Information from digital elevation models (DEMs) was gathered (Source: WWW.USGS.COM).The DEM data was used to extract the area of interest, which was then imported into Arc GIS. Overlaying the boundary map with the topographic sheet enhances the spatial analysis capabilities of GIS for groundwater potential assessment. It ensures that the study considers both administrative boundaries and topographic features in identifying suitable areas for groundwater development and management. (source: WWW.NAKSHA.COM). Subsequently, the necessary digital elevation model was created for the research region.
The study's foundation was the secondary data that were acquired from the pertinent department. For instance, information on precipitation, runoff, ground water, etc. The study has considered a number of parameters in order to predict groundwater levels. Building maps of height, fill, flow direction, flow accumulation, and slope using a Digital Elevation Model (DEM) as a base is a common approach in GIS for terrain analysis, particularly for groundwater potential assessment. Building a drainage network using elevation data involves identifying channels and streamlines within the terrain based on flow accumulation and flow direction. Integrating Landsat 8 satellite data for land use and land cover classification adds another layer of information to the analysis. Using ArcGIS weighted overlay analysis to calculate overall rainfall variation in the study area is an effective method for synthesizing rainfall data from multiple rain gauge stations. This resulted in the creation of a ground water potential zones map for Nanajangud taluk. The flow chart (Fig. 1) below provides a complete report of the analytical technique.
3.1 Topo Sheet
The precise quantitative representation of relief on topographic maps, which is usually accomplished by using contour lines but has historically involved a variety of methods, sets them apart from other types of maps due to their high level of information. In this study, the top sheet of No. D43W12—which can be seen in Fig. 3 is utilized to offer data on highways, rivers, and other features.
3.2 Elevation
Higher terrain tends to be less effective at storing water than lower terrain. Elevation data with a 30 m spatial resolution has been constructed for the current investigation using the ASTER DEM. Lower the elevation, the lower the ground water potential, and vice versa (Gedebo,2005). The research area's elevation, which varies from meters to meters above mean sea level, has been divided into five equal classes and given a weight for each class (Fig. 4).
3.3 Fill
Errors resulting from rounding elevations to the two nearest integers value or from data resolution frequently cause sinks and peaks. To guarantee accurate stream and basin demarcation, sinks need to be filled. A discontinuous derived drainage network could result from unfilled sinks. In Figs. 5 and 6, profile views of peaks and sinks are displayed. Figure 7 displays the Nanjungud filled DEM image.
3.4 Flow Direction
Determining the hydrological characteristics of a surface requires knowing the direction of flow from each raster cell. The flow direction is used to do this. This script uses a surface as the input and uses the flow direction out of each cell to show as a raster. If raster option is used as an output, a percentage-based output raster is created that shows the maximum elevation change from each cell along the flow direction to the path length between the cell centres. If the option to force all edge cells to flow outward is chosen, as seen in Fig. 8, then all cells at the surface raster's edge will flow outward from the surface raster.
3.5 Flow Accumulation
The weight of all the cells that flow into each downslope cell in the output raster is added together to determine the accumulated flow using the flow accumulation tool, as illustrated in Fig. 9. In the event that no weight raster is provided, the value of the cells in the output raster indicates how many cells flow into each cell. In this instance, every cell has a weight of 1.
3.6 Watershed delineation
A watershed is an area upslope that provides concentrated drainage, or flow, usually water, to a common outlet. It may comprise smaller watersheds known as sub basins or be a portion of a superior watershed. The boundaries dividing watersheds are identified as drainage divides. The outflow point, often called the pour point, is the location on the surface where water leaves a space. It is the border point of a watershed's lowest point. Figure 10 depicts the defined watersheds for the two research regions.
3.7 Land use and Land cover (LU/LC):
Human activity has caused significant changes to the earth's surface in recent years. Examining the kinds of features covering the study area's ground surface is crucial because vegetation—such as woods and agricultural land—traps and absorbs water in the roots of plants. However, during rainy seasons, rocky and developed land usage promotes drainage. The land cover and land use of the study area were ascertained using a Landsat 8 satellite image. Level I categorization has been carried out using the supervised classification approach. The study region is classified into six types based on the study's findings: built-up, water body, waste land, forest, and agricultural land. Figure 11 shows how weight is allocated based on LU/LC water logging and runoff qualities.
3.8 Slope
Slope affects the rate of surface water penetration and runoff; flat surfaces can retain and drain water inside the earth, enhancing ground water recharge, while steep slopes increase runoff and decrease the quantity of surface water that penetrates the ground. The research region's slope was measured in degrees using the DEM model, which was based on the ASTER data. The slope has been classified into five classes, as shown in Fig. 12, and weights have been assigned to each class.
