Geoelectrical Sounding for the Estimation of Hydraulic Conductivity of Alluvial Aquifers

摘要

Groundwater is a valuable resource for irrigation water. The use of ground-water for irrigation depends on environmental factors affecting long term sustainability and the costs of extraction which affect the economic viability. The cost of extraction depends upon the depth of drilling required and the rates of groundwater extraction that can be achieved. This is determined by the natural water flow through aquifers and so requires an estimation of hydraulic conductivity (K). In the irrigated area of Pakistan the Geoelectrical method, Vertical Electrical Sounding (VES) was tested to estimate aquifer hydraulic conductivity. A resistivity meter was used to collect VES data by employing a Schlumberger electrode configuration, with half current electrode spacings (AB/2) ranging from 2 to 180 m and the potential electrode (MN) from 1 to 40 m. The field data were interpreted using the Interpex IXlD computer software and the aquifer resistivity (p) vs depth models for each location were estimated. A total of 102 groundwater samples from nearby hydrowells at different depths were also collected for Electrical Conductivity (EC) to measure groundwater resistivities (ρ_0). The resultant formation factor (F=ρ/ρ_o) values varied between 0.79 and 12.32 for the entire study area. The extreme values of F obtained from the VES surveys were paired with extreme values of K derived from field tests to provide a linear model of F:K. Seven pumping tests were also carried out to determine K and test the F:K correlation. The empirical relationship developed between the formation factors was highly significant and as such can be helpful for the estimation of hydraulic conductivity for groundwater pumping investigations in this area. This approach to deriving a relationship between the formation factor and hydraulic conductivity can be useful for groundwater investigations elsewhere.