Spatial Distribution Of Gullies Research Articles

Quantitative effect of lithologic-geomorphic coupling on gully distribution at the regional scale: An example of the Dry Valleys (SW China)

Gully erosion is an important soil erosion type that destroys the surface structure and causes severe soil and water loss. Currently, the quantitative relationship between the spatial distribution of gullies and lithologic-geomorphic coupling is unclear. Gullies were interpreted by using high-resolution remote sensing image data to establish a database. Correlation analysis and geographic information technology were used to quantify the correlation between the gully distribution and lithologic-geomorphic types. The results show that the gully spatial distribution is characterized by clustering, and the lithologic-geomorphic type has a large effect on the spatial distribution of gullies. The coupling zone of phyllites and schists and intermediate-relief and intermediate-altitude mountains (P-II) has the greatest clustering; the zone of loose Quaternary sediments and intermediate-altitude plains (L-IP) has the least clustering. The lithologic-geomorphic coupling affects the initiation, development, and distribution of gullies; the more fragile the lithology and the greater the relief amplitude, the easier it is for gullies to form. This study will make it possible to better understand the distribution pattern and formation mechanism of gullies at a regional scale, and it will also provide a scientific reference for regional gully management.

Topo-edaphic, Vegetation Cover and Type Influence on Spatial Distribution of Gullies in Sengwa Wildlife Research Area (SWRA), North West Zimbabwe

Gully erosion is a common phenomenon in arid and semi-arid areas and is mostly influenced by soil type, topography, vegetation type and cover. The objective of the study was to determine the effect of topo-edaphic, vegetation type and cover on gully occurrence, hence map their spatial distribution in SWRA. A conventional method was used where field visit to known gully sites was done. At each site, GPS points were marked at three points, that is, at the head site, the middle and lower end of the gully. Soil samples, gully width, depth, length, vegetation type and cover were recorded for each point where GPS coordinates were collected. GPS points were overlaid on SWRA processed vegetation, soil and topographic map for analysis on the spatial distribution of gullies. Fifty-six gullies were recorded with highly affected areas on the southwestern side of the park. Associated soils types were clay and loam of the Madumabisa mudstone, colluvial and alluvial located at altitudes below 1000 meters. Gully occurrences were sighted more in mopane dominated woodlands with few recorded in areas dominated by acacia woodlands and on the edges of miombo woodlands, which occupy the high grounds of SWRA. Gully length varied from 20m in less developed gullies to 2520m for mature gullies with volumes ranging between 52m3 and 4649.4m3. Hence, topography, soil type, vegetation cover and type influence gully location and occurrence. Future research should aim to monitor changes in gully development using remote sensing as it provides a great potential for monitoring gully changes across the landscape.

Effect of Land Use Change on Gully Erosion Density in the Black Soil Region of Northeast China From 1965 to 2015: A Case Study of the Kedong County

Kedong County is typical of the black soil region of northeast China in being highly susceptible to accelerated soil erosion by gullying. Using data sourced from Corona satellite imagery for 1965, SPOT5 for 2005 and GF-1 for 2015, the spatial distribution of gullies in the research area was mapped. Land use data for 1965, 2005, and 2015 were obtained from the topographic map of 1954, and from Landsat images for 2005 and 2015. Over the last 50 years, the extent of gully erosion in the study area has increased markedly, most notably on cultivated land, while gully density rose from 2,756.16 m2/km2 to 14,294.19 m2/km2. Cultivating land on slopes, especially on slopes greater than ∼4°, may rapidly aggravate gully erosion. The greatest increases in gully density occurred in situations when cultivated land and other/degraded land were transformed, which gully erosion density increased by 49,526.69 m2/km2. Other/degraded land is the most vulnerable land in the study area, with the highest gully erosion density. In these cases, gully density initially increases and, although the “Grain for Green” project has been implemented, gully erosion density has not always declined in the recent past.

