Darcy and Apparent Velocities of Groundwater in Phreatic Aquiferous Formations in Kumba– Cameroon: Determined by use of Trigger-Tube Tracer Test Method in Dug Wells

Kumba with a population of about 144,413 people is the capital of Meme Division, in the Southwest region is one of the largest cocoa cash crop producing areas in Cameroon. The inhabitants depend mostly on groundwater through dug wells. It has a hot and humid equatorial climate with annual rainfall 2298-3400 mm and annual temperature 27° C with a short dry season (December to March) and a long rainy season (April to November). There is a need for a good understanding of the hydraulic properties of the aquiferous formations for the planning and management of the groundwater resources of this area. Twenty-one hand-dug wells at different sites in Kumba were tested using sodium chloride (NaCl) as a conservative tracer, by use of the trigger-tube tracer test method. Field estimations of groundwater flow and groundwater velocities in the phreatic aquiferous formation in Kumba through by trigger tube tracer tests gave Darcy velocities ranging from 19.63 m/d at Krammar to 634.13 m/d at Dallas and apparent velocities ranging from 39.26 m/d at Krammar to 1268.27 m/d at Dallas.

The trigger tube tracer tests carried out in some dug wells in Kumba reveals significant spatial variations in groundwater velocities and groundwater flow velocities which are relatively poor at Krammar and good at Dallas. The huge spatial variations in groundwater flows and groundwater velocities imply that groundwater flows at different rates, directions, and at different rates in different sections of the phreatic aquiferous formation in Kumba, probably due to spatial variations in permeability and existence fractures acting as groundwater conduits. Areas with low groundwater velocities like Krammar have lower permeabilities compared to those around PS Kumba Town, Dallas and CCAS. This suggests spatial variations in formation types, facies changes (transgressive and regressive), thickness and layering.