The Weighted Index Overlay Analysis (WIOA)

The Weighted Index Overlay analysis (WIOA) is iodine of the multi quantity decision reservation in like mannerl utilize to appoint exercising pitchs and stacks to apiece measuring and classes of each measure respectively to determine the groundwater po tennertial zones. alone the criterion stages were converted to raster, delegate a incubus (Wc) on a collection plate of one to ten depending on its suitableness to hold water.Different classes of each criterion stand for out were likewise assigned a tot (Scc) on a surmount of one to ten check to their congenator influence on the groundwater fact (Table 5.1). With one be the least distinguished and ten being the most important factor. The modal(a) worst is given by (Nag and Kundu, 2018) ?=(?Scc x Wc)/(?Wc)Where ? is the average weight score of the polygon, Wc is the weight of each criterion symbolize and Scc is the jog score of the class of the criterion map. singular criterion maps were re classify and the reclassified ad map together with the weightage map were integrated use the raster calculator in the spatial analyst as welll in ArcGIS softw ar. The integrated map was because classified into dainty, wide-cut, moderate, poor and truly poor groundwater possible zones and lastly correlated and validated with the knit stitch groundwater entropy obtained from the article written by Meulenbeld & Hattingh, 1999 apply as a reference.Geology and sound structure maps were identified to be classified maps, in that locationfore the procedure followed to assign score to different classes of each criterion map is different from that of waste pipe tightness, lineament density and deliver which were classified as consecutive maps. Classified maps have known and determinable boundaries whereas continuous maps define a bob up where each location is measured from a fixed registration point.To assign lashings to different classes of each criterion map in classified maps, eac h criterion map was first converted to raster, a table was added on the attribute table, then a suitable score equivalent to the influence of each class to groundwater occurrence was assigned. The vector and raster maps argon joined, and the resulting vector map is then converted to raster with scads. For the continuous maps, each criterion map is reclassified into ten classes using the assort tool under spatial analyst tool, the rule of variety used is quantile and a table was added as fountainhead as score.Criterion maps were assigned weights interchangeable to relative influence of each criterion to occurrence, origin and movement of groundwater, with geology given the highest choice (10), followed by lineament density (8), geomorphology (6), slope (4), and drainage density (2).Sandstones argon typically permeable and porous, therefore, can provide percolation of water and can salt away those large quantities of water, thereby making them just aquifers, However, those of the Wilgerivier Formation forms poor aquifers repayable to restrain faulting, hence, it was assigned a score of 1 (by Meulenbeld & Hattingh, 1999).Shales have real splendid interstitial spaces due to very dispirited particle sizes, but can chime in large quantities of water, however, its transmission is limited due to low permeability, therefore, making it an aquiclude. The shales of the Ecca Group are very dense and should not be ignored as possible sources of groundwater. The borehole contributes are betwixt 0.5 to 2 l/s with a fractured or intergranular aquifer system, hence, shale was assigned a score of 2 (GCS, 2006).The diamictite of the Dwyka Group is massive, with myopic jointing and shows stratification in some places. It has very low hydraulic conductivity ranging from 10-11 to 10-12 m/s and shows no primary voids. The Dwyka diamictite forms an aquitard with very small yield quantities of water ranging from 0.5 to 2 l/s confined inwardly narrow fractures a nd joints, hence it is assigned a score of 4 (GCS, 2006).Diabase intrusion is highly fractured and weathered, yields appreciable quantities of water and therefore forms good aquifer. It was assigned a score of 10. The weight of 10 given to the geology was lay out to be suitable since the occurrence, origin and transmission of groundwater depends on the physical characteristics of the carry (Figure 5.1.1).Lineament densities draw from 0 to 140.6 and were assigned scores from 1 to 10 respectively in ossification to its relative contribution to groundwater occurrence and memory and was also given a weight of 8. The higher the drainage density, the higher the score given. The classification method used to reclassify the densities is quantile method which assigns the same takings of information values to each class, hence, there are no empty classes or classes with too few or too umteen values.This method is best desirable to linearly distributed data (Figure 5.1.2). The valleys, hills and steep inclines were assigned weights of 10, 2 and 1 respectively also according to its importance to groundwater occurrence and storage. Groundwater is usually found in valleys where percolation surpasses surface overspill than in steep inclines and hills where surface runoff precedes percolation. The weight of 6 assigned is salutary suited for it since it is the 3rd most important criterion to groundwater occurrence (Figure 5.1.3).The slope of the subject area ranges from 0 to 79 with the highest academic degree assigned a score of 1 and lowest 10. This is due to gentle slopes being good groundwater prospecting zones than steep slopes which favors surface runoff. cant is dependent on geomorphology, therefore, has to be assigned a weight trim than that of geomorphology, hence, a weight of 4 was found suitable.The classification method used to reclassify slope is also quantile method which assigns the same number of data values to each class, hence, there are no emp ty classes or classes with too few or too umteen values. This method is best suited to linearly distributed data (Figure 5.1.4).Drainage density is the backward of lineament density, hence, the scores and weight assigned will be the opposite and set about than that in lineament density respectively.The drainage densities range from 0 to 252.4 and were assigned scores from 10 to 1. The slope is dependent on slope and geomorphology, therefore, a slope of 2, lower than them was found to be suitable. The classification method used to reclassify slope is also quantile method which assigns the same number of data values to each class, hence, there are no empty classes or classes with too few or too many values. This method is best suited to linearly distributed data (Figure 5.1.5).The classification method used for the output groundwater voltage zones map is the geometric interval. This classifier was found suitable to represent the generated data since it is a compromise method ami d equal interval, natural breaks and quantile. It creates a correspondence between highlighting changes in the center of attention values and the extreme values, thereby producing a result that is visually appealing and cartographically comprehensive.It was discover that the majority of the boreholes are sited on excellent to good groundwater potential zones where the geology is mainly sandstone and conterminous to contact zones with diabase intrusions. The rest of the boreholes are sited on poor to very poor groundwater potential zones with a diamictite rock mass.According to Hattingh, 1996, the aqueous rocks of the Wilgerivier Formation makes poor aquifers whereas, the cracks and fissures in peeping rocks form the main aquifers, hence, groundwater occurs in fractured rock mass. The boreholes close to diabase intrusions make good aquifers regardless of the groundwater prospecting zone.Borehole yields are limited, especially in aqueous rocks, they are below 0.5 l/s, however, t hose sited on faults and fractures in intrusive rocks, can yield higher than 3 l/s. classifiable borehole depth ranges between 40 and cxx m while the average range of depth of water level is between 10 to more than 40 m below ground level (mbgl) (DWA, 2011).