Application of Geospatial Technologies in Identification of Optimal Groundwater Yield Locations Case Study: Woqooyi Galbeed Region, Somalia

Abstract

Groundwater is one of the most important resources on the globe and it is reducing rapidly. Consequently, there is a need for identification of potential groundwater zones. The use of conventional geophysical techniques in siting of boreholes, sometimes results in location of boreholes in unsuitable areas. This leads to low water volume yields, or depletion of groundwater storages especially during dry months due to excessive pumping compared to their ability to naturally recharge. The study was proposed in quest to improve prediction of suitable groundwater zones, through the use of geospatial technologies to complement the existing geophysical surveys. The approach was timely, since many studies in hydrology had mostly left its application at a recommendation level. Therefore, the study sought to put such recommendation to a test, through the use of multi-criteria approach using weighted overlay analysis. The research was carried out to identify potential groundwater zones in Woqooyi Galbeed region of Somalia using geospatial techniques. Thematic layers of geology, drainage density, lineaments density, soil, Long term mean rainfall and slope were used. These thematic datasets were weighted on a scale of 1-5, according to how they strongly relate to the existence of groundwater. Through a weighted overlay analysis, a map showing high, low and poor groundwater potential zones was produced as shown in Fig 17. Validation of existing boreholes was done by overlaying them on the map of groundwater potential zones. Coincidentally, most of good performing boreholes fell within high potential groundwater zone, with a few in low and poor potential zones. It was also noted that although most of the good performing existing boreholes fell in high potential groundwater zone, they existed in concentrations and not evenly distributed within the zone. The observation lay bare the shortcomings of the geophysical survey methods. These findings underscored the fact that, the use of geospatial techniques in borehole siting does not exclude the need for geophysical survey to determine groundwater quality and volumes but rather, geospatial techniques brings to focus suitable areas as a complement to geophysical surveys. From 5

the study; 29% of the study area constituted high potential groundwater zone, 51% low potential zone while poor potential zone accounted for 20%. The study recommended the need to undertake ‘Groundwater Movement Pattern’ study, to explain isolated boreholes exhibiting high performance in poor Groundwater potential zones, and use of geospatial technologies and geophysical survey techniques in borehole siting with the former preceding the latter.