Estimation of Hydraulic Conductivity of Soils at a Watershed-Scale Using Porchet’s Method: Application in the Olezoa Waterhed, Yaounde, Cameroon

Abstract

Contamination analysis of the unsaturated zone requires information on the spatial variability of hydraulic conductivity. Two types of hydraulic tests (variable and constant charge) were identified to estimate the spatial variability of the hydraulic conductivity of the surface portion of the unsaturated zone in the Olezoa watershed. These tests were performed on 100 holes at depths ranging between 50 and 90 cm, spread throughout the watershed. The hydraulic conductivity values obtained at 50 and 90 cm are close to the absolute value for each method. However, they show a difference of 10 −1 m/s between the two types of test regardless of the depth of investigation. The representation of data in the graph indicates a staircase quartile distribution for the variable charge test. The test at constant charge, rather presents a log normal distribution which is also supported by the Kolmogorov-Smirnov test. Hydraulic conductivities have a random component and a spatial organization which results from soil and/or morphological factors. This organization thus permits the distinction of zones which could show high pollution risk.

Hydrogeological Characteristics of Shallow Hard Rock Aquifers in Yaounde (Cameroon, Central Africa)

“…In addition, depth investigation data (beyond 8 m), based on pumping tests or slug tests, indicating the level/horizon actually investigated, were also taken into account in the hydraulic description of this aquifer. Hydraulic conductivity values from infiltration tests range from 10 −7 to 10 −3 m/s [12,36]. The normal distribution (Figure 4) of the hydraulic conductivity values is unimodal and varies over four orders of magnitude, attesting the variability of this propriety of the loose materials.…”

“…Various techniques, as reported in the literature, are used to determine the hydrodynamic properties of aquifers in basement areas in general and its superficial part in particular. They include but are not limited to field methods (pumping test, slug test and tracer test, Porchet test) [12,22,34]; laboratory and mathematical methods [35], empirical formulas [36], and regional methods [37,38]. Even though accurate estimation of hydrodynamic proprieties (effective porosity, permeability, and transmissivity) may be conducted in the field environment, poor knowledge of aquifer geometry sometimes limits their potential application [39].…”

“…These alterites show a heterogeneity marked by a range of variation in hydraulic conductivity between 10 −8 and 10 −5 m/s [28,35,40,41], depending on the clay content which is low in the laminate level (base of saprolite). The variation of this hydraulic conductivity is related to topography and a weathering processes [43]; [12,30] and presents elsewhere a decrease with the depth of the soil. This decay obeys, depending on the case, a power law or an exponential function [31,[44][45][46][47].…”

“…These programs relate to (a) "physical, hydrodynamic, and bacteriological characterizations of groundwater resources in the sedimentary and basement areas of Cameroon" and (b) "the impact of climate change and human activities on the water resources of Cameroon. " The activities carried out within the framework of these programs are more implemented in the alterites of the geological formations of the South Cameroon Plateau specifically those of the region of Yaounde and its surroundings [7][8][9][10][11][12]. In fact, because of the deficit service of the water distribution network, the groundwater of shallow unconfined aquifer constitutes, for many households in this region, one of the main sources of water supply.This chapter is a review of the main results obtained during the research carried out in the aquifers of the Pan-African basement of the Yaounde series in Central Africa.…”

Landsat-8 OLI/SRTM and gravity characteristics of the Pan-African fracture aquifers of the north central Cameroon region (central Africa)

“…According to Refs. [ 9 , 10 ], the major water flow comes from deep fractures. Recently, remote sensing studies provided new insights on mineral resource mapping [ [11] , [12] , [13] , [14] , [15] , [16] , [17] ] and on spatial mapping of this reservoir [ [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] ].…”