Assessment of the Protective Capacity of Vadoze Zone over Aquifer Systems Using Secondary Geoelectrical Parameters: A Case Study Of Kaltungo Area North East, Nigeria

An assessment of the protective capacity of the vadose zone overlying the aquifer systems in the Kaltungo area was carried out to determine its influence on groundwater quality. Applying the schlumberger array with a maximum electrode spread AB/2 = 100m through VES, thirty water well points were surveyed using Omega terrameter (PIOSO1) resistivity meter. The field data was first subjected to manual interpretation through curve marching and then digitized modeled curves using computer software. The interpreted data revealed that the area is characterized by eleven different curve types representing three to five geo electrical layers. In order to assess the protective capacity of the vadoze zone over the aquifer systems, the longitudinal conductance (S) and transverse resistance (T) (secondary geoelectric parameters) were computed from the primary data using the Dar Zarouk formula. The values of S obtained range from 0.0018 to 0.4056 ohms with a mean value of 0.0135 ohms while the values of T range from 0.55 ohms to 1195.68 ohms with a mean value of 39.84 ohms. The values of S and T obtained reveal that 90% of probed points has poor protective capacity, 10 % has moderate protective capacity and 83 % has high transmissivity, 17 % has intermediate transmissivity. The T and S values are skewed towards poorly protective capacity thus making groundwater in the area highly vulnerable to contamination from the surface. To achieve good groundwater quality in the area, proper completion of newly constructed wells should install protective casing through the entire vadose zone

11th Applied isotope geochemistery conference AIG-11

36Cl measurements in groundwaters of the deep confined aquifer of the Lake Chad Basin (LCB) were performed in order to constrain groundwater geochemical ages and residence times. Twenty-seven wells were sampled in Nigeria, Niger and Chad in the southern parts of the large (700 000 km2) multilayered aquifer of the LCB. 36Cl/Cl values range between 11±1.10-15 to 148±8.10-15 at/at. The highest ratios are observed near the recharge zone of the Nigerian part of the Continental Terminal aquifer, while the lowest ones are found in wells located near the southern fringe of the present-day lake Chad. Chloride concentrations are low (below 100 mg/l) and not correlated to the 36Cl/Cl values, indicating negligible dissolution of evaporites in most samples. Reliable 36Cl ages can be calculated along the different flow paths investigated, suggesting residence times of the deep groundwaters larger than 300 000 years. These results are consistent with new AMS-14C data below the detection limit but are in contradiction with previous 14C data obtained in the area

Estimating Groundwater Recharge for Sustainable Management in the Nigerian Sector of the Chad Basin

Groundwater is the perennial source of water supply for domestic and other applications in the Nigerian sector of the Chad basin. Therefore, quantifying the current rate of recharge is fundamental to sustainable management of the resource. The chloride (Cl) mass balance technique was used to estimate the rate of recharge. Average Cl concentrations in rainfall from three stations over eight years were used as input data. Eight unsaturated zone Cl profiles were obtained and Cl concentrations in the groundwater were measured for over 400 samples from wells and boreholes. An average recharge rate of 41 mm per annum was estimated from the unsaturated zone profiles. The regional rate obtained using Cl concentrations in groundwater is slightly higher, estimated at 48 mm per ammum, which is attributable to other mechanisms of recharge such as river channels, pools, depressions and regional flow that bypass the unsaturated zone. The estimated recharge to the shallow groundwater in this region is considerable and can sustain present day abstractions. The observed decline in water table in recent years is largely due to reduced rainfall during the Sahel drought and consequent reduction in recharge, although human impacts are also identified as is common with most semi-arid areas of the world. Although the flood plains aquifers (fadamas) are probably fully recharged annually through river channels, caution must be exercised in introducing irrigation schemes. Any agricultural development should be preceded by detailed studies, so as to utilise the quantity of water that is recharged annually and must also adopt water saving techniques

Contribution of time domain electromagnetic and magnetic resonance soundings to groundwater assessment at the margin of lake Chad basin, Cameroon

At the edge of a semi-arid sedimentary basin, the Piedmont plain of the Mandara mountains is potentially a key area for the recharge of the Lake Chad Quaternary aquifer. We conducted two geophysical surveys based on magnetic resonance sounding (MRS) and Time-Domain Electromagnetism (TDEM) techniques for a better understanding of the aquifer structure at.the piedmont scale in aim to identify preferential groundwater recharge pathways. MRS water content and electrical resistivity of the medium confirmed the very heterogeneous and clayey nature of the quaternary aquifer, limiting the recharge to the sandiest areas. Thanks to the geophysical methods, these areas have been highlighted near temporary rivers and upstream of the study area near Maroua city. Because of the thickening of the aquifer downstream, the most transmissive zones are in the mid-slope of the piedmont. The geographical distribution of aquifer properties defined by geophysics and the range of MRS water content (from <2% to 26%) may be used in the future to constrain groundwater modelling and specify the recharge of the quaternary aquifer at mountain front

Rainfall geochemistry in the Sahel region of northern Nigeria

Chemical data and stable isotope (δ18O, δ2H) results are presented for monsoon rains for several years during the 1990s from northern Nigeria in the Sahel region of Africa. The isotopic data from Garin Alkali (Nigeria) are related by a line δ2H=6.33δ18O+9.9 with a weighted mean value of −3.6‰ for δ18O. The heaviest rains have the lightest isotopic compositions; the lighter rains’ enrichment is as a result of convection. The mean 1992 concentrations of Cl in rain ranged from 1.3 to 2.8 mg l−1 for the two stations in Nigeria. The early rains have higher Cl than the later events although Cl accumulations are in general directly related to rainfall amount. The Br/Cl ratios of all rains are enriched above marine values, which may in part be attributed to a preferential concentration of Br in smaller size particles, although more likely, is related to release from the biomass as the air masses pass over vegetated areas. The high Br/Cl ratios rule out dust from halite sources during the monsoon. The ratios of Na and Cl are similar to those in sea water, although all other elements (especially Ca, SO4, NO3 and K) are enriched relative to marine aerosols and indicate continental sources. The element ratios (Ca/SO4); K/Mg; K/Na) are remarkably similar to those in ash leachates from tropical vegetation and this is proposed as the main solute source in the present day monsoon rains, reinforcing the evidence of Br/Cl ratios. The chemical results show the considerable terrestrial influence and are in line with isotopic evidence, which demonstrates considerable modification by convective circulation and continental influence as the monsoon air masses track northwards over the Sahel