Influence of Geological Conditions on the Spatial Distribution of Gullies: A Case Study of the Yuanmou Dry-Hot Valley

Influence of Geological Conditions on the Spatial Distribution of Gullies: A Case Study of the Yuanmou Dry-Hot Valley

Primary environmental factors controlling gully distribution at the local and regional scale: An example from Northeastern China

Gully erosion is the main cause of global land degradation. The factors controlling gully erosion at watershed scale have been extensively studied, but the spatial pattern of gullies and their primary environmental factors are unclear. In order to explore the primary factors at the regional scale of over thousands of square kilometers, 34 sample areas were selected in northeastern China and 10 environmental factors were proposed. Based on gully interpretations from high-resolution Google Earth images and spatial analysis, kernel density estimation (with polyline features), and correlation analysis, the results show that the maximum kernel density (KD) of the 34 sample areas ranged from 0.11 to 87.16, and there were significant positive correlations between the average KD and the maximum value and standard deviation. At the regional scale, topography (relief amplitude, slope, surface roughness, surface incision, and elevation with correlation coefficients (ρ) of 0.60, 0.59, 0.57, 0.48, and 0.41 respectively) was the primary environmental factor, with a significant positive correlation with KD. The correlation coefficients of the normalized difference vegetation index (NDVI) (ρ = 0.32), annual precipitation (ρ = 0.19), and soil (silt, sand, and clay content with ρ of 0.139, −0.117, and 0.085, respectively) decreased successively with the KD. At sample area scale, there were six areas with weak correlations between environmental factors and KD, 20 areas with topographic factors, six areas with annual precipitation, and two areas with NDVI as the primary factor. The correlation between soil texture and KD was low. There were different positive or negative correlations between the environmental factors and KD. The spatial distribution of gullies in northeastern China is heterogeneous, and the primary environmental factors were diverse. This study will help to understand the spatial pattern and formation mechanism of gullies at large scale.

Effect of spatial scale on gully distribution in northeastern China

Gully erosion is one of the world’s major environmental problems, and it is also an important cause of land degradation. To reveal how gully distribution changes with spatial scale and the optimal scale for their evaluation, gullies in northeastern China were visually interpreted via high-resolution imagery, and the methods of geo-spatial statistics and kernel density estimation were used to quantitatively evaluate the distribution of gully clusters in 27 sampling areas. The results show that changes in scale always led to changes in the average value and standard deviation of the kernel density, whose trend was the same for average kernel density and standard deviation. The spatial distribution of gullies was characterized by heterogeneity; the average kernel density undergoes complex change with the scale, which varied drastically in the low-value portion of the scale range but was relatively stable in its high-value portion. For 70% of the sample areas, scale was significantly correlated with average kernel density and its standard deviation with high or medium correlation, for which the correlation coefficient of over 2/3 of the sample areas is positive. The average kernel density of each sample area varied with the scale used. These relationships were simulated with the linear, logarithmic, power, S, and exponential function models. According to the relationship between kernel density and scale, the maximum value or inflection point was then used to evaluate the optimal scale (i.e., proposed area) of the gully distribution. The optimal scale of different regions also differed among them, being closely related to the statistical characteristics of gully kernel density (correlation coefficients with standard deviation, average, and coefficient of variation were 0.60, 0.47, and 0.38, respectively).

Time will tell: temporal evolution of Martian gullies and palaeoclimatic implications

AbstractTo understand Martian palaeoclimatic conditions and the role of volatiles therein, the spatiotemporal evolution of gullies must be deciphered. While the spatial distribution of gullies has been extensively studied, their temporal evolution is poorly understood. We show that gully size is similar in very young and old craters. Gullies on the walls of very young impact craters (less than a few myr) typically cut into bedrock and are free of latitude-dependent mantle (LDM) and glacial deposits, while such deposits become increasingly evident in older craters. These observations suggest that gullies go through obliquity-driven degradation–accumulation cycles over time, controlled by: (1) LDM emplacement and degradation; and (2) glacial emplacement and removal. In glacially-influenced craters, the distribution of gullies on crater walls coincides with the extent of glacial deposits, which suggests that the melting of snow and ice played a role in the formation of these gullies. Yet, present-day activity is observed in some gullies on formerly glaciated crater walls. Moreover, in very young craters, extensive gullies have formed in the absence of LDM and glacial deposits, showing that gully formation can also be unrelated to these deposits. The Martian climate varied substantially over time, and the gully-forming mechanisms are likely to have varied accordingly.