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The importance of the study of fresh-saline water incursion cannot be over-emphasized. Borehole techniques have been widely used, but they are quite expensive, intrusive, and time consuming. The electrical resistivity method has proved very successful in groundwater assessment. This advanced technique uses the calculation of Dar-Zarrouk (D-Z) parameters, namely longitudinal unit conductance, transverse unit resistance, and longitudinal resistivity has been employed by using 50 vertical electrical sounding points to assess the groundwater and delineate the fresh-saline water interface over 1045 km area of Khanewal in Southern Punjab of Pakistan. The x-y plots and maps of D-Z parameters were produced to establish a decipherable vision for the occurrence and distribution of different water-bearing formations of fresh-saline water aquifers through a complicated situation of intermixing of different resistivity ranges for fresh-saline water bodies. This technique is useful to reduce the ambiguity produced by the process of equivalence and suppression which cause intermixing in differentiating fresh, brackish, and saline aquifers during interpretation. The fresh-saline water interface is correlated very well with the previous studies of water quality analysis carried out in Khanewal area. The results suggest that the D-Z parameters are useful for demarcating different aquifer zones. The behavior and pattern of D-Z parameters with respect to occurrence and distribution of different water-bearing formations were effectively identified and delineated in the study area.

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Abstract:In order to determine the ground water resources and potentials of the Khanewal District of Pakistan, a geophysical method in combination with pumping test data were used. An analytical relationship between the aquifer parameters interpreted from surface geoelectrical method and pumping test was established in order to estimate aquifer parameters from surface measurements where no pumping tests exist. For the said purpose, 48 geoelectric investigations were carried out using Schlumberger vertical electrical sounding (VES). Seven of the soundings were conducted where pumping tests had been carried out at borehole sites. The vertical electrical sounding stations were interpreted, and resistivities and thickness parameters were calculated.

Launched in 2014, the Global Precipitation Measurement (GPM) mission aimed at ensuring the continuity with the Tropical Rainfall Measuring Mission (TRMM) launched in 1997 that has provided unprecedented accuracy in Satellite Precipitation Estimates (SPEs) on the near-global scale. Since then, various SPE versions have been successively made available from the GPM mission. The present study assesses the potential benefits of the successive GPM based SPEs product versions that include the Integrated Multi-Satellite Retrievals for GPM (IMERG) version 3 to 5 (-v03, -v04, -v05) and the Global Satellite Mapping of Precipitation (GSMaP) version 6 to 7 (-v06, -v07). Additionally, the most effective TRMM based SPEs products are also considered to provide a first insight into the GPM effectiveness in ensuring TRMM continuity. The analysis is conducted over different geomorphic and meteorological regions of Pakistan while using 88 precipitations gauges as the reference. Results show a clear enhancement in precipitation estimates that were derived from the very last IMERG-v05 in comparison to its two previous versions IMERG-v03 and -v04. Interestingly, based on the considered statistical metrics, IMERG-v03 provides more consistent precipitation estimate than IMERG-v04, which should be considered as a transition IMERG version. As expected, GSMaP-v07 precipitation estimates are more accurate than the previous GSMaP-v06. However, the enhancement from the old to the new version is very low. More generally, the transition from TRMM to GPM is successful with an overall better performance of GPM based SPEs than TRMM ones. Finally, all of the considered SPEs have presented a strong spatial variability in terms of accuracy with none of them outperforming the others, for all of the gauges locations over the considered regions. to ensure the continuity of the TRMM mission. From the GPM mission, two new SPEs were made available: the Integrated Multi-Satellite Retrievals for GPM (IMERG) [14] and a new version of GSMaP product. Available at a 0.1 • and half-hourly and hourly temporal scales, respectively, they offer the opportunity of capturing finer local precipitation variations in space and time [15]. Due to their recent release, few studies report on GPM based SPEs.A first attempt was made by, [16] while comparing IMERG to its predecessor TMPA at the monthly timescale. The study highlighted the differences in both precipitation datasets, which vary according to surfaces and precipitations rates. Since then, numerous studies were dedicated to provide more insights into this discrepancy and highlighted the potential IMERG benefits over its predecessor TMPA at a more local scale. For example, in India, IMERG was found more accurate in the estimation of mean monsoon precipitation than TMPA [17]. In China, IMERG precipitation estimates were compared with the gauges observation at the national level considering daily [18] and monthly temporal scales [19], and a local level study reported on IMERG precipitation estimates over the Chinese Bei...

An integrated study using geophysical method in combination with pumping tests and geochemical method was carried out to delineate groundwater potential zones in Mian Channu area of Pakistan. Vertical electrical soundings (VES) using Schlumberger configuration with maximum current electrode spacing (AB/2 = 200 m) were conducted at 50 stations and 10 pumping tests at borehole sites were performed in close proximity to 10 of the VES stations. The aim of this study is to establish a correlation between the hydraulic parameters obtained from geophysical method and pumping tests so that the aquifer potential can be estimated from the geoelectrical surface measurements where no pumping tests exist. The aquifer parameters, namely, transmissivity and hydraulic conductivity were estimated from Dar Zarrouyk parameters by interpreting the layer parameters such as true resistivities and thicknesses. Geoelectrical succession of five-layer strata (i.e., topsoil, clay, clay sand, sand, and sand gravel) with sand as a dominant lithology was found in the study area. Physicochemical parameters interpreted by World Health Organization and Food and Agriculture Organization were well correlated with the aquifer parameters obtained by geoelectrical method and pumping tests. The aquifer potential zones identified by modeled resistivity, Dar Zarrouk parameters, pumped aquifer parameters, and physicochemical parameters reveal that sand and gravel sand with high values of transmissivity and hydraulic conductivity are highly promising water bearing layers in northwest of the study area. Strong correlation between estimated and pumped aquifer parameters suggest that, in case of sparse well data, geophysical technique is useful to estimate the hydraulic potential of the aquifer with varying lithology.

Selected trace metals were estimated by atomic absorption spectrometry in the water and soil samples collected from the remote region of Himalaya. The soil samples were analysed for soluble and acid extractable fraction of trace metals. In water samples, Ca, Na, Mg and K emerged as dominant contributors, whereas, Ca, Na, K, Mg, Fe and Pb were estimated at comparatively higher levels in the water extract of the soil. In case of acid extract of the soil samples, Ca, K, Fe, Mg, Mn and Na were found at elevated concentrations. Based on mean levels of the metals, following decreasing concentration order was observed in water samples: Ca > Na > Mg > K > Pb > Co > Cu > Zn > Mn > Cr > Fe > Cd > Li, however, in the acid extract of the soil, following order was noted: Ca > K > Fe > Mg > Mn > Na > Pb > Zn > Cr > Li > Cu > Co > Cd. The correlation study revealed appreciably diverse mutual relationships of trace metals in the water and soil samples. The multivariate cluster analyses exhibited divergent apportionment of trace metals in water and soil samples. Among the trace metals, Cd, Pb, Li, Zn, Cr, Cu, Mn and Co exhibited extreme to significant anthropogenic enrichment in the soil samples, while the rest of the metals were mostly contributed by the natural processes.

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