Geography Reference
In-Depth Information
The DRASTIC model is applicable in humid climates (Babiker et al., 2005;
Piscopo, 2001; Kim and Hamm, 1999; and Osborn et al., 1998) as well as in
semi-arid to arid climates (Werz and Hötzl, 2007; Al-Adamat et al., 2003;
Secunda et al., 1998). In the original DRASTIC index model, semi-
quantitative data layers were overlaid manually. However, the simple linear
model of its combination factors expressing its vulnerability index shows the
feasibility of employing the GIS for the computation of index (Fabbri and
Napolitano, 1995).
For past 15-20 years, the GIS technique has been widely used in
groundwater vulnerability mapping (Evans and Myers, 1990; Loague et al.,
1996; Hrkal, 2001; Rupert, 2001; Lake et al., 2003; Massone et al., 2010; Yin,
2013; Edet, 2014). The major advantage of GIS-based mapping is the best
combination of data layers and rapid change in the data parameters used in
vulnerability classification. Integration of DRASTIC method with GIS
involves following four steps (Massone et al., 2010).
(i) Preparation of thematic base maps (as a polygonal entity) for each
parameter under consideration using GIS software packages.
Subsequently, polygon map of each parameter is transformed into
raster format using the spatial analysis functions of GIS. A suitable
spatial cell resolution for spatial analysis can be chosen.
(ii) Procedure indicated by methodology are applied for the assignment of
weights and values to each layer of information and the application of
map algebra to obtain the aquifer vulnerability maps, called
DRASTIC and DRASTIC-P vulnerability maps. Conveniently, the
DRASTIC index values can be discretized into suitable number of
classes indicating very low, low, moderate, high and very high
vulnerability, since this is the number of classes that allows one to
recognize both the ―best‖ values and the worst ones as two
alternatives (high and very high or low and very low); this is better
than recognizing only three classes where there is only one possible
option towards each end (low or high). This is favourable to decision-
making related to the use of soil in land-use planning, in
environmental impact evaluations, etc.
(iii) Reclassification of the DRASTIC vulnerability maps to obtain the
DRASTICpriorities, which recognize five classes from priority 1
(lower values in the series) to priority 5 (higher values).
(iv) Combining the DRASTIC vulnerability map with the DRASTIC-
priorities to generate an operational vulnerability index (OVI). For
