Watershed prioritization for soil erosion mapping for the Lesser Himalayan Indian basin using PCA, WSA method in conjunction with morphometric parameters and GIS-based approach

Watersheds in the subtropical Himalayan basins are highly prone to land degradation due to deforestation, landslides, intensive agriculture, population pressure, and overgrazing, in particular, where various fluvial and denudation processes occur. It is important to assess the magnitude of problem and to understand the erosion process under normal conditions, so that effective measures can be implemented. Therefore, the study selected Kalsa watershed from the Lesser Himalayan region, where soil erosion is more prominent. Regarding this issue, to identify the hotspot of soil erosion of the basin, watershed prioritization methods using advanced geographical information system and remote sensing techniques integrated with weighted sum analysis (WSA) and principal component analysis (PCA). In addition, a comparison has been made to evaluate the performance of these models. The study considered sixteen different morphometric parameters, including linear (Rho coefficient, stream frequency, drainage density, length of overland flow, drainage texture, and constant of channel maintenance); landscape (relative relief, relief ratio, basin slope, and ruggedness number); and shape (elongation ratio, form factor, circulatory ratio, and compactness coefficient). Both the method PCA and WSA indicate the same results showing high priority, meaning the outlet watersheds have high priority. The sub-watersheds in the north-eastern part have the lowest priority. The results also show that the length overland flow, relative relief, basin relief ratio and hypsometric integral are the most important indicators. The sub-watersheds prioritize high ranks, medium ranks, and low ranks out of 10 sub-watersheds covering about 45.32%, 27.78% and 26.90% area of the Kalsa River watershed, respectively. This study will help regional planners, farmers, and governments take more detailed decisions to propose efficient soil erosion control measures and conservation priorities of the watershed. The study findings have implications for sustainable land management and conservation goal targets (target 2.3 and 2.4; target 3.9; target 13.1, 13.2 and 13.3; target 15.3 and 15.4), which finally helps to achieve the United Nation’s 2030 Agenda for Sustainable Development.

Changes in gully sizes: the role of interactions between land-use changes and other driving factors

<p>Changes in gully sizes are brought about by the interactions among gully-driving factors. The aim of this paper is to understand how interactions among land-use changes and other gully-drivers: relative relief, maximum slope, proximity to rivers and roads influence changes in gully length and gullied area. The study area covers 535 km<sup>2</sup> in the Orlu region of southeast Nigeria. Gully heads were mapped using high resolution data (0.61 – 5m) acquired in November 2009 and December 2018 while supervised land-use classification was undertaken for both years. Three land-use classes were identified: non-vegetated, open vegetation and fallow. Geomorphic variables were acquired from the 30 m SRTM-DEM while gully head distances from rivers and roads were calculated using the distance tool in ArcGIS. Two sets of multiple regression analyses were undertaken, first to understand effects of land-use changes and secondly to ascertain influence of the other driving factors on changes in gully sizes. Non-vegetated surfaces increased from 58.6 km<sup>2</sup> to 144.7 km<sup>2</sup> between 2009 and 2018, while reduction in fallowed lands from 281.2 km<sup>2</sup> to 57.8 km<sup>2</sup> was observed. Of the 58.6 km<sup>2</sup> of non-vegetated lands in 2009, 10.9 km<sup>2</sup> were converted to open vegetation, while 0.18 km<sup>2</sup> was transformed to fallow in 2018, 50.9 km<sup>2</sup> of fallow-cover remained the same between 2009 and 2018 while 29 km<sup>2</sup> were converted to non-vegetated and 201.3 km<sup>2</sup> were used for open vegetation in 2018. These land use changes will likely increase volume of surface runoff.  Gully numbers grew from 26 to 39, mean gully length increased from 0.26 to 0.43 km which translates to a mean headward retreat of 17 m yr<sup>-1</sup>. Total length of all gullies changed from 10.22 to 16.63 km. Mean gullied area increased from 13775 to 16183 m<sup>2</sup>, indicating an areal retreat of 241 m<sup>2</sup> yr<sup>-1</sup>, total gullied area grew from 0.36 km<sup>2 </sup>to 0.62 km<sup>2</sup>. Relative relief ranged between 6 – 46 m, lands around the rivers had the highest concentration of gullies, and there was a sharp rise in slope from 0 – 58.2% within a distance less than 500 m from the rivers. The first Multiple regression result indicated that associations between changes in gully length, non-vegetated and fallow land-use classes were significant at 0.05. Results of the second multiple regression analysis showed that only gully head distance from rivers had a significant positive effect on changes in gullied area. Bearing in mind the configuration of the land and rise in slope from rivers, increased volume of surface runoff (caused by changes in land use and higher slope rise) can attain higher erosive power as it approaches the river. This increased surface flow passing through gully channels on its way to the river, can enhance gully length and areal retreat.</p><p><strong>Keywords: Gully erosion, land-use changes, gully-drivers, south east Nigeria</strong></p>

