Poor drainage-induced waterlogging in Saharan groundwater-irrigated lands: Integration of geospatial, geophysical, and hydrogeological techniques

During the last decade, the desert fringes of the Nile Valley in Egypt witnessed a vast expansion of groundwater-fed reclaimed lands. However, waterlogging and drainage-induced groundwater quality issues started to be of concern in many locations in these developed areas. In this study, an integrated methodology (landscape analysis, electric geophysical survey, geochemical and isotopic data) was applied to assess the causes of the waterlogging and to examine the impact of waterlogging and associated soil salinization on the groundwater quality, using the area east of the Nile Valley in the El Minia district as a test site. Using eighteen vertical electrical sounding (VES) measurements, the distribution and thicknesses of the impermeable shale layers, which potentially prevent the infiltration of excess irrigation water into the aquifer were delineated. Geochemical and isotopic data revealed that groundwater is not impacted by subsurface discharge of agricultural drainage water and it is mainly recharged from occasional rainfall and lateral seepage from the alluvial aquifer, mainly recharged from the Nile water. Our findings suggested that in addition to the occurrence of shales, the flood irrigation and non-planned cultivation without considering the natural stream networks as well as the wrong management decisions by local farmers significantly contributed to develop the waterlogging, which might further be expanded to impact the adjacent old and low cultivated floodplain lands. Local measures to dispose the excess irrigation water directly into the subsurface through tube wells were found to be inefficient. Since the geology and hydrogeology of new developed lands surrounding the Nile Valley are similar to the test site, the applied methodology can be applicable for all these locations for sustainable agricultural development in Egypt and similar arid regions.