3.9 Stream order
One technique for giving the links in a stream network a numerical order is called stream ordering. This configuration makes it possible to identify and classify streams based on the number of tributaries they have. Certain aspects of a stream can be revealed only by understanding its sequence. Using Strahler's classification scheme, the whole drainage network of the research region was ranked from first to sixth order. Each segment of a stream or river within a river network is seen as a node in a tree when using Strahler's stream order in hydrology, with the segment downstream acting as its parent. A second-order stream is created when two first-order streams merge. A third-order stream is created when two second-order streams combine. When a lower order stream merges with a higher order stream, its order remains unchanged. As a result, when a first-order stream merges with a second-order stream, the order of the original stream does not change. A second-order stream can only become a third-order stream by merging two second-order streams. As seen in Fig. 13, the sixth order Cauvery stream makes up the Mysuru district. The stream's order is indicated by the numbers in the legend.
3.10 Lineaments
The distinguishable irregular topography characteristics on the ground are called lineaments. The orientation of the surface and underlying structural elements are shown by these features. Lineaments are signs of subterranean cracks and fissures that force groundwater to exist and function as tiny reservoirs and channels. Data on lineaments (Fig. 14) were gathered from the Mysuru District Department of Mines and Geology.
3.11 Geology
According to Basavarajappa and Manjunatha (2014), the majority of the region's geology is made up of Precambrian igneous and metamorphic rocks that are either visible at the surface or have a thin layer of transported and residual soils covering them. Plotting displays a range of Archean-aged lithology, such as schists, gneisses, granites, and charcoal (Fig. 15). The low-lying, level areas are covered with a thick layer of fertile soil, and the upper, hillier areas are covered in laterite. According to Basavarajappa et al. (2013), the Sargur group of rocks, also referred to as the Sargur Schist belt in H.D. Kote taluk, stretches for around 40 km from Sargur to Mysuru city.
Joint formations, deformational folds, and the Sargur type of structure are also observed during field trips. Using satellite imagery, the geology map was created derived from the Geological Map of Karnataka (1:250,000 Scale) and represents most of the igneous and metamorphic rocks found in the study area, such as gneisses, Charnockite, amphibolites schist, pink and grey granite, meta-ultramafites, hornblende schist, granodiorite, limestone, and dolomite (Basavarajappa et al., 2014). The geological map for the research area was provided by the Department of Mines and Geology.
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3.12 Weighted overlay Analysis
Following the establishment of the weights for each key parameter and the creation of all produced maps, data from connected departments in Mysuru was gathered for an overlay study. Spatial Analyst Tools in ArcGIS generates the "Weighted Overlay" in the Overlay Toolset using this data. The weighted overlay tool weights each raster based on its relevance (ESRI), overlays multiple rasters, and applies a common measurement scale. Five groups were created from the overlay analysis results: very low, low, moderate, high, and very high. The classification results show that there are five different sorts of areas: appropriate (14265.162 Sq.km), moderate (27918.90 Sq.km), poor (36190.84 Sq.km), extremely poor (1517.43 Sq.km), and highly suitable (9124.66 Sq.km).
3.13 Drainage density
The drainage density is one of the primary PGZ affecting factors. Due to the higher water flow, a high drainage density will result in less water infiltration into the earth. Conversely, a low drainage density will result in more surface water infiltration into the earth because there will be less surface water runoff. Stream data collected from the Department of Geology and Mines has been compared with stream data produced by the Aster DEM in the current inquiry. The drainage density of the research area was determined using the most recent stream data. To ascertain the drainage density, numerous researchers have used a range of methods; most notably, Magesh et al. (2011) used IDW. In this instance, however, the arc swat tool method is being utilized to generate a map of the drainage density.
3.14 Rainfall
One of the main ways that ground water becomes available through the water cycle is through rainfall. Rainfall totals are influenced by the surrounding environment. It varies from location to another. There is a high probability of ground water with high rainfall and a low probability of ground water with low rainfall. Rainfall affects a place differently depending on time and space, so determining its effects over an extended period of time is necessary. The yearly mean data was obtained using the interpolation method and the matching rain gauge stations. The rainfall distribution in the research area has been determined by the use of krigging. The research region was split into five zones using an equal interval categorization system once the pattern of rainfall was identified. We then assigned the proper weight to each class.
3.15 Soil
One of the main elements that affect groundwater availability is soil; understanding the many types and characteristics of soil is made possible by studying it. The permeability and porosity of soil determine how surface water percolates into the earth and moves through it. As a result, analyzing the soil is crucial to figuring out how much groundwater a location has.