GIS-based hillshade representation combined with relative relief as pseudo shade to enhance micro-topography

<p><strong>Abstract.</strong> Hillshade is a useful terrain representation that can express complicated topographic features on a map in 3D. However, the visual effects depend on the azimuth and the altitude of the light source corresponding to the target area. The purpose of this study is to provide a new method of GIS-based hillshade which can recognize various topographies in greater detail while reducing the dependency on the light source. The azimuth dependency of the light source can be traced back to the time of handwritten mapping, when cartographers combined multiple hillshades with differing azimuth settings.</p><p>The authors of this study first tried to combine three types of hillshade (A, B and C, Figure1-3) that had not only different light sources but also different grayscale gradients. Hillshade A had a light source from the upper side of the map with the darkest grayscale gradient. Hillshade B had a light source from the left side with a medium grayscale gradient. Finally, Hillshade C’s light source was from the right side of the map with the brightest grayscale gradient. We confirmed that combining Hillshades A to C reproduces the same natural shading as that of a single light source from the upper left.</p><p>The next purpose of the study was to enhance the topographic features of hillshade maps without overemphasizing the elevation factor in the GIS. We attempted to combine various topographic values through spatial analysis using a DEM in the GIS. Thus, we decided to combine a relative relief—a topographic value of maximum elevation change rate—as a pseudo shade (Figure4). However, because synthesizing the amount of relative relief in all directions overemphasizes the topography, we applied this only to downslope surfaces on the map created in the GIS. This pseudo shade works better for emphasizing micro-topography than does an upper light source in Hillshade A (Figure5).</p>

Prostorni raspored i gustoća ponikava jugoistočnog Velebita

Dolines are considered to be among the most prominent karst formations, which is why they can serve as diagnostic forms of karst. Their spatial distribution and density are important indicators of an area’s degree of karstification, as well as of an overall geomorphological development. The aim of this paper is to determine the spatial distribution and the density of dolines, and also to analyse the influence of geological structure and morphometric features of the terrain (hypsometry, slope inclination, relative relief) on the spatial distribution of dolines in the area of southeastern Velebit. Moreover, for the first time with regards to the Croatian karst, the spatial distribution of dolines was compared with the spatial distribution of entrances into caves in the southeastern Velebit’s area of Crnopac. The data on the dolines’ position were adopted from 1:25,000 scaled topographic maps. All data were digitalised and analysed with ArcGIS 10.1 software in the GIS laboratory of the Geographic Department of the Faculty of Science in Zagreb. The research showed a strong influence of morphometric parameters of the relief on dolines’ density. The most prominent occurrence of dolines is linked with the areas ranging from 1000 to 1200 meters of altitude, slope inclination lower than 2° and the relative relief of 100 – 200 m per km2. Furthermore, the highest density of dolines was recorded in the Jurassic carbonate layers, while it was determined that the zones of main faults do not have a significant influence on the increase of dolines’ density. A high degree of correlation was determined by comparing spatial distributions and density of dolines and entrances into caves.

Geoekološko vrjednovanje reljefa otoka Pašmana

The geoecological evaluation of the relief of Pašman Island from the standpoint of its touristic evaluation was conducted on the previously conducted geomorphologic analysis of the island relief. The evaluation was conducted for the needs of specific types of touristic activities (swimming, sunbathing, walking, "škraping") in the sense of its physical favourability, aesthetic value and accessibility.The method of relative relief evaluation was applied, whereby relief was evaluated within four morphographic categories: slopes, peaks, valley bottoms and beds and the coast. According to this method, as the principal restricting factor of tourist evaluation of certain parts of Pašman Island is the problem of inaccessibility, especially on the steeper south-west façade of the island (remoteness, inexistence or lack of arranged paths and wharfs). In accordance therewith, several proposals as possible solutions to the present problem were given (arrangement of paths, informing tourists on possible individual or group walks to certain destinations, organising trips with professional guides).