• R D Garg

      Articles written in Journal of Earth System Science

    • Evaluation of topographic index in relation to terrain roughness and DEM grid spacing

      Samadrita Mukherjee Sandip Mukherjee R D Garg A Bhardwaj P L N Raju

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      Topographic index is an important attribute of digital elevation model (DEM) which indicates soil saturation. It is used for estimation of run-off, soil moisture, depth of ground water and hydrological simulation. Topographic index is derived from DEMs; hence the accuracy of DEM influences its computation. Commonly the raster based grid DEM is widely used to simulate hydrological model parameter, and accuracy varies with respect to DEM grid size and morphological characteristics of terrain. In this study topographic index is evaluated in terms of DEM grid size and terrain roughness. The study was carried out on four small watersheds, having different roughness characteristics, located over the Himalayan terrain. Topographic index surface is derived for each watershed from different grid spacing DEM (10–150 m), analysed and validated. It is found that DEM grid spacing affects the topographic index. The surface representation is smooth in the coarse grid spacing and the pattern of topographic index changes with grid spacing. The spatial autocorrelation of topographic index surface reduces when calculated from larger spacing DEM. The mean of the topographic index surface increases and standard deviation decreases with the increase of grid spacing and the effect is more pronounced in the rough terrain. Accuracy of the topographic index is also evaluated with respect to grid spacing and terrain roughness by comparing the topographic index surface with respect to reference data (10 m grid spacing topographic index surface). The RMSE and mean error of topographic index surface increases in larger grid spacing and the effect is more in rugged terrain.

    • Delineation of groundwater potential zone: An AHP/ANP approach

      Etishree Agarwal Rajat Agarwal R D Garg P K Garg

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      The sustainable development and management of groundwater resource requires precise quantitative assessment based on scientific principle and modern techniques. In the present study, groundwater potential zone are delineated using remote sensing, geographical information system (GIS) and multi-criteria decision making (MCDM) techniques in Unnao district, Uttar Pradesh. The analytical network process (ANP) is a method that makes it possible for one to deal systematically, and includes the analytical hierarchy process (AHP) as a special case. The AHP and ANP are used to determine the weights of various themes and their classes for identifying the groundwater potential zone. These weights are applied in a linear combination to obtain five different groundwater potential zone in the study area, namely ‘very poor’, ‘poor’, ‘moderate’, ‘good’ and ‘very good’. It has been concluded that about 153.39 km2 area has very good groundwater potential which is only 3.37% of the total study area. However, the area having very poor groundwater potential is about 850 km2 which is about 19.63% of the study area. The area having good, moderate and poor groundwater potential is about 540.25, 1135.5, 1868.6 km2, respectively. The groundwater potential zone map was finally verified using the well yield data of 37 pumping wells, and the result was found satisfactory.

    • Accuracy of Cartosat-1 DEM and its derived attribute at multiple scale representation

      Samadrita Mukherjee Sandip Mukherjee A Bhardwaj Anirban Mukhopadhyay R D Garg S Hazra

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      Digital Elevation Model (DEM) provides basic information about terrain relief and is used for morphological characterisation, hydrological modelling and infrastructural studies. This paper investigates the accuracy of DEM and its derived attributes in multiple scales. This study was carried out for a part of Shiwalik Himalaya using Cartosat-1 stereo pair data. DEM at various cell sizes were generated and information content was compared using mean elevation, variance and entropy statistics. Various post-spacing DEMs were validated to understand variation in vertical accuracy along different scales. The vertical accuracy (3.14–7.24 m) is affected in larger spacing DEM and elevation is underestimated. Slope of terrain also has similar impacts. The DEM and slope accuracy are also affected by the terrain roughness while assessing coarser grid size.

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