructed distribution equations have a high degree of fit.

The length-width ratio of each small watershed set changes repeatedly with increasing slope. However, an analysis of the gully density and the proportion of dissected land revealed that the gully density and proportion of dissected land are larger in the slope range of 3~8°and that the length-width ratio is small in this slope range. Therefore, many relatively short gullies are located within this slope range and that gully erosion is serious.

Thanks for your attention

AC3: Comment on EGU2020-2875, Hao Ming Fan, 06 May 20201.Introduction

1.1 Serious gully erosion:

Gully destroy farmland.

After several years of farming, we can find gullies in most of the slope farmland, and these gullies destroy the land year by year.

Gully cut off country road.

The country road cut off by the gully, and farm machine can’t across the road; Farmers are worried that their crops will not get out of their fields.

Gully destroy woodland and grassland.

Trees fell into the developing gully.

1.2 The combined use of RS, GIS, and GPS is gradually emerging in the field of soil erosion . Although the precision of a remote sensing interpretation is relatively poor compared with that of an interpretation using GPS data and drone imagery , remote sensing platforms are suitable for the acquisition of data over large spatial scales.

GPS measurements are used in the study of the distribution of erosion channels in small watersheds and are combined with other watershed data for analysis. Large-scale distribution studies are based on remote sensing interpretation. There is a lack of transition between small watershed studies and large regional studies

Therefore, by selecting 20 small watersheds, erosion gullies are identified via remote sensing interpretation, and the differences in the distribution of erosion gullies between different watersheds are studied. Consequently, this work built the relationship of small-scale and large-scale studies

2. Materials and methods

2.1 Study area: Liaoning Province, China.

The center is the Liao River plain.Theland area proportions of mountainous terrain, plains, and water bodies are 58%, 33% and 9%, respectively. Mountainous hills are roughly distributed along the eastern and western sides.

2.2 Location of the small watersheds

Tab. 1 Table of parameters of the small watersheds and gullies

2.3 Data acquisition

The data on the small watersheds and gullies in this study were based on the soil erosion census data of LN collected in 2015. The extraction threshold for small watersheds was iteratively established based on a 1:50,000 digital elevation model (DEM) and 845 river basins in LN with an area of more than 50 km2, and the threshold was then compared with that of a typical small watershed. Finally, the threshold was set to 10000

A general investigation of gullies was carried out based on remote sensing images with a resolution of 2 m and a 1:50,000 DEM. Interactive GIS techniques were used to extract information on the length, area, type, longitudinal gradient, and location of the gullies. The steps in these interactive GIS techniques include (1) transforming the projection, (2) correcting the RS images to eliminate band and spot errors, (3) joining and splitting the images, and (4) loading the images into a database. The RS data are then checked through interpretation and field surveys to avoid missing data and errors, and an attribute table and spatial data for each gully can then be successfully created. The gully survey object is a channel with a length of 100~5000 m, which can be clearly identified in a remote sensing

image.

The slopes were divided into nine classes, which were derived from the Standard of Water and Soil Conservation in the Black Soil Region (SL-2009)

The DEM of the slope was converted into polygons and stored as shape files to enable the distributions to be extracted. The small watershed data and gully data were superimposed to ensure that no erosion gullies within the small watershed were statistically lost; subsequently, related parameters, such as the erosion gully length and area, were calculated. These parameters were then superimposed with the slope layer to obtain the gully slope distribution features

3. Results and discussion

3.1 Distribution characteristics of gullies in the small

Tab. 2 Correlation coefficients between the areas of small watersheds and gully parameters

Tab. 3 Correlation coefficients between the small watershed area and gully parameters

3.2 Distribution characteristics of gully density along slope gradient

Fig.2 Distribution of gully densityTab. 4 Correlation between the slope and gully density in the watershed sets

Although the gully density is not related to the proportion of each slope range in the small watershed, the influence of the topography on the gully density distribution can be determined by comparing the trend of the gully density distributions among the different small watersheds and the five watershed sets.

For slopes of 0~0.25°, the gully densities are higher in the northern and middle small watershed sets than in others. This pattern is chiefly because the proportions of the slope areas in the northern and middle watershed sets are smaller than those of the gullies within this slope range. The gully density in the middle small watershed set is obviously higher than those in the other small watershed sets in the slope gradient range from 25 to 90°.

Although the proportion of the slope gradient (0.16%) and the proportion of the gully length (0.39%) are low, they are different by a factor of 2.44, which is obviously larger than the differences associated with the other slope classes in this small watershed set. Therefore, the distribution of gullies is correlated with the topography.

3.3 Distribution characteristics of the proportion of dissected land along the slope gradient

Fig. 3 Distribution of the proportion of land cut by gullies

The gully data from the five watershed sets were again integrated with the terrain data. The results show that the proportion of land cut by gullies increases with the slope gradient, forming a single-peak curve consistent with the gully density distribution curve. The proportion of dissected land first increases and then decreases with the slope gradient, and it increases when the slope gradient is greater than 5°.

3.4 Distribution characteristics of the gully length-width ratio along the slope gradient

Fig. 4 Length-width ratio distribution of gullies

As the slope increases, the gullies gradually change from short and wide to long and thin upon reaching the first slope threshold. Although only one threshold exists in the western small watershed set, two slope thresholds exist in the eastern, middle, and southern small watershed sets. The southern small watershed set displays the first gradient threshold at 1.5°, while the other three sets present their first gradient threshold (the only one in the western small watershed set) at 3°. In these small watershed sets, when the slope is 5°, the gullies transition from being short and wide to being long and thin.

4. Conclusions

Each watershed set has its own distribution characteristics in terms of the gully density, the proportion of dissected land and the gully length-width ratio. The distribution of gullies with respect to the slope depends on both the gully parameters and the proportion of terrain in the slope grade ranges.

The gully density and the proportion of land dissected by gullies in Liaoning Province showed single-peak curves with increasing slope, with slope thresholds of 8°

and 5°, respectively. The constructed distribution equations have a high degree of fit.

The length-width ratio of each small watershed set changes repeatedly with increasing slope. However, an analysis of the gully density and the proportion of dissected land revealed that the gully density and proportion of dissected land are larger in the slope range of 3~8°and that the length-width ratio is small in this slope range. Therefore, many relatively short gullies are located within this slope range and that gully erosion is serious.

Thanks for your attention