*Aquifer Characterization: The Case of Hawassa City Aquifer DOI: http://dx.doi.org/10.5772/intechopen.91211*

#### **Figure 3.**

*(A) SWL contour map and vector map showing flow direction (2006) with color scale; (B) SWL contour map and vector map showing flow direction (2009) with color scale; (C) SWL contour map and vector map showing flow direction (2012) with color scale; (D) SWL contour map and vector map showing flow direction (2013) with color scale; (E) SWL contour map and vector map showing flow direction (2014) with color scale; (F) DWL contour map and vector map showing flow direction (2006) with color scale; (G) DWL contour map and vector map showing flow direction (2009) with color scale; (H) DWL contour map and vector map showing flow direction (2012) with color scale; (I) DWL contour map and vector map showing flow direction (2013) with color scale; and (J) DWL contour map and vector map showing flow direction (2014) with color scale.*

S-W areas. For the year 2009, the map presented shows turbulence, so the flow direction has no clear trend except for the lake shore area that receives water from the nearby aquifer. For the year 2012, relatively medium magnitude water flows into the Gara Riqata area, which produces huge water discharge for the next year 2013. The two years 2013 and 2014 results clearly reveal that significant amount of

**48**

*Resources of Water*

**3. Conclusion**

**Author details**

Hawassa, Ethiopia

**51**

Shemsu Gulta<sup>1</sup> and Brook Abate<sup>2</sup>

Technology University, Addis Ababa, Ethiopia

provided the original work is properly cited.

\*Address all correspondence to: brooka12@yahoo.com

\*

1 School of Biosystems and Environmental Engineering, Hawassa University,

2 College of Architecture and Civil Engineering, Addis Ababa Science and

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

The main aquifers tapped by the Hawassa City ground water system is unconfined and semi-confined type since no confining beds like clay are clearly identified up to 200 m depth. Weathered and fractured pumice, basalt scoriaceous rocks, fine-to-coarse-grained sand, and weathered ignimbrites are major waterbearing formations. The first water striking point is the shallowest around the lake shore (west and S-W) and as the well site goes apart to the west direction, the water striking depth is increasing and ash, fractured basalt and ash with scoriaceous basalt are dominating. The Hawassa City ground water system is of high performance and potential due to the very small drawdowns, fast recovery percentage (up to 100%), high transmissivities, and saturated thicknesses of the aquifer. The aquifer materials are highly porous and the high aquifer porosities imply aquifers of high storativity and better yield. The protective capacity of the overburden rock materials in the area is very low. Transmissivity and hydraulic conductivity values are generally high in the lake shore and central parts. Since the aquifer materials in the study area are highly permeable and relatively shallow, the groundwater has a high susceptibility of being contaminated over large area. The ground water flows from the E and S-E parts toward the central and western side of the city with a very

similar profile with the surface water flow direction.

*Aquifer Characterization: The Case of Hawassa City Aquifer*

*DOI: http://dx.doi.org/10.5772/intechopen.91211*

ground water flows from the large area of the city toward the lake shore. Thus, the ground water system feeds the lake which will in turn accelerate the lake level rise. For those months in which the pumping test of the wells conducted (i.e., March, April, and May) large amount of infiltrated water from the discharge spots join the ground water reservoir as this is the time immediately after the rainy season stops in the area. Combining these graphical results and the one for the surface water flow direction (**Figure 3A–J**), groundwater flow direction follows similar tendency of the surface water movement, that is, it follows the surface profile. This also implies the fact that the highlands are recharge areas and the lowland areas as nice spots for discharging.

### **2.3 Guide to drilling depth in Hawassa City**

Using the wire frame and the grid map of the well depth on Surfer 8 Software, one can interpolate the required depth to be drilled at specific GPS location in the study area. This is an important guide for borehole drillers and clients to estimate the depth of the water striking formation at that specific site. To do so, the Surfer 8 Software can be used to display the map as shown in **Figure 4**.

The gridding method in Surfer 8 Software uses weighted average interpolation algorithms. This means that with all other factors being equal, the closer a point is to a grid node, the more weight it carries in determining the Z value at that grid node. The difference between gridding methods is how the weighting factors are computed and applied to data points during grid node interpolation. The coefficient of determination for this analysis is found to be R<sup>2</sup> = 0.87, which indicates the strong acceptability of the guide.

To increase the likelihood that these data are honored, one can increase the number of grid lines in the X and Y direction. This increases the chance that grid nodes coincide with data points, thereby increasing the chance that the data values are applied directly to the grid file.

The geological formation at the depth to be drilled and the other parameters determined by this and other studies shall be combined to get more detailed information. Certainly, the more the depth drilled, the better will be the safe yield.
