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Evaluation of the irrigation water quality and cropped area of shrinking peri‐urban agriculture in the Gadap Basin, Karachi: An application of Wilcox's classification and geospatial techniques *
Author(s) -
Ahmed Razzaq,
Khan Shaukat Hayat,
Mahmood Khalida
Publication year - 2020
Publication title -
irrigation and drainage
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.421
H-Index - 38
eISSN - 1531-0361
pISSN - 1531-0353
DOI - 10.1002/ird.2504
Subject(s) - irrigation , sodium adsorption ratio , structural basin , agriculture , geospatial analysis , environmental science , water resource management , hydrology (agriculture) , water quality , agricultural land , geography , physical geography , geology , remote sensing , archaeology , geomorphology , geotechnical engineering , drip irrigation , biology , ecology
The Gadap Basin has been an important provider of agricultural commodities to the Karachi metropolis for centuries. However, in recent decades it has been noted that agricultural activities in this peri‐urban area of Karachi have shown a declining trend. In view of the current scenario, this study focuses on the evaluation of irrigation water quality being used in the Gadap Basin. In order to carry out this study, Wilcox's classification methods of Na + % (sodium percentage) and SAR (sodium adsorption ratio) have been applied. The results comprise 13 water samples collected from various localities over a period of two decades (1997–2016), which clearly show that with the passage of time water quality has degraded badly; in particular, sodium concentration that has increased substantially especially in the vicinity of sand and gravel excavation sites. According to Na + % calculation during 1997, 100% of samples were suitable for irrigation whereas in 2016 it had dropped to almost 50%. Similarly, the SAR has gone down, showing degradation of irrigation water quality. Moreover, the results have also been presented using geospatial techniques. The satellite imageries discriminate the sharp decline and degradation of agricultural land (60%) in the basin during the study period 1997–2016.