Overexploitation Of Groundwater And Its Impact On Quality Of Water In Winder Balochistan : An Environmental Geophysical Approach

Abstract

In Winder Town District Lasbela, Balochistan, groundwater is at a vulnerable stage due to overexploitation mainly for irrigation activities. It is situated 80 km in the north-west of Karachi city near the Makran Coast. The research was conducted through integrated geophysical and hydro-geochemical approach to map the subsurface groundwater and estimate the aquifer parameters. The study also highlighted the spatial variation for hydro-geophysical parameters integrated with hydrochemistry and hydrogeology to assess the overexploitation impact and groundwater quality of study area. There have been no integrated scientific studies conducted and documented for sustainable groundwater development of the area. Previous research on hydrogeochemistry of groundwater and data analysis were used for comparison and to develop temporal variation in the quality of water. The geophysical electrical resistivity method was selected; utilizing vertical electrical sounding (VES), and Schlumberger electrode arrangement to map the potential aquifer and other hydrogeological parameters. PASI 16-GLN earth resistivity meter was utilized to acquire 27 points, of vertical electrical sounding (VES). The maximum lateral spacing of current electrode has been kept at 300 meters (AB), to delineate electrical properties up to 150 meters’ depth. The resistance values acquired in the study area were multiplied with the Geometrical Factor (K) to estimate apparent resistivity. Finally, obtained field data from the geophysical survey was processed using computer inversion program IPI2Win developed by Moscow State University, Russia. The geophysical results delineate five layer of variable resistivity; layer 1 (1.5-3.5 m) resistivity ranges from 2-38 Ωm and an average value is 17.5 Ωm. This shows that the resistivity is higher toward the western side of the RCD highway due to dry and unsaturated sand dunes deposits. The lowervii resistivity pattern in east and the central part near the Winder River of the study area depict sandy clay and clay. In layer 2 (3.2-14.2 m) resistivity ranges from 6.32-42 Ωm and the average value is 23 Ωm. The range in the north-east of study area shows higher resistivity interpreted as sandy gravel whereas the south-west & north-west comprise sand deposits. The layer 3 (13-51 m) resistivity varies from 14-50.4 Ωm and the mean value is 29 Ωm. Layer 4 (50.4-114 m) resistivity ranges from 13.5-51.6 Ωm and an average value is 31.5 Ωm. Layer 5 resistivity value ranges from 14.1-51.4 Ωm and an average value is 27.35 Ωm. Layer 3,4 and 5 show higher resistivity in central and eastern region where as the western side shows low resistivity zones. The layer 4 and 5 are saturated and low resistivity depicts the brackish water condition toward the western side, the higher resistivity closure along the Winder River is delineated as the high potential of low TDS water zone. Due to over-pumping of groundwater in Winder Balochistan the water table declined from 15 to 45 meters. The freshwater hand pump near the coastal belt is abandoned and deeper water is more saline. In the vicinity of agriculture farm groundwater, TDS ranges from 1000-2800 ppm. The sample of groundwater from the tube well in the study area provides the spatial distribution of groundwater quality. The analysis of 94 groundwater samples were carried out for physiochemical parameters. Trace elements for the selected samples were also assessed for comparative analysis with published research of 2013. The hydrochemical analysis shows that the dominant hydro facies type is NaCl, Ca-Cl and MgSO4. The HEF-D plot, Gibbs diagram, Stiff plot, Piper diagram, Ionic ratio and statistical analysis of physiochemical analysis suggest that seawater intrusion plays a vital part in groundwater recharge due to aquifer overexploitation. The physiochemical analysis shows that the Na+>Ca2+>Mg2+>K+ (meq/l) for the cation and Cl->HCO3->SO42- (meq/l) for anions in groundwater of study area. The nitrate contamination >50 mg/l concentration was observed in the samples of Winder which can be the result of livestock activity, agriculture activity and some extent to domestic use of water. The results of the present study also compared with the previous research on groundwater which represents, decline in groundwater quality. The hydro-chemical parameters of previously published data show that composition was mainly controlled by the Mor and Pab ranges in north-eastern part of the study area. The average value of the present study for pH is 7.23, Na+ 331 mg/l, Cl- 522 mg/l, SO42- 307mg/l, 50% of sample shows high salinity hazard, the ionic ratio of HCO3-/Cl- is 0.43 and Na/Cl is 0.97 depict the impact of seawater intrusion in groundwater. The estimated irrigation water qualityviii parameter shows the average value of RSC is -7.6 (suitable), Na% 50.1, SAR 5.8 (suitable), MAR 50.6, PS 18 and PI 133.3 (good). The increase in the pH value of groundwater decreased the concentration of trace element of study area. The estimated average values are very close to permissible limit and maximum value in most of the samples exceeds the irrigation water quality standard and deteriorates the soil and crops of the area. The integrated geophysical and hydrochemical parameter maps can be utilized to categorize the low-high risk zone for agriculture activities and domestic use of water. The pumping of groundwater should be stopped from tube wells near to the coast such as UF, UG, UN, US, UD, UL, UR, UG, UT, UP, PS, KA, KZ, KT, KA and KQ. The study area is strategically very important regarding China Pakistan Economic Corridor. Urbanization and industrialization are increasing rapidly and directly stress groundwater production for agricultural activity eventually the impacts are estimated from the present study. The sustainable development of Winder is highly dependent on groundwater effective management, mitigation of seawater intrusion and government policies to exploit groundwater.