## 3 Study Area and Data Used
### Data Used
#### 3.2.2 Groundwater Influencing Factors  
Selection of the groundwater influencing factors depends on the topography, geo-environment, meteorology, and anthropogenic activities of the area being investigated. In the present study, twelve influencing factors, namely soil type, geology, elevation, slope, Topographic Wetness Index (TWI), aspect, curvature, Sediment Transport Index (STI), river density, flow direction, land use, and rainfall were selected for groundwater potential mapping. A 30-m resolution Digital Elevation Model (DEM) collected from USGS ([[https://earthexplorer.usgs.gov/](https://earthexplorer.usgs.gov/)]([https://earthexplorer.usgs.gov/](https://earthexplorer.usgs.gov/))) was used to extract the maps of the slope, aspect, curvature, elevation, STI, TWI, flow direction, and river density factors.  
The land use map was obtained from Dak Lak's Department of Natural Resources and Environment (DARD), Vietnam, at the scale of 1:50000. Geology and rainfall maps were extracted from the hydrogeological map (1:300.000 scale) collected from the central region of the Vietnam Division for Water Resources Planning and Investigation, Vietnam.  
An aspect map, which indicates relationship with the ability to accumulate and retain water on the surface, was prepared and classified into nine classes (Figure 2a). Runoff will be greater on a convex surface and accumulation of water on a concave surface. The curvature in the study area ranged from -23.5 to 30.8 (Figure 2b). Runoff also depends on the meteorological conditions and elevation of the area. In the study area, the elevation ranged from 117 to 2424 m (Figure 2c). Flow direction is another important factor as it affects runoff and infiltration, and ranged in this area from 1 to 255 (Figure 2d). Slope has a direct relationship with the hydrological process, where surface water will accumulate, and thus more infiltration leads to groundwater recharge (Figure 2e).  
A land use map is also a very important influencing factor for the assessment of groundwater potential that reflects the local conditions and anthropogenic activities in the area. The land use map was classified into different classes (Figure 2f). Concrete construction in an area increases runoff, and thus reduces recharge capacity of the ground. Similarly, deforestation increases runoff, and thus there is less infiltration in the soil.  
TWI is important in assessing groundwater potential because this factor measures topography-moisture relationships (Figure 2h). River density is another important factor as it has an inverse relationship with infiltration and recharge. River density (7.565 km/km\({}^{2}\)) in the study area was relatively high, which indicates more runoff and thus less probability of recharge (Figure 2i).  
Rainfall is one of the most important factors for groundwater potential mapping as it directly affects groundwater recharge [10; 12; 22]. The yearly average rainfall of this area varies from 4.80 to 7.23 mm (Figure 2j). Soil and geology characteristics are very important for infiltration, recharge, and formation of aquifers [14; 86]. The geology map of the study area was prepared into 31 classes (Figure 2k). Permeable soil helps in more infiltration [19]. In the study area, the soil map was prepared based on the soil types available in the study area (Figure 2l).  
Figure 2: _Cont._